Interphase delay control for ablation

Abstract

In a described example, a circuit can include an H-bridge circuit, a plurality of push-pull driver stages, and a controller. The plurality of push-pull driver stages can include a first push-pull driver stage and a second push-pull driver stage. Each of the plurality of push-pull driver stages include a pull-up stage and a pull-down stage coupled to a control terminal of a switch of the H-bridge circuit. The pull-up stage is configured to pull a voltage at the control terminal of the switch of the H-bridge circuit to a logic high. The pull-down stage is configured to pull the voltage at the control terminal of the switch of the H-bridge circuit to a logic low. The controller is configured to drive the pull-down stages for each of the plurality of push-pull driver stages based on one or more characteristics of the H-bridge circuit.

Description

INTERPHASE DELAY CONTROL FOR ABLATION

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 675,816, filed July 26, 2024, the entire content of which is incorporated herein by reference.FIELD

[0002] This description relates to systems and methods for controlling interphase delays in ablation signals.BACKGROUND

[0003] Ablation applies energy to terminate or modify electrical pathways in tissue. For example, pulsed field ablation (PF A) delivers a sequence of short-duration high-voltage pulses to perform irreversible electroporation (IRE) of tissue, such as cardiac tissue. Cardiac PFA uses significant energy to form lesions in cardiac tissue to treat atrial fibrillation, among other arrhythmias. In some circumstances, a particular cardiac anatomy of interest is the ventricles, which can present design challenges not only for the catheter, but also for the generator, as higher voltages (e.g., 4kV or 8kV peak-to-peak) are typically required to create electric fields spanning longer tissue distances, which in turn, can create greater volume lesions.SUMMARY

[0004] In a described example, a circuit includes a driver stage and an H-bridge circuit. The driver stage includes a first push-pull driver stage and a second push-pull driver stage. Each of the first and second push-pull driver stages has an output node and includes a pull-up switch, a pull-up resistor, a pull-down switch, and a pull-down resistor. The pull-up switch includes a first control terminal, a first current terminal, and a second current terminal. The first current terminal is coupled to a first power supply voltage. The pull-up resistor is in series with the pull-up switch between the first power supply voltage and an output node. The pull-down switch includes a second control terminal, a third current terminal, and a fourth current terminal. The fourth current terminal of the pulldown switch is coupled to a second power supply voltage that is less than the first power supply voltage. The pull-down resistor is in series with the pull-down switch between theoutput node and the second power supply voltage. The H-bridge circuit includes an arrangement of switches, each having a respective control terminal. The output node of the first and second push-pull driver stages is coupled to the respective control terminal of a given switch of the plurality of switches of the H-bridge circuit. The H-bridge circuit includes a pair of outputs coupled to respective ablation output terminals.

[0005] In a described example, a pulse generator circuit includes an H-bridge circuit, a plurality of push-pull driver stages, and a controller. The H-bridge circuit has first and second outputs and includes a plurality of switches. Each of the plurality of switches of the H-bridge circuit has a respective control terminal. Each driver stage of the plurality of push-pull driver stages includes a pull-up stage and a pull-down stage coupled between first and second voltages and has an output node coupled to the respective control terminal of a given switch of the plurality of switches of the H-bridge circuit, in which the pull-up stage is configured to provide approximately the first voltage at the output node, through a respective on-resistance, to turn on the given switch of the H-bridge circuit based on a respective pull-up drive logic signal, the pull-down stage is configured to provide approximately the second voltage at the output node, through a respective off- resistance, to turn off the given switch of the H-bridge circuit based on a respective pulldown drive logic signal, and the first voltage is greater than the second voltage. The controller is configured to provide a respective pull-down drive logic signal to control each of the pull-down stages for each of the plurality of push-pull driver stages, which controls the turn-off of the given switch, based on one or more characteristics of the H- bridge circuit.

[0006] In a described example, a system includes a signal generator circuit, a controller, and a catheter interface. The signal generator circuit includes an output stage and a plurality of multi-stage driver circuits. The output stage has first and second outputs and includes an arrangement of switches, each having a control input. For the plurality of multi-stage driver circuits, each is coupled between first and second voltages and having an output node coupled to the control input of a respective switch of the output stage. The first voltage is greater than the second voltage. Each of the multi-stage driver circuits includes multiple pull-down stages coupled between the output node and the second voltage. Each of the pull-down stages is configured to provide approximately the second voltage, through a respective off-resistor, at the output node based on a respective pull-down drive logic signal. The respective off-resistors of at least some of the pull-down stages have different resistances. The controller is configured to provide respective pulldown drive logic signals to control one or more of the pull-down stages for each of the multi-stage driver circuits to control turning off the respective switch of the output stage. The catheter interface has one or more interface inputs, in which the interface inputs are coupled to respective outputs of the output stage.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. l is a block diagram of an example medical device system.

[0008] FIG. 2 is a circuit diagram of an example H-bridge circuit implemented with insulated-gate bipolar transistors (IGBTs).

[0009] FIG. 3 is a timing diagram of an example bipolar pulse.

[0010] FIG. 4 is a schematic diagram of an example interphase delay control circuit.

[0011] FIG. 5 is an example timing diagram for switches of the interphase delay control circuit of FIG. 4.

[0012] FIG. 6 is a schematic representation of an example ablation system with interphase delay control.DETAILED DESCRIPTION

[0013] This description relates to systems and methods for reducing interphase delays in ablation signals, such as for minimizing interphase delays in high-voltage (e.g., greater than IkV) pulsed field ablation (PF A) generators.

[0014] For example, an ablation electrode, which is coupled to a signal generator during an ablation procedure, is positioned in contact with the target tissue of a patient such that electrical ablation energy is delivered from the ablation electrode to the target tissue to form one or more lesions. The ablation energy can be PF A, radio frequency ablation or other ablation energy types. An ablation catheter can include any number of one or more (e.g., a plurality) of ablation electrodes, each of which can be controlled by the signal generator. As described herein, the signal generator can include a driver circuit having output nodes coupled to drive respective transistors in an output stage (e.g., an H- bridge circuit). The driver circuit can include a separate multi-stage driver circuit for eachtransistor in the output stage. Additionally, a respective output stage can be provided for providing ablation energy to each of the one or more ablation electrodes, and a respective multi-stage driver stage circuit is configured to drive each transistor in each output stage. Each multi-stage driver circuit includes two or more push-pull driver stages, each having a pull-up switch and a pull-down switch, in which the pull-up switch is coupled in series with a resistor between the output node and a first voltage supply (e.g., a positive voltage) and the pull-down switch is coupled in series with another resistor between the output node and a second voltage supply (e.g., a negative voltage). The resistors for a given push-pull stage can be the same or different. The resistors in the push-pull driver stages of a given multi-stage driver can be different. For example, the resistors in the push-pull driver stages of a given multi-stage driver are configured with stepwise (e.g., increasing or decreasing) resistances. Other relative resistance values can be used in other examples. Each separate multi-stage driver circuit is configured to turn on and turn off a respective transistor in the output stage based on which push-pull driver stage (or stages) is activated and whether the pull-up or pull-down switch is activated based on respective control signals provided by a controller.

[0015] As a further example, the controller is configured to control which pull-up or pull-down switch is activated, the on-time of each switch to control turning on and off the transistors in the output stage. The controller thus can reduce switching time, conduction run-on, and pulse overshoot of the transistors in the output stage. For example, the transistors in the output stage are insulated-gate bipolar transistors (IGBTs), and the controller can activate one or more portions (e.g., pull-down switches) of the push-pull driver stages to reduce the turn-off time for each IGBT. By reducing the turn-off time for the IGBTs, the interphase delay between consecutive output pulse cycles can be reduced, thereby enabling high voltage (e.g., at least IkV, such as 2kV, 4kV, or higher) pulsed output signals to be delivered. The pulsed output signals can be mono-phasic, bi-phasic, or tri-phasic signals. Monophasic output signals contain pulses of only one polarity, either positive or negative. Bi-phasic output signals contain positive and negative pulses and at the same number each polarity. Tri-phasic output signals also contain positive and negative pulses, however, a greater number of either positive or negative pulses will be present. In an example, the output stage is configured to provide pulsed output signals of 4kV (e.g., 8kV peak-to-peak), such as for PF A. As a result, an ablation systemimplementing such a signal generator can form large volume lesions, creating an opportunity for applications to ablate previously inaccessible anatomy, including treatments for ventricular tachycardia, and super ventricular tachycardia to name a few.

[0016] For the sake of clarity of explanation, the devices, systems, and methods of the present disclosure are described in the context of ablation procedures. However, unless otherwise specified or made clear from the context, the devices, systems, and methods of the present disclosure should be understood to be generally additionally, or alternatively, applicable to medical procedures in which an ablation electrode is positioned within a patient and a plurality of return electrodes are positioned on the skin of the patient. By way of example, and not limitation, such medical procedures can include ablating tumors in cancer treatment and electro-surgery procedures in which tissue is cut and substantially simultaneously cauterized to avoid or minimize bleeding.

[0017] As used herein, the term "electrode" shall be understood to include an electrically conductive material used to make contact with a nonmetallic part (e.g., skin, tissue, blood, irrigation fluid, and combinations thereof) of an electrical circuit formed as energy is delivered to a treatment site as part of a medical procedure. Thus, more specifically, the term "ablation electrode" shall be understood to include an electrically conductive portion of a catheter for delivery of electrical energy to a treatment site through direct and / or indirect contact between the ablation electrode and the treatment site.Further, or instead, the term "return electrode" shall be understood to include an electrode forming a return path for at least a portion of electrical energy delivered by the ablation electrode to the treatment site.

[0018] FIG. 1 is a block diagram of an example medical device system 10, such as an ablation system. The system 10 includes a signal generator 12 configured to generate electrical energy (e.g., current and / or voltage) that is provided to one or more electrodes 14, which can be carried by a catheter 16 or other instrument, such as to form one or more lesions in target tissue. The signal generator 12 includes a driver circuit 18 and an output stage 20. The driver circuit 18 includes a plurality of N multi-stage driver circuits, shown as driver circuits 22 and 24 (where N is a positive integer representing the number of multi-stage driver circuits). There can be any number of two or more of the multi-stage driver circuits 22 and 24, as indicated by the ellipsis, in which each of the multi-stage driver circuits is associated with a respective switch (e.g., power transistor) 26 and 28 ofthe output stage 20. For example, each of the multi-stage driver circuits 22 and 24 can be coupled between first and second voltages (e.g., VDD and VSS voltages provided by internal circuitry not shown) and include a respective output node 30 and 32 coupled to a control input of a respective switch 26 and 28 of the output stage 20.

[0019] Each of the multi-stage driver circuits 22 and 24 includes a respective plurality of driver stages 34, 36, 38, and 40. In the example of FIG. 1, the multi-stage driver circuit 22 includes P driver stages 34 and 36 (where P is a positive integer representing the number of driver stages in the driver circuit 22) and the Nth multi-stage driver circuit 24 includes Q driver stages 34 and 36 (where Q is a positive integer representing the number of driver stages in the driver circuit 24). P and Q can be the same. Alternatively, P and Q can be different.

[0020] In an example, each of the drive stages 34 and 36 can include a pull-down stage, a pull-up stage, or a push-pull (e.g., half-bridge) stage having a respective output coupled the output node 30. The system 10 further includes a controller 42 (e.g., a microcontroller or field programmable gate array (FPGA)) configured to provide control signals (also referred to as a drive logic signals) at one or more control outputs 44, which are coupled to one or more respective control inputs of the multi-stage driver circuit 22 for controlling each of the driver stages 34 and 36. There can be one or more control outputs (e.g., P or 2P control outputs), which are coupled to control inputs for controlling each of the respective driver stages 34, 36. The controller 42 also has one or more control outputs 46 that are coupled to one or more respective control inputs of the multi-stage driver circuit 24. The controller 42 is also configured to provide control signals (e.g., drive logic signals) at the control output(s) 46 for controlling each of the driver stages 38, 40. In some examples, an isolator circuit can be coupled between the controller 42 and the signal generator 12 to galvanically isolate the controller from the signal generator.

[0021] As described herein, at least some (up to each) of the driver stages 34 and 36 have different impedances (e.g., resistances), which can define the rise and / or fall times of the drive signals provided to the switch 26 of the output stage 20. Similarly, at least some (up to each) of the driver stages 38 and 40 have different impedances (e.g., resistances), which can define the rise and / or fall times of the drive signals provided to the switch 26 of the output stage 20. The controller 42 can selectively activate one or more driver stage to define an impedance of the driver stage, which can reduce switching time,reduce conduction run-on, reduce pulse overshoot, and / or otherwise shape the waveform of the drive signals provided at drive outputs 30 and 32 for controlling the switches 26 and 28 of the output stage 20. As a further example, the controller 42 can implement such controls to decrease the interphase delays between waveforms, which can be provided for stimulating muscles or nerves or ablating tissue through the one or more electrodes 14.

[0022] As an example, the controller 42 is configured to select which driver stage 34, 36 is activated for driving the switch 26 and which driver stage 38, 40 is activated for driving the switch 28 for providing a corresponding output pulse to a respective electrode 14. As described herein, the controller 42 can activate a driver stage 34 having a first resistance for activating the switch 26 to provide a first positive pulse and activate another driver stage 36 having a second (e.g., different) resistance activating the switch 26 for a next positive pulse in the sequence that is supplied. The controller can also activate different driver stages 38, 40 to provide different resistances when activating the switch 28, such as for supplying a negative pulse to the electrode 14. By activating different combinations of the gate drivers 34, 36, 38, 40 for sequential pulses in a pulse train, the gate resistance (e.g., Rg on or Rg off) can vary for different pulses that are generated. As a result, the pulses can be delivered to the electrodes with reduced delay between consecutive pulses.

[0023] The output stage 20 includes one or more (e.g., a pair of) outputs 48 and 50. The output stage 20 can include one or more bridge circuits (e.g., a half- or full-bridge circuit) 52, in which the one or more outputs 48 and 50 are coupled to the electrode(s) 14. 56 In an example, the system 10 can include instance of the bridge circuit 52, including respective switches 26 and 28, for supplying power to each of the electrodes 14. The system can also include a power supply 53 having respective outputs 54 and 56 coupled to respective voltage inputs of the output stage 20. The power supply 52 can be configured to supply a high voltage at one of the outputs 54. The other output can provide a ground or a low voltage. In some examples, such as for PFA applications, the power supply 52 is configured to provide a positive high-voltage signal (+HV) at the output 54 and negative high voltage signal (-HV) at the output 56, which can be a negative version having equal (or approximating) magnitude as the voltage provided at the other output 54. Thus, for PFA applications, the controller 42 can control the signal generator 12 to provide alternating positive and negative high-voltage pulses at the outputs 48 and 52 (see, e.g.,pulses 162 shown in FIG. 2) and having waveform parameters based on which driver stages are activated for each output pulse.

[0024] In some examples, the system 10 includes catheter interface circuitry (also referred to herein as a catheter interface) 58 coupled between the signal generator 12 and the one or more electrode(s) 14. The catheter interface 58 thus includes first and second inputs coupled to the respective outputs 48 and 50 and respective outputs 60 and 62 (e.g., an output pair) coupled to each of the one or more electrodes 14. The catheter interface 58 can include an arrangement of connectors, couplings, and / or other electrically conductive elements configured to carry the signals from the signal generator 12 to the one or more electrodes 14. The controller 42 can set one more control parameters for the signals provided to each of the electrodes, which can be implemented in an open loop or closed loop control system and / or in response to a user input, according to application requirements, such as described herein.

[0025] FIG. 2 depicts an example H-bridge circuit 100, which can be used to implement the output stage (e.g., the output stage 20 of FIG. 1). The H-bridge circuit 100 implemented with insulated-gate bipolar transistors (IGBTs). While the example of FIG.2 is shown with IGBT’s, in other examples, different power transistors can be used. An H-bridge is an electronic circuit that switches the polarity of a voltage applied to a load. For example, the H-bridge circuit 100 of FIG. 2 can be utilized as an output stage of a signal generator to generate bi-phasic pulses for a PFA system. It will be appreciated that although examples of PFA are described herein to perform irreversible electroporation (IRE) of tissue, reversible electroporation (RE) and other types of ablation are also possible in other examples. Also, while examples described herein may refer to treating (e.g., ablating) cardiac tissue, the circuits, systems, and methods described herein are applicable to treating other types of tissue.

[0026] The H-bridge circuit 100 can include four IGBTs 110, 120, 130, 140. Each IGBT 110, 120, 130, 140 can include a respective control terminal (e.g., gate) 112, 122, 132,142, an emitter, and a collector. The emitter of IGBT 110 and the collector of IGBT 120 are coupled to a first output 152 and the emitter of IGBT 140 and the collector of IGBT 130 are coupled to a second output 154. In the example of FIG. 2, the collectors of the first IGBT 110 and the fourth IGBT 140 are coupled to a high-voltage power supply (+HV), and the emitters of the second IGBT 120 and the third IGBT 130 are coupled to ahigh-voltage power supply of opposite polarity (-HV). As described herein, the H-bridge circuit 100 can be configured to provide pulsed output signals across the outputs 152 and 154 based on control signals provided at respective gates 112, 122, 132, 142 by driver circuitry.

[0027] As seen in FIG. 2, the gates 112, 132 of the first IGBT 110 and the third IGBT 130 are configured to receive gate control signals for generating positive signal pulses across the outputs 152 and 154. The gates 122, 142 of the second IGBT 120 and the fourth IGBT 140 are configured to receive gate control signals for generating negative signal pulses across the outputs 152 and 154. The outputs 152 and 154 can be coupled to a load, such as through an interface circuit (e.g., connectors). In an example, the H-bridge circuit can be controlled (e.g., by a controller to generate multiphasic (e.g., bi-phasic) waveforms 162, such as short-duration high-voltage bi-phasic pulses, for an ablation system (e.g., PF A system).

[0028] In this regard, FIG. 3 is a timing diagram 200 of an example bi-phasic pulse 201 having a positive pulse portion and a negative pulse portion separated by an interphase delay 202. The pulse 201 is an example pulse that can be generated by the output stage 20 of FIG. 1 or H-bridge circuit 100 of FIG. 2, such as for delivering to electrodes of an ablation catheter of a PFA system. Accordingly, the description of FIG. 3 also can refer to certain aspects of FIGS. 1 and 2. It is generally desirable to have a shorter interphase delay 202 in the multiphasic waveforms generated by the PFA system. For example, shortening the interphase delays can enable an increase in the pulse rate of the therapy delivery while also reducing unwanted muscle or nerve stimulation during application. For PFA generators operating at 1.5kV, for example, currents delivered from high-voltage PFA generators using multi-electrode catheters are generally on the order of 20A. In general, MOSFET and IGBT devices switching up to 4.5kV and 70A (315 kW) pulses source and sink significant gate charge during switching from ON / OFF to OFF / ON, which therefore requires more time than lower voltage systems, such as on the order of a microsecond.

[0029] In some circumstances, a short or “shoot-through” in the vertical paths can occur if IGBTs 110, 130 do not cease conduction before IGBTs 120, 140 begin conducting. The longer IGBTs 110, 130 continue to conduct, the longer IGBTs 120, 140must be held off and wait before they can be turned on. Therefore, run-on conduction can limit the bi-phasic cycle rate.

[0030] The circuits and systems described herein can be used to control the effective turn-off time 212 associated with each of the IGBTs 110, 120, 130, 140 of the H- bridge circuit 100 (or switches 26-28 of the output stage 20), and thereby reduce the interphase delay 202. For example, interphase delay control (e.g., implemented by the controller 42 and signal generator 12 of FIG. 1 and / or the drive control circuit 300 of FIG. 4) can be used in a PFA system to reduce the turn-off time for the respective switches 26- 28 and / or IGBTs 110, 120, 130, 140. In the absence of the approach described herein, high voltage pulses (e.g., greater than IkV, such as 4kV or higher) PFA generators can lead to undesirable turn-off times due to the corresponding increases in current. The circuits, systems, and methods described herein enable a reduction in interphase delays between consecutive pulses. Reducing interphase delays can be helpful to reduce (or avoid) muscle or nerve stimulation, including that which might cause extra ventricular contractions.

[0031] FIG. 4 is a schematic diagram of an example of a drive control circuit 300 configured to control output transistors of an output stage, such as an H-bridge circuit 100. For example, the drive control circuit 300 can control turning on and turning off transistors of an output stage, such as output stage 20 of FIG. 1 or the H-bridge output stage 100 of FIG. 2. Accordingly, the description of FIG. 4 can also refer to certain aspects of FIGS. 1 and 2. As described herein, by reducing the turn-off time of the given transistor 110 and other transistors in the output stage, interphase delay in multiphasic output signal can be reduced.

[0032] In a described example, the drive control circuit 300 includes a multi-stage driver 302, an isolator 360 and a controller 350, in which an output node 352 is coupled to a control terminal 112 of the transistor 110. While for purposes of simplification the circuit 300 of FIG. 4 shows one driver 302 having its output node 352 coupled to the gate of the transistor 110, a separate instance of the multi-stage driver 302 exists for each transistor (e.g., transistors 110, 120, 130, 140) in the output stage. For example, the output node of each instance of the driver 302 is coupled to a control terminal (e.g., gates 112, 122, 132, 142) of a respective switch (e.g., transistor 110, 120, 130, 140) of the output stage (e.g., the H-bridge circuit).

[0033] The multi-stage driver 302 includes N push-pull driver stages, where N is a positive integer equal to two or more denoting the number of push-pull driver stages. In FIG. 4, the multi-stage driver 302 includes a first push-pull driver stage 310, a second push-pull driver stage 320, and a third push-pull driver stage 330. Although the example of FIG. 4 depicts the driver stage 302 including three push-pull driver stages, any number of N push-pull driver stages can be implemented. Each push-pull driver stage 310, 320, 330 can include a pull-up stage 310A, 320A, 330A and a pull-down stage 310B, 320B, 330B. Each of the pull-up stages 310A, 320A, 330A and the pull-down stages 310B, 320B, 330B are coupled to a respective output node, which is coupled to a control input of a respective transistor of the output stage being driven.

[0034] The pull-up stage 310A, 320A, 330A is configured to provide a first voltage (e.g., positive supply voltage Vdd) at the control terminal of the respective switch of the H-bridge circuit. The pull-down stage 310B, 320B, 330B is configured to provide a second, lower voltage (e.g., negative supply voltage Vss) at the control terminal of the respective switch of the H-bridge circuit. There can be different numbers of pull-up and pull-down stages. According to one example, the driver 302 can include only one of the pull-up stages 310A, 320A, 330A.

[0035] Explained another way, the driver 302 is implemented as a stepwise driver including N push-pull driver stages having different operating characteristics, which can be selectively controlled by the controller 350. In FIG. 4, each of the pull-up stages 310A, 320A, 330A includes a pull-up switch (e.g., field effect transistor) 312, 322, 332 having a control terminal 316, 326, 336, a first terminal, and a second terminal, and a pull-up resistor Rg on l, Rg_on_2, Rg on n, where each Rg on is representative of a gate resistance with the pull-up switch that is activated for turning on the transistor 110. Similarly, each pull-down stage 310B, 320B, 330B includes a pull-down switch 314, 324, 334 having a control terminal 318, 328, 338, a first terminal, and a second terminal, and a pull-down resistor Rg off l, Rg_off_2, Rg off n, where each Rg off is representative of a gate resistance with the pull-down switch that is activated for turning off the transistor 110. For each push-pull driver stage, the first terminal of the pull-up switch 312, 322, 332 can be coupled to Vdd, the second terminal of the pull-up switch 312, 322, 332 can be coupled to the pull-up resistor Rg on l, Rg_on_2, Rg on n, the pull-up resistor Rg on l, Rg_on_2, Rg on n can be coupled to the output node 352. The pull-downresistors Rg off l, Rg_off_2, Rg off n can be coupled between the output node 352 and the first terminal of the pull-down switch 314, 324, 334, and the second terminal of the pull-down switch 314, 324, 334 can be coupled to Vss. Thus, each pull-up stage 310A, 320A, 330A is configured to provide approximately Vdd at the output node 352, through its respective on-resistance Rg on l, Rg_on_2, Rg on n, to turn on the given switch 110 of the H-bridge circuit based on a respective pull-up drive logic signal. Each pull-down stage 310B, 320B, 330B is configured to provide approximately Vss at the output node, through its respective off-resistance Rg on l, Rg_on_2, Rg on n, to turn off the given switch 110 of the H-bridge circuit based on a respective pull-down drive logic signal.

[0036] The controller 350 and isolator 360 can be configured to propagate control signals to each of the drivers 302. The controller 350 is configured to selectively activate one or more of the pull-up stages 310A, 320 A, 330A to turn on the switch 110 or to activate one or more of the pull-down stages 310B, 320B, 330B to turn off the switch 110. For example, the controller 350 is an FPGA, a microcontroller unit (MCU) or other control circuitry (e.g., hardware and / or software). The controller 350 is thus configured to drive one or more of the control terminals 318, 328, 338 of the N pull-down stages 310B, 320B, 330B based on one or more characteristics of the H-bridge circuit 100 (e.g., the output stage’s switches cell structurejunction temperature, internal gate resistance, and capacitance as well as the load current and bus voltage) and / or one or more characteristics of the driver stage 302, such as the values of the pull-up resistors Rg on l, Rg_on_2, Rg on n or pull-down resistors Rg off l, Rg_off_2, Rg off n.

[0037] As a further example, the equivalent gate resistance and the stage active time are two parameters that can be used to determine which push-pull stage 310, 320, 330 is driven and its duration. For example, an optimization could be carried out by an iterative empirical process that uses the emitter current, collector-emitter, and gate-emitter voltages as the measured variables. A small (known minimum) gate resistance Rg on could be employed in a first stage to discharge the gate capacitance as fast as possible. This minimum gate resistance could be selected as the resistance value before the maximum collector-emitter voltage is exceeded and / or oscillations in the gate-emitter voltage are observed using a single push-pull driver. The minimum gate resistance can be achieved by driving one or more push-pull stages 310, 320, 330, such that the equivalent gate resistance is approximately the same as the desired minimum gate resistance. Thedriver stage 302 can include more push-pull stages (switch and pull-up / pull-down resistors Rg on / Rg off) than the number of timing stages for the turn-off switching process. An equivalent gate resistance that is approximately the same as the resistor for a single push- pull stage 310, 320, 330 could be used for the second stage. This gate resistance is larger than the one used in the first stage because a single push-pull driver may be designed for the worst-case operating point. The second stage gate resistance can be achieved by driving one or more push-pull stages 310, 320, 330. As described herein, the stages active times could be selected to reduce turn-off switching time and conduction run-on. For example, the first stage active time could initially be set to zero, and increased (e.g., in a stepwise manner) until the maximum collector-emitter voltage is exceeded. In some examples, more stages for the turn-off switching process can be used, where different equivalent gate resistances are used for each of the respective stages.

[0038] As mentioned, although FIG. 4 is depicted with the output node 352 being coupled to the gate 112 of the IGBT 110, each gate 122, 132, 142 of each other IGBT 120, 130, 140 will have its own separate instance of the multi-stage driver 302. The controller 350 can generate one or more gate drive logic signals for each interphase delay control circuit for each gate 112, 122, 132, 142 of each IGBT 110, 120, 130, 140. An isolator 360 can isolate functional sections (e.g., the controller 350 and the driver stage 302) of the interphase delay control circuit to prevent current flow between the therapy circuits and controller circuits such that no direct conduction path is permitted. Thus, the isolating circuits ensure that the patient remains electrically isolated, and the operating room clinician is protected from high voltages. The isolator 360 can generate isolated gate drive signals based on the one or more gate drive logic signals generated by the controller 350. In this way, the isolator 360 can mitigate damage to the controller 350 from high voltages (e.g., 4kV) associated with the downstream IGBTs 110, 120, 130, 140.

[0039] In this way, the drive control circuit 300 permits faster switching of the IGBTs 110, 120, 130, 140, thus allowing for optimization of the waveform parameters, such as the rise and fall time, as well as reducing the run-on conduction time, thereby providing the benefit or advantage of shorter interphase delays. According to one example, the CONTROLLER 350 or FPGA can apply a small gate resistance, apply a larger gate resistance, then switch to a smaller gate resistance.

[0040] FIG. 5 is an example timing diagram 400 for the pull-down switches 314, 324, 334 of the drive control circuit 300 of FIG. 4. According to the example of FIG. 5, a trigger signal is provided to be logic-low at time 402 enabling interphase delay control for a PFA system. For example, at time 402, the switch 314 is turned on providing Rg off l as the external gate resistance. At time 404, the switch 314 is turned off and the switch 324 is turned on, providing Rg_off_2 as the external gate resistance. At time 406, the switch 314 is turned on providing Rg_off_l || Rg_off_2 (where || indicates the resistances are in parallel) as the external gate resistance. As a further example, the above example can be implemented with the following resistor values:Rg_off_l=5 Ohms,Rg_off_2=20 Ohms, thusR^off = 5 Ohms,R|20ff = 20 Ohms,R|3off= 5 || 20 = 4 Ohms.

[0041] FIG. 6 is a schematic representation of an example PFA system 500 with interphase delay control that can be implemented during an ablation treatment being performed on a patient 502. The PFA system 500 can include a catheter 504, return electrodes 506, and a controller 508, such as including the interphase delay control circuit 300 of FIG. 4 (e.g., , and a signal generator circuit 510, including the H-bridge circuit 100 of FIG. 2, in electrical communication with one another. The catheter 504 includes an ablation electrode 512 and, in use, the ablation electrode 512 is positioned in contact with tissue in an anatomic structure (e.g., a heart chamber) of the patient 502. Electrical energy from the PFA generator 510 is delivered from the ablation electrode 512 to the tissue, a portion of the electrical energy moves from the tissue of the anatomic chamber of the patient 502 to the return electrodes 506 positioned on skin of the patient 502, and, ultimately, at least some of the electrical energy returns to the PFA generator 510 to complete the circuit formed by the PFA system 500. Additionally, or alternatively, the return electrodes 506 can be part of the catheter 504 and be positioned in contact with tissue in an anatomic structure. As described in greater detail below, the controller 508 controls distribution of the electrical energy among the return electrodes 506 in a fixed position in contact with skin of the patient 502. Accordingly, the controller 508 can reduce or eliminate the need to reposition the return electrodes 506 to maintain a desireddistribution of electrical energy through the return electrodes 506 during a medical treatment.

[0042] In general, the catheter 504 can be intravascularly deliverable to a treatment site (e.g., through insertion in a femoral artery), where the ablation electrode 512 can be positioned relative to tissue at a treatment site. For example, the ablation electrode 512 can be expandable (e.g., self-expandable and / or balloon expandable) or non-expandable for positioning relative to tissue at the treatment site. While such positioning and treatment of tissue through the delivery of electrical energy from the ablation electrode 512 to the tissue can be associated with any one or more of various different medical procedures, the PFA system 500 is herein described in the context of ablating tissue. For example, the ablation electrode 512 can be positioned in contact with tissue in a heart chamber of the patient 502 such that electrical ablation energy is delivered from the ablation electrode 512 to targeted tissue to form one or more lesions. The one or more lesions can be useful, for example, for interrupting electrical patterns associated with cardiac arrhythmia. Additionally, or alternatively, while the ablation electrode 512 is described as a single electrode, it should be appreciated that the ablation electrode 512 can be a plurality of ablation electrodes.

[0043] The PFA generator 510 can drive electrical energy from the ablation electrode 512 to the return electrodes 506. The electrical energy driven by the PFA generator 510 can be sufficient for ablating tissue in proximity to the ablation electrode 512 during a medical treatment. For example, the PFA generator 510 can be a radiofrequency (RF) energy generator (e.g., any one or more RF energy generators well known in the art) such that the ablation energy delivered by the ablation electrode 512 to the tissue can be RF energy (e.g., in the range of 350-500 kHz). Additionally, or alternatively, the PFA generator 510 can generate electrical energy in other frequency ranges (e.g., microwave or a set of electroporation pulses) suitable for medical treatment.

[0044] In certain implementations, the PFA system 500 can additionally, or alternatively, include a catheter interface unit 514 in electrical communication (e.g., wired electrical communication) with the PFA generator 510 and the catheter 504. The catheter interface unit 514 can include, for example, a graphical user interface to display information (e.g., positional information) about the ablation electrode 512 during treatment. Further, or instead, the catheter interface unit 514 can display informationabout the electrical energy driven between the ablation electrode 512 and the return electrodes 506 by the PF A generator 510. The graphical user interface or user input devices (e.g., buttons, triggers, etc.) can be included to receive user inputs responsive to which the controller is configured to control application of ablation energy to the one or more electrodes, such as described herein. As a specific example, the catheter interface unit 514 can display information related to whether the PFA system 500 is in a therapy mode and, more specifically, information related to a duration of lesion formation.

[0045] The return electrodes 506 can be positionable on skin of the patient for a monopolar configuration or be part of the catheter 504 for a bipolar configuration. For example, each one of the return electrodes 506 can be secured in a fixed position on the skin of the patient such that the return electrodes 506 remain in place when subjected to incidental forces, as may be experienced, for example, during repositioning of the patient 502 during the treatment. In certain implementations, each of the return electrodes 506 can include an adhesive surface such that the respective one of the return electrodes 506 can be releasably secured to skin of the patient 502 by placing the adhesive surface in contact with skin of the patient 502.

[0046] The return electrodes 506 can be releasably securable to skin of the patient 502 in a configuration in which the return electrodes 506 are spaced apart from one another (e.g., with one of the return electrodes 506 on the back of the patient 502 and another one of the return electrodes 506 on a leg of the patient 502). While the return electrodes 506 are described as including two electrodes, additional return electrodes 506 can be used. For example, the number of the return electrodes 506 can be selected to increase the likelihood that the current passing through any one of the return electrodes 506 is likely to remain below a predetermined threshold (e.g., to reduce the likelihood of damage to skin of the patient) during the treatment.

[0047] In general, the return electrodes 506 can be substantially similar to one another as well as to the ablation electrode 512. However, unless the distribution of the electrical energy through return electrodes 506 is controlled, differences in the distribution of the electrical energy moving from the ablation electrode 512 through the return electrodes 506 can exist during the medical treatment. Such differences can be attributable, for example, to one or more of normal manufacturing differences between the return electrodes 506, differences in contact area between each one of the return electrodes506 and skin of the patient 502, and differences in position of the return electrodes 506 relative to the ablation electrode 512. While manual adjustments (e.g., repositioning the return electrodes 506) can be made to address these differences to a degree, such manual adjustments can be time-consuming and disruptive from a workflow perspective, given that power is delivered after the patient has been positioned and the catheter 504 has been inserted and delivered to the treatment site. Additionally, or alternatively, such manual adjustments can continue to be required as conditions change during the medical treatment.

[0048] The controller 508 can include circuitry to control distribution of the electrical energy among the return electrodes 506 with the return electrodes 506 in a fixed position in contact with skin of the patient. That is, the controller 508 can distribute electrical energy from the ablation electrode 512 to the return electrodes 506 without requiring manipulation of the return electrodes 506. As used herein, the distribution of electrical energy can include distribution of current, voltage and energy, unless otherwise specified or made clear from the context.

[0049] In general, the distribution of the electrical energy by the controller 508 can be any one or more distributions suitable for a particular application. For example, the controller 508 can maintain at least one of an electrode current and an electrode voltage in each of the return electrodes 506 below a predetermined threshold (e.g., below about 1 ampere to reduce the likelihood of damage to tissue). Additionally, or alternatively, the distribution of the electrical energy by the controller 508 can be a substantially uniform distribution of at least one of current and voltage among the return electrodes 506 such that a respective one of the electrode current and the electrode voltage in the return electrodes 506 is substantially equal.EXAMPLE EMBODIMENTS:

[0050] Several aspects of the present technology are set forth in the following separately numbered examples.

[0051] Example 1. A circuit for controlling a signal provided to medical apparatus, comprising: a plurality of multi-stage driver circuits, each of the multi-stage driver circuits having a respective output, each of the multi-stage driver circuits includes a plurality of driver stages, each of the plurality of push-pull driver stages includes a pull-upstage and a pull-down stage coupled between first and second voltages, each of the plurality of push-pull driver stages also has an output node coupled to the respective output of the multi-stage driver circuit; an output stage circuit includes an arrangement of switches, each having a respective control terminal coupled to the output of a respective one of the multi-stage driver circuits, wherein the output stage circuit has a pair of outputs coupled to respective ablation output terminals, wherein, for each of the plurality of driver stages, each of the push-pull driver stages the pull-up stage is configured to provide approximately the first voltage at the output node, through a respective on-resistance, to turn on a given switch of the output stage circuit responsive to a respective pull-up drive logic signal, the pull-down stage is configured to provide approximately the second voltage at the output node, through a respective off-resi stance, to turn off the given switch of the output stage circuit based on a respective pull-down drive logic signal, and the first voltage is greater than the second voltage; and a controller configured to control one or more of the driver stages to turn off a given switch of the output stage circuit and provide a desired interphase delay to a next cycle of an output pulse provided to the respective ablation output terminals based on the respective off-resistance associated with one or more pull-down stages.

[0052] Example 2. The circuit of example 1, wherein each of the driver stages comprises: a pull-up switch including a first control terminal, a first current terminal, and a second current terminal, wherein the first current terminal is coupled to a first power supply voltage; a pull-up resistor in series with the pull-up switch between the first power supply voltage and an output node; a pull-down switch including a second control terminal, a third current terminal, and a fourth current terminal, wherein the fourth current terminal is coupled to a second power supply voltage that is less than the first power supply voltage; and a pull-down resistor in series with the pull-down switch between the output node and the second power supply voltage; and wherein for each push-pull driver stage, the pull-up resistor is coupled between the second current terminal and the output node thereof, and the pull-down resistor is coupled between the third current terminal and the output node thereof.

[0053] Example 3. The circuit according to example 2, wherein the controller configured to drive the pull-down switches of at least one of the driver stages based on one or more characteristics of the output stage circuit to facilitate turning off the given switch.

[0054] Example 4. The circuit of example 3, wherein the one or more characteristics of the output stage circuit include a gate resistance, defined by the on- resistance or off-resistance of the respective push-pull driver stages, and an active time for a given pulse provided to the respective ablation output terminals.

[0055] Example 5. The circuit of example 3, wherein: each of the pull-down switches comprise a pull-down field effect transistor and the second control terminal thereof is a gate thereof, and the controller is configured to provide one or more gate drive logic signals to control the gate of the pull-down field effect transistor of least one of the driver stages.

[0056] Example 6. The circuit according to any of examples 1 to 5, wherein the switches of the output stage circuit comprise insulated-gate bipolar transistors and the output stage circuit has first and second output terminals adapted to be coupled to respective inputs of an ablation catheter.

[0057] Example 7. The circuit of example 1, wherein each of the driver stages includes a pull-up stage and a pull-down stage having respective output nodes coupled to the respective control terminal of the given switch of the output stage circuit at the output node.

[0058] Example 8. The circuit according to any one of examples 2 to 7, wherein the output stage circuit comprises an 14-bridge circuit and has an operating voltage of at least approximately 1 kV.

[0059] Example 9. The circuit according to any one of examples 2 to 8, wherein the plurality of driver stages comprises at least three instances of the driver stages.

[0060] Example 10. The circuit of example 9, wherein the controller is configured to drive the control terminal of the pull-down switch of a first driver stage and the pull-down switch of a second driver stage simultaneously to control turning off the given switch of the output stage circuit for a first switch cycle.

[0061] Example 11. The circuit of example 10, wherein the controller is further configured to drive the respective control terminal of the pull-down switch of the second driver stage to control turning off the given switch of the output stage circuit for a second switch cycle.

[0062] Example 12. The circuit according to any of example 10, wherein the pull-down resistor of the first driver stage has a different resistance than the pull-down resistor of the second driver stage.

[0063] Example 13. A pulse generator circuit, comprising: an H-bridge circuit having first and second outputs and including a plurality of switches, each of the plurality of switches having a respective control terminal, and the H-bridge circuit having a pair of ablation output terminals adapted to be coupled to respective terminals of an ablation electrode; a plurality of push-pull driver stages, wherein each driver stage of the plurality of push-pull driver stages include a pull-up stage and a pull-down stage coupled between first and second voltages and has an output node coupled to the respective control terminal of a given switch of the plurality of switches of the H-bridge circuit, in which the pull-up stage is configured to provide approximately the first voltage at the output node, through a respective on-resistance, to turn on the given switch of the H-bridge circuit based on a respective pull-up drive logic signal, the pull-down stage is configured to provide approximately the second voltage at the output node, through a respective off-resistance, to turn off the given switch of the H-bridge circuit based on a respective pull-down drive logic signal, and the first voltage is greater than the second voltage; and a controller configured to provide a respective pull-down drive logic signal to control each of the pulldown stages for each of the plurality of push-pull driver stages, which controls turn-off of the given switch, for providing a pulse to the ablation output terminals based on one or more characteristics of the H-bridge circuit.

[0064] Example 14. The circuit of example 13, wherein each of the plurality of switches of the H-bridge circuit is an insulated-gate bipolar transistor, and wherein the one or more characteristics of the H-bridge circuit include a gate resistance, which includes the on-resistance or off-resi stance of the respective of push-pull driver stages, and an active time for a given pulse provided to the ablation output terminals.

[0065] Example 15. The circuit according to example 13 or 14, wherein: each of the pull-down stages comprise a respective pull-down field effect transistor having a gate, and the controller is configured to provide one or more pull-down drive logic signal to control the gate of one or more respective pull-down field effect transistor of least one of the plurality of push-pull driver stages.

[0066] Example 16. The circuit of example 15, further comprising an isolator configured to generate one or more isolated pull-down gate drive signals based on the one or more pull-down drive logic signals, in which each of the respective pull-down field effect transistors is configured to provide approximately the second voltage at the output node thereof based on a respective one of the isolated pull-down gate drive signals.

[0067] Example 17. The circuit of example 16, wherein the plurality of switches of H-bridge circuit is coupled between third and fourth voltages, each being greater than 1 kV, such that the H-bridge circuit is configured to provide a bi-phasic signal between the first and second outputs having a peak-to-peak voltage of at least 2 kV.

[0068] Example 18. The circuit according to any of examples 13 through 17, wherein the respective off-resistance is different for at least some of the pull-down stages, and the controller is configured to selectively control one or more of the pull-down stages to turn off the given switch of the H-bridge circuit to provide a desired interphase delay to a next cycle based on the respective off-resi stance of one or more of the pull-down stages.

[0069] Example 19. The circuit of example 18, further comprising a respective instance of the plurality of push-pull driver stages associated with each respective switch of the plurality of switches of the H-bridge circuit, wherein each respective instance of the plurality of push-pull driver stages is configured to drive each respective switch based on a respective pull-down drive logic signal provided by the controller.

[0070] Example 20. A system, comprising: a signal generator circuit, comprising: an output stage having first and second outputs and including an arrangement of switches, each having a control input; a plurality of multi-stage driver circuits, each coupled between first and second voltages and having an output node coupled to the control input of a respective switch of the output stage, wherein the first voltage is greater than the second voltage and each of the multi-stage driver circuits comprises: multiple pull-down stages coupled between output node and the second voltage, each of the pulldown stages is configured to provide approximately the second voltage, through a respective off-resistor, at the output node based a respective pull-down drive logic signal, wherein the respective off-resistor of at least some of the pull-down stages have different resistances; a controller configured to provide respective pull-down drive logic signals to control one or more of the pull-down stages for each of the multi-stage driver circuits to control turning off the respective switch of the output stage; and catheter interfacecircuitry having first and second inputs, wherein the first input is coupled to the first output and the second input is coupled to the second output.

[0071] Example 21. The system of example 20, wherein each of the multi-stage driver circuits further comprises multiple pull-up stages coupled between output node and the first voltage, each of the pull-up stages is configured to provide approximately the first voltage, at the output node based a respective pull-up drive logic signal, which is provided by the controller, to control turning on the respective switch of the output stage.

[0072] Example 22. The system of example 21, wherein the switches of the output stage are insulated-gate bipolar transistors arranged as an H-bridge circuit between third and fourth voltages, and the H-bridge circuit is configured to provide pulsed output signals between the first and second outputs based on the pull-up and pull-down drive logic signals, and a delay between consecutive pulsed output signals is based on the pulldown drive logic signal controlling the one or more of the pull-down stages.

[0073] Example 23. The system of example 22, wherein the pulsed output signals are at least one of mono-phasic, bi-phasic, or tri-phasic.

[0074] Example 24. The system of example 22, wherein each of the third and fourth voltages is greater than 1 kV and a given cycle of the pulsed output signal has a peak-to-peak voltage of at least 2 kV.

[0075] Example 25. The system according to any of examples 20 through 24, further comprising an isolator coupled between the controller and the plurality of multistage driver circuits, wherein the isolator is configured to generate one or more isolated gate drive signals based on one or more gate drive logic signals.

[0076] Various aspects disclosed herein may be combined in different combinations than the combinations specifically presented in the description and accompanying drawings. It should also be understood that, depending on the example, certain acts or events of any of the processes or methods described herein may be performed in a different sequence, may be added, merged, or left out altogether (e.g., all described acts or events may not be necessary to carry out the techniques). In addition, while certain aspects of this disclosure are described as being performed by a single module or unit for purposes of clarity, the techniques of this disclosure may be performed by a combination of units or modules associated with, for example, a medical device.

[0077] In one or more examples, the described techniques may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include non-transitory computer-readable media, which corresponds to a tangible medium such as data storage media (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer).

[0078] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor” as used herein may refer to any of the foregoing structure or any other physical structure suitable for implementation of the described techniques. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0079] In this description, the term “couple” can cover connections, communications, or signal paths that enable a functional relationship consistent with this description. For example, if device A generates a signal to control device B to perform an action: (a) in a first example, device A is coupled to device B by direct connection; or (b) in a second example, device A is coupled to device B through intervening component C if intervening component C does not alter the functional relationship between device A and device B, such that device B is controlled by device A via the control signal generated by device A.

[0080] In this description, a device that is “configured to” perform a task or function can be configured (e.g., programmed and / or hardwired) at a time of manufacturing by a manufacturer to perform the function and / or can be configurable (or reconfigurable) by a user after manufacturing to perform the function and / or other additional or alternative functions. The configuring can be through firmware and / or software programming of the device, through a construction and / or layout of hardware components and interconnections of the device, or a combination thereof. Furthermore, a circuit or device that is described herein as including certain components can instead be configured to couple to those components to form the described circuitry or device. Forexample, a structure described herein as including one or more semiconductor elements (such as transistors), one or more passive elements (such as resistors, capacitors, and / or inductors), and / or one or more sources (such as voltage and / or current sources) can instead include only the semiconductor elements within a single physical device (e.g., a semiconductor die and / or integrated circuit (IC) package) and can be configured to couple to at least some of the passive elements and / or the sources to form the described structure, either at a time of manufacture or after a time of manufacture, such as by an end-user and / or a third-party.

[0081] The phrase “based on” means “based at least in part on”. Therefore, if X is based on Y, X can be a function of Y and any number of other factors.

[0082] Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.

Claims

CLAIMSWhat is claimed is:

1. A circuit for controlling a signal provided to medical apparatus, comprising: a plurality of multi-stage driver circuits, each of the multi-stage driver circuits having a respective output, each of the multi-stage driver circuits includes a plurality of driver stages, each of the plurality of push-pull driver stages includes a pull-up stage and a pull-down stage coupled between first and second voltages, each of the plurality of push-pull driver stages also has an output node coupled to the respective output of the multi-stage driver circuit; an output stage circuit includes an arrangement of switches, each having a respective control terminal coupled to the output of a respective one of the multistage driver circuits, wherein the output stage circuit has a pair of outputs coupled to respective ablation output terminals, wherein, for each of the plurality of driver stages, each of the push-pull driver stages the pull-up stage is configured to provide approximately the first voltage at the output node, through a respective on- resistance, to turn on a given switch of the output stage circuit responsive to a respective pull-up drive logic signal, the pull-down stage is configured to provide approximately the second voltage at the output node, through a respective off- resistance, to turn off the given switch of the output stage circuit based on a respective pull-down drive logic signal, and the first voltage is greater than the second voltage; and a controller configured to control one or more of the driver stages to turn off a given switch of the output stage circuit and provide a desired interphase delay to a next cycle of an output pulse provided to the respective ablation output terminals based on the respective off-resistance associated with one or more pulldown stages.

2. The circuit of claim 1, wherein each of the driver stages comprises: a pull-up switch including a first control terminal, a first current terminal, and a second current terminal, wherein the first current terminal is coupled to a first power supply voltage; a pull-up resistor in series with the pull-up switch between the first power supply voltage and an output node; a pull-down switch including a second control terminal, a third current terminal, and a fourth current terminal, wherein the fourth current terminal is coupled to a second power supply voltage that is less than the first power supply voltage; and a pull-down resistor in series with the pull-down switch between the output node and the second power supply voltage; and wherein for each push-pull driver stage, the pull-up resistor is coupled between the second current terminal and the output node thereof, and the pull-down resistor is coupled between the third current terminal and the output node thereof.

3. The circuit according to claim 2, wherein the controller configured to drive the pull-down switches of at least one of the driver stages based on one or more characteristics of the output stage circuit to facilitate turning off the given switch.

4. The circuit of claim 3, wherein the one or more characteristics of the output stage circuit include a gate resistance, defined by the on-resistance or off-resistance of the respective push-pull driver stages, and an active time for a given pulse provided to the respective ablation output terminals.

5. The circuit of claim 3, wherein: each of the pull-down switches comprise a pull-down field effect transistor and the second control terminal thereof is a gate thereof, and the controller is configured to provide one or more gate drive logic signals to control the gate of the pull-down field effect transistor of least one of the driver stages.

6. The circuit according to any of claims 1 to 5, wherein the switches of the output stage circuit comprise insulated-gate bipolar transistors and the output stage circuit has first and second output terminals adapted to be coupled to respective inputs of an ablation catheter.

7. The circuit of claim 1, wherein each of the driver stages includes a pull-up stage and a pull-down stage having respective output nodes coupled to the respective control terminal of the given switch of the output stage circuit at the output node.

8. The circuit according to any one of claims 2 to 7, wherein the plurality of driver stages comprises at least three instances of the driver stages.

9. The circuit of claim 8, wherein the controller is configured to drive the control terminal of the pull-down switch of a first driver stage and the pull-down switch of a second driver stage simultaneously to control turning off the given switch of the output stage circuit for a first switch cycle.

10. The circuit of claim 9, wherein the controller is further configured to drive the respective control terminal of the pull-down switch of the second driver stage to control turning off the given switch of the output stage circuit for a second switch cycle.

11. The circuit according to any of claims 1 to 10, wherein the pull-down resistor of the first driver stage has a different resistance than the pull-down resistor of the second driver stage.

12. A pulse generator circuit, comprising: an H-bridge circuit having first and second outputs and including a plurality of switches, each of the plurality of switches having a respective control terminal, and the H- bridge circuit having a pair of ablation output terminals adapted to be coupled to respective terminals of an ablation electrode; a plurality of push-pull driver stages, wherein each driver stage of the plurality of push-pull driver stages include a pull-up stage and a pull-down stage coupled between firstand second voltages and has an output node coupled to the respective control terminal of a given switch of the plurality of switches of the H-bridge circuit, in which the pull-up stage is configured to provide approximately the first voltage at the output node, through a respective on-resistance, to turn on the given switch of the H-bridge circuit based on a respective pull-up drive logic signal, the pull-down stage is configured to provide approximately the second voltage at the output node, through a respective off-resistance, to turn off the given switch of the H-bridge circuit based on a respective pull-down drive logic signal, and the first voltage is greater than the second voltage; and a controller configured to provide a respective pull-down drive logic signal to control each of the pull-down stages for each of the plurality of push-pull driver stages, which controls turn-off of the given switch, for providing a pulse to the ablation output terminals based on one or more characteristics of the H-bridge circuit.

13. A system, comprising: a signal generator circuit, comprising: an output stage having first and second outputs and including an arrangement of switches, each having a control input; a plurality of multi-stage driver circuits, each coupled between first and second voltages and having an output node coupled to the control input of a respective switch of the output stage, wherein the first voltage is greater than the second voltage and each of the multi-stage driver circuits comprises: multiple pull-down stages coupled between output node and the second voltage, each of the pull-down stages is configured to provide approximately the second voltage, through a respective off-resistor, at the output node based a respective pull-down drive logic signal, wherein the respective off- resistor of at least some of the pull-down stages have different resistances; a controller configured to provide respective pull-down drive logic signals to control one or more of the pull-down stages for each of the multi-stage driver circuits to control turning off the respective switch of the output stage; andcatheter interface circuitry having first and second inputs, wherein the first input is coupled to the first output and the second input is coupled to the second output.

14. The system of claim 13, wherein each of the multi-stage driver circuits further comprises multiple pull-up stages coupled between output node and the first voltage, each of the pull-up stages is configured to provide approximately the first voltage, at the output node based a respective pull-up drive logic signal, which is provided by the controller, to control turning on the respective switch of the output stage;15. The system of claim 14, wherein the switches of the output stage are insulated-gate bipolar transistors arranged as an H-bridge circuit between third and fourth voltages, and the H-bridge circuit is configured to provide pulsed output signals between the first and second outputs based on the pull-up and pull-down drive logic signals, and a delay between consecutive pulsed output signals is based on the pull-down drive logic signal controlling the one or more of the pull-down stages.

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