Showing papers on "RF power amplifier published in 1984"

Temperature compensated automatic output control circuitry for RF signal power amplifiers with wide dynamic range

Abstract: Improved temperature compensated, automatic output control (AOC) circuitry for RF signal power amplifiers is described that maintains the output power within one-half dB of a selected one of eight power levels varying from nine milliwatts to five watts, a dynamic range of twenty-eight dB. The amplification of the RF signal amplifier is proportional to a drive current signal provided by a current amplifier. A half-wave rectifier is coupled to the output of final amplifiers for generating an output power signal that has a magnitude proportional to the output power. The half-wave rectifier is temperature compensated for and biased by a diode coupled to the rectifier by one resistor and coupled to supply voltage by another resistor. The output power voltage is further coupled to an amplifier having an amplification factor selected by level control signals. The amplified output power signal is coupled to a comparator which varies the drive current provided by the current amplifier in response to the voltage difference between the amplified output power signal and a reference voltage.

Collector amplitude modulation of the class E tuned power amplifier

Abstract: In the class E high-efficiency switching-mode tuned power amplifier, the RF output amplitude is almost exactly a linear function of the collector dc supply voltage, since conduction angles and wave shapes are not changed by the dc supply voltage. Thus the RF output can be amplitude-modulated by varying the dc supply voltage in accordance with desired amplitude-modulation (AM) envelope. Deviations from the ideal linear modulation characteristic are caused by: transistor saturation voltage; RF feedthrough from the driver via C_{cb} ; nonunity transmission of the ac modulating signal into the amplifier through the nonzero inductance of the collector shuntfeed RF choke; and differences in the magnitudes and delay times, of the RF transmission function through the RF output network, of three different frequencies: lower sideband, carrier, and upper sideband. Design criteria are given, to hold the modulation distortion below a limit chosen by the designer. Experimental results agree well with analytical predictions. Distortion of the modulation envelope can easily be held below 1 percent.

Bidirectional buffer amplifier

Abstract: Bidirectional amplifier employs a single buffer amplifier (64). The bidirectional amplifier is programmed by applying a control signal (Q) and its complementary signal (Q), which establishes the state of four pass transistors (P'1, P'2, P'3, P'4) or four CMOS transmission gates (T1, T2, T3, T4). For a first selection of the control signal, the bidirectional amplifier receives an input signal on a first lead (A') and produces an amplified signal on a second lead (B'). For a second selection of the control signal, the amplifier receives an input signal on the second lead (B') and produces an amplified output signal on the first lead (A').

Variable gain power amplifier

Abstract: A power amplifier having plural parallel amplification circuits of different gains selectively actuable to zero and maximum gains, and electronic switches to select a circuit for connection to a common output junction.

Basic limitations on waveforms achievable in single-ended switching-mode tuned (Class E) power amplifiers

Abstract: The class-E switching-mode tuned power RF amplifier achieves high efficiency (ideally 100%) even if the switching times of the active device are appreciable fractions of the period of the output waveform, by shaping the switch voltage and current waveforms so that the voltage and current transitions are displaced in time from each other. As a second-order factor, nonideal waveform shaping results in power dissipation. That dissipation could be minimized if the nonideal voltage and current waveforms could be made to have zero values at the times the switch is turned on and off. This paper shows that no configuration of linear circuit elements can provide zero voltage and zero current at both transitions of the switch, if nonzero output power is to be delivered to a load. Therefore, a jump of current and/or voltage must be tolerated at the switch turn-off and/or turn-on; the minimum jump magnitude is derived. That jump imposes a lower bound on the power dissipation, determined by the degree of nonideality of the waveform shaping. Also derived is a new general equation for the output power of a single-ended switching-mode tuned power amplifier.

Computer-Aided Error Correction of Large-Signal Load-Pull Measurements

Abstract: A versatile system is described for the large-signal characterization of microwave power MESFET's. High accuracy is obtained through vector error-correction techniques. The system is calibrated using a procedure based on conventional automatic network analyzer calibration measurements and a series of simple insertion loss measurements. The measurement system provides accurate reflection coefficient and RF power data over a wide range of device loading conditions.

VSWR Tolerant linear power amplifier

Abstract: There is disclosed a power amplifier which is useful in broadband systems having load impedances with VSWRs up to a range of 2:1 or 2.5:1. The power amplifier is constructed to change its operating conditions to match the load as presented at the output of the amplifier and is particularly useful in systems employing frequency hopping requiring broadband construction. A feedback signal from the output of the amplifier is constructed to provide a signal representing the difference between forward and reflected power which is compared in a multiplier with a signal representing current flow in the power amplifier to produce a control voltage for adjusting the supply voltage of transistors forming the power amplifier. Thereafter, if the load impedance changes, the supply voltage is also changed to minimize dissipation and maintain the efficiency of the amplifier substantially constant.

Adaptive feedforward cancellation technique that is effective in reducing amplifier harmonic distortion products as well as intermodulation distortion products

Abstract: An improved feedforward cancellation amplifier is disclosed, characterized by the arrangement of an adaptive cancellation modulator for each fundamental input signal at the input of a power bank amplifier. With such an arrangement, phase and amplitude modulation for adaptive cancellation of each fundamental signal is performed in the power amplification path of the feedforward canceller. Accordingly, the harmonics produced by the modulators for each fundamental signal are cancelled in the output of the power bank amplifier and the signal levels at the input to the power bank amplifier are less than those in the input sample path of the canceller.

Apparatus for controlling transmission output power

Abstract: In transmission output power control apparatus of the type comprising a voltage variable attenuator inputted with a transmission signal, a power amplifier amplifying the output of the attenuator, a circuit detecting a portion of the output of the power amplifier, a reference voltage generator, a comparator for comparing with each other the outputs of the detector and the reference voltage generator and producing an error signal, a DC amplifier for amplifying the error signal, the output of the DC amplifier being supplied to the voltage variable attenuator for controlling either one or both of the input level and output gain of the power amplifier, there is provided a control voltage generator for producing a gain control voltage which is used to control the gain of the DC amplifier in response to the output of the detector.

Stabilized microwave power amplifier system.

Abstract: A power amplifier (28) including a Klystron is stabilized against variations in output power with a simplified servo-loop system and cooperating temperature compensation. The system is fully solid-state, digital, and includes an operator-presettable initial power selector, a power output sensor (46), comparator logic (48), variable attenuation responsive to error signals indicative of deviation from the preset power, and temperature compensation means (14), for assured accuracy and stability.

0.5 W 2-21 GHz monolithic GaAs distributed amplifier

Abstract: A novel circuit concept to reduce the gate loss using series capacitors on the gate feeding lines has been implemented for a distributed amplifier design. It has significantly increased the gate width of the amplifier with a resultant increase of the broadband output power and efficiency. A monolithic GaAs distributed amplifier using 6 x 300-micron FETs has achieved a record output power of 0.5 W over the 2 to 21 GHz frequency band with at least 4 dB gain. The power-added efficiency was 14 percent. The linear gain was 5 plus or minus 1 dB over the same frequency band.

Feed-forward microwave power amplifier with difference signal distortion cancellation circuit

Abstract: A feed forward microwave power amplifier having a divider for dividing an input signal into two parts, a first main amplifier for amplifying one of the divided signals, means for providing a part of the output of the first amplifier as a signal S 1 , means for providing a signal S 2 by another output of the divider, a subtractor for providing the difference between S 2 and S 1 , a second amplifier having the same gain as that of the first amplifier for amplifying this difference, a 3 dB coupler for coupling an output S 4 of the first amplifier and an output S 4 e, where e is a constant, of the second amplifier to provide coupled power which is free from distortion, and adjusting means for adjusting the level of signals S 1 and S 2 so that S 2 is higher than S 1 , and the value e is in the range between 0.2 and 0.5. The particular features of the present invention, compared with a prior feed forward amplifier, are the use of a 3 dB coupler, and the configuration of the second amplifier which accepts not only the distortion component but also some desired component of the output of the first amplifier.

A High-Power Automatic Network Analyzer for Measuring the RF Power Absorbed by Biological Samples in a TEM Cell

Abstract: A device for measuring the radiofrequency (RF) power absorbed by biological samples while they are being irradiated in a transverse electromagnetic (TEM) cell is described. The report discusses the design, calibration, and performance of this automated measurement system. The power absorption analyzer is based on a six-port type of automatic network analyzer, and operates at an incident power to the TEM cell of 1 to 1000 W, over a frequency range of 100 to 1000 MHz. Experiments show that an absorbed power of 0.02 to 0.05 percent of the incident power can he measured. Measurements of the power absorbed by a 1-percent saline solution were made rising the power absorption analyzer and by an independent calorimetric measurement. The two measurement techniques show excellent agreement.

Circuit for detecting RF coil assembly position in an MR scanner

Abstract: A circuit for detecting the position of a radio frequency (RF) coil assembly in a magnetic resonance (MR) scanner includes, in the preferred embodiment, a normally closed switch connected to ground in parallel with a PIN diode which forms part of a transmit/receive (T/R) switch used to selectively couple the RF coil assembly to an RF power amplifier and an RF receiver preamplifier. The switch is operable by an actuating rod mounted to the RF coil assembly structure, whose position is to be sensed, such that when the assembly is in place the switch contacts are closed, and open when the assembly is not in place. The opening and closing of the switch shunts the PIN diode in and out, respectively, of the T/R switch circuit, thereby changing the voltage drop across other PIN diodes in the circuit. This change is sensed by a comparator circuit, the output of which is indicative of the RF coil assembly position.

RF Power amplifier for use with VHF transceivers

Abstract: An improved power amplifier is disclosed which is particularly useful with very high frequency (VHF) transceivers. The power amplifier includes a control loop configured to sense the input radio frequency signal and use that signal as a reference for comparison with the radio frequency output from the amplifier to control amplifier power output. The loop forces the amplifier's output radio frequency envelope to follow the input radio frequency envelope and thus produce a constant gain loop. A limiter in the loop forces the loop to produce a constant power output when the input signal exceeds a level set by the limiter.

ICRF heating in TFR and the problem of impurity release

Abstract: The efficiency of ICRH in TFR was limited in the 1981 experiments by an important influx of metallic impurities in the plasma core. Using carbon limiters and different materials for the antennas Faraday shield leads to a significant decrease of the metallic impurity content : in contrast with the previous results, the increase of temperature associated with the RF pulse remains now constant for more than 0.1 s. However, the power radiated by the metallic ions at the end of the RF pulse still reaches an appreciable fraction of the total RF power, particularly when using an antenna generating the RF wave from the low magnetic field side of the plasma. This effect is attributed to an interaction of the RF wave with the low density plasma located in the scrape off layer.

Apparatus for avoiding clipping of amplifier

Abstract: A preclipping control technique is utilized to prevent the occurrence of clipping distortions evidenced in the output of an amplifier. Reference means provides an upper voltage level slightly lower than the upper saturation or clipping level of the amplifier output signal, and also provides a lower voltage level slightly higher than the lower saturation or clipping level of the amplifier output signal. A comparator is connected to the output of the amplifier and compares the output signal with the reference levels. Under normal conditions, when the output signal is located within the range lying between the upper and lower reference levels, the amplifier input signal is not attenuated. However, when the output signal goes out of the range, this will activate an attenuator connected between a signal source and the amplifier to introduce a controlled attenuation in the amplifier input signal; clipping is prevented.

Electrosurgical unit with regulated output

Abstract: An electrosurgical unit having feedforward power regulation. In one embodiment there is an amplifier which produces a pulse modulated electrosurgical output signal. A microprocessor calculates an adjusted pulse width (duty cycle) just sufficient to account for the power changes due to voltage fluctuations. The microprocessor controls the pulse width of the gate voltage of a power transistor in the amplifier to regulate the amplifier output. In another embodiment the supply voltage is fed into the base drive circuitry of an amplifier power transistor through the photo-resistor side of an optoisolator. The lamp brightness of the optoisolator and thus the gain of the base drive circuitry is adjusted by the amplifier power level control. The nonlinearity of the optoisolator complements the nonlinearity of the amplifier so that the net gain in the amplifier drive at any power setting is just sufficient to account for the voltage fluctuation.

A 2—18-GHz monolithic distributed amplifier using dual-gate GaAs FET's

Abstract: This paper describes a 2-18-GHz monolithic distributed amplifier with over 6-dB gain, ± 0.5-dB gain flatness, and less than 2.0:1 VSWR. Measured noise figure is below 7.5 dB, and power output capability is greater than 17 dBm, The amplifier is designed with dual-gate GaAs FET's instead of single-gate FET's for maximum gain over the design bandwidth. Cascaded amplifier performance will also be presented.

Charge-control analysis of class E tuned power amplifier with only one inductor and one capacitor in load network

Abstract: The following paper presents the charge-control analysis of operation of the transistor as a switch in the inverter circuit in which the collector current is constant while the transistor is saturated. This paper presents the charge-control analysis of the class E high-efficiency switching-mode tuned power amplifier with only 1 inductor and 1 capacitor in the load network, along with experimental results. In this amplifier, the collector current increases linearly with time while the transistor is saturated. We assume linear charge parameters of the transistor, and rectangular-wave base-drive current. The following are determined: the waveforms of all components of the base current and the base stored charge, the switching times, the driving power, and the power gain. A new definition of the overdrive factor of the transistor is introduced and the condition of the transistor saturation is discussed. It is shown that the base current necessary to drive the transistor to the edge of saturation increases with frequency f for f > f_{\beta} .

Travelling-wave laser amplifier experiments at 1.5 μm

Abstract: The gain of a 1.5 μm semiconductor travelling-wave amplifier has been measured with signals in different polarisation states, and the amplifier has been used as a repeater in a phase-modulated coherent system.

Multiple feed Rf coils

Abstract: An Rf coil arrangement for MRI systems wherein the electrical length is reduced to improve the S/N ratio and the Rf power efficiency.

Method of compensating an amplifier system having a variable gain amplifier to achieve a constant overall system signal gain and an apparatus utilizing the same

Abstract: A variable gain amplifier is adjusted to maintain its amplification within a linear range, i.e., to prevent saturation of the amplifier, by utilizing the output of an analog-to-digital converter, which is arranged to convert an analog output of the amplifier to a digital representation, by a digital computer to effect the gain change of the amplifier. Concurrently, the output signal of the digital computer representing the output signal from the analog-to-digital converter is modified to produce a system output signal based on a constant overall gain of the system which is equivalent to the highest available gain from the amplifier. Thus, while the amplifier gain is adjusted by the computer in response to the amplitude of the input signal, the overall system gain is maintained at a level which would be available at the highest amplifier gain. The digital output of the system can subsequently be utilized as a control signal either directly or after a digital-to-analog conversion.

Radio frequency pumped mid-infrared waveguide lasers

Abstract: RF discharge waveguide laser technology has been extended from the 10.6 μm CO 2 laser to include 2.7 μm HF, 3.8 μm DF, and several rare gas mid-infrared lasers. The maximum achieved electrical efficiencies of 5.3 and 4.0 percent were demonstrated in pulsed HF and DF systems, respectively. These, as well as several low efficiency rare gas lasers were demonstrated in a 20 cm gain length device. The output power and spectral distribution were determined as a function of the gas composition, pressure, velocity, and the RF power, pulse length, and repetition rate.

Radio receiver with logarithmic signal strength detector

Abstract: A radio receiver has one or more automatic gain control (AGC) circuits that each generate the gain-determining bias current in a separate main channel section or sections, e.g. RF amplifier, mixer, IF amplifier, of the radio receiver. The receiver is for the most part formed in an integrated silicon circuit, wherein the gain-controlling current in each case biases the base-emitter junction of an amplifying grounded-emitter transistor so that the gain thereof is directly proportional to the magnitude of the AGC control current. That current in each case is caused to flow through a diode string to generate a voltage drop thereacross that is logarithmic function of the AGC control current as well as of the radio signal amplitude at the input of the AGC controlled section. The sum of those diode voltages may be taken to produce a log of the product of the gains of the AGC controlled sections. Thus a sum signal is a logarithmic function of the radio signal input to the receiver.

Variable power amplifier for audio frequency signals and method

Abstract: A variable power amplifier having a constant current differential amplifier driving a cascaded driving amplifier, a variable power amplifier including a vacuum tube for selectively amplifying output signals wherein the drive of the variable power amplifier is determined by the plate shunt resistive loading of the vacuum tube, a push-pull amplifier including an output transformer operatively coupled to the variable power amplifier and to an amplifier output terminal to amplify and apply to the amplifier output terminal a selectively amplified output signal, and a variable damping circuit including a sensing element for sensing the loading on the output tranformer and a circuit for defining a feedback loop for producing a feedback signal having magnitude and polarity which are determined by the sensing element and wherein the variable damping circuit includes a circuit for applying the feedback signal as an input to the constant current differential amplifier to control the current level thereof as a function of the loading on the output transformer as sensed by the sensing element and wherein the plate current resistive loading of the vacuum tube in the variable power amplifier determines the drive thereof to limit the power of the selectively amplified output signals applied to the amplifier output terminal as shown. The combination of a preamplifier having pluggable modules for providing controlled output signals and a variable power amplifier is shown. A method for processing audio frequency electrical signals is also shown.

A 2--18--GHz Monolithic Distributed Amplifier Using Dual-Gate GaAs FET's

Abstract: This paper describes a 2- 18-GHz monolithic distributed amplifier with over 6-dB gain, +- 0.5-dB gain flatness, and less than 2.0:1 VSWR. Measured noise figure is below 7.5 dB, and power output capability is greater than 17 dBm. The amplifier is designed with dual-gate GaAs FET's instead of single-gate FET's for maximum gain over the design bandwidth. Cascaded amplifier performance will also be presented.

Ultra high frequency power amplifier

Abstract: The invention provides a high gain ultra high frequency amplifier with high output power and low phase shift. This amplifier, whose organization is arborescent, comprises a plurality of series amplification stages (1st to 5th), each stage comprising a plurality of elementary cells. Each cell has only one input but at least two outputs. A cell is, for example, a field effect transistor, with input at the gate and outputs at two drains. The input of the first transistor forms the input of the amplifier. A metalization which joins together all the outputs of the transistors of the last stage forms the output of the amplifier. The transistors are input and output matched by means of microstrip lines, capacities and inductances. The monolithic implantation of this amplifier may, among other things, be provided concentrically about the input transistor or linearly with the transistors of the last stage on one line and those of all the other stages on another line.

Bipolar monolithic very‐wideband amplifier

Abstract: Analog basic amplifier ICs (e.g., differential amplifiers, parallel feedback amplifiers, gain control amplifiers) and equalizing amplifier ICs for repeater circuits of high-capacity optical transmission systems are designed using high-speed bipolar technology (e.g., SST-2). Particular consideration is given to reduction of base resistance, optimization of current density and pattern layout and improving breakdown voltage in applying this technology to analog circuits. Moreover, a peaking technique is applied to wideband amplifiers and a gain control amplifier is constructed which has wide linearity and can be directly connected to other differential circuits because of its constant dc level. For a differential amplifier with peaking, a gain of 15 dB and bandwidth of 1.4 GHz are realized. Expansion of bandwidth by peaking is also applied for the gain control amplifier and a gain of 28 dB, bandwidth of 630 MHz and a variable gain range of 30 dB are obtained. In addition, an equalizing amplifier with transimpedance of 70 ∼ 620 dB and bandwidth of 410 ∼ 620 MHz is constructed. Thus, it is evident that integrated repeater circuits for use in high-capacity optical transmission systems can be realized.

A high-harmonic gyro-klystron amplifier: theory and experiment†

Abstract: Experimental results of a high-harmonic gyro-klystron amplifier are presented along with small-signal theory and large-signal simulation data. In this device, axis-encircling electrons interact synchronously with high-order azimuthal cylindrical-cavity TE modes. Gain in excess of 20 dB has been achieved at the fifth and sixth harmonics of the cyclotron frequency. The requisite high-energy beam is provided by a gyro-resonant RF accelerator. Harmonic operation together with RF acceleration potentially constitute a compact high-power high-frequency amplifier.