Sine wave generation using pulsed class D amplifiers.

Abstract

To provide a sine wave generator.SOLUTION: A sine wave generator includes a resonator circuit, a control circuit and a pulse generator. The resonator circuit is configured to receive energy pulses and to generate a resonator sinusoidal signal responsively to the energy pulses. The control circuit is configured to estimate a signal measurement of the resonator sinusoidal signal, or of a signal derived from the resonator sinusoidal signal. The pulse generator is configured to generate the energy pulses responsively to the signal measurement estimated by the control circuit, and to drive the resonator circuit with the energy pulses.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates generally to electronic circuits, and more particularly to a power-efficient sinusoidal oscillator. [Background technology]

[0002] Sine wave generators, sometimes called sine wave inverters or sine wave oscillators, convert direct current (DC) from a power source into an alternating current (AC) sine wave signal. Sine wave generators are common in industry and are used in many applications. In the field of intracardiac medical procedures, for example, sine wave generators may be used in procedures such as cardiac ablation or in measuring the impedance of electrodes inserted into the heart during cardiac catheterization procedures.

[0003] Techniques for generating sine waves are summarized, for example, in Texas Instruments' application note entitled "AN-263 Sine Wave Generation Techniques SNOA665C," published October 1999 and revised April 2013.

[0004] U.S. Patent No. 4,415,962 describes one technique for generating sine waves that involves two current sources providing substantially constant current. The current sources are employed to create complementary sine waves that can be more easily combined to produce an AC output waveform.

[0005] In their November 2015 publication, "Design and Analysis of a Low Cost Wave Generator Based on Direct Digital Synthesis," Hindawi Journal of Electrical and Computer Engineering, Volume 2015, Article ID 367302, Qi et al. describe a compact, highly accurate, and economical signal generator based on direct digital synthesis (DDS) technology that can provide wave signals commonly used in experiments. Summary of the Invention [Means for solving the problem]

[0006] One embodiment of the present invention described herein provides a sine wave generator including a resonator circuit, a control circuit, and a pulse generator. The resonator circuit is configured to receive energy pulses and to generate a resonator sine wave signal in response to the energy pulses. The control circuit is configured to estimate a signal measurement of the resonator sine wave signal or of a signal derived from the resonator sine wave signal. The pulse generator is configured to generate energy pulses in response to the signal measurement estimated by the control circuit and to drive the resonator circuit with the energy pulses.

[0007] In one embodiment, the control circuit is configured to trigger the pulse generator to generate an energy pulse in synchronization with the phase of the resonator sinusoidal signal or a signal derived from the resonator sinusoidal signal. In another embodiment, the control circuit is configured to estimate the signal measurement by estimating a measurement indicative of the voltage or current of the resonator sinusoidal signal or a signal derived from the resonator sinusoidal signal. In yet another embodiment, the control circuit is configured to estimate the signal measurement by estimating a measurement indicative of the phase of the resonator sinusoidal signal or a signal derived from the resonator sinusoidal signal.

[0008] In disclosed embodiments, the resonator circuit is configured to output a resonator sine wave signal as an output of the sine wave generator. In one embodiment, the sine wave generator further includes a transformer configured to generate the sine wave generator output in response to the resonator sine wave signal. The sine wave generator may further include a series capacitor configured to prevent a DC output.

[0009] In an exemplary embodiment, the sine wave generator further includes a current protection circuit configured to limit the current or voltage of the output of the sine wave generator to a predefined current limit. In another embodiment, the control circuit is configured to set the pulse width of the energy pulses generated by the pulse generator. In yet another embodiment, the control circuit is configured to set the pulse amplitude of the energy pulses generated by the pulse generator.

[0010] According to one embodiment of the present invention, there is also provided a method for generating a sine wave using a resonator circuit, comprising receiving energy pulses and generating a resonator sine wave signal in response to the energy pulses, estimating a signal measurement of the resonator sine wave signal or a signal derived from the resonator sine wave signal, generating an energy pulse in response to the estimated signal measurement by a control circuit, and driving the resonator circuit with the energy pulses. [Brief explanation of the drawings]

[0011] The present invention will be more fully understood from the following detailed description taken in conjunction with the drawings, in which: [Figure 1] 1 is a schematic, pictorial illustration of an electro-anatomical system for performing an intracardiac medical procedure, in accordance with one embodiment of the present invention; [Figure 2] FIG. 1 is a circuit diagram that schematically illustrates a sine wave generator, in accordance with an embodiment of the present invention. [Figure 3] 4 is a graph that schematically illustrates pulse generator and resonator voltages versus a horizontal time axis, according to an exemplary embodiment of the present invention; [Figure 4]1 is a flowchart that schematically illustrates a method for generating a sine wave, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Overview Sine wave generators (sometimes called sine wave oscillators or sine wave inverters) are used in many applications, including medical, instrumentation, communications, radar, sonar, and many others.

[0013] Conventional circuits for generating sine waves include, for example, Wien bridge oscillators, phase shift oscillators, Colpitts crystal oscillators, and sine wave approximations (digital or otherwise) using filtering. These and other techniques are described in the above-referenced "AN-263 Sine Wave Generation Techniques."

[0014] Some of the approximation techniques involve generating a square wave and then filtering the square wave to get a good sine wave approximation. In these cases, the square wave can be generated by a highly efficient class D amplifier, but the square wave will have odd harmonics (π 2 / 8-1, or about 23%), and filtering out the harmonics significantly reduces the efficiency of the oscillator.

[0015]

[0006] Exemplary embodiments of the invention disclosed herein provide improved methods and apparatus for generating high-efficiency sine waves. In some exemplary embodiments, a sine wave generator includes a class D amplifier that efficiently generates square pulses and a resonator coupled to the class D amplifier that oscillates at a desired frequency. A load for the sine wave generator may be directly connected to the resonator or may be coupled to the resonator, for example, via a transformer or capacitor.

[0016] In some exemplary embodiments, the resonator has a characteristic resonator frequency (e.g., 1 / (2 * π * sqrt(L *C). The sinusoidal signal produced by the resonator is referred to herein as the "resonator sinusoidal signal." In some exemplary embodiments, the resonator sinusoidal signal has an envelope amplitude that decays over time, and when the amplitude of the resonator sinusoidal signal falls below a predetermined threshold, the Class D amplifier stimulates the resonator with a square pulse. In some exemplary embodiments, the timing of the Class D pulse is synchronized to the phase of the resonator sinusoidal signal.

[0017] In some other exemplary embodiments, the sine wave generator is configured to adjust the voltage and / or current that the sine wave generator delivers to the load by varying the pulse width generated by the class D amplifier. In the exemplary embodiments described herein below, the sine wave generator comprises control circuitry configured to perform the control and regulation functions described above.

[0018] In some other exemplary embodiments, the sine wave generator is configured to adjust the voltage and / or current that the sine wave generator delivers to the load by varying the pulse amplitude generated by the class D amplifier.

[0019] In some other exemplary embodiments, the sine wave generator is configured to adjust the voltage and / or current that the sine wave generator delivers to the load by varying the pulse width and pulse amplitude generated by the class D amplifier.

[0020] Further details are provided with reference to exemplary embodiments herein.

[0021] System Description 1 is a schematic, pictorial illustration of an electro-anatomical system 21 for performing an intracardiac medical procedure, in accordance with one embodiment of the present invention. In some embodiments, the system 21 is used to perform a cardiac ablation procedure on a patient.

[0022] 1 depicts a physician 22 using an electroanatomic catheter 23 to perform a cardiac ablation procedure on a heart 24 of a patient 25. The catheter 23 comprises one or more diagnostic electrodes 26 and at least one ablation electrode 28 at its distal end. It will be appreciated that, for simplicity, FIG. 1 only shows a catheter with three electrodes, and that other electrodes of the same or different types may be used in alternative embodiments. The electrodes are coupled to a monitoring and control unit 34 via a connector 32.

[0023] During the ablation procedure, the physician can use tracking and guidance techniques beyond the scope of this disclosure to position the ablation electrode 28 at or near the area of ​​the heart where the physician wishes to ablate. Once the ablation electrode is in place and all other preparatory procedures are completed, the physician can begin the ablation by applying a high-energy ablation signal through the ablation electrode to the ablation region within the heart. According to the exemplary embodiment depicted in FIG. 1, the ablation signal is a sine wave.

[0024] The monitoring and control unit 34 includes a high-efficiency sine wave generator 38 configured to generate a sine wave by periodically exciting a resonator with energy pulses generated by a class D amplifier. According to an exemplary embodiment, the voltage and current generated by the sine wave oscillator are automatically adjusted, making the generator highly power efficient.

[0025] 1 primarily illustrates portions relevant to embodiments of the present invention, and in particular, FIG. 1 focuses on the sine wave generator 38 of the monitor and control unit 34. Other system elements, such as the processor, signal acquisition system, external ECG recording electrodes and their connections, filtering, digitization, protection circuitry, and so forth, are omitted. However, for clarity and completeness, the monitor 52 is illustrated with an image 50 of the heart 24 of the patient 25.

[0026] 2 is a circuit diagram that schematically illustrates a sine wave generator 38 (FIG. 1) in accordance with an exemplary embodiment of the present invention. The sine wave generator 38 is configured to apply an output sine wave to a load, such as the ablation electrode 28 (FIG. 1). The sine wave generator typically includes a pulse generator 200 configured to generate energy pulses in the form of square wave voltage pulses, a class D amplifier 202 configured to amplify the energy pulses, a switch / coupler 204, a resonator 206, a transformer 208 configured to convert the resonator sine wave signal to an output sine wave signal while transforming an AC voltage to a desired output voltage, and a control circuit 214 configured to control the operation of the pulse generator 200.

[0027] In some exemplary embodiments, pulse generator 200 receives a trigger instruction from control circuitry 214 and generates a pulse in response. In some exemplary embodiments, the pulse height may be up to 1 KV, and in one embodiment, the pulse may be produced by a field-effect transistor (FET). The width of the pulse is determined in response to a pulse width input that the pulse generator receives from the control circuitry; in exemplary embodiments, the pulse width may vary between 0.1 and 1 microsecond, although any other suitable value may be used.

[0028] The class D amplifier 202 is coupled to the DC power source and configured to amplify the square wave output of the pulse generator 200. The output of the class D amplifier 202 comprises energy pulses that are the sine wave power source that the sine wave generator 38 delivers to the load.

[0029] The switch / coupler 204 is configured to couple the pulses output by the class D amplifier to the resonator 206. In some exemplary embodiments, the switch / coupler 204 comprises a switch operable to couple the class D amplifier to the resonator only when a pulse is present (so as not to short the resonator to zero when a pulse is not present), while in other embodiments the switch / coupler comprises a diode. In one embodiment, the switch / coupler further comprises a capacitor, and the coupling is capacitive.

[0030] The resonator 206 comprises a capacitor 210 and an inductor 212. Once excited, the resonator operates at a frequency f=1 / (2 * π * sqrt(L * C)) and its impedance is maximum (theoretically infinite). The signal between the resonator output terminals is called the resonator sinusoidal signal.

[0031] In some exemplary embodiments, the control circuit 214 is configured to monitor the peak-to-peak (PTP) voltage and / or current that the sine wave generator applies to the load (hereinafter referred to as the “signal measurement” of the sine wave signal). When the voltage and / or current falls below a predetermined threshold, the control circuit sends a trigger pulse to the pulse generator 200 to initiate the generation of another pulse, thereby exciting the resonator 206 with additional energy.

[0032] According to an exemplary embodiment, the pulse coupled to the resonator must be synchronized to the phase of the voltage within the resonator. To that end, the control circuit 214 further monitors the phase measurement of the resonator and times the trigger output so that new pulses are synchronized with the oscillations within the resonator.

[0033] In some exemplary embodiments, the control circuit 214 is further configured to control the width of the pulses generated by the pulse generator 200. Wider pulses typically deliver more energy at the cost of sinusoidal distortion.

[0034] Finally, the sine wave generator 38 may optionally include protection circuitry 216 configured to limit the current through the load to a predetermined current limit and / or to limit the voltage of the output signal applied to the load to a predefined voltage limit.

[0035] In summary, according to the exemplary embodiment shown in Figure 2, a resonator is excited by a square pulse, generating a sine wave that drives a load through a transformer. When the oscillation decays below a threshold, a control circuit triggers a new pulse with the appropriate phase. The square pulse is amplified by a highly efficient Class D amplifier, resulting in a high overall efficiency sine wave generator.

[0036] In an exemplary embodiment, the frequency of the sine wave is 0.5 MHz, and the voltage of the pulses sent by the class D amplifier to the resonator is up to 200 V (corresponding to a maximum ablation power of 90 W, assuming a 250 ohm load). These numbers have been chosen purely for illustrative purposes. In alternative exemplary embodiments, any other suitable numbers may be used.

[0037] It should be understood that the exemplary circuit diagram shown in FIG. 2 is presented purely for purposes of conceptual clarity. In alternative exemplary embodiments of the present invention, for example, negative signals rather than positive signals may be used in some or all of the circuit elements. In other exemplary embodiments, some or all of elements 200, 202, 204, 206, and 208 may have unipolar rather than bipolar inputs and / or outputs (see common ground). In some exemplary embodiments, there is no transformer and the resonator output is directly coupled to the load; in one embodiment, the resonator is coupled to the load via a capacitor; and in another exemplary embodiment, the transformer is coupled to the load via a capacitor to prevent DC current.

[0038] In some exemplary embodiments, resonator 202 may be replaced with a more complex resonator having multiple stages, as is known in the art.

[0039] In some exemplary embodiments, switch / coupler 204 is omitted, and instead the class D amplifier is configured as an "open drain" (e.g., the class D amplifier only drives the output when the input pulse is high).

[0040] In some exemplary embodiments, Root-Mean-Square (RMS) rather than PTP sensing of voltage and / or current is used, while in other embodiments the PTP measurements are low-pass filtered. In yet other exemplary embodiments, no voltage or current sensing is performed, and the timing of the pulses generated by pulse generator 200 is fixed (e.g., with a fixed load applied).

[0041] Some of the circuit elements described with reference to FIG. 2 may be integrated with each other and / or subdivided in different ways, for example, a pulse generator may be integrated with a class D amplifier and / or a control circuit.

[0042] 3 is a graph 300 that schematically illustrates the voltages of the pulse generator 200 and resonator 206 (FIG. 2) versus a horizontal time axis, in accordance with an exemplary embodiment of the present invention. The pulse generator applies pulses 302 that are in phase with a sine wave 304 in the resonator circuit. All pulses 302 occur when the sine wave is at a local maximum, except for the first pulse 302, which begins when the resonator is not oscillating.

[0043] As indicated by the dashed arrow, the control circuit generates a new pulse 302 when the oscillation peak voltage falls below a marked threshold, and the new pulse restores the oscillation amplitude.

[0044] It will be appreciated that the attenuation rates and relative threshold positions are shown by way of example only, and that other rates and relative thresholds may be used in embodiments.

[0045] 4 is a flowchart 400 that generally illustrates a method for generating a sine wave, in accordance with an embodiment of the present invention, performed by the relevant components of the sine wave generator illustrated in FIG. 2, including pulse generator 200, class D amplifier 202, switch / coupler 204, resonator 206, and control circuit 214.

[0046] The flowchart begins with a high energy pulse transmission step 402, where a pulse generator generates a pulse, a class D amplifier amplifies the pulse, and a switch coupler transmits the amplified pulse to a resonator which begins to oscillate and transmits a sine wave to a load.

[0047] Next, in a PTP measurement step 404, the control circuit measures the voltage and / or current of the sine wave being sent to the load. In a voltage / current comparison step 406, the control circuit compares the measured voltage or current with a predetermined threshold. The control circuit remains in the loop including steps 404 and 406 as long as the voltage or current is not below the predetermined threshold. When the voltage / current is below the threshold, the control circuit enters a synchronize to phase step 408, waits for a suitable phase of the sine wave (e.g., 90°), and then re-enters step 402 to generate another pulse and inject more energy into the resonator.

[0048] It should be understood that the exemplary flowchart shown in FIG. 4 is presented merely for purposes of conceptual clarity. In alternative embodiments, other suitable flowcharts may be used. For example, flowchart 400 may include steps for evaluating distortion in the output sinusoidal signal and for the control unit to modify the pulse width applied to the pulse generator accordingly. In an embodiment, some or all steps of flowchart 400 may be performed simultaneously.

[0049] In various exemplary embodiments, the different elements of sine wave generator 38 may be implemented using suitable hardware, such as one or more Application-Specific Integrated Circuits (ASICs), one or more Field-Programmable Gate Arrays (FPGAs), discrete components, or a combination thereof.

[0050] Although the exemplary embodiments described herein primarily address intracardiac applications such as cardiac ablation, the disclosed techniques may also be used to generate sine waves for measuring the impedance of intracardiac catheter electrodes and / or for measuring contact or proximity to tissue. Additionally, the methods and systems described herein may be used in other applications, including other suitable fields where sine wave signals are used.

[0051] It will therefore be understood that the above-described embodiments are cited by way of example, and that the present invention is not limited to what is particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described in the foregoing specification, as well as variations and modifications thereof that would occur to one skilled in the art upon reading the foregoing description, and that are not disclosed in the prior art.

[0052] [Embodiment] (1) A sine wave generator comprising: a resonator circuit configured to receive an energy pulse and to generate a resonator sinusoidal signal in response to the energy pulse; a control circuit configured to estimate a signal measurement of the resonator sinusoidal signal or of a signal derived from the resonator sinusoidal signal; a pulse generator configured to generate the energy pulses in response to the signal measurements estimated by the control circuit and to drive the resonator circuit with the energy pulses. (2) The sine wave generator of embodiment 1, wherein the control circuit is configured to trigger the pulse generator to generate the energy pulse in synchronization with the phase of the resonator sine wave signal or the signal derived from the resonator sine wave signal. (3) The sine wave generator of embodiment 1, wherein the control circuit is configured to estimate the signal measurement by estimating a measurement indicative of a voltage or current of the resonator sine wave signal or of the signal derived from the resonator sine wave signal. (4) A sine wave generator as described in embodiment 1, wherein the control circuit is configured to estimate the signal measurement by estimating a measurement indicative of the phase of the resonator sine wave signal or of the signal derived from the resonator sine wave signal. (5) A sine wave generator as described in embodiment 1, wherein the resonator circuit is configured to output the resonator sine wave signal as an output of the sine wave generator.

[0053] (6) The sine wave generator of claim 1, further comprising a transformer configured to generate an output of the sine wave generator in response to the resonator sine wave signal. (7) A sine wave generator as described in embodiment 6, further comprising a series capacitor configured to prevent DC output. (8) The sine wave generator of claim 1, further comprising a current protection circuit configured to limit the current or voltage of the output of the sine wave generator to a predefined current limit. (9) A sine wave generator as described in embodiment 1, wherein the control circuit is configured to set a pulse width of the energy pulse generated by the pulse generator. (10) A sine wave generator as described in embodiment 1, wherein the control circuit is configured to set a pulse amplitude of the energy pulse generated by the pulse generator.

[0054] (11) A method for generating a sine wave, comprising: receiving an energy pulse using a resonator circuit and generating a resonator sinusoidal signal in response to the energy pulse; estimating a signal measurement of the resonator sinusoidal signal or of a signal derived from the resonator sinusoidal signal; generating the energy pulse in response to the signal measurement estimated by the control circuit and driving the resonator circuit with the energy pulse. (12) The method of embodiment 11, further comprising triggering the pulse generator to generate the energy pulse synchronously with the phase of the resonator sinusoidal signal or the signal derived from the resonator sinusoidal signal. (13) The method of embodiment 11, wherein estimating the signal measurement value includes estimating a measurement value indicative of a voltage or current of the resonator sinusoidal signal or of the signal derived from the resonator sinusoidal signal. (14) The method of embodiment 11, wherein estimating the signal measurement value includes estimating a measurement value indicative of the phase of the resonator sinusoidal signal or of the signal derived from the resonator sinusoidal signal. (15) The method of claim 11, further comprising outputting the resonator sine wave signal as an output of the sine wave generator.

[0055] (16) The method of claim 11, further comprising generating the output of the sine wave generator with a transformer in response to the resonator sine wave signal. (17) The method of embodiment 16, further comprising preventing DC output with a series capacitor. (18) The method of claim 11, further comprising limiting the current or voltage of the output of the sine wave generator to a predefined current limit. 19. The method of claim 11, wherein generating the energy pulse includes setting a pulse width of the energy pulse. (20) The method of embodiment 11, wherein generating the energy pulse includes setting a pulse amplitude of the energy pulse.

Claims

1. 1. A sine wave generator comprising: a resonator circuit configured to receive an energy pulse and to generate a resonator sinusoidal signal in response to the energy pulse; a control circuit configured to measure the voltage and / or current of the resonator sinusoidal signal transmitted to a load connected to the resonator circuit and to trigger a pulse generation when the voltage and / or current falls below a predetermined threshold; a pulse generator including a class D amplifier configured to generate and supply energy pulses in the form of square wave voltage pulses to the resonator circuit when triggered by the control circuit; The sine wave generator, wherein the control circuit is configured to measure a phase of the resonator sine wave signal, and the pulse generator is configured to generate the energy pulses in synchronization with the phase of the resonator sine wave signal.

2. 2. The sine wave generator of claim 1, wherein the resonator circuit is configured to output the resonator sine wave signal as an output of the sine wave generator.

3. 10. The sine wave generator of claim 1, further comprising a transformer configured to generate an output of the sine wave generator in response to the resonator sine wave signal.

4. 4. The sine wave generator of claim 3, further comprising a series capacitor configured to prevent a DC output.

5. 10. The sine wave generator of claim 1, further comprising a current protection circuit configured to limit the current or voltage of the sine wave generator output to a predefined current limit.

6. 2. The sine wave generator of claim 1, wherein the control circuit is configured to set a pulse width of the energy pulses generated by the pulse generator.

7. 2. The sine wave generator of claim 1, wherein the control circuit is configured to set a pulse amplitude of the energy pulses generated by the pulse generator.

8. 1. A method of operating a sine wave generator for generating a sine wave, comprising: a resonator circuit of the sine wave generator receiving an energy pulse and generating a resonator sine wave signal in response to the energy pulse; a control circuit of the sine wave generator measuring a voltage and / or a current of the resonator sine wave signal sent to a load connected to the resonator circuit and triggering a pulse generation when the voltage and / or current falls below a predetermined threshold; a pulse generator of the sine wave generator including a class D amplifier, which when triggered by the control circuit generates and supplies an energy pulse in the form of a square wave voltage pulse to the resonator circuit; 10. A method of operating a sine wave generator, wherein measuring the resonator sine wave signal includes the control circuit measuring a phase of the resonator sine wave signal, and generating the energy pulse includes the pulse generator generating the energy pulse in synchronization with the phase of the resonator sine wave signal.

9. 9. The method of claim 8, further comprising: outputting the resonator sine wave signal from the resonator circuit as an output of the sine wave generator.

10. 9. The method of claim 8, further comprising: a transformer of said resonator circuit generating an output of said sine wave generator in response to said resonator sine wave signal.

11. 11. The method of claim 10, further comprising a series capacitor in the resonator circuit to prevent a DC output.

12. 9. The method of claim 8, further comprising a current protection circuit of the resonator circuit limiting the current or voltage of the output of the sine wave generator to a predefined current limit.

13. 9. The method of claim 8, wherein generating the energy pulses includes the control circuit setting a pulse width of the energy pulses.

14. 9. The method of claim 8, wherein generating the energy pulses includes the control circuit setting a pulse amplitude of the energy pulses.

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