Abstract: A mixer having a diode quad, and which receives two RF signals at an RF input balun having primary and secondary windings. A resonant circuit arrangement includes at least a capacitor circuit element in parallel with the secondary winding to form an open circuit termination for the second harmonics of the input RF signals.

Abstract: Double balanced mixers having transistor pairs are affected by area mismatches between the transistors. The area mismatches can be represented as a ratio between the mixer core transistors that is directly related to voltage. Thus, an input voltage into one of the mixer core transistors in a transistor pair can compensate for the area mismatch. The compensation is achieved by a voltage track and hold feedback loop to one of the mixer core transistors.

Abstract: In accordance with the present invention a mixer circuit noise reduction technique is provided. The mixer circuit of the present invention includes a gain stage for receiving a first signal and producing an output signal. The mixer circuit also includes a bias circuit coupled to the gain stage through a common node for providing a bias current to the gain stage, the bias circuit having an input for receiving a second signal, and in accordance therewith, varying the bias current. Additionally, the mixer circuit includes a frequency dependent current shunt circuit coupled between the common node and a reference voltage, wherein a first portion of the bias current frequency components within a first frequency range are coupled to the reference voltage by the shunt circuit, and a second portion of the bias current frequency components within a second frequency range are coupled to the reference voltage by the shunt circuit, the first portion being larger than the second portion.

Abstract: A single balanced downconverter includes an insulated substrate with a primary circuit and a secondary circuit, each consisting of an open annular foil element, located on opposite sides of the substrate in juxtaposition with each other and having mutual coupling. A pair of mixing diodes is connected across the ends of the secondary element, which has its center connected to ground. A 2nd local oscillator signal is applied to the primary circuit. A 1st IF signal is applied to, and a 2nd IF signal is developed from, the secondary circuit.

Abstract: A mixer with improved isolation between the RF and local oscillator frequency signals. The mixer has a substrate. A pair of cores are mounted to the substrate. Windings are wound on the cores to from a pair of baluns. A diode ring is connected between the baluns. The windings are formed from a first and second twisted pair of wires on one core and a third and fourth twisted pair of wires on another core. Some of the wires are wound on the cores but not twisted together. This winding configuration achieves superior balance between the baluns and good isolation.

Abstract: A mixer includes a first terminal and a second terminal forming a first input port for receiving a first signal having a first frequency; a second input port for receiving a second signal having a second frequency; a mixer output port for a resulting signal; a first group of valves having their control inputs coupled to the first terminal for receiving the first signal; a second group of valves having their control inputs coupled to the second terminal for receiving the first signal; and a third group of two valves having their control inputs coupled for receiving the second signal. The valves co-operate such that in operation the mixer produces the resulting signal responsive to the first and second signals. The mixer also includes at least one passive low pass filter having an inductor, the low pass filter being connected to the control input of a valve in the first and second groups.

Abstract: A method and apparatus of converting differential signals to single-ended signals. The method includes receiving a differential signal comprising a first current and a second current and applying the second current to a first load to generate a first voltage. A third current is generated in response to the first voltage. The first current is summed with the third current and applied to a second load to generate the single-ended signal.

Abstract: A circuit arrangement for providing impedance translation filtering comprises a first path and a second path. In a base band variant the first path is a feed forward path which comprises first and second series connected transconductance gain stages (10, 12), and the second path is a feedback which comprises third and fourth transconductance gain stages (18, 20), each having an inverting output. An output of the first gain stage is coupled to an input of the fourth gain stage. In operation, the impedance presented at its output determines the impedance presented at an input of the circuit arrangement.

Abstract: A surface mount, even harmonic mixer is preferably used in point-to-multipoint millimeter wave transceivers. The mixer includes an anti-parallel series arrangement of diodes in one or more ring quads to increase the input 1 dB compression point and third-order input intercept point (IP3), while maintaining the benefits inherent with even harmonic mixing.

Abstract: An output stage of a double balanced mixer having a first intermediate port and a second intermediate port includes an operational amplifier, an impedance and first and second current source devices. The operational amplifier has a first input port, a second input port and an IF output port, and the impedance is coupled between the first input port and the second input port. The first current source device has a first terminal coupled to both the first input port and the first intermediate port, which are coupled to one another. The second current source device has a second terminal coupled to both the second input port and the second intermediate port, which are coupled to one another.

Abstract: A frequency converter that includes a first low-pass filter and a band-pass filter with a first end operatively connected to a first end of the first low-pass filter. The frequency converter also includes a second low-pass filter with a first end also operatively connected to the first end of the first low-pass filter. The frequency converter, moreover, includes a first waveguide with a first end operatively connected to a second end of the second low-pass filter, with the first waveguide containing at least one frequency-mixing element, and with the first waveguide continuing for a specific length after the one frequency-mixing element and having a second end that is operatively short circuited. The frequency converter, furthermore, includes a second waveguide operatively connected to the one frequency-mixing element. The frequency converter is arranged such that the specific length of the first waveguide extends past the operative connection between the second waveguide and the one frequency-mixing element.

Abstract: A microwave broadside coupled balun integral in a multi-layer printed wiring board formed by broadside coupled conductors embedded in the multi-layer printed wiring board. The balun may be used to form components which are integrated into the multi-layer printed wiring board, such as a microwave mixer formed by two of said broadside coupled baluns embedded in a multi-layer printed wiring board and connected to a diode ring quad.

Abstract: The invention is a demodulator (50, 100) and a method of data reception and testing of a demodulator. A demodulator in accordance with the invention includes an input signal source (52, 102) having an output which during data reception is a data signal and which during testing of the demodulator is a reference signal; a tuner (54, 101) having a tuner input coupled to the output of the input signal source and a tuner output, the tuner including a frequency converter (20, 36) which frequency shifts the data signal to a lower carrier frequency during data reception to cause the tuner to output at the tuner output the lower carrier frequency modulated with the data signal and which upwardly frequency shifts the reference signal to a test carrier frequency during the testing; and a test data source (56, 105) which applies a test data signal to the tuner during the testing to cause the tuner to output at the tuner output the test carrier frequency modulated with the test data signal.

Abstract: The invention provides a broadband double-balanced mixer capable of operating across a range of frequencies from millimeter to microwave. The mixer includes a Wilkinson type splitter.

Abstract: In a diode mixer circuit MIX, a driving circuit DRIV produces a first, second, third and fourth drive signal DS1, DS2, DS3, DS4. Each drive signal is a combination of a first and a second input signal LO, RF with the following signs: DS1: +LO+RF DS2: +LO−RF DS3: −LO+RF DS4: −LO−RF A first, second, third and fourth diode D1, D2, D3, D4 transfer the first, second, third and fourth drive signal DS1, DS2, DS3, DS4 respectively, to an output O1. The first and fourth diodes D1, D4 have the same polarity relative to the output. The second and third diodes D2, D3 also have the same polarity relative to the output, but opposite to that of the first and fourth diodes D1, D4. A mixer circuit of this type is suitable for a relatively large variety of applications, notably because it may be realized in the form of an integrated circuit.

Abstract: A stabilised voltage controlled oscillator circuit comprises a closed loop circuit containing a voltage controlled oscillator (34), a local oscillator (40) and a harmonic mixer (38) that mixes a stabilised local oscillator (LO) frequency signal and a radio frequency (RF) signal from the voltage controlled oscillator (34) to obtain an intermediate frequency (IF) signal. An IF amplifier (42) is connected to a linear frequency discriminator (44) that provides an output signal to a summing amplifier (46), which is connected to the voltage controlled oscillator (34). The closed loop circuit uses the linear frequency discriminator (44) to provide a feedback signal that stabilises the voltage controlled oscillator (34).

Abstract: This mixer circuit is configured so that a second capacitor (C10 and C11) having capacitance smaller than that of a first capacitor (C1 and C3) is connected in parallel with the first capacitor (C1 and C3), the first capacitor (C1 and C3) being connected to output terminals of the diode bridge so that an anode and a cathode of respective diodes connected in series to constitute the diode bridge are made equal in electric potential to each other by the first capacitor (C1 and C3) in terms of radio frequency.

Abstract: A wide dynamic range RF mixer is shown using wide bandgap semiconductors such as SiC, GaN, AlGaN, or Diamond instead of conventional narrow bandgap semiconductors. The use of wide bandgap semiconductors will permit RF mixers to operate in higher RF environments, to be less susceptible to out-of-band jamming and interference, and to be more effective in receiving weak RF signals in the presence of strong unwanted signals.

Abstract: A diode device with a low or negligible threshold voltage includes at least one field effect transistor, the gate of the field effect transistor being connected to the drain of the field effect transistor. The threshold voltage of the diode device is approximately of the same magnitude as the potential of the gate of the field effect transistor forming part of the diode device.

Abstract: A radio (100) includes a receiver circuitry (106) for use in conjunction with a tunable antenna (101). The radio includes a controller (122) which may be a digital signal processor. The controller (122) controls various radio functions including tuning of the antenna (101), measurement of the quality of received signals, and generation of a test signal. The radio is capable of generating a test signal on a desired frequency, which is radiated within the radio, received at the antenna (101) and then processed by receiver circuitry (106). Its quality is then measured and used to control the tuning of the antenna (101). The test signal generated by the controller (122) can be mixed up to the desired frequency by using one or more of the local oscillator signals of the radio.

Abstract: A double balanced mixer consisting of two complementary solid state switches, with a high reverse-bias voltage provided by isolating the sides of the complementary solid state switches receiving the carrier signal from one another, and connecting the other sides together. If the solid state switches are designed to couple the input signal to the output signal in response to the carrier signal having an amplitude of zero volts, then a solid state switch in forward-bias will have a potential of zero volts on both sides of it. While this solid state switch is in forward-bias, the second solid state switch will be receiving the complementary carrier signal on one side, which is a high positive voltage, and zero volts on the side connected to the first solid state switch. The second solid state switch will therefore see a reverse-bias potential difference equal to the potential difference between the positive voltage of the complementary carrier signal and zero volts.

Abstract: A diode circuit in a dielectric waveguide device designed to improve the facility with which a circuit substrate is mounted in the dielectric waveguide, to make matching between a dielectric waveguide and a diode easier, and to reduce conversion losses, and a detector and a mixer using such a diode circuit. A conductor pattern is disposed so as to intersect a pair of dielectric strips substantially perpendicularly to the same, and two filter circuits are formed in the dielectric pattern on opposite sides of the dielectric strips, thereby forming a resonance circuit. A diode is mounted in the resonance circuit in series with the conductor pattern.

Abstract: A motion detection unit for detecting motion by means of Doppler frequency shift which comprises: a microwave circuit board comprising an oscillator, a hybrid coupler circuit element and a mixer; an antenna board comprising at least one transmit and receive antenna; and a ground plane layer, the two boards being superimposed with the ground plane layer intervening, wherein, in operation, the hybrid coupler circuit element divides power from the oscillator into power for the antenna transmission signal and local oscillator (LO) power to the mixer, and directs a received signal from the antenna to the mixer, the local oscillator (LO) power and the received signal being combined in the mixer to produce a Doppler signal output.

Abstract: A multiple band termination circuit, comprising a first resistor coupled in signal communication with an input and an open stub to form a nominal termination at a high frequency band, and a second resistor coupled in series to the first resistor with a high impedance transmission line, the second resistor and the first resistor cooperating together to form a nominal termination at a low frequency band.

Abstract: In a microwave transmission system a microwave signal is transmitted by a transmitter (1) using an antenna (2) to a receiver (4) which employs an antenna (3). The received signal is coupled to a mixer (17) via a waveguide section (15) having a cut off frequency being higher than the frequency of the signal generated by the local oscillator unit (18). In this way undesired emission of local oscillator signal is avoided. Furthermore no additional image rejection filter is required.

Abstract: A balanced modulator has a pair of diodes, a plurality of line patterns including a balance-to-unbalance converter, the line patterns including lines extending toward and connected to the diodes, respectively, and at least a set of capacitive stubs disposed near the lines and spaced from each other by a distance of .lambda./8 (.lambda. is the wavelength at a frequency used). The capacitive stubs are connectable to the lines by bonding wires for isolation adjustments.

Abstract: A high frequency partial transformer hybrid includes a first divided circular conductive element affixed to one side of an insulated substrate and a second split circular conductive element affixed to the other side of the substrate juxtaposed to the first element. Plated-through holes in the substrate interconnect pads on the first and second elements. Connection tabs on the elements are adapted to be connected to conductors on a printed circuit board when the substrate is orthogonally supported in a rectangular recess in the substrate. In a transformer hybrid embodiment, a third continuous circular conductive element is supported on an additional substrate in alignment with and insulated from the second element. The third element also includes connection tabs that are connectable to the conductors on the printed circuit board.

Abstract: A micro-wave mixing circuit produces producing a stable frequency conversion characteristic against a dispersion of output voltage of a local oscillation signal tapped off from a local oscillator. A micro-wave signal fed into a micro-wave signal input can be converted into an intermediate frequency signal of 1 GHz bandwidth where a stable frequency conversion characteristic is maintained against a dispersion of an output voltage of a local oscillation signal, by supplying bias current from a bias supply circuit to an anode of a Schotkky barrier diode responsive to a local oscillation output which is supplied from a local oscillator.

Abstract: A compensated mixer including a radio frequency (RF) balun through which RF signals are transferred, and a local oscillator (LO) balun for receiving an LO signal. In an exemplary implementation the mixer further includes a diode ring quad circuit for mixing RF signals received by the RF balun with the LO signal received by the LO balun. During operation the diode ring quad circuit develops, between first and second nodes therein, a capacitive reactance arising from switching at the LO frequency. The mixer further includes a compensation inductor, connected between the first and second nodes, for cancelling the effect of the capacitive reactance at the LO signal frequency.

Abstract: A mixer (1) comprising, an RF port 2 and an LO port (3) supplying two diodes (7), a junction (8) of the diodes (7) referenced to ground (9), and a differential amplifier (19) being supplied with +IF and -IF from outputs of the diodes (7), and the differential amplifier (19) supplying low LO AM noise and low frequency response of an IF port (18) at an output (20) of the differential amplifier.

Abstract: Mixers assemblies including mixer cells, baluns, quadrature mixers and image reject mixers, etc. The mixer cell may contain CPW strip RF input and slot line strip LO input. LO signal return is provided through a flip-chip mounted to a mixer contact area and the CPW RF input is preferably coupled to the contact area through a distributed or flip-chip mounted capacitor. The use of two mixer cells in novel embodiments of quadrature and image reject mixers is disclosed. CPW to slot line power dividing baluns for use within and without such mixers are also disclosed.

Abstract: A mixer includes a doubly-balanced mixer core, an RF input section coupled to the mixer core, and a biasing circuit coupled to the RF input section. The RF input section includes a first transistor coupled to a first input of the mixer core for supplying a first current thereto. The base of the first transistor is driven by an RF input current, as a result, the first current is responsive to the RF input current. The RF input section also includes a current mirror coupled to the first transistor, which mirrors the sum of the first current and the RF input current to produce a second current that is complementary to the first current for small variations of the RF input current. The current mirror is coupled to a second input of the mixer core to supply the second current thereto. A biasing circuit is coupled to the RF input section to establish a quiescent value of the first current. Padding resistor can also be used in the RF input section to provide a predetermined input impedance to the RF input current.

Abstract: In order to further suppress unwanted waves which may occur when the frequency (flo) of a local oscillation wave is lower than the frequency (fin) of a signal wave, the local oscillation wave is in-phase distributed between unit mixers (2a) and (2b) whereas the signal wave is opposite-phase distributed through a 180 degree distributer (4) to the unit mixers (2a) and (2b). The unit mixers (2a) and (2b) execute frequency mixing of thus distributed local oscillation wave and signal wave, and supply the result through a BRF (16a) or (16b) into a 180 degree combiner (6). The 180 degree combiner (6) effects an opposite-phase combination of outputs of the BRFs (16a) and (16b), and outputs the result.

Abstract: A dumbbell shaped resonator efficiently couples IF signals from short transmission lines to an output transmission line at a radio frequency (RF) mixer's IF output port. The RF mixer uses short transmission lines and terminating resistors to match impedances within the mixer and to minimize the mixer's distortion. The RF mixer, including the dumbbell resonator, is constructed on a printed circuit board and has a low manufacturing cost. Alternatively, the output transmission line is center-tapped to provide a pair of IF signals having opposite phases.

Abstract: An impedance-generating device that provides a resistance and a reactance that are non-linear functions of a signal over a wide impedance range (VariablE Non-Linear Impedance Circuit Electronics, "VENICE"). An electronic component that has a gain characteristic with a unity gain frequency that is directly proportional to that signal can be configured to generate such an impedance. Such an electronic component configured to provide a negative effective resistance and a variable non-linear reactance can be used to implement a high frequency harmonic generator. This generator can provide high order harmonics which can be used in high frequency communications systems. The electronic component can also be configured to provide only a voltage-variable non-linear reactance which can be used to implement a reactive mixer to frequency shift a high frequency signal to an intermediate frequency signal, from mixing the high frequency signal with a local oscillator signal.

Abstract: A frequency mixer for a Doppler radar module with directional recognition, can be operated with a single transmitting and receiving antenna. It is thereby possible to create a Doppler radar module with low space requirements even for transmitting and receiving frequencies below 5 GHz. In the frequency mixer, a first microstrip line is coupled to a first terminal of a first diode and a second microstrip line is coupled to a first terminal of a second diode. The two microstrip lines are connected to each other through a capacitor. An antenna is coupled to the first microstrip line and an oscillator is coupled to the second microstrip line. Second terminals of each of the diodes are connected to a fixed potential in an electrically conductive manner. A phase comparator is coupled to the two microstrip lines.

Abstract: A microwave mixing circuit of a small size for selecting a signal to be received out of plural microwave signal inputs, and converting it to an intermediate frequency signal, and a down converter comprising it are provided. A microwave input signal within a band of 12 GHz applied to one microwave signal input unit is guided through a bias terminal from a comparator into a mixer diode to which a bias current is supplied, and is converted in frequency by the mixer diode. A microwave input signal applied to other microwave signal input unit is guided through the bias terminal from the comparator into a mixer diode to which bias current is not supplied, and is hence not converted in frequency by the mixer diode. As a result, only an intermediate frequency signal of 1 GHz band corresponding to the former microwave signal appears at the intermediate frequency signal output terminal.

Abstract: In a balanced modulator, a local oscillator frequency signal is transmitted through a serial connection of the primary side conductive patterns (1p and 2p) of a first coupler (1) and a second coupler (2), wherein the two couplers (1 and 2) are connected in an opposing direction. A first output terminal of the secondary side conductive pattern (1s) of the first coupler (1) is grounded through a first effective grounding pattern (4), and a first output terminal of the secondary side conductive pattern (2s) of the second coupler (2) is grounded through a second effective grounding pattern (5). The output voltage at a second output terminal of the secondary side conductive pattern (1s) of the first coupler (1) is impressed to a terminal of a first diode (9). The output voltage at a second output terminal of the secondary side conductive pattern (2s) of the second coupler (2) is impressed to a terminal of a second diode (10).

Abstract: A planar triply-balanced microstrip mixer for microwave and millimeter wave operation includes an RF port, and IF port and an LO port. The mixer is constructed on a single side of a two-sided substrate. The single side of the substrate supports an RF balun network connected to the RF port, an IF balun network connected to the IF port, and an LO balun network connected to the LO port; a pair of crossover diode ring quad circuits arranged in a planar back-to-back configuration; and a planar microstrip feed network connecting the RF, IF, and LO ports to the diode ring quad circuits through the RF, IF and LO balun networks.

Abstract: A low power, high-performance mixer includes a Schottky diode ring and first and second active baluns. The first active balun has an input coupled to a radio frequency (RF) signal and generates a first intermediate frequency (IF) output and a set of balanced RF outputs which are directly coupled to the Schottky diode ring. A second active balun has an input coupled to a local oscillator (LO) signal and generates a second IF output and a set of balanced LO outputs which are directly coupled to the diode ring. An IF output combiner, coupled to the first and second IF outputs, generates a combined IF output from the first and second IF outputs. The mixer can alternately be implemented using first and second distributed active baluns which are directly coupled to the diode ring.

Abstract: The useful frequency range of an I/Q diode modulator is increased by adding two capacitors (15, 16) and an inductance (17), or two inductances and one capacitance, as a series-resonant circuit. The capacitors (15, 16) are connected in series and have a zero voltage at their connection point so that the inductance (17) does not influence the oscillator signal. The inductance (17) is chosen so that resonance occurs at the frequency at which leakage across the diodes would otherwise occur, so that the impedance between ground and the diode (4, 5) connection point is very low and, therefore, so is leakage between the mixer outputs. When the diode elements conduct, the voltage at the point between the diodes (4, 5 or 4a, 5a) is connected to both branches of the transformer (8) secondary so that the branches have equal voltages with the same phase. This permits an I/Q modulator or I/Q demodulator for 400 MHz or even 900 MHz frequency to be made with ordinary UHF mixer diodes.

Abstract: Wide area radio system comprising at least two central stations capable of maintaining communication to several peripheral stations within overlapping or adjacent service areas (110). Each central station is divided into a high frequency unit (992) and a low frequency function (991) operatively connected to said high frequency unit. Traffic interaction and coordination between said central stations in said radio system is provided through said low frequency functions (991) of said stations.

Abstract: A thick film balanced line multilayered structure having a substrate base of nominal 0.025 or 0.030 inch thick ceramic material, a first metal layer deposited on the substrate base, a nominal 0.003 inch thick dielectric layer deposited over and around the first metal layer, and a second metal layer deposited on top of the dielectric layer in alignment with, and parallel to, the first metal layer. The structure defines a standard circuit cell suitable for use as a balun, a capacitor or an autotransformer, for use in microwave mixers, power splitters, filters, resonators and other microwave devices. The impedance of the cell is controlled by the width of the metal layers, and ranges from 5 ohms to 125 ohms, and the frequency of the cell is controlled by the length of the metal layers.

Abstract: A non-radiative dielectric waveguide mixer includes at least one conductive plate, a dielectric waveguide held on said conductive plate and a solid-state device disposed across said dielectric waveguide for mixing at least two high-frequency signals which are propagated in opposite directions along said dielectric waveguide. The non-radiative dielectric waveguide mixer may be combined with a high-frequency signal generator and an antenna mechanism to provide a non-radiative dielectric waveguide radar module.

Abstract: The microwave impedance across an aperture in a conductive shield member of a transmission structure is varied as a microwave signal transits the aperture. The impedance is changed by positioning a variable impedance device across the aperture. A slit divides the shield member into two portions to facilitate the application of a modulating signal (56) across the device.

Abstract: Microwave two-phase modulator and mixer each comprising a balance/unbalance transformer section to which a microwave signal is applied; a synthetic/branching line section which is connected to the both ends of the balancing line of the balance/unbalance transformer section on the balancing line side; isolation diodes are mounted between diode-mounting lines section and fan-shaped patterns; a plurality of modulating characteristic-adjusting, capacitive stubs placed near the diode-mounting lines; an input line; a modulating signal input line; and a modulated signal output line. The modulating characteristics are adjusted by connecting the diode-mounting lines and the plurality of capacitive stubs by bonding wires or cutting some of the connecting wires.

Abstract: A routing YIG-tuned resonator filter integrated with an image-enhanced, double-balanced mixer. The YIG-tuned resonator filter is preferably a four-sphere YIG-tuned preselector which is integrated with a low-loss, fundamentally or harmonically mixed, image-enhanced, double-balanced mixer to provide a high level of dynamic range in a harmonically mixed front end. An input resonator of the preselector in combination with a dual PIN diode switch switches low-frequency input signals (e.g., 0 to 2.9 GHz) to a low-band mixer. For RF input signals (e.g., 2.7 to 26.5 GHz), the four-sphere YIG-tuned preselector is combined with the image-enhanced, double-balanced mixer which incorporates a GaAs monolithic diode bridge integrated circuit. This provides a cost effective front end for a microwave spectrum analyzer.

Abstract: A collector-injector mixer circuit (100) has a first differential pair of transistors having first and second transistors (102, 104) whose emitters are connected to a common first emitter terminal (110), and a second differential pair of transistors having third and fourth transistors (106, 108) whose emitters are connected to a common second emitter terminal (112). The bases of the first and fourth transistors (102, 108) are coupled to a common first base terminal (114) and the bases of the second and third transistors (104, 106) are coupled to a common second base terminal (116) between which a mixing signal is applied.

Abstract: An electrical circuit forming a dual-channel low current Low Noise Block (LNB) downconverter comprising two downconverting circuits electrically connected in series with each other and each electrically connected in parallel with a Zener diode such that power consumption is minimized and component life improved.

Abstract: A mixer converting a frequency of an input signal to an intermediate frequency has an input port receiving an input signal oscillating at a signal frequency and a sinusoidal pump wave oscillating at a pump frequency. A diode is connected between an input network linked to the input port and an output network linked to an output port of the mixer. The output network and the input network together cause the diode to switch rapidly between ON and OFF states and behave as with square wave drive. Bias circuitry connected to the diode comprises a resistor connected to receive a DC component of current from the diode, the current through the resistor solely biasing the diode.