Abstract:
In some embodiments, a microwave switch element may include one or more of the following features: (a) an electrically isolated input capable of receiving an input, (b) an amplifier electrically coupled to the input and to an active device, (c) a power source magnetically coupled to the amplifier.

Description:
FIELD OF THE INVENTION 
     Embodiments of the present invention relate to amplifiers. Particularly, embodiments of the present invention relate to switching elements. More particularly, embodiments of the present invention relate to microwave switching elements that are electrically isolated, self-biased, and optically sourced. 
     BACKGROUND OF THE INVENTION 
     Many high-power RF (radio frequency) and microwave applications include devices, such as switched power amplifiers, high-level mixers, TR (transmit receive) switches and series FET (field effect transistors) power amplifiers which require switching elements that are capable of handling high voltages and high currents (e.g., power amplifiers), switching at extremely high frequencies (e.g., microwave applications), and are isolated from surrounding structures &amp; devices (e.g., the impedance increases). 
     As power and efficiency requirements increase, it becomes more difficult to switch devices in shorter times and still maintain isolation between devices and supplies. High power devices have more internal capacitance from terminal to terminal and also more external capacitance from terminals to ground. Eventually, for device circuits, switching elements such as those shown in  FIGS. 1A-C , become unrealizable and ineffective. 
     Presently, there are various circuits (e.g., class D, E, F and S power amplifiers, GaAs ring mixers, optical data links) that have high efficiency and are fast switching. However, these circuits only operate at very low-power levels, such as low IP3 (third-order intercept point), so these current solutions are not helpful for larger power or microwave applications. 
     Presently, solutions to maximize switching times have been developed using multi-stage devices, such as Darlingtons pairs (e.g., piggy back transistor configuration), cascode FETs, series FETs, and MMICs (Monolithic Microwave Integrated Circuits), however isolation in the biasing schemes and input drive schemes limit performance. 
     Spatial combining of devices have been developed. Spatial combining of devices provides limited isolation between devices, associated losses and limited bandwidth. 
     Therefore, it may be desirable to provide a switching element that may operate with high voltage and currents, switches quickly, provides an isolated RF input and power supply and is also isolated from surrounding structures and devices. 
     SUMMARY OF THE INVENTION 
     In some embodiments, a switching element may include one or more of the following features: (a) an optically coupled input, (b) an amplifier electrically coupled to the input, (c) a power source coupled to the amplifier, and (d) an active device electrically coupled to the power source and the amplifier. 
     In some embodiments, a microwave switch element may include one or more of the following features: (a) an electrically isolated input capable of receiving an input, (b) an amplifier electrically coupled to the input and to an active device, (c) a power source magnetically coupled to the active device. 
     In some embodiments, a microwave switch element may include one or more of the following features: (a) an input to receive switching information, (b) an amplifier electrically coupled to the input to control a bias on a transistor and (c) a power source magnetically coupled to the amplifier. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which: 
         FIG. 1A  is a class D amplifier; 
         FIG. 1B  is a (Double-Balanced), DB-mixer; 
         FIG. 1C  is a series FET power amplifier; 
         FIG. 2  shows two transistor circuits in an embodiment of the present invention; 
         FIG. 3  shows a switching circuit in an embodiment of the present invention; 
         FIG. 4  shows a schematic view of an optically sourced isolated microwave switching element in an embodiment of the present invention; 
         FIG. 5  shows a block diagram view of an optically sourced isolated microwave switching element in an embodiment of the present invention; 
         FIG. 6  shows a schematic diagram of a TR switch utilizing an optically sourced isolated microwave switching element in an embodiment of the present invention; 
         FIG. 7  shows a schematic diagram of a high-power series TR, (transmit/receive) switch utilizing an optically sourced isolated microwave switching element in an embodiment of the present invention; 
         FIG. 8  shows a balanced class-D amplifier utilizing an optically sourced isolated microwave switching element in an embodiment of the present invention; 
         FIG. 9  shows a series FET amplifier utilizing an optically sourced isolated microwave switching element in an embodiment of the present invention; and 
         FIG. 10  shows a frequency mixer utilizing an optically sourced isolated microwave switching element in an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
     The following discussion is presented to enable a person skilled in the art to make and use the present teachings. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein may be applied to other embodiments and applications without departing from the present teachings. Thus, the present teachings are not intended to be limited to embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the present teachings. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of the present teachings. 
     With reference to  FIG. 2 , two transistor circuits in an embodiment of the present invention are shown. Switching circuit  10  represents a transistor circuit providing a negative bias on source  12  and a positive bias on gate  16  of transistor  14 . Transistor or active device  14  may be most any transistor, but for purposes of this description transistor  14  is a Gallium nitride (GaN) transistor. In this biasing mode, channel  18  is not depleted and current may flow freely between drain  24  and source  12 . The current necessary to charge the gate capacitors  28  to the appropriate voltage level flows through resistor  20 . However, resistor  20  provides impedance which is undesired in a switching circuit as it decreases switching time. 
     Switching circuit  22  represents switching circuit  10  when a positive bias is placed on source  12  and a negative bias is placed on gate  16  of transistor  14 . In this mode, channel  18  is depleted and no current may flow from source  12  to drain  24 . Thus, in switching circuit  10 , transistor  14  conducts current and may be said to be “on”. In switching circuit  22 , transistor  14  does not conduct current and may be said to be “off”. When transistor  14  is “on”, there is impedance due to resistor  20  and impedance between gate  16  and source  12 . It is contemplated that reducing the impedance may improve (decrease) a switching element&#39;s switching time. 
     With reference to  FIG. 3 , a switching circuit in an embodiment of the present invention is shown. Switching circuit  30  may be substantially a combination of switching circuits  10  and  22 . However, switching circuit  30  substantially reduces the impedance of circuit  30  by eliminating resistor  20  and replacing resistor  20  with power sources  32  and  34 . The power sources, being voltage sources, are very low impedance elements. In this design, power sources  32  and  34  may be oppositely biased so that power source  32  positively biases operational amplifier (op-amp)  36  and negatively biases source  38 . Likewise, power source  34  negatively biases op-amp  36  and positively biases source  38 . Op-amp  36  receives an RF input  40  and provides an input to gate  42 . RF input  40  may be a square-wave RF input instructing switching circuit  30  to turn off or on. Depending on RF input  40 , gate  42  may be positively charged with respect to source  38  in which case switching circuit  30  may be on. In this scenario, RF input  40  may cause op-amp  36  to route a positive charge from power source  32  to gate  42  and a negative charge from power source  32  may be routed to source  38 . Nothing may be received from power source  34  as its circuit may be considered open and thus no current may flow. 
     Depending on RF input  40 , op-amp  36  may route a negative charge from power source  34  to gate  42  and a positive charge from power source  34  to source  38 . This may cause transistor  44  to be in an off state as discussed in  FIG. 2 . Once again, no power may be felt from power source  32 , as its circuit may be considered open at op-amp  36  and thus no current may flow. 
     With reference to  FIG. 4 , a schematic view of an optically sourced isolated microwave switching element in an embodiment of the present invention is shown. Optically sourced isolated microwave switching element (OSISE)  100  may be comprised of MMIC  102  that may house switching circuit  30  and an optical converter  104 . An optical converter  106  may accept RF phasing information (discussed above)  108  that may be relayed via optical transmission  110  and inputted to optically coupled optical converter  104 . Optical converters  106  and  104  create isolation between the incoming phasing information and the switching circuit, thus ensuring isolation for a switching element. Optical converters  106  and  104  may operate up to speeds of 100 GHz, which is helpful for microwave applications. Further it is noticed that OSISE  100  is completely isolated from the RF input except for the transfer of information between optical controllers  106  and  104 , thus reducing any impedance between OSISE  100  and any outside circuits and increasing the switching speed. 
     With reference to  FIG. 5 , a block diagram view of an optically sourced isolated microwave switching element in an embodiment of the present invention is shown. As discussed above, implementation of high-current, high-voltage switching elements at UHF (ultra high frequencies 300 MHz to 3 GHz) thru X-Band (7 to 12.5 GHz) have been very difficult in the past due to the lack of isolation between switch elements. The optically sourced isolated microwave switching element may isolate the switching elements using optical coupling (LED [light emitting diode] to PVD [photovoltaic diode]) for the RF coupling and, in this embodiment, magnetic coupling to generate the DC biasing of the active device such as a transistor. This provides an improved switch with switching frequencies from DC to upper frequencies only limited by the speed of the optical coupling, which is currently approaching 100 GHz., yet completely decoupled from other nearby devices. 
     LED  106  is inputted with RF phasing information  108  which is routed through an LED driver  200  where the signal is amplified. RF phasing information  108  may refer to the data that will instruct OSISE  100  when to turn on and turn off. Thus it controls the switching. After exiting LED driver  200 , RF phasing information  108  goes to LED  106  where the information is converted to light. Optical transmission  110  is sent to PVD  104  located on MMIC  102  on OSISE. Optical transmission  110  is then converted to RF by PVD  104  and sent onto op-amp  36 . Op-amp  36  is biased by power source  202 . It is noted that power source  202  is shown as being inductively coupled to MMIC  102 , ie., magnetic energy is generated in the external circuitry at a lower frequency and transmitted to the receiving coils on the OSISE. However, most any type of coupling may be implemented, such as optical coupling, at another wavelength, without departing from the spirit of the invention. RF  108  may be sent from op-amp  36  to switching circuit  204  that will either turn OSISE  100  off or on. OSISE  100  has isolated switching element  204  and thus provides an isolated switching element that may handle high frequencies and large amounts of voltage and current and still switch quickly. 
     With reference to  FIGS. 6 and 7 , a schematic diagram of switches utilizing optically sourced isolated microwave switching elements in an embodiment of the present invention is shown.  FIG. 6  discloses using OSISE  100  in a basic Class D amplifier stage  300 . One topology of a Class-D amplifier implements with an N-type device on the negative supply and a P-type device on the positive supply. P-type devices are generally slower and have lower operating voltages than the equivalent N-type device and, in addition the P-type device is difficult to switch on and off due to its potential around the positive voltage rail. Using an OSISE  100  in a Class-D amplifier provides crisp switching to both the positive and negative rail which in turn will produce better efficiencies than are possible with today&#39;s topologies. Class-D amplifiers may also be designed using a 3-way transformer coupled to the output of two N-type devices. Transformers have limited bandwidth, insertion loss and are usually large and heavy. An OSISE amplifier offers a high efficiency in a compact, low weight package. 
       FIG. 7  discloses using OSISE  100  in a high-power series transmit/receive switch  320 . Using OSISEs allows switching elements to be stacked, two in each leg, to give the T/R switch a high voltage capability and at the same time providing a straight forward, non-interactive method for switching the elements from entirely on to entirely off at maximum RF voltage and current levels without concerns about sufficient biasing for either state. Switching speeds may also be dramatically increased by using the OSISEs instead of using conventional large impedances in the gates. 
     OSISE  100  may be used in a class-D single ended switch (such as  320  in  FIG. 7 ), class-D balanced switch  340  ( FIG. 8 ), and a switch-mode power amplifier switch  360  ( FIG. 9 ) all of which may be utilized in high power. For example, output power of hundreds of watts to several kilowatts is achievable using wide-bandwidth, high-efficiency RF and microwave amplifiers. OSISE  100  may provide isolation between all switch devices, between stacked switching devices, and ground. This enables improved switch behavior of each OSISE  100  which is independent of other switching elements (OSISE or not) and allows power amplifier devices to be efficiently stacked and operated in a series configuration or operated as switches tied to independent voltage supply lines. 
     With reference to  FIG. 10 , a frequency mixer  380  utilizing an optically sourced isolated microwave switching element in an embodiment of the present invention is shown. Single and doubly balanced mixers may be implemented using OSISE optically coupled, isolated, switching elements, instead of conventional switching devices. OSISE allows true, broadband, high-speed switching that is difficult or unachievable using standard device drivers and also provides the device-to-device isolation required in many mixing applications. The self-biasing feature allows complete electrical isolation of the switching elements in the mixer. 
     OSISE allows for new mixers with broadband and high level conversion performance which may accommodate higher input powers, eliminate large and costly RF filtering, reduce limiter requirements and decrease susceptibility to jamming signals. These ultra-linear, efficient mixers may promote a reduction in size, weight, power consumption and cost (SWAP+C) 
     It is believed that the present invention and many of its attendant advantages will be understood by the forgoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. Features of any of the variously described embodiments may be used in other embodiments. The form herein before described being merely an explanatory embodiment thereof. It is the intention of the following claims to encompass and include such changes.