High voltage, high efficiency sine wave generator that prevents spikes during amplitude adjustments and switching of channels

Abstract

To provide various approaches for generating a high voltage sinusoidal signal that can quickly adjust the output voltage without introducing high frequency artifacts at the output.SOLUTION: When these approaches are used, a stronger electric field can be applied to the tumor for a higher percentage of time, which can increase the effectiveness of the TTFields therapy. In some embodiments, this is achieved by preventing adjustments to the DC power supply during times when the output of the DC power supply is providing power to the output signal. In some embodiments, this is achieved by synchronizing the operation of an alternating voltage generator and an electronic switch connected to the output of the alternating voltage generator.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of U.S. Provisional Application Nos. 62 / 955,673, filed Dec. 31, 2019, and 62 / 981,875, filed Feb. 26, 2020, each of which is hereby incorporated by reference in its entirety.

Background Art

[0002] The use of TTFields therapy for treating tumors is described in U.S. Patent No. 7,805,201. TTFields therapy uses high - voltage sine - wave signals. Originally, these high - voltage sine - wave signals were obtained by using a function generator to generate a low - amplitude signal, using a linear amplifier to amplify the low - voltage signal to a high - voltage signal, and then applying the high - voltage signal to a set of electrodes (also called a transducer array) placed on the patient's body. U.S. Patent No. 9,910,453 describes an alternative method for generating the high - voltage sine - wave signal applied to the transducer array, and this alternative method provides dramatically improved efficiency over the original linear - amplifier method.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] This application describes various techniques for generating a high-voltage sine wave signal that can rapidly adjust the output voltage without introducing high-frequency artifacts (e.g., voltage spikes) in the output. When these techniques are used, a stronger electric field can be applied to the tumor for a higher percentage of the time, which can enhance the effectiveness of TTFields therapy. **Means for Solving the Problem**

[0005] One aspect of the present invention is directed to a first apparatus for generating a sine wave of frequency f. The first apparatus includes a DC power supply having a voltage control input for setting the output voltage of the DC power supply, a transformer having a primary side and a secondary side, and a power switch. The power switch has a control input, and the power switch applies the output of the DC power supply to the primary side of the transformer in a first direction when a first control signal is applied to the control input, and applies the output of the DC power supply to the primary side of the transformer in a second direction when a second control signal is applied to the control input, and is configured to remain off when neither the first control signal nor the second control signal is applied to the control input. The second direction is opposite to the first direction. The first apparatus also includes a controller programmed to (a) apply the first control signal to the control input for a duration of T / 3, then (b) wait for a duration of T / 6, then (c) apply the second control signal to the control input for a duration of T / 3, then (d) wait for a duration of T / 6, and then continuously repeat the sequence (a), (b), (c), and (d). T is the reciprocal of the frequency f. The first apparatus also includes an output filter connected to the secondary side of the transformer, and the output filter passes the frequency f and attenuates frequencies above the cut-off frequency. The controller is further programmed to control the amplitude of the sine wave of the frequency by adjusting a third control signal applied to the voltage control input of the DC power supply, and the controller is further programmed to prevent the adjustment of the third control signal from occurring when either the first control signal or the second control signal is applied to the control input.

[0006] In some embodiments of the first device, the cutoff frequency is between 2f and 4f, and the output filter has a transfer function that has a zero at 5f.

[0007] Another aspect of the present invention is directed to a second device for generating a sine wave of frequency f. The second device includes n DC power supplies, each of the n DC power supplies having a voltage control input for setting the output voltage of the respective power supply, where n is a positive integer. The second device also includes a power switch having an output terminal and a control input. The power switch is configured to (a) route the output of a selected one of the n DC power supplies to the output terminal with a selected polarity in response to 2n states of a control signal applied to the control input, or (b) remain off in response to an additional state of the control signal. The second device further includes a controller programmed such that, using equally spaced samples including a sampling point at 0°, sampled N times per cycle where N = 2 + 4n, by setting the output voltages of the n DC power supplies to levels that exist in the oversampled version of the sine wave, and then sequencing the control signal through the 2n states and the additional state, each of the n DC power supplies is routed to the output terminal of the power switch with a selected polarity at an appropriate time within the sequence to generate an oversampled version of the sine wave. And the second device also includes an output filter for filtering the current arriving from the output terminal of the power switch. The output filter passes frequency f and attenuates frequencies above the cutoff frequency. The controller is programmed to control the amplitude of the sine wave by adjusting the output voltages of the n DC power supplies via the voltage control inputs, and the controller is further programmed not to adjust the output voltages of the DC power supplies while the output of the DC power supply is routed to the output terminal of the power switch.

[0008] Some embodiments of the second device have a primary side connected to the output terminal of the power switch and a secondary side connected to the output filter, and further include a transformer configured such that current from the output terminal of the power switch reaches the output filter via the transformer.

[0009] Some embodiments of the second device have a primary side connected to the output terminal of the power switch and a secondary side connected to the output filter, and further include a transformer configured such that current from the output terminal of the power switch reaches the output filter via the transformer. In these embodiments, n = 1, which means that only a single DC power supply is present. In these embodiments, the controller is programmed to control the generation of an oversampled version of a sine wave by (a) applying a first control signal to the control input for a duration of T / 3 to route the output of the single DC power supply to the output terminal with a first polarity, then (b) waiting for a duration of T / 6, then (c) applying a second control signal to the control input for a duration of T / 3 to route the output of the single DC power supply to the output terminal with a second polarity opposite to the first polarity, then (d) waiting for a duration of T / 6, and then continuously repeating sequences (a), (b), (c), and (d). T is the reciprocal of the frequency f. Optionally, in these embodiments, the cut-off frequency is between 2f and 4f, and the output filter has a transfer function that has a zero at 5f.

[0010] In some embodiments of the second device, n > 1, and the controller is further programmed to control the amplitude of the sine wave by adjusting the output voltages of the n DC power supplies via the voltage control input while maintaining a constant ratio between the output voltages of each of the n DC power supplies. Optionally, in these embodiments, the output filter may have a transfer function that has a zero at frequencies where harmonics of the frequency f are expected to contain power.

[0011] Another aspect of the present invention is directed to a first method for generating a sine wave of frequency f. The first method includes the step of setting n DC power supplies to respective output voltages, where n is a positive integer, and using equally spaced samples including a sampling point at 0° that are sampled N times per cycle, where N = 2 + 4n, to set the output voltages of the n DC power supplies to levels present in the oversampled version of the sine wave, and then controlling the outputs of the n DC power supplies to be switched to outputs in a controlled sequence such that each of the n DC power supplies is switched to its output in each direction at an appropriate time within the sequence to generate the oversampled version of the sine wave. The first method also includes filtering the oversampled version of the sine wave such that frequencies greater than the cut-off frequency are attenuated while allowing the frequency f to pass, where the filtering implements a transfer function having zeros at frequencies where harmonics of the frequency f are expected to contain power. The amplitude of the sine wave is controlled by adjusting the output voltages of the n DC power supplies, and adjustment of the output voltage of any given one of the DC power supplies is prevented while any given one of the DC power supplies is switched to the output.

[0012] In some examples of the first method, n = 1, which means that only a single DC power supply is present, and adjustment of the output voltage of the single DC power supply occurs only during times when the output of the single DC power supply is not switched to the output.

[0013] In some examples of the first method, the filtering implements a transfer function having zeros at frequencies where harmonics of the frequency f are expected to contain power.

[0014] Another aspect of the present invention is directed to a third apparatus for generating an output waveform of frequency f. The third apparatus comprises a first DC power supply having a first voltage control input for setting the output voltage of the first DC power supply, and a second DC power supply having a second voltage control input for setting the output voltage of the second DC power supply. The third apparatus also comprises a power switch having an output terminal and a control input. The power switch routes (a) the output of the first DC power supply to the output terminal with a first polarity in response to a first state of the control input, (b) the output of the first DC power supply to the output terminal with a second polarity in response to a second state of the control input, (c) the output of the second DC power supply to the output terminal with the first polarity in response to a third state of the control input, (d) the output of the second DC power supply to the output terminal with the second polarity in response to a fourth state of the control input, and (e) is configured to remain off in response to additional states of the control input. The second polarity is opposite to the first polarity. The third apparatus also comprises an output filter for filtering the current arriving from the output terminal of the power switch. The output filter passes the frequency f and attenuates frequencies above the cut-off frequency. The third apparatus also comprises a controller programmed to operate in a first mode in which the controller sets the control input in an alternating sequence of the first and second states while keeping the first voltage control input constant. The controller is further programmed to operate in a second mode in which the controller sets the control input in an alternating sequence of the third and fourth states while keeping the second voltage control input constant. The controller is further programmed to cause a change in the amplitude of the output waveform by adjusting the second voltage control input and then switching the controller to the second mode when the controller is operating in the first mode, and the controller is further programmed to cause a change in the amplitude of the output waveform by adjusting the first voltage control input and then switching the controller to the first mode when the controller is operating in the second mode.

[0015] In some embodiments of the third device, the output waveform is a sine wave, and the setting in the alternating sequence of the control input to the first and second states is: (a) set the control input to the first state for a duration of T / 3, then (b) wait for a duration of T / 6, then (c) set the control input to the second state for a duration of T / 3, then (d) wait for a duration of T / 6, and then continuously repeat the sequences (a), (b), (c), and (d). The setting in the alternating sequence of the control input to the third and fourth states is: (e) set the control input to the third state for a duration of T / 3, then (f) wait for a duration of T / 6, then (g) set the control input to the fourth state for a duration of T / 3, then (h) wait for a duration of T / 6, and then continuously repeat the sequences (e), (f), (g), and (h). T is the reciprocal of the frequency f.

[0016] In some embodiments of the third device, when the controller is operating in the first mode, the controller is further programmed to cause a change in the amplitude of the output waveform by adjusting the second voltage control input at least 1 millisecond before the controller switches to the second mode. When the controller is operating in the second mode, the controller is further programmed to cause a change in the amplitude of the output waveform by adjusting the first voltage control input at least 1 millisecond before the controller switches to the first mode.

[0017] Some embodiments of the third device have a primary side connected to the output terminal of the power switch and a secondary side connected to the output filter, and further include a transformer configured such that current from the output terminal of the power switch reaches the output filter via the transformer. Optionally, in these embodiments, the power switch is configured to: (a) route the output of the first DC power source to the primary side of the transformer in a first direction in response to a first state of the control input; (b) route the output of the first DC power source to the primary side of the transformer in a second direction in response to a second state of the control input; (c) route the output of the second DC power source to the primary side of the transformer in the first direction in response to a third state of the control input; (d) route the output of the second DC power source to the primary side of the transformer in the second direction in response to a fourth state of the control input; and (e) be configured to remain off in response to a fifth state of the control input. The second direction is opposite to the first direction.

[0018] In some embodiments of the third device, the cut-off frequency is between 2f and 4f, and the output filter has a transfer function having a zero at 5f.

[0019] Another aspect of the present invention is directed to a second method for generating an output waveform of frequency f. The second method includes: (a) routing the output of the first DC power supply to the output terminal of the power switch with a first polarity in response to a first state of the control input of the power switch; (b) routing the output of the first DC power supply to the output terminal with a second polarity in response to a second state of the control input; (c) routing the output of the second DC power supply to the output terminal with the first polarity in response to a third state of the control input; (d) routing the output of the second DC power supply to the output terminal with the second polarity in response to a fourth state of the control input; and (e) remaining off in response to additional states of the control input. The second polarity is opposite to the first polarity. The second method also includes filtering the current arriving from the output terminal of the power switch. Filtering includes passing the frequency f and attenuating frequencies above the cut-off frequency. The second method also includes operating in a first mode in which the control input is set in an alternating sequence of the first and second states while keeping the output voltage of the first DC power supply constant. The second method also includes operating in a second mode in which the control input is set in an alternating sequence of the third and fourth states while keeping the output voltage of the second DC power supply constant. In the first mode, a change in the amplitude of the output waveform is caused by adjusting the output voltage of the second DC power supply and then switching to the second mode. And in the second mode, a change in the amplitude of the output waveform is caused by adjusting the output voltage of the first DC power supply and then switching to the first mode.

[0020] In some examples of the second method, the output waveform is a sine wave and the control input is set in an alternating sequence between a first and a second state by: (a) setting the control input to the first state for a duration of T / 3, then (b) waiting for a duration of T / 6, then (c) setting the control input to the second state for a duration of T / 3, then (d) waiting for a duration of T / 6, and then continuously repeating the sequence (a), (b), (c), and (d). In these examples, the control input is set in an alternating sequence between a third and a fourth state by: (e) setting the control input to the third state for a duration of T / 3, then (f) waiting for a duration of T / 6, then (g) setting the control input to the fourth state for a duration of T / 3, then (h) waiting for a duration of T / 6, and then continuously repeating the sequence (e), (f), (g), and (h). And in these examples, T is the reciprocal of the frequency f.

[0021] In some examples of the second method, in the first mode, a change in the amplitude of the output waveform is caused by adjusting the output voltage of the second DC power supply at least 1 millisecond before switching to the second mode, and in the second mode, a change in the amplitude of the output waveform is caused by adjusting the output voltage of the first DC power supply at least 1 millisecond before switching to the first mode.

[0022] Another aspect of the present invention is directed to a fourth apparatus for generating an alternating electrical signal for application to a first pair of electrodes and a second pair of electrodes. The fourth apparatus includes an alternating voltage generator having an output, an electronic switch, and a controller. The electronic switch has an input that receives the output of the alternating voltage generator, a first power output, and a second power output. The electronic switch is configured to operate in (a) a first mode in which the output of the alternating voltage generator is routed to the first power output and (b) a second mode in which the output of the alternating voltage generator is routed to the second power output. The electronic switch is further configured to cycle through a repeating sequence that includes the first mode and the second mode. The controller is configured to synchronize the operation of the alternating voltage generator and the electronic switch such that whenever the electronic switch switches to either the first mode or the second mode, the instantaneous output of the alternating voltage generator is less than 5V in magnitude. Within 20 milliseconds after the electronic switch switches to either the first mode or the second mode, the output voltage of the alternating voltage generator is at least 80% of the steady-state output voltage of the alternating voltage generator.

[0023] In some embodiments of the fourth apparatus, the electronic switch is configured to operate in (c) a third mode in which the output of the alternating voltage generator is not routed to either the first power output or the second power output and (d) to cycle through the first mode, the second mode, and the third mode in the following repeating sequence: (1) the first mode, (2) the third mode, (3) the second mode, and (4) the third mode. In some embodiments of the fourth apparatus, the controller is configured to synchronize the operation of the alternating voltage generator and the electronic switch such that whenever the electronic switch switches to either the first mode or the second mode, the instantaneous output of the alternating voltage generator is less than 1V in magnitude.

[0024] In some embodiments of the fourth device, within 5 milliseconds after the electronic switch switches to either the first mode or the second mode, the output voltage of the AC voltage generator is at least 80% of the steady-state output voltage of the AC voltage generator. In some embodiments of the fourth device, within 1 millisecond after the electronic switch switches to either the first mode or the second mode, the output voltage of the AC voltage generator is at least 80% of the steady-state output voltage of the AC voltage generator.

[0025] In some embodiments of the fourth device, during the transition of the electronic switch to either the first mode or the second mode, the AC voltage generator continues to operate at its full steady-state AC output voltage.

[0026] In some embodiments of the fourth device, the controller synchronizes the operations of the AC voltage generator and the electronic switch by controlling the timing of the transition of the electronic switch such that a time window during which the instantaneous output of the AC voltage generator is less than 5V in magnitude coincides with the transition. In some embodiments of the fourth device, the controller synchronizes the operations of the AC voltage generator and the electronic switch by controlling the AC voltage generator such that the output of the AC voltage generator is turned off whenever the transition of the electronic switch occurs. In some embodiments of the fourth device, the controller synchronizes the operations of the AC voltage generator and the electronic switch by both (a) controlling the timing of the transition of the electronic switch such that a time window during which the instantaneous output of the AC voltage generator is less than 5V in magnitude coincides with the transition and (b) controlling the AC voltage generator such that the output of the AC voltage generator is turned off whenever the transition of the electronic switch occurs.

[0027] In some embodiments of the fourth device, the electronic switch is configured to cycle between a first mode and a second mode in the following repeating sequence: (1) the first mode, (2) the second mode. In these embodiments, the electronic switch is configured to switch directly from the first mode to the second mode and directly from the second mode to the first mode.

[0028] Another aspect of the present invention is directed to a fifth device for generating an alternating electrical signal for application to a first pair of electrodes and a second pair of electrodes. The fifth device includes an alternating voltage generator having an output, an electronic switch, and a controller. The electronic switch has an input that receives the output of the alternating voltage generator, a first power output, and a second power output. The electronic switch is configured to operate in (a) a first mode in which the output of the alternating voltage generator is routed to the first power output and (b) a second mode in which the output of the alternating voltage generator is routed to the second power output. The electronic switch is further configured to cycle through a repeating sequence that includes the first mode and the second mode. The controller is configured to synchronize the operation of the alternating voltage generator and the electronic switch such that whenever the electronic switch switches to either the first mode or the second mode, the instantaneous output of the alternating voltage generator has a magnitude that is less than the threshold at which the subject being treated begins to feel a perceptible sensation. Within 20 milliseconds after the electronic switch switches to either the first mode or the second mode, the output voltage of the alternating voltage generator is at least 80% of the steady-state output voltage of the alternating voltage generator.

[0029] In some embodiments of the fifth device, the electronic switch is configured to operate in (c) a third mode in which the output of the alternating voltage generator is not routed to either the first power output or the second power output and (d) further configured to cycle through the following repeating sequence of the first mode, the second mode, and the third mode: (1) the first mode, (2) the third mode, (3) the second mode, and (4) the third mode.

[0030] In some embodiments of the fifth device, the controller is configured to synchronize the operations of the AC voltage generator and the electronic switch such that the instantaneous output of the AC voltage generator is less than 1V in magnitude whenever the electronic switch switches to either the first mode or the second mode.

[0031] In some embodiments of the fifth device, within 5 milliseconds after the electronic switch switches to either the first mode or the second mode, the output voltage of the AC voltage generator is at least 80% of the steady-state output voltage of the AC voltage generator. In some embodiments of the fifth device, within 1 millisecond after the electronic switch switches to either the first mode or the second mode, the output voltage of the AC voltage generator is at least 80% of the steady-state output voltage of the AC voltage generator.

[0032] In some embodiments of the fifth device, during the transition of the electronic switch to either the first mode or the second mode, the AC voltage generator continues to operate at its full steady-state AC output voltage.

[0033] In some embodiments of the fifth device, the controller synchronizes the operations of the AC voltage generator and the electronic switch by controlling the timing of the transition of the electronic switch such that the transition coincides with a time window during which the instantaneous output of the AC voltage generator has a magnitude less than a threshold value. In some embodiments of the fifth device, the controller synchronizes the operations of the AC voltage generator and the electronic switch by controlling the AC voltage generator such that the output of the AC voltage generator is turned off whenever a transition of the electronic switch occurs. In some embodiments of the fifth device, the controller synchronizes the operations of the AC voltage generator and the electronic switch by both (a) controlling the timing of the transition of the electronic switch such that the transition coincides with a time window during which the instantaneous output of the AC voltage generator has a magnitude less than a threshold value and (b) controlling the AC voltage generator such that the output of the AC voltage generator is turned off whenever a transition of the electronic switch occurs.

[0034] In some embodiments of the fifth device, the electronic switch is configured to cycle between a first mode and a second mode in the following repeating sequence: (1) the first mode, (2) the second mode. In these embodiments, the electronic switch is configured to switch directly from the first mode to the second mode and directly from the second mode to the first mode.

Brief Description of the Drawings

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Embodiments for Carrying Out the Invention

[0036] Various embodiments will be described in detail below with reference to the accompanying drawings, where like reference numerals represent like elements.

[0037] When using prior art techniques to generate high voltage sine wave signals in connection with TTFields therapy, high frequency artifacts (e.g., voltage spikes) may appear in the output under certain conditions (e.g., in response to a command to change the output voltage, or when the direction of TTFields is switched). Also, since those high frequency artifacts can cause discomfort to the person being treated with TTFields therapy, the output voltage amplitude has typically been ramped up slowly to prevent those high frequency artifacts (and the resulting discomfort) from occurring. However, using a slow ramp up has disadvantages, namely that the output voltage is not always as high as possible, which means that the electric field applied to the tumor is not always as strong as possible. Also, when the electric field is not as strong as possible, the effectiveness of the treatment may be reduced. The embodiments described herein advantageously can increase the output voltage amplitude much more rapidly without introducing high frequency artifacts. Thus, these embodiments can prevent discomfort from occurring without incurring a related decrease in the effectiveness of the treatment.

[0038] The embodiments described herein are useful in connection with generating TTFields as described in U.S. Patent No. 7,805,201, which is incorporated herein by reference. The embodiments described herein are based on the architecture described in U.S. Patent No. 9,910,453, which is incorporated herein by reference. In particular, the embodiments described herein enable the voltage of the sine wave signal (applied to the TTFields transducer array) to be adjusted more rapidly without the risk of introducing high frequency artifacts (e.g., voltage spikes) in the output. The embodiments described herein also enable the sine wave signal to be instantaneously switched on and off at full power without the risk of introducing high frequency artifacts in the output.

[0039] When generating a high-voltage signal for TTFields delivery, it should be noted that the exact shape of the signal is known at each point in time (a pure sine wave of a known frequency), and it is only the amplitude of the output signal that changes over time based on an external input (e.g., control based on the patient's skin temperature).

[0040] The embodiments described herein generate a high-voltage sine wave signal by generating a specific pulse train that results in a low-distortion sine wave of a desired amplitude and frequency when filtered using a specific low-pass filter.

[0041] FIG. 1 is a block diagram of a first embodiment of a sine wave generator that generates a sine wave having a controllable amplitude at a preset frequency f. Ultimately, the amplitude of the output sine wave will preferably be proportional to the output of a DC-DC converter 50 that is a controlled DC power supply.

[0042] In the illustrated embodiment, the DC-DC converter 50 is configured to multiply an analog voltage control input signal by 10. Thus, by proportional control between them, when a 1V voltage control signal is applied, the output becomes 10V, and when a 5V voltage control signal is applied, the output becomes 50V. Therefore, the output of the DC-DC converter 50 can take any value between 0V and 50V depending on the voltage (e.g., 0 to 5V) applied to the analog voltage control input. The controller 40 controls the output voltage of the DC-DC converter 50 by writing a control word to a digital-to-analog converter (DAC) 42. The DAC 42 then generates an analog voltage proportional to the control word, and this analog voltage is applied to the voltage control input of the DC-DC converter 50.

[0043] The output of the DC-DC converter 50 is routed to the power switch 60. The power switch 60 has a control input and, depending on the state of the control input, routes the output of the DC-DC converter 50 in either direction to the primary side of the transformer 70. More specifically, when the first control signal is applied to the control input, the power switch 60 applies the output of the DC-DC converter 50 to the primary side of the transformer 70 in the first direction. When the second control signal is applied to the control input, the power switch 60 applies the output of the DC-DC converter 50 to the primary side of the transformer 70 in a second direction opposite to the first direction. If neither the first control signal nor the second control signal is applied to the control input, the power switch 60 remains off, and in that case, the power from the DC-DC converter 50 is not routed to the primary side of the transformer 70.

[0044] FIG. 2 includes a block of one preferred method for implementing the power switch 60 using a set of four electronic control switches 61-64 connected to the primary side of the transformer 70 in an H-bridge configuration. These switches 61-64 open and close in response to a signal applied to the control input 68. As will be understood by those skilled in the relevant art, a wide variety of techniques can be used to implement these switches. For example, the switches 61-64 can be implemented using MOSFET transistors (e.g., BSC109N10NS3 manufactured by Infineon) along with appropriate circuitry to switch them on and off in response to a control signal. To apply the output of the DC-DC converter 50 to the primary side of the transformer 70 in the first direction, only switches 63 and 62 should be closed. To apply the output of the DC-DC converter 50 to the primary side of the transformer 70 in the opposite direction, only switches 61 and 64 should be closed. If all four of these switches 61-64 are off, power is not routed to the primary side of the transformer 70.

[0045] The transformer 70 is preferably a step-up transformer having a step-up ratio between 1:4 and 1:9. In some preferred embodiments, the transformer 70 is a step-up transformer having a step-up ratio of 1:6. For example, when a transformer having a step-up ratio of 1:6 is used in combination with a DC-DC converter 50 that can output up to 24V, the resulting voltage on the secondary side of the transformer 70 can be as high as 300V.

[0046] Returning to FIG. 1, the controller 40 applies a control signal to the control input of the power switcher 60 in a time-choreographed sequence to construct an oversampled version of a sine wave sampled six times per cycle using equally spaced samples. More specifically, FIG. 3 shows a sine wave 110 and an oversampled version 112 of that sine wave sampled at 0°, 60°, 120°, 180°, 240°, 300°, and 360°. Looking at this oversampled version 112, it can be seen that it contains only three voltage levels: a positive voltage +V between 60° and 180°, a negative voltage -V between 240° and 360°, and zero volts between 0° and 60° and also between 180° and 240°. Note that the zero-volt level exists because the sampling time was selected such that one of the sampling points occurs at 0° where the sine function equals zero and another one of the sampling points occurs at 180° where the sine function equals zero. This selection advantageously reduces the number of voltage levels that have to be generated to construct the oversampled version 112 of the sine wave. Also advantageously, it reduces the number of switching events, which minimizes the losses that occur during the switching process.

[0047] As a result, an oversampled version of the sine wave at the pre-set frequency f can be constructed at the output of transformer 70 by successively repeating the following four steps: (a) applying a first control signal to control input 68 for a duration of T / 3 corresponding to the 60-180° segment of waveform 112 in FIG. 3, then (b) waiting for a duration of T / 6 corresponding to the 180-240° segment of waveform 112, then (c) applying a second control signal to control input 68 for a duration of T / 3 corresponding to the 240-360° segment of waveform 112, and then (d) waiting for a duration of T / 6 corresponding to the 0-60° segment of waveform 112. Note that T is the reciprocal of the pre-set frequency f.

[0048] Controller 40 is responsible for generating these control signals in this sequence. Controller 40 can be implemented using a variety of techniques apparent to those skilled in the relevant art, including, but not limited to, a microcontroller or microprocessor programmed to perform the functions described herein. Controller 40 can also be implemented using a combination of a microcontroller or microprocessor and a hard-wired sequencer, which can be implemented using, for example, a state machine or a counter.

[0049] The output on the secondary side of transformer 70 is routed to an output filter 80 having a cut-off frequency between 2f and 4f. Output filter 80 passes the pre-set frequency f and attenuates frequencies above the cut-off frequency.

[0050] Note that when the oversampled version of the sine wave (112 in FIG. 3) is converted to the frequency domain, as a result of the fact that waveform 112 is symmetric, all even harmonics become zero. In addition, since sampling is performed six times per cycle, the third harmonic of waveform 112 also becomes zero.

[0051] Many filter designs have inherent instability at their cutoff frequencies. However, since the third harmonic component of the oversampled waveform 112 is zero, the lowest harmonic that will have any significant power will be the fifth harmonic. If the output filter 80 is designed such that its cutoff frequency matches the third harmonic, the waveform will not contain power at 3f, so the oversampled waveform 112 will not be affected by the instability near the cutoff frequency. Thus, it is most preferred to design the output filter 80 to have its cutoff frequency at 3f, in which case (a) the fundamental component is well below the cutoff frequency so as not to activate the instability, and (b) the fifth harmonic is well above the cutoff frequency so as not to activate the instability.

[0052] To further reduce higher harmonics, the output filter 80 is preferably designed such that the transfer function of the output filter has a zero located at the fifth harmonic. This can be achieved, for example, by selecting the components within the output filter 80 to implement an elliptic low-pass filter or a Chebyshev-2 low-pass filter. Typically, elliptic filters and Chebyshev-2 filters have significant ripple within the stop band and are not suitable for filtering a square wave into a sine wave. As a result, if the incoming signal happens to contain a frequency component that coincides with a crest within that ripple, that component will not be filtered out of the incoming signal. The embodiment of FIG. 1 avoids this situation by generating an oversampled waveform 112 at a preset frequency, which means that the frequency of the fifth harmonic is known in advance. By selecting the components within the output filter 80 such that its transfer function has a zero at the fifth harmonic, it is ensured that the fifth harmonic will never coincide with a crest within the ripple in the stop band.

[0053] To further reduce the higher harmonics, the output filter 80 can be designed such that its transfer function has additional zeros located at the seventh harmonic. Again, since the frequency of the seventh harmonic is known in advance, the components within the output filter 80 can be selected such that its transfer function has a zero at the seventh harmonic.

[0054] Designing the output filter 80 to have zeros at the fifth and seventh harmonics reduces the attenuation at other frequencies located between the harmonics, which is usually highly undesirable. However, since the frequency of the oversampled waveform 112 is preset in advance and only contains signals centered around odd harmonics (starting from the fifth harmonic), this design actually reduces the overall distortion of the output signal in the embodiment of FIG. 1.

[0055] If the output filter 80 is designed to have zeros at the fifth and seventh harmonics, the initial harmonic containing any significant power is the ninth harmonic. However, the power at the ninth harmonic of the oversampled waveform 112 (in FIG. 3) is relatively low in the first place, and the ninth harmonic is 6f higher than the cut-off frequency, so the power at the ninth harmonic (and all higher harmonics) in the output 100 of the output filter 80 will be low enough to generate an excellent sine wave.

[0056] FIG. 2 shows a suitable architecture for implementing the output filter 80 having a cut-off frequency and zeros at the positions shown above. Preferably, the output filter 80 is a multi-stage low-pass LC filter. In this case, the first stage of the output filter 80 includes an inductor 82 and a capacitor 83, and the subsequent stages are represented by block 85. In some embodiments, the filter 80 is a fourth-order LC low-pass filter. In some embodiments, the filter 80 is a dual M-type element low-pass filter.

[0057] When the electrical characteristics of transformer 70 are modeled, the leakage inductance of the transformer appears in series with the secondary side of transformer 70. As a result, this leakage inductance must be taken into account when calculating the inductance of the first inductor 82 in the first stage of output filter 80. In some embodiments, a transformer 70 having a leakage inductance large enough to supply all of the inductance required for the first inductor 82 is selected. In this case, the first inductor 82 can be completely eliminated from the output filter 80 and replaced with a wire. For example, if the desired value calculated for the first inductor in the output filter is 60 μH and the leakage inductance of transformer 70 is 60 μH, the first inductor 82 of the output filter can be completely eliminated.

[0058] In an alternative embodiment, the leakage inductance of transformer 70 occupies at least half of the inductance of the first stage of the low-pass LC filter. In these embodiments, starting from the value calculated for the first inductor 82, subtract only the leakage inductance of transformer 70 from that value. For example, if the value calculated for the first inductor in the first stage of the output filter is 100 μH and the leakage inductance of transformer 70 is 60 μH, a 40 μH inductor (since 100 μH - 60 μH = 40 μH) should be used as the first inductor 82 of the output filter.

[0059] FIG. 4 is a schematic diagram of an embodiment of an output filter 80 in which the inductance of transformer 70 provides all of the inductance necessary to function as a first inductor for the first stage of the output filter. The transformer in FIG. 4 has the following characteristics, namely, a turns ratio of 6:25, an inductance of 0.25 mH on the primary side (at 200 kHz), an inductance of 4.5 mH on the secondary side (at 200 kHz), and a leakage inductance between 32 μH and 36 μH (at 200 kHz), which is a Zolotov TRM085. Capacitors C33, C35, C36, C42, C43, and C44 are all 3300 pF capacitors. C40 is a 4.7 nF capacitor. C41 is a 470 pF capacitor. Inductors L5 - L8 are all 4 μH inductors. The values of these components were selected to place the zeros of the filter at the fifth and seventh harmonics when the operating frequency is 200 kHz.

[0060] An alternative design for implementing an output filter 80 having an operating frequency of 150 kHz can be achieved starting from the schematic diagram of FIG. 4 by (a) adding an additional 4.7 nF capacitor in parallel with C40 and (b) replacing the 3300 pF capacitors C33, C35, C36, C42, C43, and C44 with 5600 pF capacitors. These components were selected to place the zeros of the filter at the fifth and seventh harmonics when the operating frequency is 150 kHz.

[0061] The output impedance of the output filter 80 is preferably as close as possible to 70 ohms. In an alternative embodiment, the output impedance of the output filter 80 is between 40 ohms and 120 ohms. Since the current and voltage of the output signal 100 can vary depending on the presented load (i.e., the patient and the transducer array in the context of TTFields therapy), it is appropriate to use the output impedance within this range. However, since the output impedance is between 40 ohms and 120 ohms, even if there is a short circuit at the output, the current will not surge to a dangerous value. In addition, if the impedance of the load suddenly increases (e.g., if the electrode is partially disconnected from the patient), the decrease in current is not very significant. This is very useful as a safety feature in the context of TTFields therapy.

[0062] The controller 40 controls the amplitude of the output signal 100 by adjusting the control signal applied to the voltage control input of the DC-DC converter 50. In the illustrated embodiment, this is achieved by the controller 40 writing a control word to the DAC 42. The DAC 42 responds by outputting an analog voltage that functions as the control signal applied to the voltage control input of the DC-DC converter 50. For example, assume that the output of the DAC 42 starts at 1V, the DC-DC converter outputs 10V DC, and the transformer 70 has a step-up ratio of 1:6. Under these conditions, the pulse at the output of the secondary side of the transformer 70 will be 60V. When the controller 40 writes a new control word to the DAC 42, it raises the output of the DAC 42 to 2V. The DC-DC converter 50 responds to the new signal applied to its voltage control input by raising its output voltage to 20V DC, which (after passing through the step-up transformer 70) raises the pulse at the output of the secondary side of the transformer 70 to 120V.

[0063] Preferably, the voltage and / or current of the output signal 100 is monitored by the voltage sensing circuit 92 and / or the current sensing circuit 94. The outputs of these circuits 92, 94 are preferably fed back to the controller 40, and the controller 40 is preferably configured to suppress the generation of both the first control signal and the second control signal applied to the control input 68 of the power switcher 60 when an error state (e.g., overvoltage, overcurrent, severe voltage drop, etc.) is detected at the output 100, thereby shutting down the power switcher 60. Optionally, the shutdown of the power switcher 60 may include appropriate temperature sensors, and by routing signals from these temperature sensors back to the controller 40, it can also be triggered by an overheating condition in the load.

[0064] Note that in the illustrated embodiment, a single controller 40 is used to implement all of the control and sequencing functions described herein. However, in alternative embodiments, the programmable controller 40 may be combined with a hardwired sequencer to perform these two functions separately.

[0065] In some embodiments, the outputs of the current sensing circuit 94 and / or the voltage sensing circuit 92 are fed back to the controller 40. In these embodiments, the controller can adjust the voltage at the output of the DC-DC converter 50 by writing an appropriate control word to the DAC 42 to adjust the current or voltage of the output signal 100 to a desired level. For example, if the controller 40 is set to adjust the current to a specific level and the output of the current sensing circuit 94 indicates that the current is too low, the controller can increase the voltage at the output of the DAC 42, which causes an increase in the amplitude at the output signal 100. Similarly, if the output of the current sensing circuit 94 indicates that the current is too high, the controller can decrease the voltage at the output of the DAC 42, which causes a corresponding decrease in the amplitude at the output signal 100.

[0066] In an alternative embodiment, the transformer 70 (shown in FIGS. 1 and 2) may be omitted, in which case the two conductors at the output of the power switcher 60 are directly connected to the two conductors at the input of the output filter 80. In these embodiments, the current flows directly from the output of the power switcher 60 to the input of the output filter 80 without passing through the transformer. However, these alternative embodiments are less desirable, particularly in situations where insulation is desired and in situations where a high voltage output is desired. In addition, these alternative embodiments cannot rely on the leakage inductance of the transformer to provide some or all of the inductance required for the first stage of the filter.

[0067] Note that the design of the embodiment of FIG. 1 depends on prior knowledge of the incoming signal and the intentional construction of both the signal and the output filter 80 such that the most significant high frequencies are essentially zero (e.g., even harmonics and third harmonics) or are made zero by the output filter 80 (e.g., fifth and seventh harmonics). This helps to provide a very clean high voltage output signal at the desired frequency with very high efficiency.

[0068] The embodiment of FIG. 1 uses a single DC-DC converter 50 and implements six equally spaced sampling points per cycle. In an alternative embodiment, the number of sampling points can be increased to N = 2 + 4n, where n is a positive integer. When n = 1, the situation described above in connection with FIG. 1 results. When n = 2, the situation described below in connection with FIG. 5 using two DC-DC converters results. Other embodiments can be implemented for n>2 according to the same framework using additional DC-DC converters and even more samples (following the rule N = 2 + 4n).

[0069] FIG. 5 is a block diagram of a second embodiment of a sine wave generator that generates a sine wave having a controllable amplitude at a pre-set frequency f, where n = 2. As a result, there are two DC-DC converters 50, 50B, and 10 samples per cycle (according to the formula N = 2 + 4n) are used. It should be noted that in the embodiments of FIGS. 5-6, components having like reference numerals operate in a manner similar to the above description associated with the embodiments of FIGS. 1-2.

[0070] FIG. 7 shows a sine wave 120 and an oversampled version 122 of that sine wave sampled 10 times per cycle (i.e., at 0°, 36°, 72°, ... 324°, and 360°). Looking at this oversampled version 122, it can be seen that it contains only five voltage levels, namely, a low positive voltage +V1, a higher positive voltage +V2, a low negative voltage -V1, a higher negative voltage -V2, and zero volts (between 0° and 36°, and between 180° and 216°). Again, since one of the sampling points occurs at 0° where the sine function is equal to zero and another one of the sampling points occurs at 180° where the sine function is equal to zero, the sampling time is selected such that the zero volt level exists. This selection advantageously reduces the number of voltage levels that would otherwise have to be generated to construct the oversampled version 122 of the sine wave into two levels (i.e., V1 and V2).

[0071] As a result, the controller 40B is used to generate an oversampled version of a sine wave that is sampled N times per cycle using equally spaced samples including the sampling point at 0°, where N = 2 + 4n, by setting the output voltage of the DC power supply to a level present in the oversampled version of the sine wave and then sequencing a control signal through 2n states and an additional off state so that each of the DC power supplies is applied to the primary side of the transformer in each direction at an appropriate time within the sequence for control.

[0072] (As in the embodiments of FIGS. 5 - 6) When n = 2, an oversampled version of a sine wave of a preset frequency f can be constructed at the output of the transformer 70 by continuously repeating the following eight steps: applying V1 to the primary side of the transformer 70 in the first direction between 36° and 72°; applying V2 in the first direction between 72° and 144°; applying V1 in the first direction between 144° and 180°; remaining off between 180° and 216°; applying V1 in the second direction between 216° and 252°; applying V2 in the second direction between 252° and 324°; applying V1 in the second direction between 324° and 360°; and remaining off between 0° and 36°. Note that the ratio between V1 and V2 must remain constant in order for the resulting waveform to properly follow the oversampled version of the sine wave (122 in FIG. 7). More specifically, the ratio V2 / V1 must be equal to sin(72°) / sin(36°), which is 1.618.

[0073] The controller 40B is responsible for generating a control signal that causes these voltages to be applied to the transformer 70 in the sequence specified above to the power switcher 60B. The controller 40B is similar to the controller 40 in the embodiment of FIG. 1, except that it sequences 10 states per cycle instead of 6 states per cycle.

[0074] Here, referring to FIG. 6, the power switch 60B has a control input 68, and the power switch is configured to (a) apply a selected one of the outputs of the DC power supply in a selected direction to the primary side of the transformer 70 according to 2n states of the control signal applied to the control input 68, or (b) remain off according to an additional state of the control signal.

[0075] FIG. 6 is a block diagram of one preferred approach for implementing the power switcher 60B. This power switcher is similar to the power switcher 60 of the embodiment of FIG. 1, except that it includes additional switches 65-66 for switching the output of the second DC-DC converter in either direction across the transformer 70. More specifically, this power switcher 60B uses a set of six electronically controlled switches 61-66 connected to the primary side of the transformer 70, as shown in FIG. 6. (Similar to the corresponding switches in the embodiments of FIGS. 1-2) These switches 61-66 open and close in response to a signal applied to the control input 68. Only switches 63 and 62 should be closed to route the output of the first DC-DC converter 50 in the first direction to the primary side of the transformer 70. Only switches 61 and 64 should be closed to route the output of the first DC-DC converter 50 in the opposite direction (i.e., with opposite polarity) to the primary side of the transformer 70. Only switches 65 and 62 should be closed to route the output of the second DC-DC converter 50B in the first direction to the primary side of the transformer 70. Only switches 61 and 66 should be closed to route the output of the second DC-DC converter 50B in the opposite direction (i.e., with opposite polarity) to the primary side of the transformer 70. When all six of these switches 61-66 are off, power is not routed to the primary side of the transformer 70.

[0076] Returning to FIG. 5, the output filter 80B is connected to the secondary side of the transformer 70, and the output filter passes a preset frequency f and attenuates frequencies above the cut-off frequency. The output filter 80B is similar to the output filter 80 in the embodiments of FIGS. 1-2, except that the position of the zero in the transfer function of the output filter 80B must be adjusted in consideration of the different frequency content of the oversampled waveform 122 (shown in FIG. 7). More specifically, the output filter 80B should have a transfer function with a zero at a frequency where harmonics of the preset frequency f are expected to contain power.

[0077] For example, since waveform 122 has 10 samples per cycle, the initial harmonic that is expected to appear is the ninth harmonic. Thus, when this waveform 122 is being used, a transfer function having a zero at the ninth harmonic is useful. The cut-off frequency of the filter should also be appropriately adjusted based on the set of harmonics that are expected to appear (which can be pre-calculated by performing a Fourier transform of the waveform being used).

[0078] Optionally, the transfer function of output filter 80B can also be designed to have a zero at the next frequency at which a harmonic of the pre-set frequency f is expected to contain power. In the case of waveform 122, this is the eleventh harmonic.

[0079] Controller 40B controls the amplitude of the sine wave at output 100B of output filter 80B by adjusting the output voltages of DC power supplies 50, 50B via their voltage control inputs while maintaining a constant ratio between the output voltages of each of the DC power supplies. In the illustrated embodiment, this is achieved by writing appropriate control words to DAC 42 and DAC 42B while taking care to maintain the required ratio of sin(72°) / sin(36°) as described above. In an alternative embodiment, the second DAC 42B can be eliminated and replaced with a 1.618× hardware multiplier inserted between the output of DAC 42 and the voltage control input to the second DC-DC converter 50B.

[0080] In an alternative embodiment, transformer 70 can be omitted from the embodiment of FIG. 5, in which case the two conductors at the output of power switch 60B are directly connected to the two conductors at the input of output filter 80B. In these embodiments, current flows directly from the output of power switch 60B to the input of output filter 80B without passing through the transformer. However, these embodiments are less preferred for the same reasons discussed above in connection with FIG. 1.

[0081] It should be noted that the system described above is suitable for generating high-voltage signals of any shape as long as the pulse train resulting in the high-voltage signal can be determined prior to use either by calculation or experiment and the filter is designed accordingly.

[0082] When the output signal generated by the system is applied to the electrodes to generate TTFields (as described in Patent 7,805,201), changes in the load associated with the patient's body and the transducer array can change the output signal due to interaction with the output filter. This means that any change in this load (such as lifting the disk from the patient's body, shorting, etc.) immediately affects the output signal that is constantly monitored. Therefore, it is possible for the device to respond very quickly to these changes (for example, by shutting down the power switch 60 in response to detection of a short circuit or overload condition).

[0083] In particular, in the embodiment described above, since a sine wave is being generated at a known frequency, the exact shape of the desired output signal is known in advance at each point in time. What changes over time is only the amplitude of the output signal based on a controller that responds to external inputs (such as current measurements or temperature measurements). The embodiment described above can advantageously be used to generate a very clean narrow-band limited signal in the frequency range of 100 - 500 kHz with very low losses and very low sensitivity to the external load to which the signal generator is connected.

[0084] In an alternative embodiment, the system can be used to generate a sine wave of any desired frequency within a pre-set range by constructing a filter using components having an adjustable reactance (e.g., an adjustable capacitance or an adjustable inductance). In these embodiments, the reactance of the adjustable component is set to impart the desired transfer function characteristics to the filter. Then, as discussed above in connection with FIGS. 1 and 5, an appropriate oversampled sine wave is generated and supplied to the filter.

[0085] In other alternative embodiments, the system can be used to generate a finite number of predefined signals at a plurality of different pre-set frequencies. These embodiments can be implemented by storing the characteristics of the pulse train for each of the predefined signals in a look-up table and providing a bank of filters that can be selectively switched into the signal path to provide the filtering characteristics necessary to generate a desired one of the predefined signals. When the system is used to generate one of the predefined signals, the characteristics of the required pulse train are retrieved from memory and an appropriate filter (i.e., one that matches this pulse train) is switched into the signal path.

[0086] In other alternative embodiments, a composite signal containing a small number of discrete frequencies (e.g., between 2 and 5 frequencies) can be generated by generating an oversampled version of the composite signal and passing the oversampled version of the composite signal through an appropriate filter.

[0087] In the embodiments of FIGS. 1 and 5 described above, depending on the structure of the DC-DC converters 50 / 50B, when the output voltages of those DC-DC converters change (for example, when the controller 40 / 40B writes a new control word to the DAC 42 / 42B), high-frequency artifacts (such as spikes) may appear at the output 100 / 100B. Also, since high-frequency artifacts may cause an uncomfortable feeling in a person being treated with TTFields therapy, it is desirable to take measures to prevent such high-frequency artifacts.

[0088] One suitable approach to prevent high-frequency artifacts from appearing at the output 100 / 100B is to intentionally slow down the response time of the DC-DC converters 50 / 50B (for example, by adding a sufficiently large capacitor across the output of each DC-DC converter). However, this approach, while effective, has two drawbacks. First, additional components must be included in the circuit. And second, slowing down the response time of the system hinders the output voltage from changing rapidly in situations where rapid changes may be desirable.

[0089] FIGS. 8 - 10 show alternative approaches to prevent high-frequency artifacts from appearing at the output 100 / 100B without intentionally slowing down the response time of the DC-DC converters 50 / 50B.

[0090] More specifically, FIG. 8 shows, under steady-state conditions (for example, when the voltage at the output of the DC-DC converter 50 in FIG. 1 is held at a constant DC 20V, which means that the controller 40 in FIG. 1 is not updating the content of the DAC 42), the same waveform 112 described above in connection with FIG. 3 (appearing at the output of the power switcher 60 in FIG. 1), and a sine-wave output waveform 115 (appearing at the output 100 of the output filter 80 in FIG. 1). In this steady-state situation, the output waveform 115 operates as described above in connection with FIGS. 1 - 4 and does not contain any high-frequency artifacts.

[0091] FIG. 9 shows what happens when a DC-DC converter having a fast response time is used and the output of the DC-DC converter 50 (shown in FIG. 1) changes from DC 20V to DC 40V. As described above in connection with FIG. 1, the controller 40 can initiate this change by updating the contents of the DAC 42 at time t9. Prior to this time t9, the output waveform 215 is the same as the output waveform 115 in the example of FIG. 8. However, as soon as the controller 40 updates the contents of the DAC 42 at time t9, the output of the DAC 42 is applied to the voltage control input of the DC-DC converter 50, so the output voltage of the DC-DC converter starts to change rapidly (e.g., from 20V to 40V in the example shown). And since the power switch 60 is set to actively supply current from the DC-DC converter 50 to the transformer 70 at that instant t9, the rapid change in current is transmitted through the transformer 70 to the output filter 80, which adds high-frequency artifacts 215 to the output 100. (Note that the dashed line 222 represents the continuation of the original sine wave that existed prior to t9, and the dashed line 220 represents a clean sine wave with twice the original amplitude.)

[0092] A similar situation exists if the design of the DC-DC converter is such that spikes and / or instability may appear in the output of the DC-DC converter in response to a change in the voltage control input of the DC-DC converter (regardless of the response time of the DC-DC converter). More specifically, if the power switch 60 is set to actively supply current from the DC-DC converter 50 to the transformer 70 at the instant the voltage control input of the DC-DC converter changes, any spikes in the output of the DC-DC converter are transmitted through the transformer 70 to the output filter 80, which adds high-frequency artifacts 215 to the output 100.

[0093] During a time interval when the power switch 60 is set to actively supply current from the DC-DC converter 50 / 50B to the transformer 70, if the output voltage of the DC-DC converter changes, high-frequency artifacts may be added to the output 100. On the other hand, if the output of the DC-DC converter is changed during a time interval when the power switch 60 is not actively supplying current from the DC-DC converter 50 / 50B to the transformer 70, the high-frequency artifacts do not appear at the output 100. The controller 40 / 40B in the embodiment of FIG. 1 / FIG. 5 can utilize this dichotomy to prevent high-frequency artifacts from appearing at the output 100 / 100B. More specifically, the controller 40 / 40B does this by ensuring that the output of the DC-DC converter 50 / 50B is changed only during intervals when the power switcher 60 / 60B is not actively supplying current from the DC-DC converter.

[0094] In the context of the embodiment of FIG. 1 described above, the controller 40 achieves this by preventing the adjustment of the voltage control input of the DC-DC converter 50 when (a) the first control signal is applied to the control input of the power switcher 60 (i.e., when the power switcher 60 routes the output of the DC-DC converter 50 in one direction to the primary side of the transformer 70), or (b) the second control signal is applied to the control input of the power switcher 60 (i.e., when the power switcher 60 routes the output of the DC-DC converter 50 in the opposite direction to the primary side of the transformer 70). When neither the first control signal nor the second control signal is applied to the control input, the power switcher 60 remains off, and in that case, the controller 40 can adjust the voltage control input of the DC-DC converter 50 without introducing high-frequency artifacts at the output 100.

[0095] FIG. 10 shows how things unfold in the context of the embodiment of FIG. 1 when the output of the DC-DC converter 50 changes from DC 20V to DC 40V during a time t10 when the power switch 60 is not actively supplying current from the DC-DC converter. Prior to this time t10, the output of the DC-DC converter 50 is at a first level (e.g., 20V in the illustrated example), and the output waveform 315 is the same as the output waveform 115 in the example of FIG. 8. The controller 40 updates the content of the DAC 42 at time t10 when the power switch 60 is not actively supplying current from the DC-DC converter 50 to the transformer 70. The output voltage of the DC-DC converter 50 begins to change rapidly (e.g., from 20V to 40V in the illustrated example) and stabilizes before the power switch 60 begins routing current to the transformer 70 at t11. Since the output of the DC-DC converter 50 is already stable when the power switch 60 begins routing current to the transformer 70 at t11, the waveform entering the output filter after t11 becomes an oversampled sine wave with a different amplitude (e.g., 40V). And as described above in connection with FIGS. 1-4, when the oversampled sine wave is provided to the output filter 80, the resulting output 100 becomes a very clean sine wave.

[0096] Similarly, in the context of the embodiment of FIG. 5 described above, the controller 40B prevents high-frequency artifacts from appearing in the output 100B by ensuring that the output of any given DC-DC converter 50 / 50B is only changed during intervals when the power switch 60 is not actively supplying current from a given DC-DC converter. The controller 40B achieves this by not adjusting the output voltage of any DC power supply while its output is being routed to the output terminal of the power switch 60.

[0097] FIG. 11 is a block diagram of a third embodiment of a sine wave generator that generates a sine wave having a controllable amplitude at a pre-set frequency f. Components having like reference numerals operate in a similar manner to the corresponding components described above in connection with FIGS. 1-5.

[0098] This embodiment uses two DC-DC converters 51, 52. Each of these DC-DC converters is configured to multiply an analog voltage control input signal by a fixed number (e.g., 10). In this example, with proportional control between them, when a 1V voltage control signal is applied, the output becomes 10V, and when a 5V voltage control signal is applied, the output becomes 50V. Thus, the outputs of the DC-DC converters 51, 52 can take on any value between 0V and 50V depending on the voltage (e.g., 0-5V) applied to the analog voltage control input. The controller 40C controls the output voltages of the DC-DC converters 51, 52 by writing control words to the DACs 42, 42B. The DACs then generate analog voltages proportional to the control words, and these analog voltages are applied to the voltage control inputs of the DC-DC converters 51, 52.

[0099] The controller 40C serves to generate a control signal that causes these voltages to be applied to the transformer 70 in a sequence described below to the power switcher 60B.

[0100] FIG. 6 is a block diagram of one preferred approach for implementing the power switcher 60B. This power switcher is identical to the power switcher 60B of the embodiment of FIG. 5. More specifically, this power switcher 60B uses a set of six electronic control switches 61-66 connected to the primary side of the transformer 70 as shown in FIG. 6. These switches 61-66 open and close in response to a signal applied to the control input 68.

[0101] To route the output of the first DC-DC converter 51 in the first direction to the primary side of the transformer 70, only switches 63 and 62 should be closed. The power switcher 60B is configured to occur in response to the first state of the control input. To route the output of the first DC-DC converter 51 in the opposite direction (i.e., with the opposite polarity) to the primary side of the transformer 70, only switches 61 and 64 should be closed. The power switcher 60B is configured to occur in response to the second state of the control input.

[0102] To route the output of the second DC-DC converter 52 in the first direction to the primary side of the transformer 70, only switches 65 and 62 should be closed. The power switcher 60B is configured to occur in response to the third state of the control input. To route the output of the second DC-DC converter 52 in the opposite direction (i.e., with the opposite polarity) to the primary side of the transformer 70, only switches 61 and 66 should be closed. The power switcher 60B is configured to occur in response to the fourth state of the control input. When all six of these switches 61 - 66 are off, power is not routed to the primary side of the transformer 70. The power switcher 60B is configured to occur in response to the fifth state of the control input (also referred to herein as the additional state).

[0103] Controller 40C has the ability to operate in either a first mode or a second mode. In the first mode, while keeping the first voltage control input constant, Controller 40C generates an output waveform 100C that is powered solely from the first DC-DC converter 51 by setting the control input of power switcher 60B in an alternating sequence between a first and a second state. In some preferred embodiments, an output waveform similar to waveform 112 in FIG. 3 can be generated by (a) setting the control input in the first state for a duration of T / 3, then (b) waiting for a duration of T / 6, then (c) setting the control input in the second state for a duration of T / 3, then (d) waiting for a duration of T / 6, and then continuously repeating sequences (a), (b), (c), and (d). The amplitude of this waveform depends only on the output voltage of the DC-DC converter 51. Filtering this waveform by an output filter 80 (identical to the output filter 80 in the embodiments of FIGS. 1-2) results in a clean sine wave, as described above in connection with FIGS. 1-4.

[0104] In the second mode, while keeping the second voltage control input constant, Controller 40C generates an output waveform 100C that is powered solely from the second DC-DC converter 52 by setting the control input of power switcher 60B in an alternating sequence between a third and a fourth state. In some preferred embodiments, an output waveform similar to waveform 112 in FIG. 3 can be generated by (e) setting the control input in the third state for a duration of T / 3, then (f) waiting for a duration of T / 6, then (g) setting the control input in the fourth state for a duration of T / 3, then (h) waiting for a duration of T / 6, and then continuously repeating sequences (e), (f), (g), and (h). The amplitude of this waveform depends only on the output voltage of the DC-DC converter 52. Filtering this waveform by the output filter 80 results in a clean sine wave.

[0105] FIG. 12 shows how the embodiment of FIG. 11 facilitates a rapid change in the voltage of output signal 100C by switching between a first mode and a second mode. Trace 410 is the output voltage of the first DC-DC converter 51, trace 420 is the output voltage of the second DC-DC converter 52, and trace 430 is the output signal. FIG. 11 shows that controller 40C operates in the first mode and starts at t0. In this mode, the output waveform 430 is powered solely (set to 20V in the illustrated example) from the first DC-DC converter 51. The controller 40C controls the generation of the output waveform 430 by setting the control input of the power switcher 60B in an alternating sequence of first and second states (with standby times interspersed at appropriate times) while keeping the first voltage control input constant as described above.

[0106] While still operating in the first mode, the controller 40C determines in advance what the output voltage will be when it finally switches to the second mode. Then, at time t1, the controller 40C issues a command to move the output voltage of the second DC-DC converter 52 to the desired level. In the illustrated example, the desired level of the second DC-DC converter 52 is 40V. In particular, since the second DC-DC converter is not being used at this time, the response time of the second DC-DC converter can be very slow.

[0107] Preferably, after the output of the second DC-DC converter 52 has settled to the desired level, the controller 40C switches to the second mode. This transition from the first mode to the second mode occurs simultaneously when the power switcher 60B is in the fifth state and not routing current to the transformer 70. In the second mode, the output waveform 430 is powered exclusively (set to 40V in the illustrated example) from the second DC-DC converter 52. The controller 40C controls the generation of the output waveform 430 by setting the control input of the power switcher 60B in an alternating sequence between the third and fourth states (with standby times interspersed at appropriate times) while keeping the second voltage control input constant as described above. Preferably, a command to initiate a change in the voltage of the second DC-DC converter 52 (i.e., t1 in FIG. 12) to settle the output of the second DC-DC converter 52 to the desired level such that the output waveform 430 reaches the desired level immediately when the second mode starts at t2 occurs well in advance (e.g., at least 1 millisecond) before the controller 40C switches to the second mode (i.e., t2 in FIG. 12).

[0108] When returning from the second mode to the first mode, a similar process occurs. More specifically, while still operating in the second mode, the controller 40C determines in advance what the output voltage will be when it finally switches to the first mode. The controller 40C then issues a command at time t3 to move the output voltage of the first DC-DC converter 51 to the desired level. In the illustrated example, the new desired level of the first DC-DC converter 51 is 10V. In particular, since the first DC-DC converter is not being used at this time, the response time of the first DC-DC converter can be very slow.

[0109] Preferably, after the output of the first DC-DC converter 51 has settled to a desired level, the controller 40C switches to the first mode. This transition from the second mode to the first mode occurs simultaneously when the power switch 60B is in the fifth state and not routing current to the transformer 70. In the first mode, the output waveform 430 is powered solely (set to 10V in the illustrated example) from the first DC-DC converter 51. The controller 40C controls the generation of the output waveform 430 by setting the control input of the power switch 60B in an alternating sequence between the first and second states (with appropriate standby times interspersed at appropriate times) while keeping the first voltage control input constant as described above. Preferably, a command to initiate a change in the voltage of the first DC-DC converter 51 (i.e., t3 in FIG. 12) to cause the output of the first DC-DC converter 51 to settle to the desired level such that the output waveform 430 immediately reaches the desired level when the first mode starts at t4 occurs well in advance (e.g., at least 1 millisecond) before the controller 40C switches to the first mode (i.e., t4 in FIG. 12).

[0110] In an alternative embodiment, the transformer 70 may be omitted from the embodiment of FIG. 11, in which case the two conductors at the output of the power switch 60B are directly connected to the two conductors at the input of the output filter 80. In these embodiments, current flows directly from the output of the power switch 60B to the input of the output filter 80 without passing through the transformer. However, these embodiments are less preferred for the same reasons discussed above in connection with FIG. 1.

[0111] TTFields therapy involves inducing an electric field (e.g., at 200 kHz) through a target body part to treat tumors in the target body part. Experiments have shown that the efficiency of TTFields increases when the direction of TTFields changes during the treatment process. For example, in a prior art system of Optune®, the direction of TTFields changes every second. However, in alternative embodiments, the direction can change at different speeds (e.g., between 50 milliseconds and 10 seconds).

[0112] Figure 13 is a block diagram of a prior art system of the original Optune® for applying TTFields to a human head (or other body part) in two different directions. This is achieved using a pair of transducer arrays 25A, 25P arranged at the front and back (i.e., the front and the rear) of the head, and another pair of transducer arrays 25L, 25R arranged on the left and right sides of the human head. More specifically, when an alternating voltage is applied between transducer arrays 25L and 25R, an electric field mainly traveling in the left-to-right (LR) direction is induced in the target head. And when an alternating voltage is applied between transducer arrays 25A and 25P, an electric field mainly traveling in the front-to-back (AP) direction is induced in the target head. TTFields can also be applied to other parts of the body (e.g., the pancreas, lungs, etc.) by arranging transducer arrays on the skin of the target at the front / back of the relevant body part and at the right / left of the relevant body part.

[0113] In the embodiment of Figure 13, a single alternating voltage generator 20 is used to drive both pairs of transducer arrays (i.e., 25L / R and 25A / P). This is achieved by routing the output of the alternating voltage generator 20 to a switch 22. Depending on the state of the control signal, the switch 22 routes the signal from the alternating voltage generator 20 across either one of the pairs of transducer arrays (i.e., 25L / R) or the other pair of transducer arrays (i.e., 25A / P).

[0114] Figure 14 is a timing diagram showing the sequence between two directions LR and AP used in the original Optune®. In this approach, switch 22 routes the output of the AC voltage generator 20 to the left and right transducer arrays (25L / R) for 1 second, then (b) routes the output of the AC voltage generator 20 to the front and rear transducer arrays (25A / P) for 1 second, and then repeats steps (a) and (b) in an alternating sequence. A short time period (e.g., 5 - 10 milliseconds) during which the output of the AC voltage generator 20 is not routed to either pair of transducer arrays (25L / R, 25A / P) is inserted between each step (indicated by label off).

[0115] One problem addressed during the design of the original Optune® is described in relation to Figure 15. More specifically, when switch 22 switches from the off state to either the LR state or the AP state (trace 525) while the instantaneous output voltage 520 generated by the AC voltage generator 20 is substantial (e.g., >10V), the output waveform is similar to trace 530 including spike 532. Such a spike 532 can cause an unpleasant sensation to the subject, so the original Optune® was designed to prevent such spikes from occurring. More specifically, this was achieved by ramping down the output voltage of the AC voltage generator 20 from its steady-state value to zero V during a 100 - millisecond interval preceding each off state, as shown in trace 540 of Figure 16A, and then ramping up the output voltage back to its steady-state value during a 100 - millisecond interval following each off state. The ramp rate was about 1V / millisecond, which was slow enough to avoid spikes that the patient might notice.

[0116] The waveform resulting from the output of the AC voltage generator 20 was similar to the waveform shown in FIG. 16B (except that the actual frequency of the sine wave generated by the AC voltage generator 20 was orders of magnitude larger than the sine wave shown). Note that the x-axis scale in FIG. 16B is magnified 4 times relative to FIG. 16A to show additional detail. Also, since the system operated at its peak output voltage 80% of the time and only 20% of the time was spent ramping up the voltage, ramping down the voltage, or turning the voltage off, this solution worked very well in the context of the original Optune®.

[0117] Here, a similar approach is used, but investigate what happens when the interval during which the AC voltage is applied to either the LR or AP transducer array is shortened from 1 second to 0.25 seconds. If the same 1 V / millisecond ramp-down and ramp-up techniques described above in connection with FIG. 16A are used at this new time scale, the output voltage of the AC voltage generator 20 follows trace 550 in FIG. 17A. And as a result, the waveform at the output of the AC voltage generator 20 is similar to the waveform shown in FIG. 17B (again, except that the actual frequency of the sine wave generated by the AC voltage generator 20 is orders of magnitude larger than the sine wave shown). Note that the x-axis scale in FIG. 17B is magnified 4 times relative to FIG. 17A to show additional detail.

[0118] However, the peak output voltage is applied to the transducer array for only 20% of the time, which means that the maximum electric field is applied to the subject for only 20% of the time, so this solution is not very ideal. Therefore, unlike the prior art situation shown in FIGS. 16A / 16B (where the output voltage is ramped up / down to ensure patient comfort and the ramping reduces the proportion of time spent at the peak voltage by a small amount), using the same ramp slope when the switching time is reduced to 0.25 seconds will reduce the proportion of time spent at the peak voltage by a very large amount (as shown in FIGS. 17A / 17B). Further, if the interval during which the alternating voltage is applied to either the LR or AP transducer array is reduced to less than 0.20 seconds, the situation will deteriorate further, and in that case, the peak voltage (and the corresponding peak electric field strength) will never be reached.

[0119] The embodiment of FIG. 18 uses a different approach to avoid spikes similar to spike 532 shown in FIG. 15. More specifically, the embodiment of FIG. 18 has an alternating voltage generator 30 and a switch 32, and the synchronization between these two functional blocks is relied upon to avoid spikes, as will be described below in connection with FIGS. 19 - 23. In some preferred embodiments, the alternating voltage generator 30 in FIG. 18 is implemented using the approach described above in connection with FIGS. 1 - 7. The switch 32 is configured to (a) route the output of the alternating voltage generator 30 to the left and right transducer arrays (25L / R) in response to a first state of its control input, (b) route the output of the alternating voltage generator 30 to the front and rear transducer arrays (25A / P) in response to a second state of its control input, or (c) remain off in response to a third state of its control input. The switch 32 can be implemented using any of a variety of techniques apparent to those skilled in the relevant art, including but not limited to field - effect transistors, solid - state relays, etc.

[0120] In the illustrated embodiment, synchronization between the AC voltage generator 30 and the switch 32 is implemented using a synchronization controller 35 programmed to send control signals to the AC voltage generator 30 and / or the switch 32 to adjust those components such that the signals described below are generated in the time relationships described below. Various alternative techniques for synchronizing the AC voltage generator 30 and the switch 32 may also be used. For example, synchronization may be achieved by allowing the AC voltage generator 30 to operate freely (as described below in connection with FIG. 20) and adjusting the switching time of the switch 32. Alternatively, synchronization may be achieved by allowing the switch 32 to switch automatically (as described below in connection with FIG. 21) and turning off the AC voltage generator 30 prior to each switching event. Yet another alternative for achieving synchronization is to control the timing of both the AC voltage generator 30 and the switch 32.

[0121] FIG. 19 is a timing diagram showing the ordering between two directions LR and AP for the embodiment of FIG. 18. In this embodiment, the switch 32 routes the output of the AC voltage generator 30 to the left and right transducer arrays (25L / R) for a duration T, then (b) routes the output of the AC voltage generator 30 to the front and rear transducer arrays (25A / P) for a duration T, and then repeats steps (a) and (b) in an alternating sequence. A short time period (e.g., 5 to 10 milliseconds) during which the output of the AC voltage generator 30 is not routed to any pair of the transducer arrays is inserted between each step (indicated by the label off). This can be choreographed by repeatedly adjusting the control input of the switch 32 such that the LR mode, the AP mode, and the off mode cycle in the following repeating sequence: (1) LR mode, (2) off mode, (3) AP mode, and (4) off mode.

[0122] In this embodiment, since the output voltage of the voltage generator 30 is not slowly ramped up and down (as in the prior art embodiment described above in connection with FIG. 16), the duration T can be made much shorter than 1 second. Instead, the output of the AC voltage generator 30 either remains at its full value at all times (as will be described below in connection with FIG. 20) or jumps to its full value immediately after the switch 32 changes state (as will be described below in connection with FIG. 21). In either case, the signal applied to the transducer arrays 25A / P, 25L / R is at its full value for most of the time (e.g., >90% or >95% of the time). And keeping the TTFields stronger for a greater percentage of the time can advantageously improve the effectiveness of TTFields treatment. In some embodiments, the duration T is longer than 20 milliseconds. In some embodiments, the duration T is between 0.1 second and 0.5 second. In some embodiments, the duration T is between 0.2 second and 0.3 second. In particular, in contrast to the situation described above in connection with FIGS. 17A / 17B, regardless of how short the duration of T is, the system operates at its full output voltage for a large percentage of the time.

[0123] FIG. 20 shows a first technique for achieving synchronization between the AC voltage generator 30 and the switch 32, which operates by controlling the timing of the transition of the switch 32 from the off state to either the LR state or the AP state (shown by trace 635) so that the transition coincides with a time window during which the instantaneous magnitude of the output of the AC voltage generator is sufficiently small so that the jump from the off state to a small voltage does not cause a perceptible sensation to the subject being treated.

[0124] The voltage threshold that results in perception can vary from person to person and may also depend on which part of the body is in contact with the transducer array. For example, at various parts of the body, jumps from an off state to any of 1V, 1.5V, 2V, 2.5V, 3V, 3.5V, 4V, 4.5V, or 5V are imperceptible. Thus, to prevent the switching from causing a perceptible sensation, the transition from the off state to either the LR state or the AP state should be timed to coincide with a time window while the instantaneous output magnitude of the AC voltage generator is below those thresholds. In this approach, the output voltage of the AC voltage generator 30 can remain at 100% of the time, its full steady-state value, as indicated by trace 630. In some preferred embodiments, the transition occurs when the instantaneous output of the AC voltage generator is less than 1V in magnitude.

[0125] For example, assume that the perception threshold for a given subject is 5V and the output of the AC voltage generator 30 is 100V pk-pk (meaning that the instantaneous output value of the AC voltage generator 30 ranges between +50V and -50V). The instantaneous output of the AC voltage generator is less than 5V in magnitude for the first 5.7° of each 360° cycle, the middle 11.4° of each cycle, and the last 5.7° of each cycle. By restricting the switching of switch 32 from the off state to either the LR state or the AP state to these specific time windows, the signal 640 applied to the transducer array (25L / R or 25A / P) will not have any spikes greater than 5V in magnitude, which means that they are not perceptible to the subject. Note that if the AC voltage generator is operating at 200 kHz, 11.4° corresponds to 0.16 microseconds, and this window is long enough to facilitate synchronization by aligning the switching of switch 32 to the specific time windows identified in this paragraph.

[0126] In some preferred embodiments, the switching of switch 32 from the off state to either the LR state or the AP state is restricted to those time windows during which the instantaneous output of the AC voltage generator is less than 1V in magnitude. Assuming the same 100V pk-pk output voltage, the instantaneous output of the AC voltage generator is less than 1V in magnitude at the first 1.1° of each cycle, the middle 2.2° of each cycle, and the last 1.1° of each cycle. By restricting the switching of switch 32 to these specific time windows, the signal 640 applied to the transducer array (25L / R or 25A / P) will never have any spikes greater than 1V in magnitude. As will be understood by those skilled in the art, the timing of switch 32 can be adjusted similarly for other thresholds.

[0127] In the example shown in FIG. 20, the output voltage of the AC voltage generator 30 remains at its full steady-state value 100% of the time, as indicated by trace 630. In this situation, the signal 640 applied to the transducer array (25L / R or 25A / P) jumps instantaneously to its full steady-state output voltage as soon as it is turned on. Thus, the signal applied to the transducer arrays 25A / P, 25L / R is almost always at its full value. And as described above, maintaining TTFields stronger for a greater percentage of time can advantageously improve the effectiveness of TTFields treatment. However, it should be noted that the output voltage of the AC voltage generator 30 during the very early stages of the LR or AP state is not critical, and in alternative embodiments, it is acceptable for the output voltage of the AC voltage generator to drop to some extent. However, the output of the AC voltage generator 30 preferably reaches at least 80% of the steady-state output voltage of the AC voltage generator within 20 milliseconds after the electronic switch switches from the off state to either the LR state or the AP state. In some preferred embodiments, this occurs within 5 milliseconds. Also, in some preferred embodiments, this occurs within 1 millisecond.

[0128] When the switch 32 switches back from either the LR state or the AP state to the off state, similar synchronization of the switching of the switch 32 to the small magnitude portion of the output sine wave of the AC voltage generator (i.e., 1V, 1.5V, 2V, 2.5V, 3V, 3.5V, 4V, 4.5V, or 5V or less in magnitude) is preferably implemented.

[0129] FIG. 21 shows a second method for achieving synchronization between the AC voltage generator 30 and the switch 32 in FIG. 18. This method operates by reducing the instantaneous output voltage of the AC voltage generator 30 to less than 5V in magnitude prior to switching the switch 32 from the off state to either the LR state or the AP state in order to prevent spikes from appearing in the conductors connected to the transducer arrays 25L / R and 25A / P when the switch 32 changes state. In some preferred embodiments, the instantaneous output voltage of the AC voltage generator 30 is reduced to less than 1V (e.g., to 0V) in magnitude prior to switching of the switch 32.

[0130] Reducing the output voltage of the AC voltage generator 30 to 0V is easy to achieve when any of the embodiments described above in connection with FIGS. 1 - 6 and FIGS. 10 - 12 are used as the AC voltage generator. For example, when the AC voltage generator of FIGS. 1 and 2 is used, its output can be set to zero by ensuring that neither the first control signal nor the second control signal is applied to the control input of the power switcher 60, which means that all switches (i.e., switches 61 - 64) within the power switcher 60 remain off. Similarly, when the AC voltage generator of FIGS. 5 and 6 is used, its output can be set to zero by sending a control signal to the power switcher 60B that switches all switches (i.e., switches 61 - 66) within the power switcher 60B to the off state.

[0131] In FIG. 21, the upper trace 650 shows the output of the AC voltage generator 30, the central trace 655 shows the state of the switch 32, and the lower trace 660 shows one of the outputs (LR or AP) of the switch 32. Assume that the switch 32 starts in the off state and at t20, the switch 32 is set to route the output of the AC voltage generator 30 to either the LR pair 25L / R of the transducer array or the AP pair 25A / P of the transducer array. At some time before t20, a control signal is sent to the AC voltage generator 30 to reduce the output voltage of the AC voltage generator 30 to zero. When the switch 32 is switched at t20, the output of the AC voltage generator 30 is 0V, so at that time no spikes appear in the conductors connected to the transducer arrays 25L / R and 25A / P.

[0132] After a short time interval (e.g., <0.1 milliseconds), at t21, the synchronization controller 35 (see FIG. 18) starts sending a control signal to the AC voltage generator 30 (as described above in connection with FIGS. 1-6 and FIGS. 10-12), which causes the AC voltage generator 30 to start generating the sine wave 650. Due to the configuration of the AC voltage generator, in particular the output filter 80 / 80B in the embodiments of FIGS. 1-5, the AC voltage generator 30 does not introduce any spikes in the output 650 at t21, so the spikes do not propagate to the output 660. Also, since the switch 32 has already settled into its current state, the switch 32 does not introduce any spikes in the output 660 (supplied to the transducer arrays 25L / R or 25A / P) at t21.

[0133] In particular, as shown in FIG. 21, the output voltage 650 of the AC voltage generator 30 preferably jumps immediately to its full steady-state output voltage without a ramp-up period. Thus, the signals applied to the transducer arrays 25A / P, 25L / R are almost always at their full value. And as described above, keeping TTFields stronger for a greater percentage of the time can advantageously improve the effectiveness of TTFields treatment. FIG. 22 shows the immediate jump to the full steady-state output voltage on a longer time scale, which is in marked contrast to the prior art configuration shown in FIG. 16. However, it should be noted that the output voltage of the AC voltage generator 30 during the very early stages of the LR or AP states is not critical, and in alternative embodiments, it is acceptable for the output voltage of the AC voltage generator not to jump immediately to its full steady-state voltage. However, the output of the AC voltage generator 30 should preferably reach at least 80% of the steady-state output voltage of the AC voltage generator within 20 milliseconds after the electronic switch switches from the off state to either the LR state or the AP state. In some preferred embodiments, this occurs within 5 milliseconds. Also, in some preferred embodiments, this occurs within 1 millisecond.

[0134] FIG. 21 also shows an exemplary technique for synchronizing the AC voltage generator 30 and the switch 32 when reaching when switching from either the LR state or the AP state to the off state. At time t22, the AC voltage generator 30 generates a sine wave at its full steady-state output voltage, and the switch 32 remains set to route the output of the AC voltage generator 30 to either the LR pair of the transducer array 25L / R or the AP pair of the transducer array 25A / P. At time t23, the controller stops generating the signal (described above in connection with FIGS. 1-6 and FIGS. 10-12) to the power switcher 60 / 60B, which reduces the output of the AC voltage generator 30 to 0V. Also, due to the configuration of the AC voltage generator described above, at t23, no spike appears at the output 650, which means that no spike appears at the output 660 of the switch 32. After a short time interval (e.g., <0.1 milliseconds), at t24, the switch 32 is set to the off state. Also, since the output of the AC voltage generator 30 is 0V at t24, no spike is introduced into the conductor extending between the switch 32 and the transducer array 25 at t24.

[0135] In the embodiments described above in connection with FIGS. 18 and 19, the switch 32 (a) routes the output of the AC voltage generator 30 to the left and right transducer arrays (25L / R) for a duration T, then (b) routes the output of the AC voltage generator 30 to the front and rear transducer arrays (25A / P) for a duration T, and then repeats steps (a) and (b) in an alternating sequence. A short time period (e.g., 5-10 milliseconds) during which the output of the AC voltage generator 30 is not routed to any pair of the transducer arrays is inserted between each step. This is choreographed by repeatedly adjusting the control input of the switch 32 so that the LR mode, the AP mode, and the off mode cycle through the following repeating sequence: (1) LR mode, (2) off mode, (3) AP mode, and (4) off mode.

[0136] In a variation of these embodiments, the off mode (i.e., a short time period during which the output of the AC voltage generator 30 is not routed to any pair of the transducer array) is omitted. In this variation, switch 32 routes (a) the output of the AC voltage generator 30 to the left and right transducer arrays (25L / R) for a duration T, then (b) routes the output of the AC voltage generator 30 to the front and rear transducer arrays (25A / P) for a duration T, and then repeats steps (a) and (b) in an alternating sequence of two steps. This is choreographed by repeatedly adjusting the control input of switch 32 so that the LR mode and the AP mode cycle in the following repeating sequence: (1) LR mode, (2) AP mode.

[0137] In this variation where the off mode is omitted, the duration T can also be made much shorter than 1 second for the same reasons explained above. And here again, in contrast to the situation described above in connection with FIGS. 17A / 17B, regardless of how short the duration of T is, the system operates at its full output voltage for a large percentage of the time (e.g., 100% of the time).

[0138] The transition of switch 32 from the LR state to the AP state and from the AP state to the LR state is timed to coincide with a time window during which the instantaneous magnitude of the output of the AC voltage generator is small enough so as not to cause a perceptible sensation to the subject being treated. More specifically, the transition between the LR state and the AP state should be timed to coincide with a time window during which the instantaneous output magnitude of the AC voltage generator is below the same threshold as in the embodiments of FIGS. 18 - 20 that includes an off state (e.g., at the first 1.1° of each cycle, the middle 2.2° of each cycle, and the last 1.1° of each cycle).

[0139] FIG. 23 shows an example of the timing for synchronizing the transition of switch 32 (shown in FIG. 18) between the LR state and the AP state with the output of the AC voltage generator 30 (shown by trace 670 in FIG. 18) such that the transition between the LR state and the AP state (shown by trace 675 in FIG. 23) coincides with a window of time during which the instantaneous magnitude of the output of the AC voltage generator 30 is close to zero (e.g., <5V or <1V).

[0140] The embodiments described above in connection with FIGS. 18-22 advantageously enable driving the transducer array at full power for a much larger percentage of the time than was possible in prior art systems without the risk of introducing voltage spikes that could cause discomfort in the person being treated. Also, driving the transducer array at full power can advantageously enhance the effectiveness of treatment using TTFields.

[0141] Finally, while the embodiments described above in connection with FIGS. 18-23 discuss switching the AC voltage between a first pair of transducer arrays disposed on the front / rear of the associated body part and a second pair of transducer arrays disposed on the front / back of the associated body part, this technique can be extended to three or more pairs of transducer arrays. For example, a third pair of transducer arrays can be disposed on the top / bottom of the associated body part, in which case the AC voltage is switched in a repeating sequence between the first, second, and third pairs of transducer arrays in a manner similar to the switching described above in connection with FIGS. 18-23.

[0142] Although the present invention has been disclosed with reference to specific embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the scope and range of the present invention as defined in the appended claims. Accordingly, the present invention is not limited to the described embodiments and is intended to have the full scope defined by the following claims and the equivalents thereof.

Explanation of Reference Numerals

[0143] 20 AC voltage generator 22 Switch 25A Transducer array 25L Transducer array 25P Transducer array 25R Transducer array 30 AC voltage generator 32 Switch 35 Synchronization controller 40 Controller, programmable controller 40B Controller 40C Controller 42 Digital - analog converter (DAC), DAC 50 DC power supply, DC - DC converter, first DC - DC converter 51 DC - DC converter, first DC - DC converter 52 DC - DC converter, second DC - DC converter 50B DC - DC converter, second DC - DC converter 60 Power switcher 60B Power switcher, power switch 61 Electronically controlled switch, switch 62 Electronically controlled switch, switch 63 Electronically controlled switch, switch 65 Electronically controlled switch, switch 66 Electronically controlled switch, switch 64 Electronically controlled switch, switch 68 Control input 70 Transformer 80 Output Filter 80B Output Filter 82 Inductor, First Inductor 83 Capacitor 85 Block 92 Voltage Sensing Circuit, Circuit 94 Current Sensing Circuit, Circuit 100 Output, Output Signal 100B Output 100C Output Waveform 110 Sine Wave 112 Oversampled Version, Waveform 115 Sine Wave Output Waveform, Output Waveform 120 Sine Wave 122 Oversampled Version 215 Output Waveform, High Frequency Artifact 220 Dashed Line 222 Dashed Line 315 Output Waveform 410 Trace 420 Trace 430 Trace, Output Waveform 520 Instantaneous Output Voltage 525 Trace 530 Trace 532 Spike 540 Trace 550 Trace 630 Trace 635 Trace 640 Signal 650 Trace, Sine Wave, Output, Output Voltage 655 Trace 660 Trace, Output 675 Trace

Claims

1. 1. An apparatus for generating an alternating electrical signal for application to a first pair of electrodes and a second pair of electrodes, the apparatus comprising: an AC voltage generator having an output; an electronic switch having an input to receive the output of the AC voltage generator, a first power output, and a second power output, the electronic switch configured to (a) operate in a first mode to route the output of the AC voltage generator to the first power output, and (b) operate in a second mode to route the output of the AC voltage generator to the second power output, the electronic switch further configured to cycle through a repeating sequence including the first mode and the second mode; a controller configured to synchronize operation of the AC voltage generator and the electronic switch such that whenever the electronic switch switches to either the first mode or the second mode, an instantaneous output of the AC voltage generator is less than 5V in magnitude. Equipped with within 20 milliseconds after the electronic switch switches to either the first mode or the second mode, the output voltage of the AC voltage generator is at least 80% of the steady state output voltage of the AC voltage generator. Device.

2. 2. The apparatus of claim 1, wherein the electronic switch is further configured to: (c) operate in a third mode in which the output of the AC voltage generator is not routed to either the first power output or the second power output; and (d) cycle through the first mode, the second mode, and the third mode in the following repeating sequence: (1) first mode, (2) third mode, (3) second mode, and (4) third mode.

3. 2. The apparatus of claim 1, wherein the controller is configured to synchronize operation of the AC voltage generator and the electronic switch such that whenever the electronic switch switches to either the first mode or the second mode, the instantaneous output of the AC voltage generator is less than 1 V in magnitude.

4. 2. The apparatus of claim 1, wherein within 5 milliseconds after the electronic switch switches to either the first mode or the second mode, the output voltage of the AC voltage generator is at least 80% of a steady-state output voltage of the AC voltage generator.

5. 2. The apparatus of claim 1, wherein within 1 millisecond of the electronic switch switching to either the first mode or the second mode, the output voltage of the AC voltage generator is at least 80% of a steady-state output voltage of the AC voltage generator.

6. 2. The apparatus of claim 1, wherein during a transition of the electronic switch to either the first mode or the second mode, the AC voltage generator continues to operate at its full steady-state AC output voltage.

7. 2. The apparatus of claim 1, wherein the controller synchronizes operation of the AC voltage generator and the electronic switch by controlling timing of transitions of the electronic switch such that the transitions coincide with a window of time during which the instantaneous output of the AC voltage generator is less than 5 volts in magnitude.

8. 2. The apparatus of claim 1, wherein the controller synchronizes the operation of the AC voltage generator and the electronic switch by controlling the AC voltage generator such that the output of the AC voltage generator is turned off whenever a transition of the electronic switch occurs.

9. 2. The apparatus of claim 1, wherein the controller synchronizes operation of the AC voltage generator and the electronic switch by both: (a) controlling timing of transitions of the electronic switch such that transitions coincide with windows of time during which the instantaneous output of the AC voltage generator is less than 5 volts in magnitude; and (b) controlling the AC voltage generator such that the output of the AC voltage generator is turned off whenever a transition of the electronic switch occurs.

10. 2. The apparatus of claim 1, wherein the electronic switch is configured to cycle through the first mode and the second mode in the following repeating sequence: (1) first mode, (2) second mode, and the electronic switch is configured to switch directly from the first mode to the second mode and to switch directly from the second mode to the first mode.

11. 1. An apparatus for generating an alternating electrical signal for application to a first pair of electrodes and a second pair of electrodes, the apparatus comprising: an AC voltage generator having an output; an electronic switch having an input to receive the output of the AC voltage generator, a first power output, and a second power output, the electronic switch configured to (a) operate in a first mode to route the output of the AC voltage generator to the first power output, and (b) operate in a second mode to route the output of the AC voltage generator to the second power output, the electronic switch further configured to cycle through a repeating sequence including the first mode and the second mode; a controller configured to synchronize operation of the AC voltage generator and the electronic switch such that whenever the electronic switch switches to either the first mode or the second mode, the instantaneous output of the AC voltage generator has a magnitude below a threshold at which a subject being treated begins to feel a perceptible sensation; Equipped with within 20 milliseconds after the electronic switch switches to either the first mode or the second mode, the output voltage of the AC voltage generator is at least 80% of the steady state output voltage of the AC voltage generator. Device.

12. 12. The apparatus of claim 11, wherein the electronic switch is further configured to (c) operate in a third mode in which the output of the AC voltage generator is not routed to either the first power output or the second power output, and (d) cycle through the first mode, the second mode, and the third mode in the following repeating sequence: (1) first mode, (2) third mode, (3) second mode, and (4) third mode.

13. 12. The apparatus of claim 11, wherein the controller is configured to synchronize operation of the AC voltage generator and the electronic switch such that whenever the electronic switch switches to either the first mode or the second mode, the instantaneous output of the AC voltage generator is less than 1 V in magnitude.

14. 12. The apparatus of claim 11, wherein within 5 milliseconds after the electronic switch switches to either the first mode or the second mode, the output voltage of the AC voltage generator is at least 80% of a steady-state output voltage of the AC voltage generator.

15. 12. The apparatus of claim 11, wherein within 1 millisecond of the electronic switch switching to either the first mode or the second mode, the output voltage of the AC voltage generator is at least 80% of a steady-state output voltage of the AC voltage generator.

16. 12. The apparatus of claim 11, wherein during a transition of the electronic switch to either the first mode or the second mode, the AC voltage generator continues to operate at its full steady-state AC output voltage.

17. 12. The apparatus of claim 11, wherein the controller synchronizes operation of the AC voltage generator and the electronic switch by controlling timing of transitions of the electronic switch such that the transitions coincide with windows of time during which the instantaneous output of the AC voltage generator has a magnitude below the threshold.

18. 12. The apparatus of claim 11, wherein the controller synchronizes the operation of the AC voltage generator and the electronic switch by controlling the AC voltage generator such that the output of the AC voltage generator is turned off whenever a transition of the electronic switch occurs.

19. 12. The apparatus of claim 11 , wherein the controller synchronizes operation of the AC voltage generator and the electronic switch by both: (a) controlling timing of transitions of the electronic switch such that transitions coincide with windows of time during which the instantaneous output of the AC voltage generator has a magnitude below the threshold, and (b) controlling the AC voltage generator such that the output of the AC voltage generator is turned off whenever a transition of the electronic switch occurs.

20. 12. The apparatus of claim 11, wherein the electronic switch is configured to cycle through the first mode and the second mode in the following repeating sequence: (1) first mode, (2) second mode, and the electronic switch is configured to switch directly from the first mode to the second mode and directly from the second mode to the first mode.

21. 1. An apparatus for generating a sine wave of frequency f, the apparatus comprising: a DC power supply having a voltage control input that sets an output voltage of the DC power supply; a transformer having a primary side and a secondary side; a power switch having a control input configured to apply the output of the DC power supply to the primary side of the transformer in a first direction when a first control signal is applied to the control input, to apply the output of the DC power supply to the primary side of the transformer in a second direction when a second control signal is applied to the control input, and to remain off when neither the first control signal nor the second control signal is applied to the control input, the second direction being opposite to the first direction; a controller programmed to: (a) apply the first control signal to the control input for a duration of T / 3, then (b) wait for a duration of T / 6, then (c) apply the second control signal to the control input for a duration of T / 3, then (d) wait for a duration of T / 6, then continuously repeat the sequence (a), (b), (c), and (d), where T is the reciprocal of the frequency f; an output filter connected to the secondary side of the transformer, the output filter passing the frequency f and attenuating frequencies above a cutoff frequency; Equipped with the controller is further programmed to control an amplitude of the sine wave at the frequency by adjusting a third control signal applied to the voltage control input of the DC power supply, the controller being further programmed to prevent adjustment of the third control signal from occurring when either the first control signal or the second control signal is applied to the control input. Device.

22. 22. The apparatus of claim 21, wherein the cutoff frequency is between 2f and 4f, and the output filter has a transfer function that has a zero at 5f.

23. 1. An apparatus for generating a sine wave of frequency f, the apparatus comprising: n DC power supplies, each of the n DC power supplies having a voltage control input that sets an output voltage of the respective power supply, n being a positive integer; a power switch having an output terminal and a control input, the power switch configured to: (a) route an output of a selected one of the n DC power sources to the output terminal with a selected polarity in response to 2n states of a control signal applied to the control input, or (b) remain off in response to additional states of the control signal; a controller programmed to control the generation of an oversampled version of a sine wave by setting the output voltages of the n DC power supplies to levels present in the oversampled version of the sine wave and then routing each of the n DC power supplies with the selected polarity to the output terminal of the power switch at the appropriate time in a sequence to generate an oversampled version of the sine wave by sequencing the control signal through the 2n states and the additional state; an output filter for filtering a current coming from the output terminal of the power switch, the output filter passing the frequency f and attenuating frequencies above a cutoff frequency; Equipped with the controller is programmed to control the amplitude of the sine wave by adjusting the output voltages of the n DC power supplies via the voltage control inputs, the controller being further programmed not to adjust the output voltages of the DC power supplies while the outputs of the DC power supplies are routed to the output terminals of the power switch. Device.

24. 24. The apparatus of claim 23, further comprising a transformer having a primary side connected to the output terminal of the power switch and a secondary side connected to the output filter, wherein current from the output terminal of the power switch is configured to reach the output filter through the transformer.

25. n=1, meaning there is only a single DC power source, 24. The apparatus of claim 23, wherein the controller is programmed to control the generation of the oversampled version of the sine wave by: (a) applying a first control signal to the control input for a duration of T / 3 to cause the power switch to route the output of the single DC power supply to the output terminal with a first polarity, then (b) waiting for a duration of T / 6, then (c) applying a second control signal to the control input for a duration of T / 3 to cause the power switch to route the output of the single DC power supply to the output terminal with a second polarity opposite to the first polarity, then (d) waiting for a duration of T / 6, then continuously repeating a sequence (a), (b), (c), and (d), where T is the inverse of the frequency f.

26. 26. The apparatus of claim 25, wherein the cutoff frequency is between 2f and 4f, and the output filter has a transfer function that has a zero at 5f.

27. 24. The apparatus of claim 23, wherein n>1, and the controller is further programmed to control an amplitude of the sine wave by adjusting the output voltages of the n DC power supplies via the voltage control inputs while maintaining a constant ratio between the output voltages of each of the n DC power supplies.

28. 28. The apparatus of claim 27, wherein the output filter has a transfer function that has zeros at frequencies where harmonics of frequency f are expected to contain power.

29. 1. A method for generating a sine wave of frequency f, the method comprising: setting n DC power supplies to respective output voltages, n being a positive integer; generating an oversampled version of a sine wave, sampled N times per cycle using equally spaced samples including a sampling point at 0°, where N=2+4n, by setting the output voltages of the n DC power supplies to levels present in the oversampled version of the sine wave and then switching the outputs of the n DC power supplies to their outputs in a controlled sequence such that each of the n DC power supplies is switched to its output in each direction at the appropriate time in the sequence to generate the oversampled version of the sine wave; filtering the oversampled version of the sine wave to pass frequency f and attenuate frequencies above a cutoff frequency, the filtering implementing a transfer function that has zeros at frequencies where harmonics of frequency f are expected to contain power; Including, the amplitude of the sine wave is controlled by adjusting the output voltages of the n DC power supplies, and adjustment of the output voltage of any given one of the DC power supplies is prevented while that given one of the DC power supplies is switched to the output. method.

30. 30. The method of claim 29, wherein n=1, meaning there is only a single DC power supply, and regulation of the output voltage of the single DC power supply occurs only during times when the output of the single DC power supply is not switched to the output.

31. 30. The method of claim 29, wherein the filtering implements a transfer function that has zeros at frequencies where harmonics of frequency f are expected to contain power.

32. 1. An apparatus for generating an output waveform at a frequency f, the apparatus comprising: a first DC power supply having a first voltage control input for setting an output voltage of the first DC power supply; a second DC power supply having a second voltage control input for setting an output voltage of the second DC power supply; a power switch having an output terminal and a control input, the power switch configured to: (a) route the output of the first DC power source to the output terminal with a first polarity in response to a first state of the control input; (b) route the output of the first DC power source to the output terminal with a second polarity in response to a second state of the control input; (c) route the output of the second DC power source to the output terminal with the first polarity in response to a third state of the control input; (d) route the output of the second DC power source to the output terminal with the second polarity in response to a fourth state of the control input; and (e) remain off in response to an additional state of the control input, the second polarity being opposite to the first polarity; an output filter for filtering a current coming from the output terminal of the power switch, the output filter passing the frequency f and attenuating frequencies above a cut-off frequency; a controller, the controller being programmed to operate in a first mode to set the control input to the first and second states in an alternating sequence while holding the first voltage control input constant, the controller being further programmed to operate in a second mode to set the control input to the third and fourth states in an alternating sequence while holding the second voltage control input constant; Equipped with the controller is further programmed such that, when the controller is operating in the first mode, the controller causes a change in amplitude of the output waveform by adjusting the second voltage control input and then switching the controller to the second mode; the controller is further programmed to, when the controller is operating in the second mode, cause a change in amplitude of the output waveform by adjusting the first voltage control input and then switching the controller to the first mode. Device.

33. the output waveform is a sine wave; setting the control input to the first and second states in the alternating sequence includes: (a) placing the control input in the first state for a duration of T / 3, then (b) waiting for a duration of T / 6, then (c) placing the control input in the second state for a duration of T / 3, then (d) waiting for a duration of T / 6, then continuously repeating the sequence (a), (b), (c), and (d); setting the control input to the third and fourth states in the alternating sequence includes: (e) placing the control input in the third state for a duration of T / 3, then (f) waiting for a duration of T / 6, then (g) placing the control input in the fourth state for a duration of T / 3, then (h) waiting for a duration of T / 6, then continuously repeating the sequence (e), (f), (g), and (h); T is the reciprocal of the frequency f.

33. The apparatus of claim 32.

34. the controller is further programmed to, when the controller is operating in the first mode, cause a change in amplitude of the output waveform by adjusting the second voltage control input at least 1 millisecond before switching the controller to the second mode; the controller is further programmed to, when the controller is operating in the second mode, cause a change in amplitude of the output waveform by adjusting the first voltage control input at least 1 millisecond before switching the controller to the first mode.

33. The apparatus of claim 32.

35. 33. The apparatus of claim 32, further comprising a transformer having a primary side connected to the output terminal of the power switch and a secondary side connected to the output filter, wherein the current from the output terminal of the power switch is configured to reach the output filter through a transformer.

36. 36. The apparatus of claim 35, wherein the power switch is configured to: (a) route the output of the first DC power source in a first direction to the primary side of the transformer in response to the first state of the control input; (b) route the output of the first DC power source in a second direction to the primary side of the transformer in response to the second state of the control input; (c) route the output of the second DC power source in the first direction to the primary side of the transformer in response to the third state of the control input; (d) route the output of the second DC power source in the second direction to the primary side of the transformer in response to the fourth state of the control input; and (e) remain off in response to a fifth state of the control input, the second direction being opposite to the first direction.

37. 33. The apparatus of claim 32, wherein the cutoff frequency is between 2f and 4f, and the output filter has a transfer function that has a zero at 5f.

38. 1. A method for generating an output waveform at a frequency f, the method comprising: (b) routing the output of the first DC power source to the output terminal of the power switch with a first polarity in response to a first state of a control input of the power switch; (c) routing the output of the first DC power source to the output terminal with a second polarity in response to a second state of the control input; (d) routing the output of the second DC power source to the output terminal with the first polarity in response to a third state of the control input; (e) routing the output of the second DC power source to the output terminal with the second polarity in response to a fourth state of the control input; and (e) remaining off in response to a further state of the control input, the second polarity being opposite to the first polarity. filtering a current coming from the output terminal of the power switch, the filtering comprising passing the frequency f and attenuating frequencies above a cut-off frequency; operating in a first mode in which the control input is set to the first and second states in an alternating sequence while holding the output voltage of the first DC power source constant; operating in a second mode in which the control input is set to the third and fourth states in an alternating sequence while holding the output voltage of the second DC power source constant; Including, In the first mode, a change in the amplitude of the output waveform is caused by adjusting the output voltage of the second DC power source and then switching to the second mode; In the second mode, a change in the amplitude of the output waveform is caused by adjusting the output voltage of the first DC power source and then switching to the first mode. method.

39. the output waveform is a sine wave; the control input is set to the first and second states in the alternating sequence by (a) placing the control input in the first state for a duration of T / 3, then (b) waiting for a duration of T / 6, then (c) placing the control input in the second state for a duration of T / 3, then (d) waiting for a duration of T / 6, then continuously repeating the sequence (a), (b), (c), and (d); the control input is set to the third and fourth states in the alternating sequence by (e) placing the control input in the third state for a duration of T / 3, then (f) waiting for a duration of T / 6, then (g) placing the control input in the fourth state for a duration of T / 3, then (h) waiting for a duration of T / 6, then successively repeating the sequence (e), (f), (g), and (h); T is the reciprocal of the frequency f. The method of claim 38.

40. in the first mode, the change in amplitude of the output waveform is caused by adjusting the output voltage of the second DC power source at least 1 millisecond before switching to the second mode; In the second mode, the change in amplitude of the output waveform is caused by adjusting the output voltage of the first DC power supply at least 1 millisecond before switching to the first mode. The method of claim 38.

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