Showing papers on "RF power amplifier published in 1988"

Multiple electrode plasma reactor power distribution system.

Abstract: A multiple electrode plasma reactor arranged with electrical circuitry which allows for improved power distribution and plasma uniformity without requiring perfectly symmetrical power feeds, the high frequency RF power from generator (102) is introduced into a matching network (104) in the normal fashion, however, upon exiting match network (104) the power is fed through a differential drive transformer (106). The power from the output coil (107) of the transformer is then split, and fed through separated feed through circuits (108) and (110) respectively to each of the powered electrodes (112) and (114) respectively disposed within the grounded chamber (118). To achieve uniformity, the electrodes are preferably formed as planar members and the spacing between the powered electrodes (112) and (114) and the grounded surfaces (116), (120) and (122) is equal throughout. The differential drive transformer circuit applies the same RF current to each powered electrode creating a uniform plasma between the two powered electrodes and the grounded surfaces.

A programmable, arbitrary waveform electrosurgical device

Abstract: The programmable electrosurgical device is an arbitrary waveform generator that provides feedback control of selected output variables. A desktop computer provides the human interface and controls the operation of the electrosurgical device. The generated waveform drives an RF amplifier. The electrosurgical device samples the instantaneous voltage and current of the amplifier's output. Any one of several variables-voltage, current, power, or impedance-may be selected for feedback control. >

High-efficiency 5-watt power amplifier with harmonic tuning

Abstract: An X-band power amplifier using harmonic tuning and a GaAs FET is described. The amplifier has demonstrated 36% power-added efficiency with 5 W of output power and a 6.0-dB gain at 10 GHz. The key to this design is determining and matching the optimum load impedance for power-added efficiency at the first two harmonics. Nonlinear models were used to study the effects of harmonic tuning and to determine the optimum harmonic terminations. Two amplifiers were designed that demonstrated high-efficiency power amplification at the 0.5-W and 5-W power levels, respectively. The effects of harmonic loading were demonstrated in the 0.5-W amplifier, where the maximum efficiency measured for a device tuned only at the fundamental was 44%, while the measured efficiency of the amplifier with optimum harmonic tuning was 49.3%. >

Adaptive thermal protection for a power amplifier by remote sense.

Abstract: An adaptive thermal protection method and arrangement for a power amplifier by remote sense is disclosed in Fig. 2 which maximizes the amount of output power from electronic equipment such as a radio frequency (RF) power amplifier (118), having a finite heat sink (119) and operating intermittently over a period of time. This method and apparatus utilizes a remote temperature sensor (110A) and knowledge of the on/off, or key/dekey times in conjunction with a stored, predetermined thermal model to adjust the operating power level to a maximum permissible point within a range of operating power levels such that the projected temperature of the power amplifier does not exceed a preset limit. In so doing, the apparatus and method combines the advantages of thermal protection and power maximization and effects gradual changes in the operating power level by adapting to variable environmental and operational conditions.

Low temperature plasma generator with minimal RF emissions

Abstract: A low temperature plasma generator having reduced radio frequency (RF) emissions, and a method for reducing the RF emissions of a plasma generator. A low temperature plasma generator (100) includes a pair of electrodes (150 and 160) that are energized by an RF power supply (138) through a balanced impedance matching network (200). The impedance matching network includes a balun transformer (158), matched variable inductors (222 and 230), a fixed capacitor (240) in parallel with a variable capacitor (244) and a fixed capacitor (242) in parallel with a variable capacitor (246). The RF potential on electrodes (150 and 160) varies sinusoidally between opposite positive and negative values with respect to ground potential, such that the net potential on the two electrodes with respect to ground is always substantially equaol to zero, thus eliminating a glow discharge current and radiation emissions that otherwise are produced by similar prior art low temperature plasma generators.

Digitally controlled variable power amplifier

Abstract: The invention relates to a digitally controlled variable power amplifier for radio frequency signals. The power amplifier has application to power amplifiers for driving the individual elements of a phased array radar system in which accurate tapering of the power supplied to individual antenna elements is desired for sidelobe control in the face of jamming and other circumstances. In this application, each power amplifier must maintain a stable phase transfer response and should remain at a high power transfer efficiency at each reduced power setting. This performance is achieved by the use of a power transistor of a segmented dual gate design. The segments of the second gate electrode are of digitally scaled widths and are individually energized to activate digitally scaled regions of the transistor. These regions are operated in a saturated class "A" mode in all power settings to achieve the desired stable phase transfer response and high power added efficiency.

Adjustable delay circuit

Abstract: A delay element for producing an output signal in response to a change in state of an input signal includes variable gain first and second amplifiers (A1, A2) and a delay buffer (12) having a fixed delay. The input signal is applied as input to the first amplifier (A1) and the delay buffer (12) while the output of the delay buffer (12) is applied as input to the second amplifier (A2). The outputs of the first and second amplifiers are summed to provide the output signal. When the gain of the first amplifier (A1) is high and the gain of the second amplifier is low, the output signal will respond to the change in state of the input signal with minimum delay. When the gain of the first amplifier (A1) is low and the gain of the second ampli­fier (A2) is high, the output signal will respond to the change in state of the input signal with maximum delay. The delay in change of state of the output signal in response to a change of state in the input signal may be adjusted with high resolution to a time intermediate between the minimum and maximum delays by adjusting the gains of the first (A1) and second (A2) amplifiers.

Power amplifier combiner for improving linearity of an output

Abstract: A high power amplifier combiner for improving the linearity of an output of an amplifier. At least two prelinearizers are used to suppress all distortion products by using feedforward cancelling techniques. The effects of compression associated with the operation of the high power amplifier are reduced.

Equal power amplifier system for active phase array antenna and method of arranging same

Abstract: An equal power amplifier system (100) for amplifying a plurality of signals for transmission by an active phase array antenna (20), and a compact plural level beam-forming network (98) for forming a plurality of such signals, for example on excitation patterns for frequency scanned virtual beams, are disclosed. The amplifier system uses at most only a few sizes of power amplifiers (130, 134) to amplify efficiently numerous signals having significantly different amplitudes. This is accomplished by distributing the task of amplifying signal pairs (Ai, Bi) composed of one large amplitude signal and one small amplitude signal to an equal power amplifying apparatus (130; 230), which includes two hybrid couplers (236, 238) and two equally sized power amplifiers (232, 234). The first hybrid coupler (236) divides the two signals (Ai, Bi) for input into the two power amplifiers. The second hybrid coupler (238) receives the intermediate amplified signals from the power amplifiers and through constructive and destructive interference produces amplified output signals (Ai*, Bi*) corresponding to the input signals. Also disclosed is a method for properly selecting pairs of signals from an amplitude distribution (200; 202) for application to such equal power amplifying apparatuses of the amplifier system in order to operate the power amplifiers therein at or near peak efficiency. The beam-forming network (98) is arranged on two levels to simplify interconnection of the selected pairs of outputs of its line summers (176) for input into the equal power amplifier system. The amplifier system and beam-forming network may be used together, for example, in the transmit antenna system of a geosynchronous satellite (10) or mobile earth station.

V-band GaAs MMIC low-noise and power amplifiers

Abstract: GaAs MESFET amplifiers with on-chip DC-blocking and bias networks which were fabricated from both VPE and MBE materials, are reported. The low-noise designs resulted in a single-stage MMIC, low-noise amplifier achieving a 6.5-dB noise figure and a 4.1-dB gain at 59 GHz, as well as a cascaded six-stage amplifier exhibiting an 8-dB minimum noise figure and a 30-dB gain from 56.2 to 60 GHz. The single-stage power amplifier provides over 4.5 dB of gain from 57 to 60.5 GHz, with a maximum output power of 95 mW and a corresponding power-added efficiency at 11% at 58 GHz. Maximum power-added efficiency of 15.3% at 73 mW was also obtained. A cascaded four-stage amplifier demonstrated stable operation, achieving 17 dB of gain and 85 mW of output power. A two-stage balanced amplifier provided 136 mW of output power and 7.5 dB of linear gain from 56.6 to 61.5 GHz. >

FM laser transmitter

Abstract: A laser transmitter utilizes optical far field combination of two independent lasers (80,90) and variation of RF exciting power (86) to one (80) to produce sufficient frequency modulation. Two bores (122,124) within the same dielectric body (120) are provided with two independent sets of electrodes (134,135, 138,139) and two independent RF power sources (150,152). The lasers are operated at different frequencies and the beams transmitted in parallel adjacent paths to provide a combined far field optical beam component at the beat frequency of the two lasers. Variation of the frequency of one of the lasers provides frequency modulation of the far field beat frequency, enabling reception and demodulation of the modulated beam without use of a local oscillator laser at the receiver. The transmitter may also be used in a laser radar.

Gain monitoring of distortion cancellation amplifiers in a feedforward linear amplifier

Abstract: A monitor signal injection system for a feedforward cancellation amplifier having at least one stage in which monitor signals having a constant relatively large amplitude are injected into, for example, a main amplifier. The monitor signals are used to measure the status of all individual components of the amplifier and are useful for fault detection and isolation. In addition, the monitor signals are cancelled in the output to a very low level and as a result, on-line monitoring can be performed without significant radiation of power from a load antenna.

Quasi-monolithic 4-GHz power amplifiers with 65-percent power-added efficiency

Abstract: A highly miniaturized C-band 1-W GaAs FET amplifier, part of a three-stage power amplifier for communications satellite applications, has been designed, fabricated, and tested. It achieves a maximum power-added efficiency of 65%, and occupies an area of 0.20 by 0.36 inches. The circuit uses a low-reactance termination at the second harmonic and low-loss quasimonolithic circuitry. Intermodulation distortion performance at intermediate and high drive levels was found to be comparable to that of a class A amplifier. These results were obtained on the first fabrication run and with no circuit tuning. >

RF power amplifier protection

Abstract: An RF power amplifier is operated by supplying an RF signal to the amplifier for amplification and thereby providing an output RF signal to the amplifier's output circuit which has an impedance matching output network connected in series with a load. A detector serves to detect any reflected power in the output circuit. The RF power amplifier is turned off when the detected RF power exceeds a reference level. The amplifier is protected by discontinuing the supply of the RF signal to the amplifier while it is turned off and, instead, a frequency signal is supplied to the RF amplifier having a frequency that corresponds with that of any current flowing in the output circuit.

RF power supply for supplying a regulated power amplified unmodulated drive signal to an RF modulator

Abstract: An RF power supply serves to supply a regulated power amplified RF drive signal to an RF transmitter. The supply includes an RF oscillator for providing an RF input signal. A DC voltage source provides a DC voltage V. A plurality of power amplifiers are provided with each receiving the input RF signal and each having an input for receiving a DC voltage signal, and each serving to amplify the input RF signal by an amount dependent upon the magnitude of the DC voltage signal supplied to its input and thereby provide an amplified RF signal. The amplified RF signals are combined to provide an RF drive signal. The DC voltage V is directly supplied to the input of at least a first one of the power amplifiers. A regulating means serves to regulate the magnitude of the RF drive signal with the regulating means including circuitry for applying a fractional portion of the DC voltage V to the input of at least a second one of the power amplifiers with the fractional portion varying as a function of any variation in the magnitude of the DC drive signal with respect to a desired magnitude thereof.

A high efficiency Ka-band monolithic GaAs FET amplifier

Abstract: A monolithic three-stage Ka-band GaAs FET power amplifier has been designed and fabricated on MBE (molecular-beam epitaxy)-grown material with a highly doped (8*10/sup 17/ cm/sup -3/) channel. Devices with gate length of 0.25 mu m and gate width of 50 mu m, 100 mu m, and 250 mu m were cascaded. The gate and drain bias networks were also integrated. A maximum small-signal gain of 26 dB was obtained with 4 V on the drain and 0 V on the gate. When biased for large-signal operation, the amplifier was capable of generating 112 mW output power with 16-dB gain and 21.6% power-added efficiency at 34 GHz. It is believed that this is a record efficiency for a GaAs MMIC (microwave monolithic integrated circuit) amplifier at this frequency. >

Distributed antenna system

Abstract: A distributed antenna system comprises a plurality N of spaced apart antennas (3), each antenna being connected to a RF line (2) via a circulator (4), wherein each circulator (4) is arranged to pass to its associated antenna a fraction 1/N of the RF power incident thereon. This can allow cost savings in providing the components needed for the antenna installation.

Gallium arsenide power monolithic microwave integrated circuit

Abstract: A gallium arsenide monolithic microwave integrated circuit amplifier comprising a first stage having a common gate field effect transistor to provide matching of the input impedance, a second stage having a common source field effect transistor to provide class A gain, and a third stage having a common source open drain field effect transistor to provide class B gain for the amplifier. This monolithic integrated circuit amplifier provides a gain of greater than 25 decibels over a frequency band of 400 Hz-1.5 GHz.

Power consumption control apparatus

Abstract: In some applications of power amplifiers, a prescribed or given amount of distortion is permissible under many operational conditions, as long as lesser amounts of distortion are available upon command. It has been ascertained as a part of the present invention that, by reducing the bias current in one or more of the output stages of a power amplifier, acceptable distortion specifications can be maintained under conditions of low power consumption and low output power requirements while retaining the ability to have more demanding linearity requirement specifications by increasing the bias current to a more linear portion of the I-V (current-voltage) curve and optionally providing increased output signal power. The bias condition of reduced power results in a conservation of electrical power requirements, a reduction of heat and temperature problems within the amplifier enclosure and accordingly an increase in component life and circuit reliability. An environment where such an amplifier finds useful application is in a communication system having the potential for signal fading between transmitter and receiver wherein a potential solution is to increase signal power output from the transmitter in a signal fading condition.

Ka-band monolithic GaAs FET power amplifier modules

Abstract: Monolithic GaAs FET power amplifiers consisting of several power-combined devices are fabricated and evaluated. The baseline monolithic chip design consists of a single stage 400- mu m FET amplifier and a six-way traveling-wave power divider/combiner with a single-stage amplifier in each of the six arms. Several chip combinations were used to make a 1-W amplifier with 5-dB gain and a 0.55-W amplifier with 27-dB gain at 34 GHz. A two-way hybrid combining scheme making use of 0.6-W monolithic chips producing 1 W of output power is also described. >

Low phase noise voltage controlled oscillator

Abstract: A varactor diode tuned voltage controlled oscillator which simultaneously optimizes several techniques to minimize AM to FM conversion in the LC resonant circuit to provide an RF signal having minimum phase noise is described. A high gain current limiting RF amplifier is coupled to a high Q, high capacitance, low impedance LC resonant circuit by an impedance transformation network to provide a high tank circulating power having minimum RF voltage fluctuations. The RF voltage across the varactor tuning diodes is further reduced by connecting two varactor diodes in series, back-to-back, or by connecting a fixed capacitance in series with the parallel connected varactor diodes.

On The Path To A Terawatt: High Power Microwave Experiments At Aurora'

Abstract: The Aurora electron-beam generator driving a reflex diode has produced the largest single microwave pulse measured in the laboratory to date (early 1988). In this experiment up to 374 J per pulse is extracted from the device into two radial waveguides. The maximum peak power is 22 GW obtained in a single narrow spike; the peak average power is 9 GW over 20 ns. The power flux through the 0.061-m2 area of the two WR975 waveguides is 145 GW/m2, four times the flux once thought to be present in a previous experiment'. In many aspects the experimental results agree with simulation predictions. This paper discusses the recent measurements and indicates directions for further developments with the potential for terawatt peak RF power pulses.

V-band monolithic power MESFET amplifiers

Abstract: Monolithic GaAs power amplifiers developed for V-band applications are described. A single-stage amplifier provided >4-dB gain from 50 to 56 GHz, with output power of 95 mW and a power-added efficiency of 11% at 55 GHz. A cascaded amplifier achieved 16.2-dB gain and output power of 85 mW. An optimized device structure together with computer-aided design (CAD) programs resulted in the use of MESFETs with larger gate width than those previously reported, achieving the high-output-power monolithic circuits from the initial design. Built-in, DC-blocking capacitors and bias networks allowed the cascading of these MMICs, providing usable power gain with stable operation. >

Apparatus and method for paralleling power field effect transistors in high frequency amplifiers

Abstract: Switching power amplifier circuits for use in a frequency range from 0.5 MHz to 100 MHz are described. The power amplifier circuits have power field effect transistor (FET) devices as output components and the FET devices are driven by bipolar transistor devices without frequency limiting components. The power amplifier circuits can be coupled in parallel and the coupled amplifier circuits can be operated in a push-pull mode of operation for increased power. The systems using these amplifier devices can operate in a Class A, B, C, D, E, F and S modes. In particular, a Class D amplifier system is described that uses the switching power amplifier circuits in the extended frequency range.

High power class-E amplifier for high-frequency induction heating applications

Abstract: Design and construction details are given for a 500 W output class E amplifier operating at 33 MHz suitable for highfrequency induction heating applications The unit utilised a single TO3P packed MOSFET to achieve the power output

Computer control of a Class-E amplifier

Abstract: High frequency electrical power supplies used in many industrial applications have to be able to withstand appreciable variations in load impedance. This paper describes the use of a computer to control a Class-E amplifier power supply which is being developed for high frequency induction and dielectric heating applications.

Modulator producing phase modulation by combining amplitude modulated signals

Abstract: A system is described for using the modulation of the phase of a RF carrier as means of transmitting information. The RF input is split into four quadrature components each of which is passed through individual amplitude control attenuators and then summed in a combiner to create the required phase-controlled RF signal. The resultant signal is then amplified in an RF signal amplifier chain as required to achieve the desired output level. The RF output level is sampled and routed back to an in-phase splitter the output of which is compared to the corresponding individual quadrature components of the unmodulated RF signal to generate a signal which is compared with a processor generated modulation reference signal in a control loop amplifier and the resulting error signal is applied to the individual attenuators to adjust the output amplitude of each quadrature component. The quadrature components are then combined to obtain the desired phase-modulated RF output signal.

A TDMA indoor radio communications system using cyclical slow frequency hopping and coding-experimental results and implementation issues

Abstract: The authors describe the principle, implementation, and performance of an experimental 1.5-GHz radio communications system within a medium-size office building. The system features 1-Mb/s TDMA (time division multiple access) for service flexibility and slow frequency hopping and coding for immunity against multipath fading and interference. Measurements show that with a hallway-mounted distributed antenna system and with the mobile unit transmitting only 1 mW of peak RF power, only a single 384-bit frame out of a total of about 200,000 transmitted frames suffered an unrecoverable error. The same excellent performance was obtained from a central antenna, but only with the transmitted power increased to 100 mW. >

Predistortion Linearisation of Amplifiers for UHF Mobile Radio

Abstract: Predistortion introduced to correct for amplifier nonlinearity is a technique well known in principle, but its application has been restricted to relatively expensive high power amplifier installations. Small cells for FM and TDMA mobile communications systems require linear transmitter amplifiers with power outputs of about 100 mW to 1 W. This paper describes the theory and evaluation of a 1 GHz medium power amplifier whose performance has been enhanced by a simple predistorter circuit. Tests over a temperature range of -10°C to 52°C show that a significant improvement in linearity can be maintained for all amplifier drive levels up to a maximum drive level by means of a simple diode and resistor predistorter circuit that includes an external bias which needs to respond to temperature but not to drive level.