Abstract:
A generator for use with an electrosurgical device is provided. The generator has a gain stage electrically disposed between a first voltage rail and a second voltage rail, wherein the gain stage includes an input and an output. A voltage source operably coupled to the gain stage input and configured to provide an input signal thereto responsive to a drive control signal is also provided. The generator also has one or more sensors configured to sense an operational parameter of the amplifier and to provide a sensor signal corresponding thereto and a controller adapted to receive the sensor signal(s) and in response thereto provide a drive control signal to the voltage source. The generator has an amplifier output configured to supply an output voltage corresponding to the first voltage rail and the second voltage rail when the output of the gain stage falls between a voltage of the first voltage rail and a voltage of the second voltage rail and is configured to supply a peak voltage output when the voltage output is falls greater than the voltage of the first voltage rail or less than the voltage of the second voltage rail.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Divisional Application of U.S. patent application Ser. No. 14/058,929 filed on Oct. 21, 2013 which is a Divisional Application of U.S. patent application Ser. No. 12/619,234 filed on Nov. 16, 2009 now U.S. Pat. No. 8,610,501, the contents of both applications are expressly incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to systems for providing energy to biological tissue and, more particularly, to improved apparatus for amplifying energy for use during electrosurgical procedures. 
       BACKGROUND OF RELATED ART 
       [0003]    Energy-based tissue treatment is well known in the art. Various types of energy (e.g., electrical, ultrasonic, microwave, cryogenic, thermal, laser, etc.) are applied to tissue to achieve a desired result. Electrosurgery involves application of high radio frequency electrical current to a surgical site to cut, ablate, coagulate or seal tissue. In monopolar electrosurgery, a source or active electrode delivers radio frequency energy from the electrosurgical generator to the tissue and a return electrode carries the current back to the generator. In monopolar electrosurgery, the source electrode is typically part of the surgical instrument held by the surgeon and applied to the tissue to be treated. A patient return electrode is placed remotely from the active electrode to carry the current back to the generator. 
         [0004]    Ablation is most commonly a monopolar procedure that is particularly useful in the field of cancer treatment, where one or more RF ablation needle electrodes (usually having elongated cylindrical geometry) are inserted into a living body and placed in the tumor region of an affected organ. A typical form of such needle electrodes incorporates an insulated sheath from which an exposed (uninsulated) tip extends. When an RF energy is provided between the return electrode and the inserted ablation electrode, RF current flows from the needle electrode through the body. Typically, the current density is very high near the tip of the needle electrode, which tends to heat and destroy surrounding issue. 
         [0005]    In bipolar electrosurgery, one of the electrodes of the hand-held instrument functions as the active electrode and the other as the return electrode. The return electrode is placed in close proximity to the active electrode such that an electrical circuit is formed between the two electrodes (e.g., electrosurgical forceps). In this manner, the applied electrical current is limited to the body tissue positioned immediately adjacent the electrodes. When the electrodes are sufficiently separated from one another, the electrical circuit is open and thus inadvertent contact with body tissue with either of the separated electrodes does not cause current to flow. 
         [0006]    Commonly used power amplifiers are known to be inefficient. For example, a class A/B microwave power amplifier typically exhibits an efficiency of about 35%. That is, to achieve a surgical signal of 250 W, a class A/B power amplifier requires about 714 W of power, of which 464 W is dissipated as thermal energy. The resulting heat becomes difficult to manage and may require the use of bulky and costly cooling systems, e.g., fans and heat sinks. Additionally, the excess heat may cause thermal stress to other components of the generator, shortening generator life, decreasing reliability, and increasing maintenance costs. Additionally, a class A/B amplifier may exhibit crossover distortion that introduces undesirable harmonics into the surgical signal, which are known to cause radiofrequency interference in excess of acceptable limits. 
         [0007]    Because electrosurgery requires very large ranges of voltage and current while maintaining a very high conversion efficiency to reduce the size and heat sink needs, some electrosurgical devices use a tuned resonance circuit driven by a class C or class E output. However, such an arrangement has a disadvantage in that the quality factor or Q factor changes with the load applied to the circuit making it difficult to maintain the desired voltage or current at the output. A manifestation of this disadvantage may be excessive or undesired “ringing” at the output for underdamped or high Q situations of loading. Class A/B/outputs do not suffer from this disadvantage because their output impedances are typically much lower. 
       SUMMARY 
       [0008]    The present disclosure provides an apparatus for a generator. In accordance with the present disclosure, the generator includes a gain stage electrically disposed between a first voltage rail and a second voltage rail, wherein the gain stage includes an input and an output, a voltage source operably coupled to the gain stage input and configured to provide an input signal thereto responsive to a drive control signal, at least one sensor configured to sense an operational parameter of the amplifier and to provide a sensor signal corresponding thereto, a controller adapted to receive the at least one sensor signal and in response thereto provide the drive control signal to the voltage source. An amplifier output is provided and configured to supply an output voltage corresponding to the first voltage rail and the second voltage rail when the output of the gain stage falls between a voltage of the first voltage rail and a voltage of the second voltage rail and is configured to supply a peak voltage output when the voltage output is greater than the voltage of the first voltage rail or less than the voltage of the second voltage rail. 
         [0009]    In other embodiments, the gain stage further comprises a class A/B amplifier having at least two gain elements arranged in a push-pull configuration. The at least two gain elements are selected from the group consisting of bipolar transistors, field-effect transistors, and laterally diffused metal oxide semiconductors. The sensor is configured to sense an output voltage or a bias current. The gain stage may also include a bias circuit where the controller operably couples to the bias circuit and is configured to provide a bias voltage thereto responsive to a bias control signal and wherein the controller provides a bias control signal to the bias controller in response to the at least one sensor signal. 
         [0010]    In another embodiment, an electrosurgical generator is provided having a voltage source, a gain stage, a class resonant-H amplifier, at least one switch, and a controller operable to control an output of the voltage source and control the at least one switch based on a pulse width modulated signal. The at least one switch may be a field effect transistor. The electrosurgical generator may also include at least one sensor operable to sense an operational parameter of the amplifier and to provide a sensor signal corresponding thereto. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the following detailed description when taken in conjunction with the accompanying drawings in which: 
           [0012]      FIGS. 1A-1B  are schematic block diagrams of an electrosurgical system according to the present disclosure for use with various instrument types; 
           [0013]      FIG. 2  is a schematic block diagram of a class resonant-H RF electrosurgical generator according to an embodiment of the present disclosure; 
           [0014]      FIG. 3  is a schematic block diagram of a parallel resonant converter according to an embodiment of the present disclosure; 
           [0015]      FIG. 4  is a graph representing voltage outputs of the class resonant-H RF electrosurgical generator according to an embodiment of the present disclosure; 
           [0016]      FIG. 5  is a graph representing voltage outputs of the class resonant-H RF electrosurgical generator according to an embodiment of the present disclosure; 
           [0017]      FIG. 6  is a schematic block diagram of a class resonant-H RF electrosurgical generator according to an embodiment of the present disclosure; 
           [0018]      FIG. 7  is a schematic block diagram of a generator according to another embodiment of the present disclosure; and 
           [0019]      FIG. 8  is a timing chart for the signals applied to the generator of  FIG. 7  according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Particular embodiments of the present disclosure are described hereinbelow with reference to the accompanying drawings; however, it is to be understood that the disclosed embodiments are merely exemplary of the disclosure, which may be embodied in various forms. Well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure in virtually any appropriately detailed structure. 
         [0021]    The generator according to the present disclosure can perform ablation, monopolar and bipolar electrosurgical procedures, including vessel sealing procedures. The generator may include a plurality of outputs for interfacing with various electrosurgical instruments (e.g., a monopolar active electrode, return electrode, bipolar electrosurgical forceps, footswitch, etc.). Further, the generator includes electronic circuitry configured for generating radio frequency power specifically suited for various electrosurgical modes (e.g., cutting, blending, division, etc.) and procedures (e.g., monopolar, bipolar, vessel sealing). 
         [0022]      FIG. 1A  is a schematic illustration of a monopolar electrosurgical system  1  according to one embodiment of the present disclosure. The system  1  includes an electrosurgical instrument  2  having one or more electrodes for treating tissue of a patient P. The instrument  2  is a monopolar type instrument including one or more active electrodes (e.g., electrosurgical cutting probe, ablation electrode(s), etc.). Electrosurgical RF energy is supplied to the instrument  2  by a generator  20  via a supply line  4 , which is connected to an active terminal  212  ( FIG. 7 ) of the generator  20 , allowing the instrument  2  to coagulate, ablate and/or otherwise treat tissue. The energy is returned to the generator  20  through a return electrode  6  via a return line  8  at a return terminal  211  ( FIG. 7 ) of the generator  20 . The active terminal  212  and the return terminal  211  are connectors configured to interface with plugs (not explicitly shown) of the instrument  2  and the return electrode  6 , which are disposed at the ends of the supply line  4  and the return line  8 , respectively. 
         [0023]    The system  1  may include a plurality of return electrodes  6  that are arranged to minimize the chances of tissue damage by maximizing the overall contact area with the patient P. In addition, the generator  20  and the return electrode  6  may be configured for monitoring so-called “tissue-to-patient” contact to insure that sufficient contact exists therebetween to further minimize chances of tissue damage. In one embodiment, the active electrode  6  may be used to operate in a liquid environment, wherein the tissue is submerged in an electrolyte solution. 
         [0024]      FIG. 1B  is a schematic illustration of a bipolar electrosurgical system  3  according to the present disclosure. The system  3  includes a bipolar electrosurgical forceps  10  having one or more electrodes for treating tissue of a patient P. The electrosurgical forceps  10  include opposing jaw members having an active electrode  14  and a return electrode  16 , respectively, disposed therein. The active electrode  14  and the return electrode  16  are connected to the generator  20  through cable  18 , which includes the supply and return lines  4 ,  8  coupled to the active and return terminals  212 ,  211 , respectively ( FIG. 7 ). The electrosurgical forceps  10  are coupled to the generator  20  at a connector  21  having connections to the active and return terminals  212  and  211  (e.g., pins) via a plug disposed at the end of the cable  18 , wherein the plug includes contacts from the supply and return lines  4 ,  8 . 
         [0025]      FIG. 2  shows a schematic diagram of the generator  20  employing an example of a class resonant-H amplifier  200  in accordance with an embodiment of the present disclosure. A Class I-I amplifier creates an infinitely variable supply rail. This is done by modulating the supply rails so that the rails are only a few volts larger than the output signal at any given time. The output stage, which is typically a linear class A/B topology, operates at its maximum efficiency all the time. Resonant switched mode converters can be used to create the tracking rails. Significant efficiency gains, especially for sinusoidal waveforms, can be achieved using a class resonant-H amplifier. As shown in  FIG. 2 , the digital signal processor (DSP) signal synthesizer  201  provides an input voltage and is coupled to bias and predriver amplifier  203 . The input voltage has a wave form similar to sine wave, but it is not necessarily limited to a sine wave. The wave form for the input voltage may be a triangular wave, square wave, a series of pulses, a pulse width modulated (PWM) signal or any other waveform used to drive an electrosurgical generator. 
         [0026]    However, the best efficiency of the class resonant-H is obtained with sinusoid waveforms. This is graphically exemplified in  FIG. 5 , where a waveform containing add-order harmonics must be contained within a sinusoidal envelope of the fundamental. This compensation might be performed by the DSP signal synthesizer  201 . 
         [0027]    The input voltage is fed into voltage gain stage  203 , amplifier  204  and amplifier  205  of class resonant-H amplifier  200 . Voltage gain stage  203  amplifies the input voltage and provides the amplified voltage as an output to a class A/B amplifier  208 . Voltage gain stage  203  may include a transformer to provide patient isolation between the voltage source  201  and the patient. Alternatively, isolation may be provided at the output of the amplifier  200 . Voltage gain stage  203  may also include a bias circuit that can be controlled by controller  214  to provide a bias voltage for the class A/B amplifier  208 . The combined power amplifier formed by  203  and  208  may be run open-loop or closed-loop. Closed-loop operation may be effected by addition of feedback network  202 . 
         [0028]    Amplifier  208  may include two transistors in a push-pull configuration and may be a part of the voltage gain stage  203  discrete components. The two transistors in amplifier  208  may be bipolar transistors, field-effect transistors, and laterally diffused metal oxide semiconductors 
         [0029]    Amplifiers  204  and  205  may be class C, E or F amplifiers or they may be PWM resonant class D amplifiers, an example of which is shown in Fig,  3 . PWM resonant class D amplifier  250  receives a signal from DSP signal synthesizer  201  and is inputted into a PWM controller  252  that outputs a PWM signal, shown as V g (t), to field effect transistor (FET) Q3.The low pass filter  254 , comprising inductor L and capacitor Cp, passes the average value of the square wave output of Q3 to generate a waveform shown as V CP (t). A voltage source VB provides a DC offset such that V OUT  does not fall below V B . An optional feed back path may be provided that applies a transfer function H FB  to V CP (t) before providing the signal to PWM controller  252 . 
         [0030]    Amplifiers  204  and  205  provide a positive voltage and a negative voltage power supply rails as shown in  FIG. 4 . In  FIG. 4 , positive voltage power supply rail (+V(t))  302  and negative voltage power supply rail (−V(t))  304  track the output voltage  306 . As shown in  FIG. 4 , when the output voltage is less than +V B  or greater than −V B , the output of the amplifier  200  is +V B  or −V B  which is applied to the linear devices in the generator thereby keeping them in a forward bias. When a peak appears in output voltage  306 , the supply rails  302  and  304  also peak. 
         [0031]    A more complete implementation of a class resonant-H RF electrosurgical generator is provided in  FIG. 6 . During non-peak operation current flows from +V B  and −V B  through diodes D5 and D7 respectively. When a peak appears at the bases of transistors Q1 and Q2 in the class A/B amplifier  208 , the parallel resonant output of L1, C1 and L2 C2 are alternatively activated by pulse width modulation (see  FIG. 3  V g (t) and V CP (t) waveforms) of switch networks M1, D1 and M2, D2. The AC outputs are in turn rectified by D4 and D6. Inductor L CC  and resistor R CC  may be included in the RF electrosurgical generator for highly capacitive loads while capacitor C LC  and resistor R LC  may be included for highly inductive loads. 
         [0032]    The generator  20  includes suitable input controls (e.g., buttons, activators, switches, touch screen, etc.) for controlling the generator  20 . In addition, the generator  20  may include one or more display screens for providing the user with variety of output information (e.g., intensity settings, treatment complete indicators, etc.). The controls allow the user to adjust power of the RF energy, waveform, as well as the level of maximum arc energy allowed which varies depending on desired tissue effects and other parameters to achieve the desired waveform suitable for a particular task (e.g., coagulating, tissue sealing, intensity setting, etc.). The instrument  2  may also include a plurality of input controls that may be redundant with certain input controls of the generator  20 . Placing the input controls at the instrument  2  allows for easier and faster modification of RF energy parameters during the surgical procedure without requiring interaction with the generator  20 . 
         [0033]    In particular, the active terminal  212  generates either continuous or pulsed sinusoidal waveforms of high RF energy. The active terminal  212  is configured to generate a plurality of waveforms having various duty cycles, peak voltages, crest factors, and other suitable parameters. Certain types of waveforms are suitable for specific electrosurgical modes. For instance, the active terminal  212  generates a 100% duty cycle sinusoidal waveform in cut mode, which is best suited for ablating, fusing and dissecting tissue and a 1-25% duty cycle waveform in coagulation mode, which is best used for cauterizing tissue to stop bleeding. 
         [0034]    The generator  20  may include a plurality of connectors to accommodate various types of electrosurgical instruments (e.g., instrument  2 , electrosurgical forceps  10 , etc.). Further, the generator  20  may operate in monopolar or bipolar modes by including a switching mechanism (e.g., relays) to switch the supply of RF energy between the connectors, such that, for instance, when the instrument  2  is connected to the generator  20 , only the monopolar plug receives RF energy. 
         [0035]    The controller  214  includes a microprocessor  215  operably connected to a memory  216 , which may be volatile type memory (e.g., RAM) and/or non-volatile type memory (e.g., flash media, disk media, etc.). The controller  214  includes an output port that is operably connected to a variable DSP signal synthesizer  201 , +V g  terminal  221 , −V g  terminal  222 , +HVDC terminal  206  and/or −HVDC terminal  207  allowing the controller  214  to control the output of the generator  20  according to either open and/or closed control loop schemes. Those skilled in the art will appreciate that the microprocessor  215  may be substituted by any logic processor or analog circuitry (e.g., control circuit) adapted to perform the calculations discussed herein. 
         [0036]    The generator  20  may implement a closed and/or open loop control schemes which include a sensor circuit  212  having a plurality of sensors measuring a variety of tissue and energy properties (e.g., tissue impedance, tissue temperature, output current and/or voltage, etc.), and providing feedback to the controller  214 . A current sensor can be disposed at either the active or return current path or both and voltage can be sensed at the active electrode(s). The controller  214  then transmits appropriate signals to the DSP signal synthesizer  201 , voltage gain stage  203 , +V g  terminal  221 , −V g  terminal  222 , +HVDC terminal  206  and/or −HVDC terminal  207 , which then adjust AC or DC power supply, respectively, by using a maximum allowable energy which varies according to the selected mode. The controller  214  also receives input signals from the input controls of the generator  20  or the instrument  2 . The controller  214  utilizes the input signals to adjust power output by the generator  20  and/or performs other control functions thereon. 
         [0037]    The sensor circuit  212  measures the electrical current (I) and voltage (V) supplied by the active terminal  212  in real time to characterize the electrosurgical process during both the matching sinusoidal and non-sinusoidal durations for a predetermined sampling period, the former being of short duration (e.g., half a cycle) and the latter being of long duration (e.g.,  15  cycles). This allows for the measured electrical properties to be used as dynamic input control variables to achieve feedback control. The current and voltage values may also be used to derive other electrical parameters, such as power (P=V*I) and impedance (Z=V/l). The sensor circuit  212  also measures properties of the current and voltage waveforms and determines the shape thereof 
         [0038]      FIG. 7  shows a schematic diagram of an electrosurgical generator  300  in accordance with another embodiment of the present disclosure. The generator  300  has a voltage source  201 , buffer  202 , a voltage gain stage  203 , a +HVDC supply  206  and a −HVDC supply  207  as in generator  20 . Further, the generator has a sensor  312  similar to sensor  212  described above and a controller  314  with microprocessor  314  and memory  315  somewhat similar to the controller  214 , microprocessor  215  and memory  216  described above with regard to  FIG. 2 . 
         [0039]    In generator  300 , the output of the voltage gains stage  203  is fed into the class A/B amplifier  305  at the +V IN  and −V IN  terminals. Instead of using parallel resonant converters as shown in  FIG. 2 , generator  300  utilizes series-parallel, or LCLC, converters driven in full-bridge by active field effect transistor (FET) switches  301 ,  302 ,  303  and  304 . Controller  314  supplies phase-shifted PWM timing signals to FET switches  301 ,  302 ,  303  and  304  as shown in  FIG. 8 . The duty cycle of the PWM signals (e.g., D=0.75) affects the voltage output such that V OUT  is proportional to D·HVDC. The duty cycle is determined by the amount of overlap in a phase-shifted PWM converter The current flows from FET  301  to FET  304  when signal A′ overlaps signal B and current flows from FET  303  to FET  302  when signal B′ overlaps signal A. As shown in  FIG. 8 , signals A and A′ and B and B′ are phase shifted 180° and offset by time t. 
         [0040]    Components L S , C S , L P  and C P  are selected to provide resonant output amplitudes that are proportional to the phase-shifted PWM duty cycles times the power supply rails HVDC. Terminal  30  supplies a positive voltage bias (+V B ) which is a small DC bias voltage that is required to supply bias current to amplifier  305 . +V B  is coupled to inductor LB to provide a float voltage that is supplied to the linear class amplifier  305 . A negative voltage bias (−V B )  307  is also coupled to the amplifier  305  to supply bias current to the amplifier  305 . An inductor LB may be coupled between amplifier  305  and terminal  307  based on whether the output is balanced or unbalanced. Inductor L B  is connected when the output is balanced at a low input or quiescent (below ±V B ). 
         [0041]    While several embodiments of the disclosure have been shown in the drawings and/or discussed herein, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. The claims can encompass embodiments in hardware, software, or a combination thereof. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.