Patent Publication Number: US-2023140703-A1

Title: Two stage pin diode driver with energy recovery

Description:
CLAIM OF PRIORITY UNDER 35 U.S.C. § 119 
     The present Application for Patent claims priority to Provisional Application No. 63/274,123 entitled “TWO STAGE PIN DIODE DRIVER WITH ENERGY RECOVERY” filed Nov. 1, 2021, and assigned to the assignee hereof and hereby expressly incorporated by reference herein. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to diode driver circuits, and more particularly to a PIN diode driver that employs a two-stage circuit. 
     DESCRIPTION OF RELATED ART 
     PIN diodes are electrical devices having an un-doped or lightly doped intrinsic (I) semiconductor region sandwiched between heavily doped regions, and have various applications, for instance, as switching devices in impedance matching networks, and especially in radio-frequency (RF) match networks. 
     The “PIN” designation derives from the three-part sandwich structure of this diode: a lightly doped intrinsic region (I) sandwiched between a heavily doped p-type semiconductor (P) and a heavily doped n-type semiconductor (N). In general, PIN diodes obey conventional diode behavior at low frequency input signals, but for higher frequency input signals they operate as a resistor in the forward biased or on-state, and as a small capacitor in the reverse biased or off-state. As such, PIN diodes are often utilized in attenuators, fast switches, radio frequency (RF) applications, and high voltage electronic applications where high isolation and low loss are desired. 
     In one particular implementation, PIN diodes are used in an impedance match network configured to match a changing load impedance of a plasma load to a desired impedance (e.g., 50 ohm) into which a high-power RF generator can efficiently deliver power. In such an implementation, the PIN diodes serve to connect or disconnect reactive components, typically capacitors, of the impedance matching network to quickly alter the properties of the matching network by switching the reactive elements in and out of the network. Regardless of the specific use, high-speed switching of PIN diodes may involve high power consumption each switch cycle, which is exacerbated in devices using multiple PIN diodes. 
     Moreover, driving high power PIN diodes at high speeds as required for PIN diode matches and switches is a difficult problem. Under forward bias conditions, the diode stores charge in its intrinsic region. To quickly remove this charge requires high voltage but discharging this charge from a high voltage supply takes a lot of energy. In order to recover stored energy rather than supplying and then dumping the energy, resonant circuits can be used. But resonant circuits create a dangerous situation where the PIN diode snaps off when the charge is finally extracted from the PIN diode. This sudden turn-off of the current through the PIN diode creates high voltages across the PIN diode if driven through an inductor (as is typical for energy recovery) which can lead to PIN diode failure. It is with these observations in mind, among others, that aspects of the present disclosure were conceived. 
     SUMMARY OF THE DISCLOSURE 
     The following presents a simplified summary relating to one or more aspects and/or embodiments disclosed herein. As such, the following summary should not be considered an extensive overview relating to all contemplated aspects and/or embodiments, nor should the following summary be regarded to identify key or critical elements relating to all contemplated aspects and/or embodiments or to delineate the scope associated with any particular aspect and/or embodiment. Accordingly, the following summary has the sole purpose to present certain concepts relating to one or more aspects and/or embodiments relating to the mechanisms disclosed herein in a simplified form to precede the detailed description presented below. 
     Aspects of the present disclosure generally relate to apparatus, systems and methods for radio-frequency (RF) switching circuits, and more particularly for a PIN diode driver circuit for high speed, high repetition rate and/or high power applications. In one example, the drive circuit includes a two-stage drive circuit, and in another example includes a two-stage drive circuit in combination with one or more low voltage reverse bias supplies. In PIN diode driver circuits incorporating one or more low voltage reverse bias supplies, a lower voltage, or voltages, intended to clear charge from the intrinsic region but using relatively little power to do so, is applied first before applying a higher voltage that holds a reverse bias on the PIN diode once the intrinsic region is largely cleared of charge. 
     In some aspects, the techniques described herein relate to a method for driving a PIN diode where the driving includes changing a voltage, V, of a controlled node connected to a PIN diode from a first voltage, V 1 , to a second voltage, V 2 , and from V 2  to V 1 , the method including: changing from V 1  to V 2 , wherein changing from V 1  to V 2  includes: disconnecting the controlled node from a first holding power supply by breaking a first connection, connecting the controlled node to a mid-voltage power supply through a first resonant circuit via a second connection, maintaining the second connection until the first resonant circuit causes the current from the mid-voltage power supply to reverse direction, breaking the second connection as soon as the current reverses direction, and connecting the controlled node to a second holding supply via a third connection after the second connection to the mid-voltage supply has been broken; and changing from V 2  to V 1 , wherein changing from V 2  to V 1  includes: disconnecting the controlled node from the second holding power supply by breaking the third connection, connecting the controlled node to the mid-voltage power supply through a second resonant circuit via a fourth connection, maintaining the fourth connection until the second resonant circuit causes the current from the mid-voltage power supply to reverse direction, breaking the fourth connection as soon as the current reverses direction, and connecting the controlled node to the first holding supply via the first connection after the fourth connection to the mid-voltage power supply has been broken. 
     In some aspects, the techniques described herein relate to a method, wherein the first and second resonant circuits are the same circuit. 
     In some aspects, the techniques described herein relate to a method, wherein the first and second resonant circuits have at least one component that is not common between them. 
     In some aspects, the techniques described herein relate to a method, wherein in the changing from V 1  to V 2  the mid-voltage power supply delivers energy, and in the changing from V 2  to V 1  the mid-voltage power supply recovers energy. 
     In some aspects, the techniques described herein relate to a method, wherein in the changing from V 2  to V 1  the mid-voltage power supply delivers energy, and in the changing from V 1  to V 2  the mid-voltage power supply recovers energy. 
     In some aspects, the techniques described herein relate to a method, wherein energy is recovered to the first or second holding power supply shortly before the current from the mid-voltage power supply reverses direction. 
     In some aspects, the techniques described herein relate to a method, wherein a power converter is connected between an output of the first holding supply and a power sink. 
     In some aspects, the techniques described herein relate to a method, wherein the power sink is an output of the mid-voltage power supply. 
     In some aspects, the techniques described herein relate to a method, wherein a power converter is connected between an output of the second holding supply and a power sink. 
     In some aspects, the techniques described herein relate to a method, wherein the power sink is the output of the mid-voltage power supply. 
     In some aspects, the techniques described herein relate to a method, wherein the controlled node is connected to a PIN diode through a radio frequency (RF) blocking circuit that provides a low impedance to direct current (DC) current and attenuates transmission of RF power through the RF blocking device. 
     In some aspects, the techniques described herein relate to a method, further including, after disconnecting the controlled node from the first holding power supply and before connecting the controlled node to the mid-voltage power supply through the first resonant circuit, connecting one or more low voltage reverse bias supplies to the controlled node in a sequence of increasing voltage when changing from V 1  to V 2 . 
     In some aspects, the techniques described herein relate to a method, wherein each of the low voltage supplies disconnect from the controlled node if current drawn from a respective low-voltage power supply reverses direction. 
     In some aspects, the techniques described herein relate to a method, wherein one of the one or more low voltage reverse bias supplies is at least partially coupled between the first holding supply and the controlled node. 
     In some aspects, the techniques described herein relate to a method, wherein the RF blocking circuit connects the controlled node to a cathode of the PIN diode, the output of the first holding supply is a negative current when the first holding supply is connected to the controlled node and a negative voltage when the first holding supply is not connected to the controlled node. 
     In some aspects, the techniques described herein relate to a method, wherein an output of the mid-voltage power supply is a positive voltage, but less positive than an output of the second holding supply. 
     In some aspects, the techniques described herein relate to a method, wherein the RF blocking circuit connects the controlled node to an anode of the PIN diode, the output of the first holding supply is a positive current when the first holding supply is connected to the controlled node and a positive voltage when the first holding supply is not connected to the controlled node. 
     In some aspects, the techniques described herein relate to a method, wherein an output of the mid-voltage power supply is a negative voltage, but less negative than an output of the second holding supply. 
     In some aspects, the techniques described herein relate to a method, wherein a magnitude of current provided by the first holding supply is increased for a short time after connecting the controlled node to the first holding supply. 
     In some aspects, the techniques described herein relate to a method, wherein the short time is between 1 microsecond and 100 microseconds, and a magnitude of the current is increased to a level between 2 and 100 times a magnitude of the current after the short time has elapsed. 
     In some aspects, the techniques described herein relate to a method for driving a PIN diode, the method including: controllably charging and discharging the PIN diode to place the PIN diode in an OFF state and an ON state, respectively; recovering stored energy when the PIN diode is discharged; and holding a voltage across a series combination of the PIN diode and a RF blocking device with a holding supply when the PIN diode turns to the OFF state, where the RF blocking device primarily passes DC current and primarily attenuates RF power. 
     In some aspects, the techniques described herein relate to a method, further including: increasing forward current through the PIN diode above a baseline forward current for a short time after discharging the PIN diode. 
     In some aspects, the techniques described herein relate to a method, further including charging and discharging the PIN diode with a single mid-voltage power supply. 
     In some aspects, the techniques described herein relate to a method, further including providing one or more low voltage reverse bias supplies for charging the PIN diode from a voltage substantially lower than that of the holding supply. 
     In some aspects, the techniques described herein relate to a method, further including: recovering energy to the holding supply. 
     In some aspects, the techniques described herein relate to a method, further including transferring power from the holding supply to the mid-voltage supply via a power converter. 
     In some aspects, the techniques described herein relate to a method wherein a capacitor is operably coupled with the PIN diode as part of a match network, the PIN diode connecting the capacitor in the match network when discharged and disconnecting the capacitor from the match network when charged, the energy recovered further including energy stored in the capacitor. 
     In some aspects, the techniques described herein relate to an apparatus including: charge-discharge circuitry configured to charge and discharge a PIN diode to place the PIN diode in an OFF state and an ON state, respectively. an energy recovery component configured to recover stored energy when the PIN diode is discharged; and a holding stage incorporating a holding supply configured to hold a voltage across a series combination of the PIN diode and a RF blocking device when the PIN diode is in the OFF state, where the RF blocking device primarily passes DC current and primarily attenuates RF power. 
     In some aspects, the techniques described herein relate to an apparatus, further including: a current booster configured to boost current directly after discharging the PIN diode. 
     In some aspects, the techniques described herein relate to an apparatus, further including a mid-voltage power supply coupled to the charge-discharge circuitry and configured to provide current to the PIN diode through the charge-discharge circuitry and the RF blocking device. 
     In some aspects, the techniques described herein relate to an apparatus, further including: recovering energy to the holding supply. 
     In some aspects, the techniques described herein relate to an apparatus, further including a power converter coupled between the holding supply and the mid-voltage supply to transfer power from the holding supply to the mid-voltage supply using the energy recovered to the holding supply. 
     In some aspects, the techniques described herein relate to an apparatus, further including one or more low voltage reverse bias supplies for charging the PIN diode from a voltage substantially lower than that of the holding supply. 
     In some aspects, the techniques described herein relate to an apparatus, further including a capacitor operably coupled with the PIN diode as part of a match network, the PIN diode connecting the capacitor in the match network when discharged and disconnecting the capacitor from the match network when charged, the energy recovered further including energy stored in the capacitor. 
     In some aspects, the techniques described herein relate to an apparatus, the holding stage further including a second holding supply configured to conduct current through the PIN diode and a RF blocking device when the PIN diode turns to the on state. 
     In some aspects, the techniques described herein relate to a non-transitory, tangible processor-readable storage medium, encoded with processor readable instructions to perform a method for driving a PIN diode, the method including: charging and discharging a PIN diode to place the PIN diode in an OFF state and an ON state, respectively; recovering stored energy when the PIN diode is discharged; and holding a voltage across a series combination of the PIN diode and a RF blocking device when the PIN diode is in the OFF state, where the RF blocking device primarily passes DC current and primarily attenuates RF power. 
     In some aspects, the techniques described herein relate to a non-transitory, tangible processor-readable storage medium, wherein the method further includes boosting current after discharging the PIN diode. 
     In some aspects, the techniques described herein relate to a non-transitory, tangible processor-readable storage medium, wherein the method further includes holding the voltage across the series combination of the PIN diode and the RF blocking device using a higher voltage supply than a one performing the charging and discharging of the PIN diode. 
     In some aspects, the techniques described herein relate to a non-transitory, tangible processor-readable storage medium, wherein the method further includes recovering the stored energy through a holding supply configured to perform the holding the voltage across the series combination of the PIN diode and the RF blocking device. 
     In some aspects, the techniques described herein relate to a non-transitory, tangible processor-readable storage medium, wherein the method further includes, during the ON state of the PIN diode, providing a first current to the PIN diode via a resonant circuit to transition the PIN diode to the OFF state, and then holding the voltage across the PIN diode to maintain a reverse bias voltage on the PIN diode. 
     In some aspects, the techniques described herein relate to a non-transitory, tangible processor-readable storage medium, wherein the method further includes, during the OFF state of the PIN diode, drawing a second current from the PIN diode via the resonant circuit to transition the PIN diode to the ON state, and then holding the second current from the PIN diode to maintain a forward bias on the PIN diode. 
     Other embodiments of the disclosure can be characterized as a variable impedance matching network comprising a variable reactance element comprising a PIN diode coupled with a capacitor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various objects and advantages and a more complete understanding of the present disclosure are apparent and more readily appreciated by referring to the following detailed description and to the appended claims when taken in conjunction with the accompanying drawings: 
         FIG.  1 A  illustrates a conventional dual supply PIN diode driver circuit. 
         FIG.  1 B  illustrates another conventional dual supply PIN diode driver circuit. 
         FIG.  2 A  illustrates a PIN diode equivalent circuit for  FIG.  1 A . 
         FIG.  2 B  illustrates another PIN diode equivalent circuit for  FIG.  1 B   
         FIG.  3    is a block diagram illustrating an example of a two-stage PIN diode driver which may be used in implementing embodiments of the present disclosure. 
         FIG.  4 A  illustrates early charge cycle operation of an example two-stage PIN diode driver circuit. 
         FIG.  4 B  illustrates late charge cycle operation of the example two-stage PIN diode driver circuit. 
         FIG.  4 C  illustrates a hold PIN cycle operation of the example two-stage PIN diode driver circuit. 
         FIG.  4 D  illustrates early discharge cycle operation of the example two-stage PIN diode driver circuit. 
         FIG.  4 E  illustrates late discharge cycle operation of the example two-stage PIN diode driver circuit. 
         FIG.  4 F  illustrates a hold PIN cycle operation of the example two-stage PIN diode driver circuit. 
         FIG.  4 G  illustrates current and voltage waveforms corresponding to an example two-stage PIN diode driver circuit under ideal conditions. 
         FIG.  4 H  illustrates current and voltage waveforms corresponding to an example two-stage PIN diode driver circuit under less-than-ideal conditions. 
         FIG.  5    illustrates another example two-stage PIN diode driver circuit. 
         FIG.  6 A  illustrates first low voltage charge cycle operation of an example two-stage PIN diode driver circuit combining the two-stage circuit with two low-voltage reverse bias power supplies as well as a current boost circuit. 
         FIG.  6 B  illustrates second low voltage charge cycle operation of the example two-stage PIN diode driver circuit combining the two-stage circuit with two low-voltage reverse bias power supplies as well as a current boost circuit. 
         FIG.  6 C  illustrates a current boost cycle operation of the example two-stage PIN diode driver circuit combining the two-stage circuit with two low-voltage reverse bias power supplies as well as a current boost circuit. 
         FIGS.  6 D  illustrates the operation of an example two-stage PIN diode driver circuit combined with two low-voltage reverse bias power supplies as well as a current boost circuit. 
         FIG.  6 E  illustrates another embodiment of operation of the example two-stage PIN diode driver circuit combined with two low-voltage reverse bias power supplies as well as a current boost circuit. 
         FIG.  7    is a method for controlling a two-stage PIN diode driver circuit when changing the PIN diode from a forward biased ON state to a reverse biased OFF state. 
         FIG.  8    is a method for controlling a two-stage PIN diode driver circuit when changing the PIN diode from a reverse biased OFF state to a forward biased ON state. 
         FIG.  9    is a method for controlling a two-stage PIN diode driver circuit combined with one or more low-voltage reverse bias power supplies when changing the PIN diode from a forward biased ON state to a reverse biased OFF state. 
         FIG.  10    is a method for controlling a two-stage PIN diode driver circuit combined with a current boost circuit when changing the PIN diode from a reverse biased OFF state to a forward biased ON state. 
         FIG.  11    is a diagram illustrating an example of a computing system which may be used in implementing embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Prior to describing the embodiments in detail, it is expedient to define terms as used in this document. 
     The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. 
     Preliminary note: the flowcharts and block diagrams in the following Figures illustrate the functionality and operation of possible implementations of a two-stage, or two-stage in combination with a one or more low voltage reverse bias supplies, PIN diode driver according to various embodiments of the present disclosure. It should be noted that, in some alternative implementations, the functions noted in each block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. For instance, the operations of charging the PIN diode, holding a voltage across the PIN diode, and discharging the PIN diode can be reversed (e.g., discharging, holding, and then charging). 
     As noted earlier, a PIN diode is an electrical diode device with an un-doped or lightly doped intrinsic (I) semiconductor region sandwiched between a heavily doped p-type semiconductor region (P) and a heavily doped n-type semiconductor region (N); hence, the “PIN diode” designation. In general, PIN diodes obey conventional diode behavior for low frequency input signals, but operate as a resistor in the forward biased or on-state and as a small capacitor in the reverse biased or off-state for higher frequency input signals. As such, PIN diodes are often utilized in attenuators, fast switches, radio frequency (RF) applications, and high voltage electronic applications where high isolation and low loss are desired. In one particular implementation, PIN diodes are used in an impedance match network configured to match a changing load impedance of a plasma load to a desired impedance (e.g., 50 ohm or 70 ohm) so that a high-power RF generator can efficiently deliver power. In such an implementation, the PIN diodes serve to connect or disconnect reactive components, typically capacitors, of the impedance matching network to quickly alter the properties of the matching network by switching the reactive elements in and out of the network. 
     PIN diodes in a switching circuit typically have an accompanying PIN diode driver circuit or switch driver that provides a controlled forward bias current and a reverse bias voltage. For example,  FIGS.  1 A and  1 B  illustrate two conventional dual supply PIN diode driver circuits,  100 ,  101 . Each circuit includes a respective PIN-type diode  102 ,  104 , which may in turn be connected to some type of RF circuitry, for example. Each PIN diode  102 ,  104  is driven by two power supplies (supplies  110  and  114  for circuit  100 , and supplies  112  and  116  for circuit  101 ) to provide a forward bias current and a reverse bias voltage to the respective PIN diodes. For example, in the circuit  100 , the low voltage forward bias current supply  110  is serially connected to a switch  118  and the high voltage reverse bias voltage supply  114  is also connected to a switch  120 . When the switch  118  is closed (and switch  120  is open), the forward bias current supply  110  provides a forward bias current to the PIN diode  102 . When switch  120  is closed (and switch  118  is opened), the reverse bias voltage supply  114  provides a reverse bias voltage across the PIN diode  102 . Similarly, in circuit  101 , a high voltage reverse bias voltage supply  116  is serially connected to a switch  122  to provide a reverse bias voltage across the PIN diode  104  when switch  122  is closed and a low voltage forward bias current supply  112  provides a forward bias current to the PIN diode  104  when switch  124  is closed. The inductors  106 ,  108  in the circuits  100 ,  101  may be inductors, but are also meant more generally to symbolize any circuits that pass direct-current (DC) at low frequencies, but suppresses the RF frequency applied to the PIN diodes  102 ,  104  by the RF circuitry. Some non-limiting examples of the type of circuits that may be at position  106 ,  108  include an RF choke, a parallel resonant LC tank or tanks, a quarter wavelength (at RF frequency) transmission line, etc. 
     Operation of the PIN diode driver circuit is now described in greater detail, and again refers to circuit  100  as an example. To forward bias the PIN diode  102 , switch  118  is closed and switch  120  is open. The low voltage current supply  110  provides a forward bias current to the PIN diode  102 . When the PIN diode is forward biased, holes from the P region material and electrons from the N region material of the diode  102  are injected into the sandwiched I region material. As the charges in the diode  102  cannot recombine instantaneously, a net charge is stored in the I region that decays exponentially if not continuously replenished with a time constant known as the carrier lifetime. The diode thus acts as a resistor with an effective “on” resistance value at RF frequency. An equivalent forward biased circuit  202  is illustrated in  FIG.  2 A . 
     To reverse-bias the PIN diode  102 , switch  118  is opened and switch  120  is closed to provide a reverse bias voltage to the PIN diode from the high voltage reverse bias voltage supply  114 . During reverse-bias operation, the PIN diode  102  has an equivalent circuit ( 204  of  FIG.  2 B ) of a large resistor shunted by a small capacitance. By varying aspects of the PIN diode  102 , a variety of forward-bias resistance and reverse-bias capacitance may be achieved for specific application in various contexts. 
     The potential performance issue with conventional PIN diode driver circuits  100 ,  101  is that such PIN diode drivers may consume large amounts of power when used in high speed, high repetition rate and/or high-power applications. For purposes of illustration, when a PIN diode  102  is used in a high-power application with frequencies ranging from 3 to 30 MHz, the PIN diode  102  may be forward biased with 1 amp from the forward bias current supply  110  and reverse biased with 1500 V from the reverse bias voltage supply  114 . The carrier lifetime for a typical diode in such an application may be about 12 μs. To quickly (e.g., in a time period shorter than the carrier lifetime) switch from the forward biased (on) state to the reverse biased (off) state, the charge to be removed from the diode  102  tends to be the product of the forward current and carrier lifetime. In the example referenced immediately above, a charge of 12 μC is to be removed to switch from the forward biased to reverse biased state. If this charge is removed by the high voltage power supply  114 , the energy expended is the product of the power supply voltage and the charge, i.e., 1500 V×12 μC=18 mJ. If this operation is performed at a high repetition rate, the power required can be prohibitive for many types of applications. For example, if the operation of the PIN diode  102  is to be performed at a 10 kHz repetition rate, the power from the high voltage power supply  114  in this example is 18 mJ×10 kHz=180 W. 
     To reduce the power expended in removing charge from the I region, reactive circuit elements can be used to either reduce expended energy or recover stored energy. For instance, the inductors  106  and  108  in combination with how the switches  118  and  120  or  122  and  124  are operated can be used to reduce expended energy or recover stored energy. However, reactive circuit elements create a dangerous situation where the PIN diode snaps off when the charge is being extracted from the I region. This sudden turn-off or sudden reduction of the current through the PIN diode creates a high voltage across the PIN diode if driven through an inductor (e.g.,  106  and  108 ) as is typical for energy recovery, and this can lead to PIN diode failure. 
     One solution to this high-power consumption and rapid turn-off and overvoltage of the PIN diode is implementation of a two-stage (or dual-stage) driver circuit comprising a resonant stage for energy recovery followed by a holding stage. Such a two-stage driver circuit simultaneously achieves: 1) fast switching; 2) energy recovery; and 3) avoidance of a dangerous voltage spike when the diode snaps off. Using a first (resonant) stage followed by a second (holding) stage provides the ability to drive PIN diodes at high speed without requiring excessive power because energy is recovered in the system. The holding stage serves both to limit the voltage when the diode snaps off, and to hold the high reverse voltage and supply the current in the ON state. In the process of limiting the voltage, energy is recovered to a high voltage supply, in the holding stage, that is connected to the hold circuitry. Since the recovered energy generally exceeds the energy input to the system via the high-voltage supply, the excess recovered energy can be passed back to the resonant stage, optionally via a power converter. This excess recovered energy can also be passed to other sources besides the resonant stage or dissipated as heat (though this is typically not desired). 
     The two-stage drivers disclosed herein may enable high-speed solid-state matches (SSMs) in which matching to different states in a multi-level (multi-state) system is possible (instead of matching either the highest power state or matching to some average impedance presented to the generator). Other possible applications of high-speed PIN diodes switches (enabled by two-stage drivers) may comprise switching signal paths, selecting between different adjustable matches, etc. 
     Referring to  FIG.  3   , shown is a block diagram depicting an example of a two-stage driver presented in terms of functional components. As shown, the exemplary two-stage driver  300  comprises a resonant stage  302  and a holding stage  304  coupled to an optional RF blocking device  306 , which in turn, is coupled to a PIN diode  308  coupled to a target circuit  310 , such as the rest of an impedance match network comprising at least one capacitor, and wherein switching of the PIN diode  308  switches the capacitor in and out of the impedance matching network. The resonant stage  302  comprises a mid-voltage supply  312  as well as charge-discharge circuitry  314  comprising switches  316  and energy storage elements  318 . In most cases only a single mid-voltage supply is used, but it is possible to use more than one mid-voltage supply. One may for example use a mid-voltage supply of 100 V to swing the cathode of PIN diode  308  between roughly −0.7 V and roughly 200 V and use a mid-voltage supply of 850 V to swing the cathode of PIN diode  308  between 200 V and 1500 V. It is the action of the resonant energy storage elements  318  that allows voltage swings of roughly double the voltage of the mid-voltage supplies. The holding stage  304  comprises a high-voltage supply or supplies  320 , a low voltage or current supply or supplies  324  and hold and current boost circuitry  322 . Some of the additional supplies making up the high voltage supply or supplies  320  may be much lower in voltage than the high voltage holding supply (e.g., 10 V or 50 V compared to 1500 V), but they are lumped in with the high-voltage supply because of how they may be used as illustrated in  FIG.  6 A- 6 E . An optional power converter  326  may be coupled between the high-voltage supply  320  and the mid-voltage supply  312  to move energy recovered by the holding stage  304  to the mid-voltage supply  312 . The grouping of the circuitry comprising the two-stage driver  300  is to assist in explaining the operation of the circuitry and may not reflect the physical arrangement of the various circuit components. For example, multiple two-stage drivers may be connected to a single mid-voltage supply, a single high-voltage supply, and share the low-voltage supplies (optionally current supplies) and a single optional power converter may be connected between the shared high-voltage and shared mid-voltage supplies. Alternatively, a variable output supply could replace multiple low-voltage supplies in the holding stage  304 . 
     In this embodiment, the rest of the circuit  310  in which the PIN diode  308  is used (RF circuitry) and an optional RF blocking device  306  depict aspects that may be implemented in connection with a solid-state match. Although other applications of the two-stage drivers are certainly contemplated, for purposes of providing a complete example, the present disclosure describes embodiments in the context of solid-state matches. Other applications of the two-stage driver include situations where a capacitor needs to be repeatedly charged and discharged such as driving the gate of a MOSFET. 
     In the present embodiment, the mid-voltage supply  312  applies power to enable the charge-discharge circuitry  314  to charge and discharge the PIN diode  308  (as well as any capacitive elements connected to the PIN diode  308 ) and thus cause the voltage across the PIN diode  308  to swing. By charging and discharging from the same voltage provided by the mid-voltage supply  312 , energy supplied when charging is recovered when discharging. This energy recovery is a consequence of the fact that the energy supplied when charging is equal to the charge supplied by the mid-voltage supply  312  multiplied by the voltage of the mid-voltage supply  312  and when discharging the energy recovered is the charge recovered to the mid-voltage supply  312  multiplied by the voltage of the mid-voltage power supply. A charging voltage swing of more than double the voltage of the mid-voltage supply  312  may be achieved because of the time it takes for the PIN diode  308  to recover in which time additional energy is stored in the energy storage element(s)  318  (e.g., a resonant inductor such as L 1  in  FIG.  4   ). Depending on the design of the circuit  300 , not all of the energy stored in the energy storage element(s) may be used to swing the voltage and the additional energy may be recovered to the high-voltage supply  320 . 
     For example, and using the details shown in the embodiment of  FIG.  4   , which is one non-limiting implementation of the circuit in  FIG.  3   , during the charge cycle (toward reverse biasing of the PIN diode  408 ) of the circuit of  FIG.  4   , the cathode voltage of the PIN diode  408  is swung from roughly −0.7 V to roughly 1500 V. All voltages mentioned here are with respect to the node labeled REF in  FIG.  4   . Towards the end of the charge cycle the diode DS 3  in the circuit of  FIG.  4    will generally conduct and current will flow into the high voltage supply labeled Vhigh of the holding stage  404  in  FIG.  4    resulting in energy being recovered to the high voltage supply. For this reason, the high voltage supply Vhigh can also be referred to as an energy recovery component. Once the PIN diode  408  cathode voltage is at 1500 V, or current stops flowing through the mid-voltage supply (Vmid) even if the PIN diode  408  cathode voltage is not at 1500 V, the switch S 3  (that is part of the holding stage  404 ) may be closed to hold the PIN diode cathode voltage at 1500 V, i.e., hold the PIN diode  408  of  FIG.  4    in the OFF state. Depending on the properties of the PIN diode  408  and the design of the driver, the cathode voltage of PIN diode  408  may not swing to 1500 V and no energy will be recovered to the high voltage supply. The case where energy is recovered to the high voltage holding supply is illustrated in  FIG.  4 G  and the case where energy is not recovered to the high voltage supply is illustrated in  FIG.  4 H . 
     A discharging voltage swing of roughly double the difference in voltage between the high voltage supply and the mid-voltage supply is achieved during the discharge cycle (toward forward biasing). Since the voltage of the mid-voltage supply is generally less than half of the voltage of the high-voltage supply, this swing is generally sufficient to swing the cathode of the PIN diode  408  in the circuit of  FIG.  4    from roughly 1500 V to roughly −0.7 V. During the discharge cycle some of the energy used in the charging cycle is recovered into the mid-voltage supply. Depending on the properties of the PIN diode and the design of the driver, the cathode voltage of PIN diode  408  may not swing to −0.7 V. The case where the cathode of PIN diode  408  swings below −0.7 V is illustrated in  FIG.  4 G  and the case where the cathode of PIN diode  408  does not swing below −0.7 V is illustrated in  FIG.  4 H . 
     A small (often negligible) amount of energy may be recovered to one of the low voltage supplies in the holding stage towards the end of the discharge cycle. Once the discharge voltage swing is complete and the diode cathode voltage is at roughly a minimum forward bias voltage (e.g., −0.7 V), or current stops flowing through the mid-voltage supply even if the PIN diode  408  cathode voltage is not at a minimum forward bias voltage, switch S 4  of  FIG.  4    that is part of the holding stage may close to supply the PIN diode with forward current. More specifically, a forward bias current and a reverse bias voltage is provided to the PIN diode via closing of switch S 4 . 
       FIG.  4 A  through  FIG.  4 F  break the operation of the two-stage PIN diode driver into cycles. The PIN diode  408  may stay an indeterminate amount of time in either the ON state labeled the “Hold PIN diode on cycle” in  FIG.  4 F  or the OFF state labeled “Hold PIN diode off cycle” in  FIG.  4 C . To change the PIN diode from the ON to the OFF state, the cycles shown in  FIG.  4 A through  4 C  are executed. As shown in  FIG.  4 A , the process to change the PIN diode from the ON state to the OFF state (i.e., changing a voltage V at a controlled node  412  from V 1  to V 2 ) starts by opening S 4  in  FIG.  4 A  to disconnect the controlled node  412  from the forward bias current supply Vcur. After S 4  is open, S 1  is closed to connect the mid-voltage supply Vmid to the controlled node  412  through a resonant circuit  414  consisting of L 1  and C 1  in  FIG.  4 A . In some instances (not shown), C 1  (part of the resonant circuit) may be on the PIN diode  408  side of the RF blocking device  406 . The resonant circuit  414  causes current through the mid-voltage supply to increase from zero to a maximum value and back down to zero. If not for the diode D 1 , current through the mid-voltage supply may decrease below zero, but this is prevented by diode D 1 . The direction of current flow during this early charge cycle is indicated by  401  on  FIG.  4 A  and also shown as the rising electrical potential and current at  422  in  FIG.  4 G and  4 H . 
     As shown in  FIG.  4 B , after some time the voltage of the controlled node  412  may rise to a level where DS 3  in  FIG.  4 B  conducts limiting the voltage of the controlled node  412  to no higher than a diode voltage drop above the voltage of the high voltage holding supply Vhigh in  FIG.  4 B . Current flow during this late charge cycle is labeled  403  in  FIG.  4 B  and can also be seen in cycle  424  in  FIG.  4 G . Current flowing in the direction indicated by  403  results in energy being supplied to the high voltage holding supply Vhigh in  FIG.  4 B . For this reason, the high voltage supply Vhigh can also be referred to as an energy recovery component. Depending on the properties of the PIN diode  408  and design of the driver circuit the late charge cycle may or may not exist (note that cycle  424  does not exist in  FIG.  4 H ). The voltage and current waveforms in the case where a late charge cycle  424  exists are shown in  FIG.  4 G . The case where a late charge cycle does not exist is shown in  FIG.  4 H . The duration of the early charge cycle together with the late charge cycle (if it exists) as depicted in  FIGS.  4 A,  4 B and  4 G or  4 H  depends on the properties of the PIN diode as well as the design of the driver but is typically on the order of a few microseconds, e.g., 2 microseconds. 
     After current stops flowing through the mid-voltage supply (first due to D 1  blocking the flow of reverse current through the mid-voltage supply Vmid) switch S 1  is opened as shown in  FIG.  4 C . After switch S 1  is opened, switch S 3  is closed to hold the controlled node  412  at the voltage of the high voltage holding supply Vhigh in  FIG.  4 C  (see cycle  426  in  FIGS.  4 G and  4 H ). The direction of the initial current flow when S 3  is closed is labeled  405 . This current is significant for a short time period after S 3  is closed. The PIN diode  408  is in the OFF (reverse biased) state and this cycle is labeled the hold PIN diode off cycle on  FIG.  4 C  and the PIN diode  408  can stay in this state for an indeterminate amount of time. 
     To change the PIN diode  408  from the OFF to the ON state, the cycles shown in  FIG.  4 D through  4 F  are executed (i.e., changing the voltage V at the controlled node  412  from V 2  to V 1 ). As shown in  FIG.  4 D , the process to change the PIN diode  408  from the OFF state to the ON state starts by opening switch S 3  in  FIG.  4 D  to disconnect the controlled node  412  from the high voltage holding supply Vhigh. After switch S 3  is open, switch S 2  is closed to connect the mid-voltage supply Vmid to the controlled node  412  though the resonant circuit (L 1  and C 1  in  FIG.  4 D ). The direction of current flow after closure of S 2  is labeled  407 . Note that this direction of current flow means that energy is recovered to the mid-voltage power supply Vmid in  FIG.  4 D , and also shown as the falling electrical potential and current at  428  in  FIGS.  4 G and  4 H . The recovered energy is from energy stored in the capacitors of the resonant circuit (C 1  in  FIG.  4 D ) as well as in the PIN diode  408  as well as in capacitors that may be connected to the PIN diode  408  e.g., the capacitor labeled C 2  in  FIG.  4 D . 
     Due to the resonant circuit  414  the voltage of the controlled node  412  may drop below the voltage of the current power supply Vcur causing current to flow through the diode DS 4 . This late discharge cycle depicted in  FIG.  4 E  may or may not exist depending on the properties of the PIN diode and the design of the driver circuit. In the case where the late discharge cycle exists, the voltage and current waveforms are shown in  FIG.  4 G . In the case where the late discharge cycle does not exist, the voltage and current waveforms are shown in  FIG.  4 H . The combined duration of the early and late discharge cycles depends on the properties of the PIN diode and the design of the driver, but is generally on the order of a few microseconds, e.g., 2 microseconds. The current through the mid-voltage supply will first increase in the direction shown  409  to a maximum value before it will start decreasing again. If not for diode D 2  the current through the mid-voltage supply may reverse direction, but this is prevented by diode D 2 . 
     After current stops flowing through the mid-voltage supply (first due to D 2  blocking the flow of reverse current) switch S 2  is opened as shown in  FIG.  4 F . After switch S 2  is opened, switch S 4  is closed to connect the controlled node  412  to the current supply (Vcur in  FIG.  4 F , the second holding power supply). The current supply Vcur supplies current through the PIN diode  408  to keep the PIN diode  408  in the ON state. The PIN diode  408  is now in the ON (forward biased) state, and this cycle is labeled the hold PIN diode  408  on cycle on  FIG.  4 F  and the PIN diode  408  can stay in this state for an indeterminate amount of time. 
       FIG.  5    shows a two-stage PIN diode driver connected to a PIN diode  508 . In this example circuit the cathode of the PIN diode  508  is connected to the reference node labeled REF in  FIG.  5    and the controlled node  512  is connected to the anode of the PIN diode  508 . The operation of this circuit can be obtained from the operation of the circuit of  FIG.  4    by reversing all diodes, reversing the polarities of all voltages and reversing the direction of the currents compared to that of  FIG.  4   , otherwise the operation is identical. 
       FIG.  6 A  shows a two-stage PIN diode driver further incorporating two low-voltage reverse bias power supplies as well as current boost circuitry. The addition of the two low-level reverse bias power supplies further reduces energy consumption of the two-stage PIN diode driver. The addition of current boost circuitry (e.g., Vbst, S 7 , and DS 7 ) improves RF switching performance by increasing the current above nominal levels for a short period of time when transitioning the PIN diode  608  to the ON state to more quickly increase electron and hole concentrations in the intrinsic region of the PIN diode  608  in order to reduce diode ON state resistance and thus RF losses, if RF is applied through the RF circuitry  610 , more quickly. 
     Referring back to  FIG.  4 G and  4 H , notice that in the early charge cycle  422 , there is simultaneously voltage across  440  ( FIG.  4 G ) or  441  ( FIG.  4 H ) and current through the PIN diode  432  ( FIG.  4 G ) or  433  ( FIG.  4 H ). Certainly, in the early part of the early charge cycle  422  (and depending on the PIN diode properties more likely during the entire early charge cycle) the power represented by the product of this voltage and current is wasted power because the current is conduction current and not displacement current, i.e., energy is not stored in the PIN diode, but wasted as heat. By first charging the PIN diode from a lower voltage, charge can be cleared from the intrinsic region using less energy. More than one low voltage may be used to optimize energy loss and total switching time. As such, though  FIGS.  6 A- 6 E  show two low voltage discharge supplies, one or more such low voltage supplies can be implemented, with each of two or more of these being of increasing voltage and sequentially switched into connection with the controlled node 
       FIG.  6 A  shows a first low voltage charge cycle that is inserted between the hold PIN diode on cycle  420  in  FIG.  4 G and  4 H  and the early charge cycle  422  in  FIG.  4 G and  4 H . As shown in  FIG.  6 A , after disconnecting the controlled node  612  from the current supply Vcur and before closing switch S 1  to start the early charge cycle, the controlled node  612  is first connected to a first low voltage reverse bias power supply Vdisch by closing S 5  in  FIG.  6 A  (see also cycle  628  in  FIG.  6 D ). After some time as shown in  FIG.  6 B , the controlled node  612  may be connected to a second low voltage reverse bias power supply Vdisch 2  (see also cycle  630  in  FIG.  6 D ). After some time removing charge from the PIN diode  608  using the second low voltage reverse bias power supply, switch S 1  in  FIG.  6 B  is closed to start the early charge cycle  622  in  FIG.  6 D . The resulting waveforms are shown in  FIG.  6 D . The total time to transition the PIN diode  608  from ON to OFF state (end of hold PIN diode on cycle  620  to start of hold PIN diode off cycle  626  in  FIG.  6 D ) depends on the properties of the PIN diode and design of the driver but is generally on the order of a few microseconds, e.g., 5 microseconds. 
       FIG.  6 C  shows the use of a current boost power supply Vbst in  FIG.  6 C  together with other circuitry (including S 7  and D 4 ) to temporarily boost PIN diode forward current  607  when the PIN diode is first turned ON. As shown in  FIG.  6 E , after completion of the early and late (if it exists) discharge cycles  622 , and  624 , both switches S 4  and S 7  in  FIG.  6 C  are closed to increase, or boost, forward current through the PIN diode for a short period of time. This increased forward current increases the concentration of electrons and holes in the PIN diode  608  intrinsic region more quickly thus reducing ON-resistance of the diode  608  more quickly and thus reducing losses due to RF current flowing through the PIN diode  608  as a result of the RF circuitry  610 . After some time switch S 7  in  FIG.  6 C  is opened allowing the PIN diode  608  forward current to return to normal levels. This current boost can increase the PIN diode  608  forward current by a factor 2 to 100 and for a duration of 1 to 100 microsecond, depending on how the design is optimized for loss and power consumption. Although only two low voltage reverse bias power supplies Vdisch are shown in  FIG.  6 A- 6 E , those of skill in the art will appreciate that one or more than two can also be implemented without undue experimentation. 
       FIG.  7    shows a method  700  for controlling a two-stage PIN diode driver circuit when changing the PIN diode from a forward biased ON state to a reverse biased OFF state. The method starts with the diode in the forward biased ON state. First the PIN diode is disconnected from a forward bias current supply (operation  702 ). For instance, this could involve opening of S 4  as seen when going from  FIG.  4 H to  4 A . Next the PIN diode is connected to a mid-voltage reverse bias power supply through a resonant network (operation  704 ). One implementation of this operation is seen with the closing of S 1  in  FIG.  4 A . This connection to the mid-voltage reverse bias power supply through a resonant circuit causes the current drawn from the mid-voltage reverse bias power supply to increase to a maximum value before decreasing again. If this connection is maintained, the current through the mid-voltage reverse bias power supply will change direction, but this is prevented by disconnecting the PIN diode from the mid-voltage reverse bias power supply as soon as the current reverses direction (operation  706 ). Operation  706  can be enabled by placing a diode (e.g., diode D 1  in  FIG.  4 A ) in series with the switch (e.g., switch S 1  in  FIG.  4 A ) connecting the PIN diode to the mid-voltage reverse bias power supply through a resonant network. For instance, S 1  can be opened as seen in  FIG.  4 C . Finally, the PIN diode is connected to a high-voltage reverse bias power supply (operation  708 ) to hold the PIN diode in the reverse biased (OFF) state, such as seen with the closing of S 3  in  FIG.  4 C . 
       FIG.  8    shows a method  800  for controlling a two-stage PIN diode driver circuit when changing the PIN diode from a reverse biased OFF state to a forward biased ON state. The method starts with the diode in the reverse biased OFF state. First the PIN diode is disconnected from the high voltage reverse bias power supply (operation  802 ) (e.g., opening of S 3  in  FIG.  4 D ). Next the PIN diode is connected to a mid-voltage reverse bias power supply through a resonant network (operation  804 ) (e.g., closing of S 2  in  FIG.  4 D ). This connection to the mid-voltage reverse bias power supply through a resonant circuit causes the current drawn from the mid-voltage reverse bias power supply to increase to a maximum value before decreasing again. If this connection is maintained, the current through the mid-voltage reverse bias power supply will change direction, but this is prevented by disconnecting the PIN diode from the mid-voltage reverse bias power supply as soon as the current reverses direction (operation  806 ). Operation  806  can be enabled by placing a diode (e.g., diode D 2  in  FIG.  4 A ) in series with the switch (e.g., switch S 2  in  FIG.  4 A ) and connecting the PIN diode to the mid-voltage reverse bias power supply through a resonant network. Finally, the PIN diode is connected to forward bias current supply (operation  808 ) to hold the PIN diode in the forward biased (ON) state (e.g., closing of S 4  in  FIG.  4 F ). 
       FIG.  9    shows a method  900  for controlling a two-stage PIN diode driver circuit combined with one or more low-voltage reverse bias power supplies when changing the PIN diode from a forward biased ON state to a reverse biased OFF state. The method starts with the diode in the forward biased ON state. First the PIN diode is disconnected from the forward bias current supply (operation  902 ) (e.g., opening S 1  in  FIG.  6 A ). Next the PIN diode is connected to one or more low voltage reverse bias power supplies (operation  904 ) (e.g., closing S 5   FIG.  6 A  and then closing S 5  and opening S 6  in  FIG.  6 B ). By first removing charge from the intrinsic region of the PIN diode with a low voltage reverse bias power supply the energy expended in reverse biasing the PIN diode can be further reduced. If there is more than one low voltage reverse bias power supply, then these supplies can be connected to the controlled node  612  in an increasing sequence of reverse bias voltage (e.g., S 5  before S 6  in  FIG.  6 B ). The circuit is designed such that each of the low voltage reverse bias power supplies disconnects from the PIN diode if the PIN diode voltage reverse bias is higher than the voltage of the low voltage reverse bias power supply, or equivalently if the current through the low voltage reverse bias power supply reverses direction. This can be accomplished in some embodiments by diodes (e.g., diodes D 5  and D 6  in  FIG.  6 A ). In other words,  FIG.  9    is similar to  FIG.  8    but with operation  904  inserted between  802  and  804 . Next the PIN diode is connected to a mid-voltage reverse bias power supply through a resonant network (operation  906 ) (e.g., closing of Si). This connection to the mid-voltage reverse bias power supply through a resonant circuit causes the current drawn from the mid-voltage reverse bias power supply to increase to a maximum value before decreasing again. If this connection is maintained, the current through the mid-voltage reverse bias power supply will change direction, but this is prevented by disconnecting the PIN diode from the mid-voltage reverse bias power supply as soon as the current reverses direction (operation  908 ). Operation  908  can be enabled by placing a diode (e.g., diode D 1  in  FIG.  6 A ) in series with the switch (e.g., switch S 1  in  FIG.  6 A ) connecting the PIN diode to the mid-voltage reverse bias power supply through a resonant network. Finally, the PIN diode is connected to a high-voltage reverse bias power supply (operation  910 ) to hold the PIN diode in the reverse biased (OFF) state (e.g., closing S 3 ). 
       FIG.  10    shows a method  1000  for controlling a two-stage PIN diode driver circuit combined with a current boost circuit when changing the PIN diode from a reverse biased OFF state to a forward biased ON state. The method starts with the diode in the reverse biased OFF state. First the PIN diode is disconnected from the high voltage reverse bias power supply (operation  1002 ). Next the PIN diode is connected to a mid-voltage reverse bias power supply through a resonant network (operation  1004 ). This connection to the mid-voltage reverse bias power supply through a resonant circuit causes the current drawn from the mid-voltage reverse bias power supply to increase to a maximum value before decreasing again. If this connection is maintained, the current through the mid-voltage reverse bias power supply will change direction, but this is prevented by disconnecting the PIN diode from the mid-voltage reverse bias power supply as soon as the current reverses direction (operation  1006 ). Operation  1006  can be enabled by placing a diode (e.g., diode D 2  in  FIG.  6 A ) in series with the switch (e.g. switch S 2  in  FIG.  6 A ) connecting the PIN diode to the mid-voltage reverse bias power supply through a resonant network. Next the PIN diode is connected to a high current forward current supply (operation  1008 ). The high current forward current power supply can supply a current that is 2 to 100 times higher than the nominal forward current and the duration of the higher than nominal current can be from 1 to 100 microseconds. Both the magnitude of the current and the duration of the higher than nominal current depend on how the circuit is optimized for performance and power consumption. Finally, the PIN diode is disconnected from the high current forward bias current supply and connected to the forward bias current supply (operation  1010 ) to hold the PIN diode in the forward biased (ON) state. 
     The description of the resonant-charge discharge circuitry together with the holding circuitry described above in terms of driving a PIN diode can be generalized as the problem of repeatedly driving a node in a circuit between two voltages (e.g., V 1  and V 2  or V 2  and V 1 ). Especially if the load is capacitive, the methods described here are advantageous because they provide methods for doing so without having to dissipate the energy stored in the capacitive load during the discharge cycle and they provide protection against overshoot and undershoot of the voltage. In general terms then a method can be described as changing a voltage, V, of a controlled node ( 412  in  FIG.  4  or  612    in  FIG.  6   ) from a first voltage, V 1 , to a second voltage, V 2 , and from V 2  to V 1 ; the method to change from V 1  to V 2  comprising: disconnecting the controlled node from a first holding power supply (opening switch S 4  in  FIG.  4 A ), connecting (closing S 1  in  FIG.  4 A ) the controlled node to a mid-voltage power supply through a resonant circuit (L 1  and C 1  in  FIG.  4    also taking into account the PIN diode  408  and RF blocking device  406 ), maintaining this connection until the current from the mid-voltage power supply reverses direction because of the resonant circuit, breaking this connection as soon as the current reverses direction (D 1  blocking reverse current flow followed by opening S 1  in  FIG.  4 C ), and connecting (closing S 3  in  FIG.  4 C ) the controlled node to a second holding supply (V high  in  FIG.  4 C ) after the connection to the mid-voltage supply has been broken; and the method to change from V 3  to V 1  comprising: disconnecting the controlled node from the second holding power supply (opening switch S 3  in  FIG.  4 D ), connecting (closing switch S 2  in  FIG.  4 D ) the controlled node to the mid-voltage supply through a resonant circuit, maintaining this connection until the current from the mid-voltage power supply reverses direction because of the resonant circuit, breaking this connection as soon as the current reverses direction (D 2  blocking reverse current flow followed by opening S 2  in  FIG.  4 F ), and connecting the controlled node to the first holding supply (closing S 4  in  FIG.  4 F ) after the connection to the mid-voltage supply has been broken. 
     In the context of this disclosure, charging of a PIN diode means increasing the cathode to anode voltage of the PIN diode, generally from around −0.7 V to some high voltage such as 1500 V, but it can also be a smaller positive voltage such as 20 V. Similarly, in the context of this disclosure, discharging of the PIN diode means decreasing the cathode to anode voltage, generally from some high voltage to around −0.7 V. Because this driver can also be used to drive capacitive loads that do not involve PIN diodes, in general charging means that energy is provided by the driver and discharging means that energy can be recovered by the driver. In some cases, the charge and discharge cycles are indistinguishable, and any one of the two cycles can be considered the charging and the other the discharging cycle. This happens when for example a capacitor is charged from −5 V to 5 V and back with a mid-voltage supply at 0 V (replaced by a ground connection), the high-voltage supply is 5 V and the low voltage supply is −5 V. 
     In alternative embodiments, two power supplies may be used to charge and discharge the PIN diode as disclosed in U.S. Pat. No. 10,742,212, which is incorporated herein by reference as an example of how two voltage supplies may provide a forward bias current to the PIN diode and the reverse bias voltage across the PIN diode. 
     In the context of a solid-state match, the RF blocking device may include inductors in series between the charge-discharge circuitry and the PIN diode, but more generally the RF blocking device may be any circuit that primarily passes direct-current (DC) at low frequencies between the charge-discharge circuitry and the PIN diode while primarily attenuating RF frequencies applied to the PIN diode by the RF circuitry. Examples of the types of circuits that may be used to implement the RF blocking device include an RF choke, a parallel resonant LC tank or tanks, a quarter wavelength (at the applied RF frequency) transmission line, etc. 
     As discussed above, under forward bias conditions the PIN diode stores charge in the intrinsic region. To quickly remove this charge and enable energy recovery, the first stage comprises resonant circuitry. Applicant found that this creates a dangerous situation where the PIN diode snaps off when the charge is extracted from the PIN diode, and this sudden turn-off of the current through the PIN diode creates high voltages across the PIN diode when driven through the inductor of the energy recovery component, which can lead to PIN diode failure. As compared to known systems, the holding stage, in general, prevents this dangerous voltage spike from occurring when the diode snaps off. More specifically, the holding stage functions to both to limit the voltage when the PIN diode turns off (and recovers energy in the process under some conditions) and holds the high reverse voltage and supplies the current in the ON state. Another aspect of the depicted embodiment is the current booster, which adds a current boost at turn-on to quickly re-establish carriers in the intrinsic region and to limit RF losses at turn-on. 
     In terms of applications, when the two-stage driver is implemented in connection with a solid-state match, multiple PIN diodes may be switched within the time window of a pulse (a power state) of an RF generator. More specifically, it is contemplated that a solid-state match may tune to states down to 50 microseconds in duration by enabling the PIN diodes to switch between the OFF and ON states in 10 microseconds or less. 
     The methods described in connection with the embodiments disclosed herein may be embodied directly in hardware, in processor-executable code encoded in a non-transitory tangible processor readable storage medium, or in a combination of the two. Referring to  FIG.  11    for example, shown is a block diagram depicting physical components that may be utilized to realize control of the first and second stages of  FIGS.  3 ,  4 , and  6    according to an exemplary embodiment. As shown, in this embodiment a display portion  1112  and nonvolatile memory  1120  are coupled to a bus  1122  that is also coupled to random access memory (“RAM”)  1124 , a processing portion (which includes N processing components)  1126 , an optional field programmable gate array (FPGA)  1127 , and a transceiver component  1128  that includes N transceivers. Although the components depicted in  FIG.  11    represent physical components,  FIG.  11    is not intended to be a detailed hardware diagram; thus many of the components depicted in  FIG.  11    may be realized by common constructs or distributed among additional physical components. Moreover, it is contemplated that other existing and yet-to-be developed physical components and architectures may be utilized to implement the functional components described with reference to  FIG.  11   . 
     This display portion  1112  generally operates to provide a user interface for a user, and in several implementations, the display is realized by a touchscreen display. In general, the nonvolatile memory  1120  is non-transitory memory that functions to store (e.g., persistently store) data and processor-executable code (including executable code that is associated with effectuating the methods described herein). In some embodiments for example, the nonvolatile memory  1120  includes bootloader code, operating system code, file system code, and non-transitory processor-executable code to facilitate the execution of methods described with reference to  FIGS.  7 - 10    described further herein. 
     In many implementations, the nonvolatile memory  1120  is realized by flash memory (e.g., NAND or ONENAND memory), but it is contemplated that other memory types may be utilized as well. Although it may be possible to execute the code from the nonvolatile memory  1120 , the executable code in the nonvolatile memory is typically loaded into RAM  1124  and executed by one or more of the N processing components in the processing portion  1126 . 
     The N processing components in connection with RAM  1124  generally operate to execute the instructions stored in nonvolatile memory  1120  to enable Methods to switch a PIN diode, for instance, coupling a PIN diode in and out of a match network. For example, non-transitory, processor-executable code to effectuate the methods described with reference to  FIG.  7 - 10    may be persistently stored in nonvolatile memory  1120  and executed by the N processing components in connection with RAM  1124 . As one of ordinarily skill in the art will appreciate, the processing portion  1126  may include a video processor, digital signal processor (DSP), micro-controller, graphics processing unit (GPU), or other hardware processing components or combinations of hardware and software processing components (e.g., an FPGA or an FPGA including digital logic processing portions). 
     In addition, or in the alternative, the processing portion  1126  may be configured to effectuate one or more aspects of the methodologies described herein (e.g., the methods described with reference to  FIGS.  7 - 10   ). For example, non-transitory processor-readable instructions may be stored in the nonvolatile memory  1120  or in RAM  1124  and when executed on the processing portion  1126 , cause the processing portion  1126  to perform methods to control switching of PIN diode. Alternatively, non-transitory FPGA-configuration-instructions may be persistently stored in nonvolatile memory  1120  and accessed by the processing portion  1126  (e.g., during boot up) to configure the hardware-configurable portions of the processing portion  1126  to effectuate the functions of the first and second stages. 
     The depicted transceiver component  1128  includes N transceiver chains, which may be used for communicating with external devices via wireless or wireline networks. Each of the N transceiver chains may represent a transceiver associated with a particular communication scheme (e.g., WiFi, Ethernet, Profibus, etc.). 
     Some portions are presented in terms of algorithms or symbolic representations of operations on data bits or binary digital signals stored within a computing system memory, such as a computer memory. These algorithmic descriptions or representations are examples of techniques used by those of ordinary skill in the data processing arts to convey the substance of their work to others skilled in the art. An algorithm is a self-consistent sequence of operations or similar processing leading to a desired result. In this context, operations or processing involves physical manipulation of physical quantities. Typically, although not necessarily, such quantities may take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared or otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to such signals as bits, data, values, elements, symbols, characters, terms, numbers, numerals or the like. It should be understood, however, that all of these and similar terms are to be associated with appropriate physical quantities and are merely convenient labels. Unless specifically stated otherwise, it is appreciated that throughout this specification discussions utilizing terms such as “processing,” “computing,” “calculating,” “determining,” and “identifying” or the like refer to actions or processes of a computing device, such as one or more computers or a similar electronic computing device or devices, that manipulate or transform data represented as physical electronic or magnetic quantities within memories, registers, or other information storage devices, transmission devices, or display devices of the computing platform. 
     As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. 
     As used herein, the recitation of “at least one of A, B and C” is intended to mean “either A, B, C or any combination of A, B and C.” The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. 
     It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present disclosure. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “under,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” or “under” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary terms “below” and “under” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, and/or groups but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items, and may be abbreviated as “/”. 
     It will be understood that when an element or layer is referred to as being “on,” “connected to,” “coupled to,” or “adjacent to” another element or layer, it can be directly on, connected, coupled, or adjacent to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” “directly coupled to,” or “immediately adjacent to” another element or layer, there are no intervening elements or layers present. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and/or the present specification and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.