Direct-coupled Amplifier Research Articles

Power Amplification of Microwave FM Communication Signals Using a Phase-Locked Voltage-Tuned Oscillator

An analog phase-locked oscillator is used as a power amplifier for FM communications signals. Intended service is for FDM telephone message service or television relay. The output power is generated in a varactor-tuned oscillator, which is synchronized with a weak input signal using a phase-lock loop. This involves a phase detector and a wide-band direct-coupled video amplifier whose output is applied to the tuning varactor. The paper is largely theoretical, relating the parameters of the feedback loop to the performance of the overall device. Explicit expressions are derived for the noise figure, the frequency response of the modulation characteristic, AM-PM conversion, and nonlinearity effects in terms of differential gain and intermodulation. In addition, two experimental models are described, together with certain measured data. The phase-lock method differs in many ways from multistage reflection amplifiers and appears to offer advantages for many applications. The device has adequate bandwidth and linearity for a single FDM-FM signal with 1800 or more channels, but must be tuned to the intended frequeucy. Tuning procedures are simple. High gain of 25-35 dB is obtainable in a single microwave "stage." Most of this gain may be associated with the functions of phase detection, video amplification, and VCO tuning. Of major importance, with respect to noise, is that the device is functionally equivalent to a high-gain low-noise microwave preamplifier followed by a low-gain power amplifier stage in which the preamplifier has the noise figure of the phase detector combined with the video amplifier, and the power stage has a noise figure appropriate to the class of power diode used. FM noise generation is substantially lower than in a high-gain reflection amplifier using the same class of microwave power diode throughout.

Automatic Error Compensatton in DC Amplifiers

When operational amplifiers are exposed to high levels of neutron fluence or total ionizing dose, significant changes may be observed in input voltages and currents. These changes may produce large errors at the output of direct-coupled amplifier stages. Therefore, the need exists for automatic compensation techniques. Hlowever, previously introduced techniques compensate only for errors in the main amplifier and neglect the errors induced by the compensating circuitry. In this paper, the techniques introduced compensate not only for errors in the main operational amplifier, but also for errors induced by the compensation circuitry. Included in the paper is a theoretical analysis of each compensation technique, along with advantages and disadvantages of each. Important design criteria and information necessary for proper selection of semiconductor switches will also be included. Introduced in this paper will be compensation circuitry for both resistive and capacitive feedback networks.

A modified chopping method of drift elimination in direct coupled DC amplifiers

The results of measurements of a circuit composed mainly of discrete components and designed for applications in measuring and control equipment are presented. However, it seems to be quite possible to build such a circuit using integrated circuit techniques and a limited number of discrete components.

A Pulse Processor for X-Ray Spectrometry with Si(Li)-Detectors

This paper describes the general features of a pulse processor for use with opto-electronic charge sensitive head amplifiers particularly with Si(Li) X-ray detectors. The instrument contains time-variant filters with direct coupled amplifiers and comprehensive pile-up protection and live time correction. The test results indicate that the system can cope with extremely wide range of signal processing times, counting rates and changes of spectral content without any appreciable degradation in energy resolution and with useful output rates for input rates up to well over 50,000 events/sec.

A very stable electrode system for recording human scalp potentials with direct-coupled amplifiers

Electrochemical factors involved in DC recordings are presented. Described is an electrode system which uses long flexible tubes to separate the metal-electrolyte interface of an electrode from the electrolyte-skin interface. Using commercially available Ag/AgCl skin potential electrodes, the system gave less than 0.5 μV/h drift occurring at each metal-electrolyte interface. The stability of the electrode bias potential is unaffected by connecting the bridge tubes to the subject or by other disturbances that occur during recording. In 1 h recordings from four subjects, the total measured potential changed at an average rate of 9 μV/min—a five fold improvement over previously described electrodes.

A Versatile, Linear, Interface Amplifier for Signal Averaging

A direct coupled linear amplifier is described which has been used as an interface between time mode operated multichannel analyzers or instrument computers and electromagnet control amplifiers or voltage controlled oscillators for magnetic resonance signal averaging. The amplifier accepts the analog memory channel address voltage from the analyzer or instrument computer and attenuates, biases, amplifies, and inverts the signal as required. Operating techniques and circuit stability are discussed.

A differential zero-correction amplifier

The maintenance of a constant equivalent input offset voltage with time and temperature is one of the most difficult problems in direct-coupled amplifiers. An improved zero-correction technique is used to realize a differential amplifier with a very low input offset voltage.

Power losses in small samples of silicon iron

Apparatus is described which enables power loss measurements to be made for small specimens of silicon iron. A reflecting dynamometer wattmeter is used and its sensitivity is increased by means of a direct coupled amplifier in the voltage circuit. Excitation of the magnetic circuit is obtained from a direct-coupled liquid-cooled power amplifier enabling measurements to be made over a frequency range of 3 to 1000 Hz for flux densities up to 1.9 Wb m-2.

アナログICを用いた計測制御用mV入力直結直流増幅器

アナログICを用いた計測制御用mV入力直結直流増幅器

A direct-coupled hybrid IC amplifier with 1-ns rise time

This paper describes the design and operation of a wide-band direct-coupled pulse amplifier, with a voltage gain of 10 and a rise time of 1 ns. Computer-aided analysis and simulation are used to optimize the design and to predict the performance of the amplifier. Good agreement is obtained between the predicted and experimental results. In an attempt to improve the frequency response through the reduction of parasitic capacitive and inductive effects, the amplifier has been fabricated as a hybrid IC by use of thin-film resistors and silicon chip transistors mounted on a ceramic substrate.

A high-performance monolithic IF amplifier incorporating electronic gain control

A direct-coupled monolithic IF amplifier that incorporates an active gain control stage and exhibits a power gain of 50 dB and an AGC range of 60 dB at 50 MHz is described. This circuit has negligible change in either input or output admittance, and has excellent signal linearity over the full range of gain control. Experimental and theoretical analyses are made of the large signal response, stability, available gain, and noise behavior of the circuit. An application to color television is discussed in which the functions of the 45-MHz IF amplifier and the dc-AGC circuitry are fabricated on a single die.

Drift Compensation in Transistorized Differential Amplifier (d.c.)

Emitter coupled differential amplifier with constant current feed is often used as the input stage in high gain direct coupled amplifiers. Although, the problem of zero drift can be partially solved by using matched pair transistors in such amplifier stages, but there is a limit to which drift compensation is achieved in such stages. The paper presents two methods by which further reduction in drift is possible in transistorized differential amplifiers. In both methods temperature sensitive devices are used for compensation of drift resulting from the change in ambient temperature. The circuits were analysed and the condition for minimum possible drift was found out mathematically. Finally the experimental results and the limitations of these circuits were discussed.

Very Low-Drift Complimentary Semiconductor Network dc Amplifiers

This paper describes a new approach to the fabrication of a variety of monolithic direct coupled amplifiers with typical equivalent differential input drifts of 0.1 to 0.2 /spl mu/v//spl deg/C. These amplifiers exhibit a significant improvement in temperature stability over current state-of-the-art IC amplifiers, and complete with chopper stabilized units in many respects. In these amplifiers, a monolithic silicon wafer is maintained at a near constant temperature by means of an electrically separate temperature-control circuit diffused within the same substrate. A thermal-electrical analogy is used to predict temperature gradients on the surface of the silicon bar. Performance of several amplfier circuit configurations is discussed.

Transistors in Current-Analog Computing

A system of electronic analog computing is described in which current is used as the variable. The paper indicates that the circuit properties of transistors make them especially suitable for use in operational amplifiers for this computing technique. Experimental direct-coupled amplifiers are shown which have been built and evaluated using low- power, low-frequency transistors. The amplifiers have been employed under laboratory conditions to per form the operations of summation, scale-change, integration, and differentiation. The factors which determine computing accuracy are analyzed, and a new technique of error predic tion (based on square-wave output) is discussed. The paper concludes that the current-analog meth od promises to use transistors effectively.

A Direct-Coupled DC Amplifier Compensated to 20 kc for Use with Photoemissive Devices

The relative advantages of the use of a negative-feedback operational amplifier as an electrometer amplifier are investigated. This investigation was made because of the need for a detection system with a frequency response from dc to 20 kc. A theoretical analysis of the compensation circuits used to obtain extended frequency response is given. This analysis indicates a dependence of the compensation networks upon the external capacitive loading. Important practical considerations are given. An expression is derived that gives the compensation network parameters as well as the frequency response in terms of absolute gain of the amplifier.

Apparatus Drawings Project. Report Number 30A. A Versatile RC-Filtered Low-Voltage Power Supply and a Calibrated Direct-Coupled Amplifier

A versatile RC-filtered power supply and a calibrated direct-coupled amplifier are described. The power supply furnishes operating power to various electronic devices developed for two large introductory laboratories. It provides about 250 V dc at its rated output of 70 mA, and 2.5 A at 6.3 V ac. The direct-coupled amplifier has 6 output ranges, from 0.5 to 150 V full scale. Its normal input resistance is 22 MΩ, with stable operation at input resistances of 125 MΩ being practical. Output is displayed on an external 100-μA meter. The method of achieving calibration accuracies of ±2% or better, using ±10% tolerance carbon resistors is described. Both instruments are stable and extremely reliable, requiring only standard commercial components and conventional tools and techniques for construction. The cost for parts is $16.26 and $22.05, respectively. The article contains full information regarding construction.

Apparatus Drawings Project. Report Number 28. Versatile X-Y Projector Plotter

The apparatus described is a simple X-Y plotter designed to fit the slide stage of a standard 10- ×10-in. overhead projector. Graphs are drawn with felt pens on the projector's normal writing medium, a disposable plastic foil strip. A magnified image of the graph, as it is being drawn, can be projected at any size suitable for the lecture room involved. The plotter consists of two servo-balanced slide-wire potentiometers set at 90° to each other, with simple, direct-coupled amplifiers controlling the motors. Each potentiometer has a carriage, fitted with a slide-wire contact and a slotted arm, coupled to its servo-motor by a cable system. The pen, passing through both arm slots at their intersection, records all carriage movements. Both axes have a sensitivity of ca 18 v/in. over a range of 180 v that can be traversed in about 4 sec. The low-cost electronic circuits are as simple as is consistent with stability and reliability. Full information regarding construction of both mechanical and electrical systems is given.

The Development of the Electro-Magnetic Blood Flowmeter

Electromagnetic blood flowmeters were first constructed and used by Kolin in 1936 and, independently, by Wetterer in 1937. These early instruments consisted essentially of a large dc electromagnet, a pair of electrodes, and a string galvanometer; they made possible the recording of flow in exposed, large arteries of anesthetized animals under stringent experimental conditions. Modern electromagnetic flowmeters, using tiny, surgically implantable magnet-electrode assemblies and complex-electronic circuits, permit the recording of instantaneous and mean flows in large and small arteries in unanesthetized animals engaged in ordinary activities, as well as in anesthetized human patients whose vessels are exposed during surgical operations. Major steps in the development of the modern flowmeter include: 1) the early use of a sinusoidal ac-excited magnet to obviate the use of direct-coupled amplifiers and cumbersome, nonpolarizable electrodes; 2) the development of demodulation techniques for eliminating from the ac signal those induced voltages unrelated to flow: 3) the introduction of the squarewave and triangular-wave excited magnet to facilitate such signal-from-noise separation; 4) the miniaturization of magnetelectrode assemblies suitable for surgical implantation; and 5) improvements in circuitry resulting in greater electrical stability and freedom from noise.

Losses in Silicon Iron at Very Low Frequencies and High Flux Densities

Past measurements of losses in soft magnetic materials magnetized to high flux densities have been largely confined to determination of a quasi-static hysteresis loss over a nondescript cycle of magnetization and losses with sinusoidal magnetization with frequencies greater than 15 cps. However, since the simple concept of a hysteresis loss combined with an eddy current loss in a homogeneous medium has become outmoded, measurements of losses resulting from sinusiodal magnetization over a frequency spectrum from near zero to power frequencies are desirable. This paper describes losses in (110) [001] textured silicon iron strips which were magnetized with sinusoidal induction of negligible distortion in the frequency range 0.02–100 cps. Flux density amplitudes of 10, 15, and 17 kilogauss were used. A direct-coupled amplifier with very large negative feedback and a low distortion oscillator were used to excite the specimens. Losses in the range 0.02–0.4 cps were obtained from loop measurements;bridge measurements were made in the range 0.4–100 cps. The measurements reveal a sharp drop in the loss per cycle as the frequency is decreased from 1.5 to 0.02 cps. The downward concavity of the loss-frequency curve which has been observed previously for the power frequency range is therefore, even more prominent at very low frequencies. The effect increases with the amplitude of the flux density.

Some advantages of silicon transistors in circuit design

After transistors had been used for industrial instrumentation within the Development and Engineering Group of the United Kingdom Atomic Energy Authority for some years, silicon transistors were adopted for general-purpose use, as they were expected to be more reliable than germanium transistors. It has since become apparent that they possess more advantages over germanium transistors than is generally recognized, or was thought at the time of their adoption. For example, direct coupling of transistor circuits is facilitated and the number of components required may be much reduced; the use electrolytic capacitors may be avoided. The paper compares the performance of silicon and germanium transistors from the viewpoint of the circuit designer; physical origins of their characteristics are not discussed. A range of circuits which take advantage of the characteristics peculiar to silicon transistors is described. The circuits are for direct-coupled amplifiers, current amplifiers for small signals, switching applications and multivibrators with long periods.