Showing papers on "RF power amplifier published in 1970"

Amplifier protection circuit

Abstract: A protection circuit for a transmitter amplifier is provided which senses the forward power level and develops a first voltage which is compared with a reference voltage to provide a control voltage which controls the power developed by the transmitter amplifier. Increase in the forward power level is detected changing the control voltage to cause a reduction in the forward power developed by the transmitter amplifier. Decrease in forward power level is detected changing the control voltage to cause an increase in forward power developed by the transmitter amplifier. Reflected power is sensed developing a second voltage which causes a reduction in reference voltage when reflected power exceeds a predetermined level. Reduction of the reference voltage also changes the control voltage to reduce the forward power of the transmitter amplifier to a safe level. An increase in transmitter amplifier temperature beyond a predetermined level is sensed causing a reduction in the reference voltage to change the control voltage thereby reducing the power of the transmitter amplifier to a safe level.

Logarithmic rf amplifier employing successive detection

Abstract: A logarithmic radio frequency amplifier is disclosed which employs a series of cascaded RF amplifier stages. Each amplifier stage includes a detector for demodulating the output of each amplifier to produce a video signal. A limiter is provided for each detector for limiting the video signal output of each of the detectors. The limited video output from each successive stage is applied to a summing delay line to produce the logarithmic video output at the end of the delay line.

Signal conditioner and bit synchronizer

Abstract: A signal conditioning circuit for use in a digital communication system for restoring the waveform of a received signal which may have been degraded during transmission. The incoming signal is applied to a variable gain amplifier, filter and direct current amplifier and the resulting output signal is compared both positively and negatively to predetermined reference values. Where the output signal deviates from these two references, a digital control signal is developed for adjusting the gain of the variable gain amplifier and the baseline of the direct current amplifier such that the output pulse conforms to a predetermined value.

Theoretical efficiencies of class-D power amplifiers

Abstract: The theoretical efficiencies of class-D amplifiers are compared with those of conventional amplifiers by means of a power balance. As a result of certain similarities, it is suggested that class-AD and class-BD modes of operation should be defined. The class-D amplifier converts the collector dissipation of a conventional amplifier into load power components at a large number of modulation frequencies. When these are removed by filtering, a high overall efficiency results. The analysis presented includes an idealised treatment of the class-D amplifier with an inductive load, and enables constructive comparisons to be made.

Automatic impedance matching system for RF sputtering

Abstract: A previously described' “L” type matching network used for rf sputtering is shown here as part of Fig. 1. The purpose of the network is to transform the complex impedance of a sputtering system to a purely resistive value of 50 Ω. This makes possible the use of a transmission line with a characteristic impedance of 50 for the conveyance of rf power to the system. The rf power is conveniently monitored by a power meter in the transmission line. Since the power meter is capable of measuring both forward and reflected power, the voltage standing wave ratio (VSWR) on the transmission line can be computed. The VSWR will be unity when the matching network is adjusted so that the transmission line is terminated in its characteristic impedance. Practically, it is difficult to achieve a VSWR of unity (zero reflected power), so the network is adjusted to approach that optimum state as nearly as possible.

Single antenna signal retransmission device

Abstract: A device for receiving a signal via an antenna and for retransmitting via the same antenna an augmented signal of identical frequency and coherent phase. A circulator connected to the antenna directs the received signal to a diode switch and thence to a broadband RF amplifier. The switch periodically, alternately isolates and passes the received signal to the amplifier in response to a square wave control signal having a frequency considerably lower than that of the received signal. The sampled, amplified signal is delayed by a time duration substantially equal to one-half the period of the control signal, and then supplied via the circulator to the antenna. The device is useful as an augmentation amplifier, and for enhancing radar target reflectivity.

RF power transistor metallization failure

Abstract: RF power transistors employing aluminum metallization can degrade and fail when the aluminum carries high-current densities at elevated temperatures. Two distinct mechanisms promoted by electromigration lead to failure. These are 1) the growth of etch pits filled with aluminum which penetrate and short the emitter-base junctions and 2) a reconstruction of the metallization which increases the electrical resistance reducing the device efficiency.

Feed-fordward amplifier

Abstract: The parameters of a feed-forward compensated amplifier are redefined such that the error correcting signal and the uncorrected signal combine in phase at maximum output power. It is then shown that for this condition a directional coupler can be used as the error injection network with minimal loss of error signal power or main signal power. This results in the most efficient use of both the main signal amplifier and the error signal amplifier and, in addition, produces an impedance match in the main signal wavepath, in the error signal wavepath and at the output terminal of the overall amplifier.

Power amplifier including plurality of push-pull amplifier sections having outputs coupled in parallel

Abstract: A high power semiconductor amplifier, which may be used as the power amplifier of a radio transmitter, includes a plurality of push-pull amplifier sections cooperating to provide the required output power. The amplifier sections are coupled by broadband transformers having ferrite cores and a plurality of inter-wound coils. This affords direct current isolation of the sections and a high degree of coupling as required for broadband operation and provides stable high gain operation with the signals in the two amplifier sections being in very close phase relationship so that they can be combined in-phase for maximum efficiency. The coupling circuit at the output of the sections includes the secondary windings of the transformers connected in parallel circuit branches extending from the reference potential to the output line to reduce the effect of stray reactances. The amplifier is usable over a wide range of frequencies with a minimum of adjustment.

Feed-forward amplifier having arbitrary gain-frequency characteristic

Abstract: Frequency-shaping of the gain characteristic of a feed-forward, error-corrected amplifier using main and error amplifiers having essentially flat, or frequency-independent gain characteristics, is achieved by tapering the power division characteristics of: the input coupler, which extracts a reference signal component from the input signal; the sampling coupler, which compares the output from the main amplifier with the reference signal to form an error signal; and the error injection coupler, which injects the error signal into the main signal path. In a second embodiment of the invention, the band-shaping burden is shared between the amplifiers and the couplers.

Power amplifier including plurality of push-pull amplifier sections coupled by ferrite matching transformers

Abstract: A high power semiconductor amplifier, which may be used as the power amplifier of a radio transmitter, includes a plurality of push-pull amplifier sections cooperating to provide the required output power. The amplifier sections are coupled by broadband transformers having ferrite cores and a plurality of inter-wound coils. This provides direct current isolation of the sections and a high degree of coupling as required for broadband operation, and also results in stable operation and signals in the two amplifier sections which are in close phase relationship so that the outputs thereof can be combined in-phase for maximum efficiency. The coupling circuit at the input and/or the output of the sections includes windings of the transformers in series with a variable reactance element for tuning the same. The amplifier is usable over a wide range of frequencies with a minimum of adjustment.

High-Rate rf Sputtering System

Abstract: A sputtering target system utilizing high vacuum as the electrical insulator is described. This technique permits the application of high rf power to the target. Power up to 5000 W has been applied to a 7.3-cm-diam electrode bonded to a 10-cm-diam Al2O3 target. Under the proper conditions of geometry, gas pressure, and magnetic field, this has resulted in deposition rates of Al2O3 in excess of 6300 A/min. For an SiO2 target with 3000-W input, deposition rates in excess of 10 000 A/min have been obtained. Typical deposition rates of Al2O3, are given for this target system as a function of rf power, magnetic field, and gas pressure.

Liquid Helium Temperature cw NMR S/N Improvement Using a MOSFET rf Amplifier

Abstract: Improvement of the signal‐to‐noise (S/N) ratio of cw NMR spectrometers by cooling circuit components to liquid helium temperature is discussed. Criteria for design of a low temperature circuit using a twin‐T bridge and MOSFET amplifier are presented. A liquid helium temperature spectrometer for operation at 16 MHz which improves S/N ratio by a factor of 5 over conventional techniques is described.

Reduction of Substrate Heating during rf Sputtering

Abstract: Substrate heating in the rf planar diode during sputtering, thought to be the result of bombardment by secondary electrons produced at the target electrode and accelerated across the cathode dark space, is shown to be reduced by the addition of an rf choke in series with the substrate table. This rf choke allows an rf potential to be present at the substrate table while constraining it to be at dc ground. Since the electrons respond to the total instantaneous value of the electric field, it is shown that they are repelled by the substrates for a portion of the rf period. Low energy secondaries produced during the attractive portion of the rf cycle appear to be trapped within the discharge by time-varying space charge fields. Ions, go first order, respond only to the dc component of the electric field so that there is no excess ion bombardment of the substrates. Direct measurements show that with this effect, about 5% of the net forward rf power is dissipated at the substrate table, whereas in the normal rf planar diode, about 10% of the net forward rf power is dissipated at the substrate table.

Retuning Effects and Dynamic Instability of a Radio‐Frequency Capacitive Discharge

Abstract: A discharge plasma is established in air at pressures of 0.2–20 Torr in the rf electric field between parallel‐plate electrodes in a resonant circuit at 14 MHz. By adjusting a calibrated tuning capacitor in parallel with the electrodes, one can observe a wide range of plasma conditions extending from normal extinction at low rf potential and power to an apparent dynamic instability at high potential and power. The loading effect of the plasma is found to be that of a lossy capacitance. Net input rf power to the plasma‐loaded circuit at the tuning condition just below the threshold for dynamic instability is found to be ∼10 times that for a plasma maintained at the tuning condition for the resonant circuit without plasma. The retuning effects are discussed on the basis of the nonlinearity of the plasma medium, and a possible mechanism for the dynamic instability is proposed.

A One-Watt CW High-Efficiency X-Band Avalanche-Diode Amplifier (Correspondence)

Abstract: An X-band avalanche-diode amplifier circuit is described which provides accurate and independent in-band impedance control (R and +jx) and orthogonal second-harmonic reactance control. Low-level gains of 13 dB with 500 MHz of bandwidth have been achieved using this circuit. Power outputs of 1 watt CW with 5 dB of gain and 14.7-percent generation efficiency have also been realized by carefully controlling the in-band and second-harmonic load impedance.

Radio frequency pulse transmitter

Abstract: In a pulse transmitter for airborne distance measuring equipment, the final stage of a two-stage RF amplifier is modulated by a primary modulating pulse having a gradual rise and decay, and the drive stage is modulated by a secondary modulating pulse which envelopes the primary modulating pulse in time so that the final stage has adequate drive before the primary modulating pulse occurs.

Amplifier protection circuit responsive to temperature and overcurrent

Abstract: A protection circuit for the transistorized power amplifier of a transmitter is provided in the form of a normally shunted reactive circuit coupled in series with the input to the power amplifier stage means of a current stepdown transformer. When excessive current is drawn by the power amplifier or when an excessive temperature is reached the shunting circuit is opened thereby connecting the reactive component in series between the driver stage and the power amplifier stage to partially detune the driver output, reducing the drive to the power amplifier stage.

Power Amplification with Anomalous Avalanche Diodes

Abstract: The experiment described in this paper is performed for the purpose of obtaining additional information that might help to elucidate the operating principle of the anomalous mode. The diodes under investigation are of a silicon p/sup +/-n-n/sup +/ mesa structure. The breakdown voltage is 160 volts; the punch-through voltage is 60 volts. The test setup is similar to a conventional reflection-type amplifier with the diode mounted in a coaxial-cavity-like circuit. The reverse-bias pulse drives the diode to a low avalanche current level at which anomalous operation would normally commence. In this case, however, the tuning and loading of the cavity and its associated stubs is intentionally arranged to minimize free-running oscillations. Any residual RF power is reduced to the level of weak instabilities without any strong harmonics or subharmonic. Only in the presence of an input driving power with a frequency at or near the resonance frequency of the system, does an amplified power of the same frequency appear at the output port. Starting from the residual level the output power increases proportionally with the input power until at higher drives a saturation level is reached. In this particular case, operating at 410 MHz, saturation is reached at 18.5 watts with a maximum power gain of 12 dB and a bandwidth of 26 MHz. This output is approximately 20 to 30 dB higher in amplitude than any observable peak in the residual broad-band frequency spectrum Operating the diode as a free-running "hard" oscillator at the same current level and frequency, 18.8 Watts of RF power is obtained. The initial and steady-state power levels are substantially the same for both amplifier and oscillator. A plausible evaluation of these results can be obtained following van der Pol's differential equation for a forced negative-resistance oscillator.

Stable power amplifier circuit

Abstract: An integrated circuit power amplifier utilizes a quasicomplementary power output stage incorporating an NPN Darlington amplifier for one section and a field-aided lateral PNP transistor cascaded to an NPN Darlington amplifier for the other section. Feedback from the amplifier output terminal to an intermediate stage coupled to the input of the power output stage is separated into DC and AC feedback paths. The biasing of the power output stage includes an epitaxial resistance matched to the field-aided transistor bulk resistance to cancel the effect of the bulk resistance for improved output stage thermal stability.

Power measuring and leveling system using a self-balancing bridge

Abstract: With no RF power applied to a bolometer positioned in a selfbalancing DC bridge, the voltage across a diagonal is nulled with the output of a potentiometer. The diagonal voltage V is measured. The output of the potentiometer is applied to a unity gain buffer amplifier. Part of the power in the output of an RF power source is applied to the bolometer, and the difference Delta V between diagonal and the amplifier output voltages is measured. Using V and Delta V, the power applied to the bolometer is calculated. The diagonal and potentiometer voltages are compared to derive a difference signal used to adjust the level of power applied to the bolometer. Part of the power in the output of the RF source is also applied to a load.

High gain mos linear integrated circuit amplifier

Abstract: A low power dissipation high load impedance metal-oxide semiconductor field-effect transistor (MOS FET) linear integrated circuit amplifier capable of operation at relatively low power supply voltages with high gain.

Computer Aided Design and Analysis of a 2-4 GHz Broadband Balanced Microstrip Amplifier

Abstract: In this paper, a computer-aided design and analysis of a 2-4 GHz broadband balanced microstrip amplifier using a full computer simulation program developed by the author and others is presented. A short and efficient CAD procedure for broadband amplifier design is introduced. The first step is to design an initial narrow-band high gain microstrip amplifier at 3-GHz central frequency. The second step is to optimize the initial lengths and widths of the input and output microstrip-matching circuits to get the broadband amplifier over the range 2-4 GHz. The analysis of both narrow and broadband amplifiers is investigated. In addition, with the design and analysis of a low-pass microstrip filter, the paper introduces the design and analysis of a Lange coupler. The final AC schematic diagram of the designed amplifier with the lengths and widths of microstrip lines is presented. Key Words: Computer-Aided Design and Analysis, Microstrip Amplifier, Microwave Amplifier.

Repeatered submarine cable system

Abstract: As we go to wider bands for submarine cable systems, it becomes difficult to achieve the required power output in undersea repeaters. Two key limitations in determining signal power output capability are the deliverable d.c. power and the temperature rise in the transistors. The present invention is directed to a repeater which employs a class B, rather than the usual class A, output amplifier with energy storage and regulation to overcome both limitations.

Pulse transmitter including means for controlling the amplitude and phase of output pulses

Abstract: A transmission system for transmitting pulses of radio frequency energy includes a radio frequency amplifier output stage, and a source of pulses connected to the input of the amplifier stage. The output signals of the amplifier stage are modulated by means of a modulator connected to modulate the output current of the amplifier. The modulating signals is synchronized with the input pulses.

High gain amplifier and feedback arrangement for current driving a single coil

Abstract: A high gain amplifier and feedback arrangement utilizing a class B power stage for current driving a single coil wherein the precession coil of a spinning magnet gyroscope is controlled by sending a precise current through the coil. A first operational amplifier with differential input terminals generates either a positive or negative output. A positive output drives one side of the class B output stage to control current flow in one direction through the load. A negative output drives the other side of the class B output stage by way of a second operational amplifier connected as an inverter to control current in the inverse direction through the load. The load current is arranged to provide feedback to the first operational amplifier so that the load current is a replica of the input for both directions of current flow in the load. An output stage switching transistor is conducting or cut off when the corresponding class B stage side conducts or is cut off. The two output stage switching transistors are controlled from a switching differential pair of transistors which in turn is controlled by the output of the first operational amplifier. Switching of all switching transistors and circuits occurs when the input signal passes through zero at which time the load current is zero.

Amplifier characteristics of Darlington composite transistor

Abstract: A study has been made of the amplifier characteristics of the common collector composite transistor in which the circuits have been, analysed to obtain the expressions of current gain, voltage gain, input resistance, power gain and output resistance in terms of the various parameters of the individual transistors. Further, the expressions obtained have been simplified for similar transistors of the composite system. The variation of current gain, voltage gain, input resistance, power gain with load resistance and output resistance with source resistance has also been studied and a set of curves is given showing these variations.

High RF power current oscillations in zinc oxide at room temperature

Abstract: Experimental results are presented which indicate the possibility of using n-type ZnO single crystals for relatively high RF power current oscillators, operating at room temperature Devices generating up to 5 watts, at frequencies in the range of 1-10 MHz, have been consistently produced