High-voltage, high-efficiency sine wave generator that prevents spikes during channel switching and amplitude adjustment

Abstract

This application describes various methods for generating a high-voltage sinusoidal signal in which the output voltage is rapidly adjusted without introducing high-frequency artifacts into the output. When such an approach is used, a stronger electric field can be provided to the tumor for a high time rate, and the effectiveness of tumor treatment field therapy can be enhanced. In some embodiments, this is achieved by not adjusting the DC voltage source when the output of the DC voltage source drives the output signal. In some embodiments, this is achieved by synchronizing the operation of an AC voltage generator and an electronic switch connected to the output of the AC voltage generator.

Description

Technology Field

[0001] This application claims the benefit of U.S. provisional applications 62 / 955,673 (filed December 31, 2019) and 62 / 981,875 (filed February 26, 2020), each of which is incorporated herein by reference in its entirety.

[0002] This technology relates to a high-voltage, high-efficiency sine wave generator that prevents spikes during the switching and amplitude adjustment of channels. Background Technology

[0003] Treating tumors using tumor treatment field therapy is described in U.S. Patent 7,805,201. Tumor treatment field therapy uses high-voltage sinusoidal signals. Originally, these high-voltage sinusoidal signals were obtained by generating a low-amplitude signal with a function generator and using a linear amplifier, amplifying the low-voltage signal into a high-voltage signal, and then applying the high-voltage signal to a set of electrodes (also called a transducer array) positioned on the patient's body. U.S. Patent 9,910,453 describes an alternative approach for generating a high-voltage sinusoidal signal applied to a transducer array, which provides significantly improved efficiency compared to the original linear amplifier approach. The problem to be solved

[0004] This technology is intended to provide a technology that prevents spikes during the switching and amplitude adjustment of channels. means of solving the problem

[0005] This application describes various approaches for generating a high-voltage sinusoidal signal in which the output voltage can be rapidly adjusted without introducing high-frequency artifacts (e.g., voltage spikes) into the output. Using these approaches, a stronger electric field can be delivered to the tumor for a higher rate of time, which can increase the efficacy of tumor therapeutic field therapy.

[0006] One aspect of the invention relates to a first device for generating a sinusoidal wave of frequency f. The first device comprises a DC power source, wherein the DC power source has a voltage control input for setting the output voltage of the DC source; a transformer having a primary side and a secondary side; and a power switch. The power switch has a control input, and when a first control signal is provided to the control input, the output of the DC power source is applied to the primary side of the transformer in a first direction, when a second control signal is provided to the control input, the output of the DC power source is applied to the primary side of the transformer in a second direction, and is turned off when the first and second control signals are not provided to the control input. The second direction is opposite to the first direction. The first device further comprises a controller, wherein the controller (a) provides the first control signal to the control input for a duration of T / 3, (b) waits for a duration of T / 6, (c) provides the second control signal to the control input for a duration of T / 3, (d) waits for a duration of T / 6, and then repeats the sequence of (a), (b), (c), and (d). T is the reciprocal of frequency f. The first device comprises an output filter connected to the secondary side of the transformer, wherein the output filter passes frequency f and attenuates the frequency that cuts off the cutoff frequency. The controller is further programmed to control the amplitude of a sinusoidal wave at the frequency by adjusting a third control signal provided to the voltage control input of the DC power source, and the controller is further programmed to prevent adjustment of the third control signal from occurring when either the first control signal or the second control signal is provided to the control input.

[0007] In some embodiments of the first device, the cutoff frequency is between 2f and 4f, and the output filter has a zero at 5f.

[0008] One aspect of the invention relates to a second device that generates a sinusoidal wave of frequency f. The second device comprises n DC power sources, each of which has a voltage control input that sets the output voltage of each of the n power sources, and n is a positive integer. The second device comprises a power switch having a control input and output terminals, wherein the power switch (a) routes the output of one of the n DC power sources to the output terminals with a selected polarity in response to 2n states of a control signal provided to the control input, or (b) remains in an off state in response to an additional state of the control signal. The second device includes a controller, which is programmed to control the generation of an oversampled version of a sine wave sampled N times per cycle using evenly distributed samples including a sampling point including 0°, where N = 2+4n, and the output voltages of the n DC power sources are set to levels present in the oversampled version of the sine wave, and each of the n DC power sources is routed to the output terminal of the power switch with a suitable selected polarity within a suitable time in the sequence to generate the oversampled version of the sine wave by sequencing the control signal through the 2n states and the additional state. The second device includes an output filter that filters the current originating from the output terminal of the power switch. The output filter passes a frequency f and attenuates frequencies above the cutoff frequency. The controller is programmed to control the amplitude of the sinusoidal wave by adjusting the output voltage of the n DC power source through the voltage control inputs, and the controller is additionally programmed not to adjust the output voltage of the DC power source when the output is routed to the output terminal of the power switch.

[0009] Some embodiments of the second device further include a transformer comprising a primary side connected to the output terminal of the power switch and a secondary side connected to the output filter, and the transformer is configured so that the current from the output terminal of the power switch passes through the transformer to reach the output filter.

[0010] Some embodiments of the second device further include a transformer comprising a primary side connected to the output terminal of the power switch and a secondary side connected to the output filter, wherein the transformer is configured such that the current from the output terminal of the power switch passes through the transformer to reach the output filter. In these embodiments, n = 1 means that there is a single DC power source. In these embodiments, the controller (a) applies a first control signal to the control input for a duration of T / 3 so that the power switch routes the output of the single DC power source to the output terminals with a first polarity, then (b) waits for a duration of T / 6, then (c) applies a second control signal to the control input for a duration of T / 3 so that the power switch routes the output of the single DC power source to the output terminals with a second polarity opposite to the first polarity, then (d) waits for a duration of T / 6, then repeats the sequence of (a), (b), (c), and (d) in succession. The above T is the reciprocal of the frequency f. Optionally, the cutoff frequency is between 2f and 4f, and the output filter has a transfer function with a zero at 5f.

[0011] In some embodiments of the second device, n > 1, and the controller is further programmed to control the amplitude of the sinusoidal wave by adjusting the output voltages of the n DC power sources through the voltage control inputs while maintaining a fixed ratio between the output voltages of each of the n DC power sources. Optionally, in these embodiments, the output filter has a transfer function having a zero at the harmonic frequency of the frequency f predicted to contain power.

[0012] Another aspect of the method relates to a first method for generating a sinusoidal wave of frequency f. The first method comprises the step of setting n DC power sources to their respective output voltages, where n is a positive integer; generating an oversampled version of a sinusoidal wave sampled N times per cycle using evenly spaced samples including a sampling point including 0°, where N = 2+4n, and setting the output voltage of the n DC power source to a level present in the oversampled version of the sinusoidal wave, and then switching to output according to the sequence which controls the outputs of the n DC power sources so that each of the n DC power sources is switched in their respective directions at a suitable time in the sequence to generate the oversampled version of the sinusoidal wave. The first method also comprises the step of filtering the oversampled version of the sinusoidal wave to attenuate frequencies above the cutoff frequency and to pass the frequency f, wherein the filtering is implemented by a transfer function that includes a zero at the frequency of the harmonic of frequency f predicted to contain power. The amplitude of the above sinusoidal wave is controlled by adjusting the output voltage of the n DC power sources, and when any one of the given DC power sources is switched as an output, the adjustment of the output voltage of any one of the given DC power sources is prevented.

[0013] According to some aspects of the first method, n = 1, meaning that only a single DC power source exists, and adjustment of the output voltage of the single DC power source is made only when the output of the single DC voltage source is not switched to the output.

[0014] According to some aspects of the first method, the filtering is performed by implementing a transfer function having a zero at a harmonic frequency of frequency f, which is predicted to contain power.

[0015] Another aspect of the present invention relates to a third device that generates an output waveform of frequency f. The third device comprises a first DC power source, wherein the first DC power source has a first voltage control input for setting the output voltage of the first DC power source; and a second DC power source, wherein the second DC power source has a second voltage control input for setting the output voltage of the second DC power source. The third device comprises a power switch having a control input and an output terminal, wherein the power switch (a) routes 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) routes 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) routes the output of the second DC power source to the output terminal with a first polarity in response to a third state of the control input, (d) routes the output of the second DC power source to the output terminal with a second polarity in response to a fourth state of the control input, and (e) turns off in response to an additional state of the control input. The second polarity is opposite to the first polarity. The third device comprises an output filter that filters the current arriving at the output terminal of the power switch, wherein the output filter passes the frequency f and attenuates frequencies exceeding the cutoff frequency. The third device includes a controller, said controller is programmed to operate in a first mode in which the first and second states alternate in a sequence while maintaining the first voltage control input constant. The controller is further programmed to operate in a second mode in which the third and fourth states alternate in a sequence while maintaining the second voltage control input constant.The controller is further programmed such that when the controller operates in the first mode, the controller changes the amplitude of the output waveform by adjusting the second voltage control input and then switches the controller to the second mode, and when the controller operates in the second mode, the controller changes the amplitude of the output waveform by adjusting the first voltage control input and then switches the controller to the first mode.

[0016] In some embodiments of the third device, the output waveform is a sinusoidal wave, and setting the control input to a sequence in which the first and second states alternate is (a) keeping the control input in the first state for a duration of T / 3, then, (b) waiting for a duration of T / 6, then, (c) keeping 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 of (a), (b), (c), and (d), and setting the control input to a sequence in which the third and fourth states alternate is (e) keeping the control input in the third state for a duration of T / 3, then, (f) waiting for a duration of T / 6, then, (g) keeping 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 of (e), (f), (g), and (h). Repeatedly, the above T is the reciprocal of the above frequency f.

[0017] In some embodiments of the third device, the controller is further programmed to change the amplitude of the output waveform by adjusting the second voltage control input at least 1 ms prior to the controller switching to the second mode when the controller is operating in the first mode, and the controller is further programmed to change the amplitude of the output waveform by adjusting the first voltage control input at least 1 ms prior to the controller switching to the first mode when the controller is operating in the second mode.

[0018] Some embodiments of the third device further include a transformer comprising a primary side connected to the output terminal of the power switch and a secondary side connected to the output filter, wherein the transformer is configured such that current starting from the output terminal of the power switch passes through the transformer and reaches the output filter. Optionally, in this embodiment, the power switch (a) routes the output of the first DC voltage source in a first direction to the primary side of the transformer in response to the first state of the control input, (b) routes the output of the first DC voltage source in a second direction to the primary side of the transformer in response to the second state of the control input, (c) routes the output of the third DC voltage source in a first direction to the primary side of the transformer in response to the third state of the control input, (d) routes the output of the second DC voltage source in a first direction to the primary side of the transformer in response to the fourth state of the control input, and (e) turns off in response to the fifth state of the control input, wherein the second direction is opposite to the first direction.

[0019] In some embodiments of the third device, the cutoff frequency is between 2f and 4f, and the output filter has a transfer function having a zero at 5f.

[0020] Another aspect of the invention relates to a second method for generating an output waveform of frequency f. The second method comprises the steps of: (b) routing the output of a first DC power source to an 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 an output terminal of the power switch with a second polarity in response to a second state of a control input of the power switch; (d) routing the output of the second DC power source to an output terminal of the power switch with a second polarity in response to a third state of a control input of the power switch; (e) turning off in response to an additional state of the control input, wherein the second polarity is opposite to the first polarity. The second method further comprises the step of filtering the current arriving at the output terminal of the power switch. The filtering above passes frequency f and blocks frequencies exceeding the cutoff frequency. The second method includes the step of operating in a first mode in which the output voltage of the first DC power source is maintained constant and the control input is set to an alternating sequence of the first and second states. The second method includes the step of operating in a second mode in which the output voltage of the second DC power source is maintained constant and the control input is set to an alternating sequence of the third and fourth states. In the first mode, changes in the amplitude of the output waveform occur by adjusting the output voltage of the second DC voltage source and subsequently switch to the second mode. In the second mode, changes in the amplitude of the output waveform occur by adjusting the output voltage of the first DC voltage source and subsequently switch to the first mode.

[0021] In some embodiments of the second method, the output waveform is a sinusoidal wave, and (a) the control input is set to the first state for a duration of T / 3, then (b) wait for a duration of T / 6, then (c) the control input is set to the second state for a duration of T / 3, then (d) wait for a duration of T / 6, then the sequence of (a), (b), (c), and (d) is repeated in succession so that the control input is set to a sequence in which the first and second states alternate. In this embodiment, (e) the control input is set to the third state for a duration of T / 3, then (f) wait for a duration of T / 6, then (g) the control input is set to the third state for a duration of T / 3, then (h) wait for a duration of T / 6, then the sequence (e, (f), (g), and (h) is repeated in succession so that the control input is set to a sequence in which the third and fourth states alternate. T is the reciprocal of the frequency f.

[0022] In some embodiments of the second method, in the first mode, a change in the amplitude of the output waveform is achieved by adjusting the output voltage of the second DC power source at least 1 ms prior to switching to the second mode, and in the second mode, a change in the amplitude of the output waveform is achieved by adjusting the output voltage of the first DC power source at least 1 ms prior to switching to the first mode.

[0023] Another aspect of the invention relates to a fourth device for generating alternating current (AC) electrical signals to be applied to a first electrode pair and a second electrode pair. The fourth device includes an AC voltage generator having an output, an electronic switch, and a controller. The electronic switch includes an input receiving the output of the AC voltage generator, and a first power output and a second power output. The electronic switch operates in (a) a first mode for routing the output of the AC voltage generator to the first power output, and (b) a second mode for routing the output of the AC voltage generator to the second power output. The electronic switch is configured to cycle through a sequence that repeats the first mode and the second mode. The controller is configured to synchronize the operation of the AC voltage generator and the electronic switch such that when the electronic switch switches to the first mode or the second mode, the amplitude of the instantaneous output of the AC voltage generator is less than 5V. Within 20ms after the electronic switch switches to 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.

[0024] In some embodiments of the fourth device, the electronic switch cycles through (c) a third mode in which the output of the AC voltage generator is not routed to the first power output or the second power output, and (d) a sequence that repeats (1) the first mode, (2) the third mode, (3) the second mode, and (4) the third mode. In some embodiments, the controller synchronizes the operation of the AC voltage generator and the electronic switch such that when the electronic switch switches to the first mode or the second mode, the amplitude of the instantaneous output of the AC voltage generator is less than 1V.

[0025] In some embodiments of the fourth device, within 5 ms after the electronic switch switches to 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 ms after the electronic switch switches to 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.

[0026] In some embodiments of the fourth device, the AC voltage generator continues to operate at a maximum steady-state AC voltage even during the electronic switch switching between the first mode and the second mode.

[0027] In some embodiments of the fourth device, the controller synchronizes the operation of the AC voltage generator and the electronic switch by controlling the timing of the switching of the electronic switch such that the switching is equal to a time window in which the amplitude of the instantaneous output of the AC voltage generator is less than 5V. In some embodiments of the fourth device, the controller synchronizes the operation of the AC voltage generator and the electronic switch by controlling the AC voltage generator so that the output of the AC voltage generator is turned off whenever the switching of the electronic switch occurs. In some embodiments of the fourth device, the controller synchronizes the AC voltage generator and the electronic switch by (a) controlling the timing of the switching of the electronic switch such that the switching is equal to a time window in which the amplitude of the instantaneous output of the AC voltage generator is less than 5V, and (b) controlling the AC voltage generator so that the output of the AC voltage generator is turned off whenever the switching of the electronic switch occurs.

[0028] In some embodiments of the fourth device, the electronic switch is configured to cycle through a repeating sequence of (1) the first mode and (2) the second mode, and the electronic switch is switched directly from the first mode to the second mode and directly from the second mode to the first mode.

[0029] Another aspect of the invention relates to a fifth device that generates an alternating current electrical signal applied to a first electrode pair and a second electrode pair. The fifth device includes an alternating current voltage generator having an output, an electronic switch, and a controller. The electronic switch has an input that receives the output of the alternating current voltage generator, and a first power output and a second power output. The electronic switch operates in (a) a first mode that routes the output of the alternating current voltage generator to the first power output and (b) a second mode that routes the output of the alternating current voltage generator to the second power output. The electronic switch operates by cyclically circulating a repeating sequence including the first mode and the second mode. The controller synchronizes the operation of the alternating current voltage generator and the electronic switch such that whenever the electronic switch switches to the first mode or the second mode, the amplitude of the instantaneous output of the alternating current voltage generator is below a threshold value perceptible to the processing target. Within 20 ms after the electronic switch switches to the first mode or the second mode, the output voltage of the alternating current voltage generator is at least 80% of the steady-state voltage of the alternating current voltage generator.

[0030] In some embodiments of the fifth device, the electronic switch cycles through (c) a third mode in which the output of the AC voltage generator is not routed to the first power output or the second power output, and (d) a sequence that repeats (1) the first mode, (2) the third mode, (3) the second mode, and (4) the third mode.

[0031] In some embodiments of the fifth device, the controller synchronizes the operation of the AC voltage generator and the electronic switch such that when the electronic switch is switched to the first mode or the second mode, the amplitude of the instantaneous output of the AC voltage generator is less than 1V.

[0032] In some embodiments of the fifth device, within 5ms after the electronic switch switches to 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 1ms after the electronic switch switches to 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.

[0033] In some embodiments of the fifth device, the AC voltage generator continues to operate at a maximum steady-state AC voltage even during the switching of the electronic switch to the first mode or the second mode.

[0034] In some embodiments of the fifth device, the controller synchronizes the operation of the AC voltage generator and the electronic switch by controlling the timing of the switching of the electronic switch such that the switching is equal to a time window in which the amplitude of the instantaneous output of the AC voltage generator is less than the threshold value. In some embodiments of the fifth device, the controller synchronizes the operation of the AC voltage generator and the electronic switch by controlling the AC voltage generator so that the output of the AC voltage generator is turned off whenever the switching of the electronic switch occurs. In some embodiments of the fifth device, the controller synchronizes the AC voltage generator and the electronic switch by (a) controlling the timing of the switching of the electronic switch such that the switching is equal to a time window in which the amplitude of the instantaneous output of the AC voltage generator is less than the threshold value, and (b) controlling the AC voltage generator so that the output of the AC voltage generator is turned off whenever the switching of the electronic switch occurs.

[0035] In some embodiments of the fifth device, the electronic switch is configured to cycle through a repeating sequence of (1) the first mode and (2) the second mode, and the electronic switch is switched directly from the first mode to the second mode and directly from the second mode to the first mode. Effects of the invention

[0036] According to the present technology, a high-voltage, high-efficiency sine wave generator is provided that can prevent spikes during the switching and amplitude adjustment of channels. Brief explanation of the drawing

[0037] FIG. 1 is a block diagram of a first embodiment of a sinusoidal generator that generates a sinusoidal wave at a preset frequency f with a controllable amplitude. FIG. 2 illustrates a block diagram of a suitable architecture for implementing an output filter and a preferred approach for implementing a power switcher. Figure 3 shows a sine wave and an oversampled version of the sine wave sampled 6 times per cycle. Figure 4 is a schematic diagram of an example of an output filter. FIG. 5 is a block diagram of a second embodiment of a sinusoidal generator that generates a sinusoidal wave at a preset frequency f with a controllable amplitude. FIG. 6 is a block diagram of one preferred approach for implementing a power switcher in the embodiment of FIG. 5. Figure 7 shows a sine wave and an oversampled version of the sine wave sampled 10 times per cycle. Figure 8 illustrates a sine wave output waveform under steady-state conditions. Figure 9 shows how the sinusoidal output waveform changes when the output of the DC-DC converter used to power the sinusoidal output changes at a specific time in the cycle. Figure 10 shows how the sinusoidal output waveform changes when the output of the DC-DC converter used to power the sinusoidal output changes at different times of the cycle. FIG. 11 is a block diagram of a third embodiment of a sinusoidal generator that generates a sinusoidal wave having a controllable amplitude. FIG. 12 illustrates a waveform showing how the embodiment of FIG. 11 enables a rapid change in the voltage of the output signal. FIG. 13 is a block diagram of a conventional technology system for applying a tumor treatment field to a human head. Figure 14 is a timing diagram showing the sequencing between the two directions LR and AP used in the conventional technology system of Figure 13. Figure 15 illustrates a waveform containing significant spikes. FIG. 16A illustrates a conventional approach to avoid the spike of FIG. 15 by ramping the output voltage of the AC generator up and down at 1-second intervals between switching events. FIG. 16B is a schematic diagram of the instantaneous output voltage of an AC generator using the ramp rate shown in FIG. 16A. FIG. 17A illustrates what happens when the approach of FIG. 16 is used at intervals of 0.25 seconds between switching events. FIG. 17B is a schematic diagram of the instantaneous output voltage of an AC generator using the ramp rate shown in FIG. 17A. FIG. 18 illustrates an embodiment that synchronizes the operation of an AC voltage generator and a switch. FIG. 19 is a timing diagram showing the order between two directions for the embodiment of FIG. 18. FIG. 20 illustrates a first approach for achieving synchronization between the switch of FIG. 18 embodiment and an AC voltage generator by precisely adjusting the switching of the switch. FIG. 21 illustrates a second approach for achieving synchronization between the switch of FIG. 18 embodiment and the AC voltage generator by controlling the output of the AC voltage generator. Figure 22 illustrates how the output of an AC voltage generator jumps immediately to the full steady-state output voltage when the approach of Figure 21 is used. FIG. 23 illustrates another approach to achieving synchronization between the switch of FIG. 18 embodiment and the AC voltage generator by precisely adjusting the switching of the switch. Specific details for implementing the invention

[0038] When using prior art approaches to generate high-voltage sinusoidal signals in relation to Tumor-Treating Fields (TTFields) therapy, high-frequency artifacts (e.g., voltage spikes) may appear in the output in response to specific conditions (e.g., commands to change the output voltage or when the direction of the Tumor-Treating Field is switched). Since these high-frequency artifacts can cause unpleasant sensations to the patient being treated with TTField therapy, the output voltage amplitude is typically increased slowly to prevent the occurrence of high-frequency artifacts (and the resulting unpleasant sensations). However, using a slow ramp-up has the disadvantage that the output voltage is not always as high as possible. This means that the electric field applied to the tumor is not always that strong. And if the electric field is not as strong as expected, the therapeutic effect may be reduced. The embodiments described herein can advantageously increase the output voltage amplitude much more rapidly without introducing high-frequency artifacts. Therefore, these embodiments can prevent the occurrence of unpleasant sensations without causing an associated reduction in therapeutic efficacy.

[0039] The embodiments described herein are useful in relation to generating a tumor therapeutic field as described in U.S. Patent 7,805,201, which is incorporated herein by reference. The embodiments described herein are based on the architecture described in U.S. Patent 9,910,453, incorporated herein by reference. In particular, the embodiments described herein can more quickly adjust the voltage of a sinusoidal signal (applied to a tumor therapeutic field transducer array) without the risk of introducing high-frequency artifacts (e.g., voltage spikes) into the output. The embodiments described herein can also immediately turn the sinusoidal signal on and off at maximum power without the risk of introducing high-frequency artifacts into the output.

[0040] When generating a high-voltage signal for tumor treatment field delivery, the exact shape of the signal is known at every moment (a pure sine wave of a known frequency), and based on external input (e.g., control based on the patient's skin temperature), only the amplitude of the output signal changes over time.

[0041] The embodiment described herein generates a high-voltage sinusoidal signal by generating a specific pulse train that produces a low-distortion sinusoidal wave of the desired amplitude and frequency when filtered using a specific low-pass filter.

[0042] FIG. 1 is a block diagram of a first embodiment of a sinusoidal generator that generates a sinusoidal wave at a preset frequency f with a controllable amplitude. Ultimately, the amplitude of the output sinusoidal wave will be proportional to the output of a DC power source (50), which is preferably a controlled DC-DC converter.

[0043] In the illustrated embodiment, the DC-DC converter (50) is configured to multiply the analog voltage control input signal by 10, so when a 1V voltage control signal is applied, the output will be 10V, and when a V voltage control signal is applied, the output will be 50V, with proportional control occurring between them. Therefore, the output of the DC-DC converter (50) can take any value between 0 and 50V depending on the voltage (e.g., 0-5V) 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 the digital-to-analog converter (DAC) (42). The DAC (42) 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).

[0044] The output of the DC-DC converter (50) is routed to the power switcher (60). The power switcher (60) has a control input and, depending on the state of the control input, routes the output of the DC-DC converter (50) to connect it in a certain direction to the primary side of the transformer 70. More specifically, when a first control signal is applied to the control input, the power switcher (60) will apply the output of the DC-DC converter (50) to the primary side of the transformer (70) in a first direction. When a second control signal is applied to the control input, the power switcher (60) will apply 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. When neither the first control signal nor the second control signal is applied to the control input, the power switcher (60) will remain in an off state, and in this case, power from the DC-DC converter (50) is not routed to the primary side of the transformer (70).

[0045] FIG. 2 includes a block diagram of one preferred approach to implementing a power switcher (60) using a set of four electronic control switches (61-64) connected to the primary side of a transformer (70) in an H-bridge configuration. These switches (61-64) are closed and opened in response to a signal applied to a control input (68). As understood by those skilled in the art, various techniques may be used to implement these switches. For example, the switches (61-64) may be implemented using MOSFET transistors (e.g., BSC109N10NS3 manufactured by Infineon) with appropriate logic for turning the switches on and off in response to a control signal. Only switches (63, 62) need to be closed to apply the output of the DC-DC converter (50) to the primary side of the transformer (70) in the first direction. In order to apply the output of the DC-DC converter (50) in the opposite direction to the primary side of the transformer (70), only switches (61, 64) must be closed. When all four of these switches (61-64) are turned off, power is not routed to the primary side of the transformer (70).

[0046] 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 with a step-up ratio of 1:6 is used with a DC-DC converter (50) capable of outputting up to 24V, the secondary voltage of the transformer (70) can be raised up to 300V.

[0047] Returning to FIG. 1, the controller (40) provides a control signal to the control input of the power switcher (60) in a timed order to construct an oversampled version of a sine wave that is sampled six times per cycle using samples with equal intervals. More specifically, FIG. 3 illustrates an oversampled version of a sine wave (110) and a sine wave (112) sampled at 0°, 60°, 120°, 180°, 240°, 300°, and 360°. Looking at this oversampled version 112, it is clear that it contains only three voltage levels: a positive voltage +V between 60° and 180°, a negative voltage -V between 240° and 360°, and 0 volts between 0° and 60° and between 180° and 240°. Since the sampling time was selected such that one of the sampling points occurs at 0° and one of the sampling points occurs at 180°, a 0-volt level exists, where the sine function is 0. This selection advantageously reduces the number of voltage levels that must be generated to form an oversampled version (112) of the sine wave. It also advantageously reduces the number of switching events, thereby minimizing losses that occur during the switching process.

[0048] Consequently, an oversampled version of a sine wave at a preset frequency f can be configured at the output of a transformer (70) by continuously repeating the steps of: (a) providing a first control signal to a control input (68) having a duration of T / 3 corresponding to the 60-180° segment of the waveform (112) of FIG. 3; (b) waiting for a duration of T / 6 corresponding to the 180-240° segment of the waveform (112); (c) applying a second control signal to the control input (68) for a duration of T / 3 corresponding to the 240-360° segment of the waveform (112); and (d) waiting for a duration of T / 6 corresponding to the 0-60° segment of the waveform (112). T is the reciprocal of the preset frequency f.

[0049] The controller (40) serves to generate these control signals in this order. The controller (40) may be implemented using various approaches that will be obvious to a person skilled in the relevant technical field, including but not limited to a microcontroller or microprocessor programmed to perform the functions described herein. The controller (40) may also be implemented using a microcontroller or microprocessor combined with a hardwired sequencer, the latter of which may be implemented using, for example, a state machine or a counter.

[0050] The secondary output of the transformer (70) is routed to an output filter (80) having a cutoff frequency between 2f and 4f. The output filter (80) passes a preset frequency (f) and attenuates frequencies above the cutoff frequency.

[0051] It should be noted that when the oversampled version of the sine wave (112 in FIG. 3) is converted into the frequency domain, all even harmonics become zero as a result of the fact that the waveform (112) is symmetrical. Also, since sampling is performed 6 times per period, the third harmonic of the waveform (112) also becomes zero.

[0052] Many filter designs have inherent instability at the cutoff frequency. However, since the third harmonic component of the oversampled waveform (112) is zero, the lowest harmonic with significant power is the fifth harmonic. If the output filter (80) is designed so that the cutoff frequency matches the third harmonic, the oversampled waveform (112) will not be affected by instability near the cutoff frequency. This is because the waveform does not contain power at 3f. Therefore, it is most desirable to design an output filter (80) with a cutoff frequency of 3f. In this case, (a) the fundamental component must be much lower than the cutoff frequency so as not to activate instability, and (b) the fifth harmonic must be sufficiently higher than the cutoff frequency so as not to activate instability.

[0053] To further reduce higher harmonics, the output filter (80) is preferably designed so that the transfer function of the output filter has a zero located at the fifth harmonic. This can be achieved, for example, by selecting components within the output filter (80) to implement an elliptic low-pass filter or a Chebyshev-2 low-pass filter. Generally, elliptic filters and Chebyshev-2 filters are not suitable for filtering square waves into sine waves because they have significant ripple in the stopband. Consequently, if the incoming signal contains frequency components that match the crests within the corresponding ripple, those components are not filtered from 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 will be known in advance. By selecting a component within the output filter (80) such that the transfer function becomes zero at the fifth harmonic, it is ensured that the fifth harmonic never coincides with the crest within the ripple of the stop band.

[0054] To further reduce higher harmonics, the output filter (80) may be designed so that its transfer function has an additional zero located at the 7th harmonic. Here again, since the frequency of the 7th harmonic is known in advance, the component within the output filter (80) may be selected so that the transfer function has a zero at the 7th harmonic.

[0055] Designing an output filter (80) with zeros at the 5th and 7th harmonics reduces attenuation at other frequencies located between the harmonics, which is generally very undesirable. However, since the frequency of the oversampled waveform (112) is preset and contains only signals distributed around odd harmonics (starting from the 5th harmonic), this design actually reduces the overall distortion of the output signal in the embodiment of FIG. 1.

[0056] When the output filter (80) is designed to be zero at the 5th and 7th harmonics, the initial harmonic containing any significant power will be the 9th harmonic. However, since the 9th harmonic power of the oversampled waveform (112, FIG. 3) is relatively low and the 9th harmonic is 6f higher than the cutoff frequency, the power of the 9th harmonic (and all higher harmonics) at the output (100) of the output filter (80) will be low enough to produce a good sine wave.

[0057] FIG. 2 illustrates a suitable architecture for implementing an output filter (80) with the aforementioned cutoff frequency and zero point. 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 subsequent stages are indicated by blocks (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.

[0058] When modeling the electrical characteristics of the transformer (70), the leakage inductance of the transformer appears in series with the secondary side of the transformer (70). Consequently, this leakage inductance must be taken into account when calculating the inductance of the first inductor (81) of the first stage of the output filter (80). In some embodiments, a transformer (70) having a leakage inductance large enough to supply all the necessary inductance to the first inductor (82) is selected. In this case, the first inductor (82) can be completely removed from the output filter (80) and replaced with a wire. For example, if the calculated desired value for the first inductor of the output filter is 60μH and the leakage inductance of the transformer (70) is 60μH, the first inductor (82) of the output filter can be completely removed.

[0059] In an alternative embodiment, the leakage inductance of the transformer (70) accounts for at least half of the inductance of the first stage of the low-pass LC filter. In this embodiment, starting from the calculated value for the first inductor (82), the value is reduced by the leakage inductance of the transformer (70). For example, if the calculated value for the first inductor in the first stage of the output filter is 100μH and the leakage inductance of the transformer (70) is 60μH, then a 40μH inductor should be used as the first inductor (82) of the output filter (since 100μH - 60μH = 40μH).

[0060] FIG. 4 is a schematic diagram of an embodiment of an output filter (80) in which the inductance of the transformer (70) provides all the inductance necessary for the first inductor to act as the first inductor for the first stage of the output filter. The transformer of FIG. 4 is a Zolotov TRM085 with a winding 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 of 32 to 36 μH (at 200 kHz). 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 5th and 7th harmonics when the operating frequency is 200 kHz.

[0061] An alternative design for implementing an output filter with an operating frequency of 150 kHz can be implemented starting from the circuit 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 5th and 7th harmonics when the operating frequency is 150 kHz.

[0062] 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. Using an output impedance in this range is appropriate because the current and voltage of the output signal (100) can vary depending on the load provided (i.e., the patient and transducer array in the context of tumor treatment field therapy). However, because the output impedance is between 40 and 120 ohms, the current does not surge to dangerous values ​​even if there is a short circuit at the outlet. Also, if the impedance of the load suddenly increases (e.g., if the electrode is partially disconnected from the patient), the current does not decrease significantly. This is very useful as a safety feature in the context of tumor treatment field therapy.

[0063] 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. The DAC (42) responds by outputting an analog voltage that serves as the control signal applied to the voltage control input of the DC-DC converter (50). For example, assume that the DAC (42) starts at 1V, the DC-DC converter outputs 10VDC, and the transformer (70) has a step-up ratio of 1:6. Under these conditions, the pulse at the secondary output of the transformer (70) becomes 60V. When the controller (40) writes a new control word to the DAC (42) that increases the output of the DAC (42) to 2V, the DC-DC converter (50) will increase the output voltage to 20V DC and respond to the new signal applied to the voltage control input, which will cause the pulse on the secondary side of the transformer (70) to increase to 120V (after passing through the step-up transformer (70).

[0064] Preferably, the voltage and / or current of the output signal (100) are monitored by a voltage sensing circuit (92) and / or a current sensing circuit (94). The outputs of these circuits (92, 94) are preferably fed back to a controller (40), and the controller (40) is preferably configured to shut down the power switcher (60) by suppressing the generation of both a first control signal and a second control signal applied to the control input (68) of the power switcher (60) when an error condition (e.g., overvoltage, overcurrent, severe voltage drop, etc.) is detected at the output (100). Optionally, the shutdown of the power switcher (60) may also be triggered by an overheating condition of the load by including a suitable temperature sensor and routing a signal from this temperature sensor back to the controller (40).

[0065] Note that in the illustrated embodiment, a single controller (40) is used to implement all the control and sequencing functions described herein. However, in an alternative embodiment, the programmable controller (40) may be combined with a hardwired sequencer to perform each of these two functions.

[0066] In some embodiments, the output of the current sensing circuit (94) and / or the voltage sensing circuit (92) is 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, when 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 results in an increase in the amplitude of the output signal (100). Similarly, when 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 results in a corresponding decrease in the amplitude of the output signal 100.

[0067] In an alternative embodiment, the transformer (70, illustrated in FIG. 1 and 2) may be omitted, in which case two conductors at the output of the power switcher (60) are directly connected to two conductors at the input of the output filter (80). In these embodiments, current flows directly from the output of the power switcher (60) to the input of the output filter (80) without an intermediate transformer. However, this alternative embodiment is less desirable, particularly in situations where insulation is desirable and high voltage output is desired. Additionally, this alternative embodiment cannot rely on the leakage inductance of the transformer to provide part or all of the inductance required for the first stage of the filter.

[0068] It should be noted that the design of the embodiment of FIG. 1 relies on prior knowledge and the intentional configuration of the signal and output filter (80) such that the most important harmonics of the input signal (even harmonics and 3rd harmonics) are essentially zero or become zero by the output filter (80). This helps to provide a very clean high-voltage output signal with very high efficiency at the desired frequency.

[0069] 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. The situation described above in relation to FIG. 1 when n=1 is described. The situation in relation to FIG. 5 using two DC-DC converters when n=2 is described below. Other embodiments for n > 2 can be implemented according to the same framework using additional DC-DC converters and many more samples (following the rule that N=2+4n).

[0070] FIG. 5 is a block diagram of a second embodiment of a sinusoidal generator that generates a sinusoidal wave of a preset frequency f with a controllable amplitude where n=2. Consequently, it includes two DC-DC converters (50, 50B) and 10 samples per cycle are used (according to the formula N=2+4n). Note that in the embodiment of FIG. 5-6, components having similar reference numbers operate in a manner similar to the above description in relation to the embodiment of FIG. 1-2.

[0071] FIG. 7 illustrates a sine wave (120) and an oversampled version of a sine wave (122) sampled 10 times per cycle (i.e., 0°, 36°, 72°, … 324° and 360°). Looking at this oversampled version 112, it becomes clear that it contains only five voltage levels: a low positive voltage +V1, a high positive voltage +V2, a low negative voltage -V1, a high negative voltage -V2, and 0 volts (between 0° and 36° and between 180° and 216°). The reason the 0 volt level exists here is that the sampling times were chosen so that one of the sampling points occurs at 0° and one of the sampling points occurs at 180°. Here, the sine function is 0. This choice advantageously reduces the number of voltage levels that must be generated to make the oversampled version (122) of the sine wave consist of two levels (i.e., V1 and V2).

[0072] Consequently, the controller (40B) can be used to control the generation of an oversampled version of a sine wave that is sampled N times per cycle using uniformly spaced samples including a sampling point at 0°, where N=2+4n, and the output voltage of the DC power supply is set to a level present in the oversampled version of the sine wave, and the control signal is sequenced through the 2n state and additional off state to generate the oversampled sine wave version, so that each DC power supply is applied to the primary side of the transformer in each direction at appropriate times in sequence.

[0073] When n=2 (as in the embodiment of FIG. 5-6), an oversampled version of a sine wave at a preset frequency f can be formed at the output of the transformer (70) by repeating the following 8 steps in succession: applying V1 to the primary side of the transformer (70) in a first direction between 36° and 72°; applying V2 in a first direction between 72° and 144°; applying V1 in a first direction between 144° and 180°; keeping it off between 180° and 216°; applying V1 in a second direction between 216° and 252°; applying V2 in a second direction between 252° and 324°; applying V1 in a second direction between 324° and 360°; and keeping it off between 0° and 36°. To properly track the oversampled sine wave version of the resulting waveform (122 in Fig. 7), the ratio between V1 and V2 must be kept constant. More specifically, the ratio V2 / V1 must be equal to sin(72°) / sin(36°), which is 1.618.

[0074] The controller (40B) serves to generate a control signal that causes the power switcher (60B) to apply these voltages to the transformer (70) in the order identified above. The controller (40B) is similar to the controller (40) of the embodiment of FIG. 1, except that it sequences through 10 states per cycle instead of 6 states per cycle.

[0075] Now, referring to FIG. 6, the power switch (60B) has a control input (68), and the power switch is configured to (a) apply one selected output of the DC power in a selected direction to the primary side of the transformer (70) in response to the 2n state of the control signal applied to the control input (68), or (b) maintain an off state in response to the additional state of the control signal.

[0076] FIG. 6 is a block diagram of one preferred approach for implementing a 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 both directions across the transformer (70). 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. (Similar to the corresponding switches in the embodiment of FIG. 1-2) these switches (61-66) are conducted and shut off in response to a signal applied to the control input (68). To connect the output of the first DC-DC converter (50) to the primary side of the transformer (70) in the first direction, only switches (63, 62) need to be closed. To route the output of the first DC-DC converter (50) to the primary side of the transformer (70) in the opposite direction (i.e., opposite polarity), only switches (61, 64) must be closed. To route the output of the second DC-DC converter (50B) to the primary side of the transformer (70) in the first direction, only switches (65, 62) must be closed. To route the output of the second DC-DC converter (50B) to the primary side of the transformer (70) in the opposite direction, only switches (65, 62) must be closed. To connect the output of the second DC-DC converter (50B) to the primary side of the transformer (70) in the opposite direction (i.e., opposite polarity), only switches (61, 66) must be closed. When all six of these switches (61-66) are off, power is not routed to the primary side of the transformer (70).

[0077] 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 cutoff frequency. The output filter (80B) is similar to the output filter (80) of the embodiment in FIG. 1-2, but the positions of the zeros in the transfer function of the output filter (80B) must be adjusted to correspond to the frequency of the oversampled waveform (122) ( FIG. 7). More specifically, the output filter (80B) must have a transfer function having zeros at frequencies where the harmonics of the preset frequency f are expected to contain power.

[0078] For example, since the waveform (122) has 10 samples per cycle, the first harmonic expected to appear is the 9th harmonic. Therefore, a transfer function having a zero at the 9th harmonic will be useful when this waveform (122) is used. The cutoff frequency of the filter must also be adjusted appropriately according to the set of harmonics expected to appear (which can be calculated in advance through the Fourier transform of the waveform in use).

[0079] Optionally, the transfer function of the output filter (80B) may be designed so that the harmonic of a preset frequency f has a zero at the next frequency where power is expected to be contained. For waveform (122), this is the 11th harmonic.

[0080] The controller (40B) controls the amplitude of the sinusoidal wave at the output (100B) of the output filter (80B) by adjusting the output voltage of the DC power supply (50, 50B) through the voltage control input of the DC power supply (50, 50B) while maintaining a fixed ratio between the output voltages. In the illustrated embodiment of each DC power supply, this is achieved by writing appropriate control words to the 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) may be removed and replaced with a 1.618x hardware multiplier inserted between the output of the DAC (42) and the voltage control input to the second DC-DC converter (50B).

[0081] In an alternative embodiment, the transformer (70) may be omitted in the embodiment of FIG. 5, in which case two conductors at the output of the power switcher (60B) are directly connected to two conductors at the input of the output filter (80B). In these embodiments, current flows directly from the output of the power switcher (60B) to the input of the output filter (80B) without an intermediate transformer. However, this embodiment is less preferred for the same reasons discussed above in relation to FIG. 1.

[0082] The system described above is suitable for generating all forms of high-voltage signals, provided that the pulse train to be generated can be determined prior to use through calculation or experiment and the filter is designed accordingly.

[0083] When the output signal generated by the system is applied to the electrode to create a tumor treatment field (as described in U.S. Patent 7,805,201), changes in the load associated with the patient's body or the transducer array can alter the output signal due to interaction with the output filter. That is, any change in such load (e.g., lifting a disc from the patient's body or a short circuit, etc.) immediately affects the output signal, and this is continuously monitored. Thus, it is possible for the device to respond very quickly to these changes (e.g., by shutting down the power switcher (60) in response to the detection of a short circuit or overload condition).

[0084] In particular, in the aforementioned embodiment, since a sine wave is generated at a known frequency, the exact shape of the desired output signal is known in advance at every moment. Based on a controller responding to an external input (e.g., current measurement or temperature measurement), only the amplitude of the output signal changes over time. The embodiment described above can be advantageously used to generate a very clean, narrowband-limited signal in a frequency range of 100-500 kHz, and has very low loss and very low sensitivity to an external load to which the signal generator is connected.

[0085] In an alternative embodiment, the system may be used to generate a sine wave at any desired frequency within a preset range by constructing a filter using a component having an adjustable reactance (e.g., adjustable capacitance or adjustable inductance). In this embodiment, the reactance of the adjustable component is set to impart desired transfer function characteristics to the filter. Then, an appropriately oversampled sine wave is generated and fed to the filter as discussed above in relation to FIGS. 1 and 5.

[0086] In another alternative embodiment, the system may be used to generate a finite number of predefined signals at a plurality of different preset frequencies. This embodiment may be implemented by storing the characteristics of a pulse train for each of the predefined signals in a lookup table and providing a filter bank that can be optionally switched to a signal path to provide the filtering characteristics necessary to generate a desired signal among the predefined signals. When the system is used to generate one of the predefined signals, the characteristics of the pulse train required are retrieved from memory, and an appropriate filter (i.e., a filter that matches this pulse train) is switched to the signal path.

[0087] In another alternative embodiment, a composite signal comprising a small number of discrete frequencies (among 2 to 5 frequencies) can be generated by creating an oversampled version of the composite signal and passing the oversampled version of the composite signal through a suitable filter.

[0088] In the embodiments of FIG. 1 and FIG. 5 described above, depending on the configuration of the DC-DC converter (50 / 50B), there is a possibility that high-frequency artifacts (e.g., spikes) may occur in the output 100 / 100B when the output voltage of the DC-DC changes (e.g., when the controller 40 / 40B writes a new control word to the DAC 42 / 42B). And since high-frequency artifacts can cause unpleasant sensations to a person receiving treatment in the tumor treatment field, it is desirable to take measures to prevent such high-frequency artifacts.

[0089] One appropriate approach to prevent high-frequency artifacts from appearing in the output (100 / 100B) is to intentionally slow down the response time of the DC-DC converter (50 / 50B) (for example, by adding a sufficiently large capacitor to the output of each DC-DC converter). However, while this approach is effective, it has two drawbacks. First, additional components must be included in the circuit. Second, slowing down the system's response time prevents the output voltage from changing rapidly, even in situations where abrupt changes are required.

[0090] FIGS. 8 to 10 illustrate an alternative approach to prevent high-frequency artifacts from appearing in the output (100 / 100B) without intentionally slowing down the response time of the DC-DC converter (50 / 50B).

[0091] More specifically, FIG. 8 illustrates the same waveform (112) described above in relation to FIG. 3 (appearing at the output of the power switcher (60) of FIG. 1) and the sine wave output waveform (115) (appearing at the output of the output filter (80) of FIG. 1) under steady-state conditions (i.e., when the voltage of the DC-DC converter output of FIG. 1 is maintained at a constant 20VDC and the controller (40) of FIG. 1 does not update the contents of the DAC (42). In this steady-state condition, the output waveform (115) will operate as described above in relation to FIG. 1-4 and will not contain any high-frequency artifacts.

[0092] FIG. 9 illustrates how the situation changes when a fast-response DC-DC converter is used and the output of the DC-DC converter (50) (see FIG. 1) changes from 20VDC to 40VDC. As described above in relation to 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) will be 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 voltage of the DC-DC converter will begin to change rapidly because the output of the DAC (42) is applied to the voltage control input of the DC-DC converter (50) (e.g., from 20V to 40V in the illustrated example). And since the power switch (60) is set to actively source current from the DC-DC converter (50) to the transformer (70) at that moment t9, the sudden change in current will go through the transformer (70) to the output filter (80) and add high-frequency artifacts (215) to the output (100) (the dotted line (222) represents a continuation of the original sinusoidal wave that existed before t9, and the dotted line (220) represents a clean sinusoidal wave with twice the original amplitude).

[0093] A similar situation exists in the case of a DC-DC converter design in which 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 (independent of the response time of the DC-DC converter). More specifically, when the power switch (60) is set to actively source current from the DC-DC converter (50) to the transformer (70) at the moment the voltage control input of the DC-DC converter changes, any spike in the output of the DC-DC converter will travel through the transformer (70) to the output filter (80), and the output filter (80) will add high-frequency artifacts (215) to the output (100).

[0094] In certain situations, if the output voltage of the DC-DC converter changes during the time interval when the power switch (60) actively sources current from the DC-DC converter (50 / 50B) to the transformer (70), high-frequency artifacts may be added to the output (100). On the other hand, if the output of the DC-DC converter changes during the time interval when the power switch (60) does not actively source current from the DC-DC converter (50 / 50B) to the transformer (70), high-frequency artifacts will not appear in the output (100). The controller (40 / 40B) of the embodiment of FIG. 1 / 5 may utilize this dichotomy to prevent high-frequency artifacts from appearing in the output (100 / 100B). More specifically, the controller (40 / 40B) does this by ensuring that the output of the DC-DC converter (50 / 50B) changes only during the interval when the power switcher (60 / 60B) is not actively sourcing current from the DC-DC converter.

[0095] In the context of the embodiment of FIG. 1 described above, the controller (40) prevents the adjustment of the voltage control input of the DC-DC converter (50) from occurring when (a) a 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) to the primary side of the transformer (70) in the first direction) or (b) a 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) to the primary side of the transformer (70) in the opposite direction). When neither the first control signal nor the second control signal is applied to the control input, the power switcher (60) will remain off, in which case the controller (40) adjusts the voltage control input of the DC-DC converter (50), but no high-frequency artifacts are introduced into the output (100).

[0096] FIG. 10 illustrates how the situation unfolds in the context of the embodiment of FIG. 1 when the output of the DC-DC converter (50) changes from 20VDC to 40VDC during time t10 when the power switch (60) is not actively sourcing current from the DC-DC converter. Prior to this time t10, the output of the DC-DC converter (50) will be at a first level (e.g., 20V in the illustrated example), and the output waveform (315) will be the same as the output waveform (115) in the example of FIG. 8. The controller (40) updates the contents of the DAC (42) at time t10 when the power switch (60) is not actively sourcing current from the DC-DC converter (50) to the transformer (70). The output voltage of the DC-DC converter (50) will start to change rapidly (e.g., from 20V to 40V in the example given) and will stabilize before the power switch (60) starts routing the current to the transformer (70) at t11. Since the output of the DC-DC converter (50) is already stabilized when the power switch (60) starts providing the current to the transformer (70) at t11, the waveform entering the output filter after t11 will be an oversampled sine wave with a different amplitude (e.g., 40V). And as described above in relation to FIGS. 1 through 4, when the oversampled sine wave is provided to the output filter (80), the resulting output (100) will be a very clean sine wave.

[0097] Similarly, in relation to the embodiment of FIG. 5 described above, the controller (40B) prevents high-frequency artifacts from appearing at the output (100B) by ensuring that the output of any given DC-DC converter (50 / 50B) is changed only during the interval when the power switch (60) is not actively sourcing current from the given DC-DC converter. The controller (40B) achieves this by not adjusting the output voltage of any DC power source while the output is routed to the output terminal of the power switcher (60).

[0098] FIG. 11 is a block diagram of a third embodiment of a sinusoidal generator that generates a sinusoidal wave at a preset frequency f with a controllable amplitude. Components with similar reference numbers operate in a manner similar to the corresponding components described above in relation to FIG. 1-5.

[0099] 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 value (e.g., 10). In this example, 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, with proportional control applied in between. Thus, the output of the DC-DC converters (51, 52) can take any value between 0 and 50V depending on the voltage (e.g., 0-5V) applied to the analog voltage control input. The controller (40C) controls the output voltage of the DC-DC converters (51, 52) by writing a control word to the DAC (42, 42B). The DAC then generates an analog voltage proportional to the control word, and this analog voltage is provided to the voltage control input of the DC-DC converters (51, 52).

[0100] The controller (40C) performs the role of generating a control signal that causes the power switcher (60B) to apply this voltage to the transformer (70) in the order described below.

[0101] FIG. 6 is a block diagram of one preferred approach for implementing a 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 a transformer (70) as shown in FIG. 6. These switches (61-66) open and close in response to a signal provided to a control input 68.

[0102] To route the output of the first DC-DC converter (51) in the first direction on the primary side of the transformer (70), only switches (63, 62) must be closed. The power switcher (60B) is configured so that this occurs 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., opposite polarity) on the primary side of the transformer (70), only switches (61, 64) must be closed. The power switcher (60B) is configured so that this occurs in response to the second state of the control input.

[0103] To route the output of the second DC-DC converter (52) in the first direction on the primary side of the transformer (70), only switches (65, 62) must be closed. The power switcher (60B) is configured to occur in response to a third state of the control input. To route the output of the second DC-DC converter (52) in the opposite direction (i.e., opposite polarity) on the primary side of the transformer (70), only switches (61, 66) must be closed. The power switcher (60B) is configured to occur in response to a 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 a fifth state of the control input (also referred to herein as an additional state).

[0104] The controller (40C) may operate in a first mode or a second mode. In the first mode, the controller (40C) maintains the first voltage control input of the power switcher (60B) constant and generates an output waveform (100C) by receiving power only from the first DC-DC converter (51) by setting the control input in an alternating sequence between the first and second states. In some preferred embodiments, a waveform similar to the waveform (112) of FIG. 3 is formed by (a) forming the control input into the first state for a period of T / 3, (b) waiting for a period of T / 6, (c) forming the control input into the second state for a period of T / 3, and then (d) waiting for a period of T / 6, and then repeating the sequence (a), (b), (c), and (d). The amplitude of this waveform will depend only on the output voltage of the DC-DC converter (51). If this waveform is filtered by an output filter (80) (identical to the output filter (80) of the embodiment of FIG. 1-2), a clean sine wave (as described above in relation to FIG. 1-4) can be obtained.

[0105] In the second mode, the controller (40C) maintains the second voltage control input of the power switcher (60B) constant and sets the control input in a sequence that alternates between the third and fourth states, thereby receiving power only from the second DC-DC converter (52) and generating an output waveform (100C). In some preferred embodiments, a waveform similar to the waveform (112) of FIG. 3 is formed by (e) forming the control input into the third state for a period of T / 3, (f) waiting for a period of T / 6, (g) forming the control input into the fourth state for a period of T / 3, and then (h) waiting for a period of T / 6, and then continuously repeating the sequence (e), (f), (g), and (h). The amplitude of this waveform will depend only on the output voltage of the DC-DC converter (52). A clean sine wave can be obtained by filtering this waveform with an output filter (80).

[0106] FIG. 12 illustrates a method in which an embodiment of FIG. 11 enables a rapid change in the voltage of an 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 starts at t0, and the controller (40C) operates in the first mode. In this mode, the output waveform (430) is powered exclusively by the first DC-DC converter (51) (set to 20V in the illustrated example). 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 first and second states (with a waiting time interspersed at appropriate times) while keeping the first voltage-control input constant as described above.

[0107] While still operating in the first mode, the controller (40C) predetermines what the output voltage will be when switching to the second mode. Then, the controller (40C) provides a command at time t1 to cause the output voltage of the second DC-DC converter (52) to move to a desired level. In the illustrated example, the desired level for the second DC-DC converter (52) is 40V. In particular, the response time of the second DC-DC converter can be very slow because the second DC-DC converter is not being used at this point.

[0108] Preferably, after the output of the second DC-DC converter (52) stabilizes to a desired level, the controller (40C) switches to a second mode. This switch from the first mode to the second mode occurs when the power switcher (60B) is in a fifth state and is not routing current to the transformer (70). In the second mode, the output waveform (430) is powered only by the second DC-DC converter (52) (set to 40V in the illustrated example). The controller (40C) controls the generation of the output waveform (430) by setting the control input of the power switcher (60B) to alternate between the third and fourth states (with waiting times interspersed at appropriate times) while maintaining the second voltage control input constant as described above. Preferably, the command to start the voltage change of the second DC-DC converter (52) occurs at a time sufficient before (at least 1 ms) for the controller (40C) to switch to the second mode and for the output of the second DC-DC converter (52) to stabilize at a desired level. Thus, when the second mode starts at t2, the output waveform (430) will immediately reach the desired level.

[0109] A similar process occurs when switching back from the second mode to the first mode. More specifically, while operating in the second mode, the controller (40C) predetermines what the output voltage will be when switching to the first mode. Subsequently, the controller (40C) provides a command at time t3, which causes the output voltage of the first DC-DC converter (52) to move to a desired level. In the illustrated example, the new desired level for the first DC-DC converter (51) is 10V. In particular, since the first DC-DC converter is not used at this stage, the response time of the first DC-DC converter may be very slow.

[0110] Preferably, after the output of the first DC-DC converter (51) stabilizes to a desired level, the controller (40C) switches to the first mode. This switch from the second mode to the first mode occurs when the power switcher (60B) is in the fifth state and is not routing current to the transformer (70). In the first mode, the output waveform (430) is powered only by the first DC-DC converter (51) (set to 10V in the illustrated example). The controller (40C) controls the generation of the output waveform (430) by setting the control input of the power switcher (60B) to an alternating sequence between the first and second states (with waiting times interspersed at appropriate times) while maintaining the first voltage control input constant as described above. Preferably, the command to initiate the voltage change of the first DC-DC converter (51) (i.e., t3 in FIG. 12) occurs sufficiently earlier (e.g., at least 1 ms) before the controller (40C) switches to the first mode (i.e., t4 in FIG. 12) so that the output of the first DC-DC converter (51) stabilizes to a desired level, so that when the first mode starts at t4, the output waveform (430) is at the desired level. In an alternative embodiment, the transformer (70) may be omitted from the embodiment of FIG. 11, in which case two conductors at the output of the power switcher (60B) are directly connected to two conductors at the input of the output filter (80). In these embodiments, current flows directly from the output of the power switcher (60B) to the input of the output filter (80) without an intermediate transformer. However, such an embodiment is less preferred for the same reasons discussed above in relation to FIG. 1.

[0111] Tumor therapeutic field therapy involves inducing an electric field (e.g., at 200 kHz) through a target body part to treat a tumor in that body part. Experiments have shown that the efficacy of the tumor therapeutic field increases when the direction of the tumor therapeutic field changes during the treatment process. For example, in the Optune® prior art system, the direction of the tumor therapeutic field changes every second. However, in an alternative embodiment, the direction may change at a different rate (e.g., between 50 ms and 10 s).

[0112] FIG. 13 is a block diagram of the original Optune® conventional technology system for applying a tumor treatment field to a person's head (or other body parts) in two different directions. This is achieved by using a pair of transducer arrays (25A, 25P) located on the front and back (i.e., front and back) of the head and another pair of transducer arrays (25L, 25R) located on the left and right sides of the person's head. More specifically, when an AC voltage is applied between the transducer arrays (25L, 25R), an electric field flowing mainly in the left-right (LR) direction will be induced in the subject's head. And when an AC voltage is applied between the transducer arrays (25A, 25P), an electric field flowing mainly in the front-back (AP) direction will be induced in the subject's head. The tumor treatment field can also be applied to other parts of the body (e.g., pancreas, lungs, etc.) by placing transducer arrays on the subject's skin on the front / back and right / left sides of the corresponding body parts.

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

[0114] FIG. 14 is a timing diagram showing the sequencing between the two directions LR and AP used in the original Optune®. In this approach, the switch (22) routes (a) the output of the AC voltage generator (20) to the left and right transducer array (25L / R) for 1 second, and (b) the output of the AC voltage generator (20) to the forward and backward transducer array (25A / P) for 1 second, and then alternately repeats steps (a) and (b). A short period (e.g., 5-10 ms) during which the output of the AC voltage generator (20) is not routed to the pair of transducer arrays (25L / R, 25A / P) is inserted between each step (indicated as OFF).

[0115] One problem that was resolved during the original design of Optune® is described in relation to FIG. 15. More specifically, when the instantaneous output voltage (520) generated by the AC voltage generator (20) is substantial (e.g., >10V) and the switch (22) is switched from the OFF state to the LR state or AP state (trace 525), the output waveform will be similar to trace (530) containing spikes (532). Since such spikes (532) can cause an uncomfortable sensation, the original Optune® was designed so that such spikes do not occur. More specifically, this was achieved by ramping down the output voltage of the AC voltage generator (20) from the normal state value to 0V during a 100ms interval preceding each OFF state, as shown in FIG. 16A, trace (540), and then ramping up the output voltage back to the normal state value during a 100ms interval following each OFF state. The ramp rate was about 1 V / ms, which is slow enough to avoid spikes that the patient can detect.

[0116] The resulting waveform at the output of the AC voltage generator (20) is similar to the waveform shown in FIG. 16B (except that the actual frequency of the sine curve generated by the AC voltage generator (20) would be tens of times higher than the illustrated sine curve). Note that the x-axis scale in FIG. 16B has been magnified four times compared to FIG. 16A to show additional details. And this solution worked very well in the context of the original Optune®. The system operated at the maximum output voltage for 80% of the operating time, and operated for only 20% of the time when the voltage was raised, lowered, or turned off.

[0117] Now, let us examine what happens when a similar approach is used, but the interval at which the AC voltage is applied to the LR or AP transducer array is reduced from 1 second to 0.25 seconds. If the same 1 V / ms ramp-down and ramp-up approach described above with respect to FIG. 16A is used in this new time scale, the output voltage of the AC voltage generator (20) will follow the trace (550) of FIG. 17A. And as a result, the waveform at the output of the AC voltage generator (20) will be similar to the waveform shown in FIG. 17B (however, once again, the actual frequency of the sine wave generated by the AC voltage generator (20) will be much higher than the shown sine wave). Note that the x-axis scale of FIG. 17B has been magnified four times relative to FIG. 17A to show additional details.

[0118] However, this solution is not ideal because the peak output voltage is applied to the transducer array for only 20% of the time, which means the maximum electric field is applied to the target for only 20% of the time. Therefore, unlike the conventional technical situation illustrated in FIG. 16A / B (where the output voltage was ramped up / ramped down to ensure patient comfort, and the ramp slightly reduced the percentage of time spent at the peak voltage), if the same ramping slope is used when the switching time is shortened to 0.25 seconds, the percentage of time spent at the peak voltage will decrease very significantly (as shown in FIG. 17A / B). Furthermore, the situation worsens if the interval during which the AC voltage is applied to the LR or AP transducer array is reduced to less than 0.20 seconds, in which case the peak voltage (and corresponding peak electric field strength) is not reached.

[0119] The embodiment of FIG. 18 uses a different approach to avoid spikes similar to the spike (532) shown in FIG. 15. More specifically, the embodiment of FIG. 18 includes an AC voltage generator (30) and a switch (32), and relies on synchronization between these two functional blocks to avoid spikes as described below in relation to FIG. 19 through 23. In some preferred embodiments, the AC voltage generator (30) of FIG. 18 is implemented using the approach described above in relation to FIG. 1 through 7. The switch (32) routes the output of the AC voltage generator (30) to the left and right transducer array (25L / R) in response to a first state of the control input; routes the output of the AC voltage generator (30) to the front and rear transducer array (25A / P) in response to a second state of the control input; or (c) remains off in response to a third state of the control input. The switch (32) can be implemented using any of the various approaches that will be obvious to a person skilled in the relevant technical field, 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 transmit control signals to the AC voltage generator (30) and / or the switch (32), so that the signals described below are generated with the time relationship described below. Various alternative approaches to synchronizing the AC voltage generator (30) and the switch (32) may be used. For example, synchronization can be achieved by allowing the AC voltage generator (30) to operate freely and adjusting the switching time of the switch (32) (described below in relation to FIG. 20). Alternatively, synchronization can be achieved by allowing the switch (32) to switch automatically and turning off the AC voltage generator (30) before each switching event (described below in relation to FIG. 21). Another alternative to 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 sequencing 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, and routes the output of the AC voltage generator (30) to the front and rear transducer arrays (25A / P) for a duration T, and then alternately repeats (a) and (b). A short period (e.g., 5-10 ms) during which the output of the AC voltage generator (30) is not routed to the pairs of transducer arrays is inserted between each step (labeled OFF). This can be configured by repeatedly adjusting the control input of the switch (32) to cycle through the LR mode, AP mode, and OFF mode into the following repeated sequence of (1) LR mode, (2) OFF mode, (3) AP mode, and (4) OFF mode.

[0122] In this embodiment, the duration T may be much shorter than 1 second because the output voltage of the voltage generator (30) does not slowly ramp up and ramp down (as in the prior art embodiment described above with reference to FIG. 16). Instead, the output of the AC voltage generator (30) is maintained at a maximum value continuously (as described below with reference to FIG. 20) or jumps to a maximum value immediately after the switch (32) switches the state (as described below with reference to FIG. 21). In either case, the signal applied to the transducer array (25A / P, 25L / R) will be at a maximum value for most of the time (e.g., >90% or >95% of the time). And maintaining the tumor treatment field more strongly for a longer period of time can advantageously improve the efficiency of tumor treatment field processing. In some embodiments, the duration (T) is greater than 20 ms. In some embodiments, the duration T is 0.1 to 0.5 seconds. In some embodiments, the duration T is 0.2 to 0.3 seconds. In particular, in contrast to the situation described above with respect to Fig. 17A / B, the system operates at the maximum output voltage for most of the time, regardless of how short the duration of T is.

[0123] FIG. 20 illustrates a first approach to achieving synchronization between a switch (32) and an AC voltage generator (30) by controlling the timing of the transition from the OFF state to the LR state or AP state (trace 635), such that the transition is aligned with windows of time such that the instantaneous output magnitude of the AC voltage generator is sufficiently small so that even if the subject receiving treatment jumps to a small voltage from the OFF state, they do not experience a perceptible sensation.

[0124] The voltage threshold that causes perception may vary from person to person and may also vary depending on which part of the body is in contact with the transducer array. For example, jumping from the OFF state to 1V, 1.5V, 2V, 2.5V, 3V, 3.5V, 4V, 4.5V, or 5V in various parts of the body may not be detectable. Therefore, to prevent the switching from causing a detectable sensation, the transition from the OFF state to the LR state or AP state must be timed so that the instantaneous output magnitude of the AC voltage generator matches a time window that is less than or equal to that threshold. In this approach, the output voltage of the AC voltage generator (30) may be maintained at a 100% full steady-state value for the duration of the time, as illustrated by the trace (630). In some preferred embodiments, the transition occurs when the instantaneous output magnitude of the AC voltage generator is less than 1V.

[0125] For example, let us assume that the threshold of perception for a given target is 5V and the output of the AC voltage generator (30) is 100V pk-pk (i.e., the instantaneous output value of the AC voltage generator 30 is between +50 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 limiting the transition from the OFF state of the switch (32) to the LR state or AP state to these specific time windows, the signal (640) applied to the transducer array (25L / R or 25A / P) does not contain any spikes with an absolute magnitude greater than 5V, and thus, means that the target cannot detect it. It should be noted that when the AC voltage generator operates at 200 kHz, 11.4° corresponds to 0.16 μs, and this window is long enough to facilitate synchronization by aligning the switching of the switch (32) to the specific time window identified in this paragraph.

[0126] In some preferred embodiments, switching the switch (32) from the OFF state to the LR state or AP state is limited to a time window in which the magnitude of the instantaneous output of the AC voltage generator is less than 1V. 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 limiting the switching of the switch (32) from the OFF state to the LR state or AP state to these specific time windows, the signal (640) applied to the transducer array (25L / R or 25A / P) does not contain any spikes greater than 1V in magnitude. As understood by those skilled in the art, the timing of the switch (32) can be similarly adjusted for other thresholds.

[0127] In the example illustrated in FIG. 20, the output voltage of the AC voltage generator (30) is maintained at a full steady-state value for 100% of the time, as illustrated by the trace (630). In this situation, the applied signal (640) transducer array (25L / R or 25A / P) jumps immediately to a full steady-state output voltage as soon as it is turned on. Therefore, the signal applied to the transducer array (25A / P, 25L / R) will almost always be at its maximum value. And as mentioned above, the tumor treatment field can be maintained more strongly for a longer period of time, thereby advantageously improving the efficiency of tumor treatment field processing. However, the output voltage of the AC voltage generator (30) at the very beginning of the LR or AP state is not critical, and in an alternative embodiment, it is acceptable for the output voltage of the AC voltage generator to drop to some extent. However, it is desirable that the output of the AC voltage generator (30) reach at least 80% of the steady-state output voltage of the AC voltage generator within 20ms after the electronic switch is switched from the OFF state to the LR state or AP state. In some preferred embodiments, this occurs within 5ms. And in some preferred embodiments, this occurs within 1ms.

[0128] The output sinusoidal wave of the AC voltage generator of the low-size portion (i.e., 1V, 1.5V, 2V, 2.5V, 3V, 3.5V, 4V, 4.5V, or 5V or less) is preferably implemented when the switch (32) is switched back to the OFF state from the LR state or AP state.

[0129] FIG. 21 illustrates a second approach to achieving synchronization between the AC voltage generator (30) and the switch (32) of FIG. 18. This approach operates by reducing the instantaneous output voltage of the AC voltage generator (30) to a magnitude of less than 5V before switching the switch (32) from the OFF state to the LR state or AP state to prevent spikes from appearing on the conductors leading to the transducer array (25L / R and 25A / P) when the switch (32) switches states. In some preferred embodiments, the instantaneous output voltage of the AC voltage generator (30) is reduced to a magnitude of less than 1V (e.g., to 0V) before the switching of the switch (32).

[0130] Reducing the output voltage of the AC voltage generator (30) to 0V can be easily achieved when any of the embodiments described above in relation to FIGS. 1-6 and FIGS. 10-12 is used as the AC voltage generator. For example, when the AC voltage generator of FIGS. 1 and FIG. 2 is used, the output can be set to 0 by keeping all switches (i.e., switches 61-64) of the power switcher (60) in an off state so that neither the first control signal nor the second control signal is applied to the control input of the power switcher (60). Similarly, when the AC voltage generator of FIGS. 5 and FIG. 6 is used, the output can be set to 0 by sending a control signal to the power switcher (60B) so that all switches of the power switcher (60B) are turned off.

[0131] In FIG. 21, the upper trace (650) shows the output of the AC voltage generator (30); the middle 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). It is assumed 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 the LR pair of the transducer array (25L / R) or the AP pair of the transducer array (25A / P). At some time prior to 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. Since the output of the AC voltage generator (30) is 0V when the switch (32) is switched at t20, no spike will appear in the conductors leading to the transducer arrays (25L / R and 25A / P) at that time.

[0132] After a short time (e.g., <0.1ms), at t21, the synchronization controller (35) (see FIG. 18) begins to transmit a control signal (e.g., as described above in relation to FIG. 1-6 and 10-12) to the AC voltage generator (30), which causes the AC voltage generator (30) to begin generating a sine wave (650). With the configuration of the AC voltage generator (e.g., as described above in relation to FIG. 1-6 and 10-12), particularly the output filter (80 / 80B) of the FIG. 1-5 embodiment, the AC voltage generator (30) will not introduce any spikes to the output (650) at t21, and thus no spikes will propagate to the output (660). And when the switch (32) is already settled in its current state, the switch (32) will not introduce any spikes to the output (660) (supplied to the transducer array (25L / R or 25A / P)) at t21.

[0133] In particular, as illustrated in FIG. 21, the output voltage (650) of the AC voltage generator (30) preferably jumps immediately to the full steady-state output voltage without a ramp-up period. Thus, the signal applied to the transducer array (25A / P, 25L / R) will almost always be at its maximum value. And as mentioned above, maintaining the tumor treatment field more strongly for a longer period of time can advantageously improve the efficiency of the tumor treatment field processing. FIG. 22 illustrates an immediate jump to the full steady-state output voltage over a longer time scale, which stands in stark contrast to the conventional configuration illustrated in FIG. 16. However, the output voltage of the AC voltage generator (30) is not critical during the very beginning of the LR or AP state, and in an alternative embodiment, it is permissible for the output voltage of the AC voltage generator not to jump immediately to the full steady-state voltage. However, it is desirable that the output of the AC voltage generator (30) reaches at least 80% of the normal state output voltage of the AC voltage generator within 20ms after the electronic switch is switched from the OFF state to the LR state or AP state. In some preferred embodiments, this occurs within 5ms. And in some preferred embodiments, this occurs within 1ms.

[0134] FIG. 21 also illustrates an exemplary approach for synchronizing the AC voltage generator (30) and the switch (32) when the time comes to switch from the LR state or the AP state to the OFF state. At time t22, the AC voltage generator (30) generates a sinusoidal wave at the maximum steady-state output voltage, and the switch (32) is configured to route the output of the AC voltage generator (30) to 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 a signal (described above in relation to FIG. 1-6 and 10-12) to the power switcher (60 / 60B) that causes the output of the AC voltage generator (30) to drop to 0V. And due to the configuration of the AC voltage generator described above, no spike appears at the output (650) at t23, that is, no spike appears at the output (660) of the switch (32). After a short while (e.g., < 0.1ms), at t24, the switch (32) is set to the OFF state. And since the output of the AC voltage generator (30) is 0V at t24, no spike will be introduced into the conductor connecting the switch (32) and the transducer array (25) at t24.

[0135] In the embodiment described above with reference to FIGS. 18 and 19, 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, (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 alternately repeats steps (a) and (b). A short period (e.g., 5-10 ms) during which the output of the AC voltage generator (30) is not routed to the pairs of transducer arrays is inserted between each step. This is configured by repeatedly adjusting the control input of the switch (32) to cycle through the LR mode, AP mode, and OFF mode into the following repeated sequence of (1) LR mode, (2) OFF mode, (3) AP mode, and (4) OFF mode.

[0136] In variations of these embodiments, the OFF mode (i.e., a short duration during which the output of the AC voltage generator (30) is not routed to a pair of transducer arrays) is omitted. In this variation, 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, and routes the output of the AC voltage generator (30) to the front and rear transducer arrays (25A / P) for a duration T, and repeats steps (a) and (b) in an alternating order. This is configured to cycle through the LR mode and the AP mode in a sequence that repeats (1) LR mode and (2) AP mode by repeatedly adjusting the control input of the switch (32).

[0137] In this variant where the OFF mode is omitted, the duration (T) can also be much shorter than 1 second for the same reasons as described above. And here again, unlike the situation described above in relation to FIG. 17A / B, the system operates at the full output voltage for most of the time (e.g., 100% of the time) regardless of how short the duration of T is.

[0138] The transition of the switch (32) from the LR state to the AP state and from the AP state to the LR state is timed such that the instantaneous magnitude of the output of the AC voltage generator is sufficiently small so that the transition coincides with a time window, so that the subject receiving treatment does not experience a perceptible sensation. The transition is timed such that the instantaneous magnitude of the output of the AC voltage generator is sufficiently small so that the subject receiving treatment does not experience a perceptible sensation. More specifically, the transition between the LR and AP states must be timed such that the instantaneous output magnitude of the AC voltage generator is below the same threshold mentioned above in the embodiment of FIG. 18-20, which includes the OFF state (e.g., 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 illustrates an example of timing for synchronizing the transition between the LR and AP states with the output of the AC voltage generator (30) (indicated by trace 670) (see FIG. 18) so that the transition between the LR and AP states (indicated by trace 675 in FIG. 23) matches the time window that is close to the output of the AC voltage generator (30) (e.g., < 5 V or < 1 V) of the LR and AP states.

[0140] The embodiment described above in relation to FIGS. 18 to 22 advantageously enables driving a transducer array at maximum power for a much longer period than was possible in the prior art system without introducing voltage spikes that could cause discomfort to the person receiving treatment. And driving the transducer array at maximum power can advantageously increase the efficiency of treatment using a tumor treatment field.

[0141] Finally, regarding FIGS. 18 to 23, the embodiment described above discusses switching an AC voltage between a first pair of transducer arrays located in front / rear of the relevant body part and a second pair of transducers located in front / rear of the relevant body part, but depending on the relevant body part, this approach can be extended to two or more pairs of transducer arrays. For example, a third pair of transducer arrays may be located above / below the relevant body part, in which case the AC voltage is similar to the switching described above with respect to FIGS. 18-23.

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

Claims

Claim 1 A device for generating alternating current (AC) electrical signals to be applied to a first electrode pair and a second electrode pair, wherein the device comprises: an alternating current voltage generator having an output; an input receiving the output of the alternating current voltage generator and an electronic switch including a first power output and a second power output, wherein the electronic switch operates in a first mode that routes the output of the alternating current voltage generator to the first power output, and (b) operates in a second mode that routes the output of the alternating current voltage generator to the second power output, and wherein the electronic switch is configured to cycle through a sequence that repeats the first mode and the second mode; A device comprising a controller that synchronizes the operation of the AC voltage generator and the electronic switch such that the switching of the electronic switch to the first mode or the second mode is limited to a time window corresponding to the first 5.7°, middle 11.4°, and last 5.7° of each 360° of the AC voltage generator, wherein within 20ms after the electronic switch is switched to 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. Claim 2 In claim 1, the electronic switch is a device that cycles through a sequence of (1) a first mode, (2) a third mode, (3) a second mode, and (4) a third mode, in which the output of the AC voltage generator is not routed to the first power output or the second power output. Claim 3 In claim 1, the controller is a device for synchronizing the operation of the AC voltage generator and the electronic switch such that the switching of the electronic switch to the first mode or the second mode is limited to a time window corresponding to the first 1.1°, middle 2.2°, and last 1.1° of each 360° cycle of the AC voltage generator. Claim 4 The device according to claim 1, wherein, within 5ms after the electronic switch switches to 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. Claim 5 The device according to claim 1, wherein within 1 ms after the electronic switch switches to 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. Claim 6 In claim 1, the AC voltage generator is a device in which the electronic switch continues to operate at a maximum steady-state AC voltage even during the switching of the first mode or the second mode. Claim 7 In claim 1, the controller is a device that synchronizes the operation of the AC voltage generator and the electronic switch by controlling the time of the switching of the electronic switch such that the switching is equal to the time window corresponding to the first 5.7°, middle 11.4°, and last 5.7° of each 360° cycle of the AC voltage generator. Claim 8 In claim 1, the controller is a device that synchronizes the operation of the AC voltage generator and the electronic switch by controlling the AC voltage generator so that the output of the AC voltage generator is turned off whenever the switching of the electronic switch occurs. Claim 9 In claim 1, the controller is a device that synchronizes the AC voltage generator and the electronic switch by (a) controlling the switching timing of the electronic switch so that the switching corresponds to a time window corresponding to the first 5.7°, middle 11.4°, and last 5.7° of each 360° cycle of the AC voltage generator, and (b) controlling the AC voltage generator so that the output of the AC voltage generator is turned off whenever the switching of the electronic switch occurs. Claim 10 In claim 1, the electronic switch is configured to cycle through a repeating sequence of (1) the first mode and (2) the second mode, and the electronic switch is a device that switches directly from the first mode to the second mode and switches directly from the second mode to the first mode. Claim 11 A device for generating an alternating current electrical signal applied to a first electrode pair and a second electrode pair, wherein the device comprises: an alternating current voltage generator having an output; an input receiving the output of the alternating current voltage generator and an electronic switch having a first power output and a second power output, wherein the electronic switch operates in (a) a first mode for routing the output of the alternating current voltage generator to the first power output and (b) a second mode for routing the output of the alternating current voltage generator to the second power output, and the electronic switch operates by circulating a repeating sequence including the first mode and the second mode; A device comprising a controller that synchronizes the operation of the AC voltage generator and the electronic switch such that whenever the electronic switch switches to the first mode or the second mode, the amplitude of the instantaneous output of the AC voltage generator becomes less than a threshold value perceptible to a processing target, wherein within 20ms after the electronic switch switches to the first mode or the second mode, the output voltage of the AC voltage generator is at least 80% of the steady-state voltage of the AC voltage generator, and the threshold value perceptible to the processing target is greater than 0 and less than 5V. Claim 12 In claim 11, the electronic switch is a device that cycles through a sequence of (1) a first mode, (2) a third mode, (3) a second mode, and (4) a third mode, in which the output of the AC voltage generator is not routed to the first power output or the second power output. Claim 13 In claim 11, the controller is a device that synchronizes the operation of the AC voltage generator and the electronic switch such that when the electronic switch switches to the first mode or the second mode, the amplitude of the instantaneous output of the AC voltage generator is less than 1V. Claim 14 In claim 11, the device is a device in which, within 5ms after the electronic switch switches to 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. Claim 15 In claim 11, the device is a device in which, within 1 ms after the electronic switch switches to 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. Claim 16 In claim 11, the AC voltage generator is a device in which the electronic switch continues to operate at a maximum steady-state AC voltage even during the switching of the first mode or the second mode. Claim 17 In claim 11, the controller is a device that synchronizes the operation of the AC voltage generator and the electronic switch by controlling the time of switching of the electronic switch such that the switching is equal to the time window in which the amplitude of the instantaneous output of the AC voltage generator is less than the threshold value. Claim 18 In claim 11, the controller is a device that synchronizes the operation of the AC voltage generator and the electronic switch by controlling the AC voltage generator so that the output of the AC voltage generator is turned off whenever the switching of the electronic switch occurs. Claim 19 In claim 11, the controller is a device that synchronizes the AC voltage generator and the electronic switch by (a) controlling the switching timing of the electronic switch so that the switching coincides with a time window in which the amplitude of the instantaneous output of the AC voltage generator is less than a threshold value, and (b) controlling the AC voltage generator so that the output of the AC voltage generator is turned off whenever the switching of the electronic switch occurs. Claim 20 In claim 11, the electronic switch is configured to cycle through a repeating sequence of (1) the first mode and (2) the second mode, and the electronic switch is a device that switches directly from the first mode to the second mode and switches directly from the second mode to the first mode. Claim 21 delete Claim 22 delete Claim 23 delete Claim 24 delete Claim 25 delete Claim 26 delete Claim 27 delete Claim 28 delete Claim 29 delete Claim 30 delete Claim 31 delete Claim 32 delete Claim 33 delete Claim 34 delete Claim 35 delete Claim 36 delete Claim 37 delete Claim 38 delete Claim 39 delete Claim 40 delete

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