Showing papers on "Amplifier published in 1971"

Microwave transistors: Theory and design

Abstract: Microwave transistors are useful as small-signal amplifiers to 6 GHz and power amplifiers to 4 GHz. Nearly all microwave transistors are of the silicon planar type. Power transistors use three types of geometries--interdigitated, overlay, and mesh--while small-signal transistors use interdigitated only. The general theory of the frequency response of transistors is reviewed, including active and inactive elements. A condensed description of the design and processing steps for a silicon microwave transistor is given. A final section deals with the types of high-frequency measurements used in the design and analysis of transistors.

Intermodulation rejection capabilities of field-effect transistor radio frequency amplifiers and mixers

Abstract: Mixers and amplifier circuits are disclosed which may include a plurality of identical FETs connected in parallel to form a composite FET. The decreased input impedance of the composite FET as compared to the input impedance of a single FET results in a decrease in intermodulation. The composite FET may also be a power or large signal FET. In either case, the pinch-off voltage of the composite FET can also be increased to provide a still further decrease in intermodulation.

Electrocardiogram Recording with Pasteless Electrodes

Abstract: Experimentation regarding various aspects of a technique for recording electrocardiographic potentials from unprepared skin, without the use of conventional paste, is described. Because of the relatively high skin-to-electrode impedances encountered without electrolytic paste, high input impedance amplifiers must be utilized for acquisition of the signal. In order to minimize susceptibility to external electrostatic and electromagnetic interference, an inherent problem with high input impedance amplifiers, buffer amplifiers were incorporated directly within the electrode housing. Of the different metals tested, stainless steel proved to be the most stable skin contact material for pasteless operation. The integrated electrode-buffer amplifiers described comply with specifications of the American Heart Association and should prove useful as a direct replacement for conventional paste-type electrodes in existing clinical EKG equipment as well as for long-term applications such as space missions and intensive-care-unit patient monitoring, where frequent attention to the electrodes is inconvenient.

High Temperature Electronics.

Abstract: : The fabrication of a silicon carbide (SiC) junction field effect transistor (J-FET) was shown practicable. Several amplifier designs were breadboarded with silicon devices to study the required parameters. A simplified building block amplifier was constructed and tested. (Author)

A study of the constant-temperature hot-wire anemometer

Abstract: The conventional ‘bridge-feedback amplifier’ constant-temperature hot-wire anemometer is analysed to determine its static and dynamic response. The effects of moderate feedback amplifier gain, bridge imbalance, stray bridge reactance, amplifier offset voltage, lack of common mode rejection, amplifier frequency response and departure from constant transconducture are included. The root loci of the system are mapped out and the consequences of the analysis are discussed from the viewpoint of both the operator and the designer.

A normal mode theory for the Rayleigh wave amplifier

Abstract: A Rayleigh acoustic wave traveling on the surface of a semi-infinite piezoelectric medium may be amplified by interaction with drifting carriers in an adjacent semiconductor. The gain and frequency response of this interaction is determined here by using a normal mode expansion of the Rayleigh wave piezoelectric fields. The configuration which uses a thin semiconductor film supported by a semi-infinite dielectric and separated from the piezoelectric by a small air gap is described in detail and the results are expressed in a form that clearly shows the effect of piezoelectric, air gap, and semiconductor parameters. Comparisons with experimental data for the lithium niobate-silicon film configuration show that acoustic gains on the order of 100 dB/cm can be obtained in the frequency range above 0.1 GHz.

Gain-sensitivity product-a figure of merit for hybrid-integrated filters using single operational amplifiers

Abstract: It is shown that a different measure of performance must be used to evaluate hybrid-integrated active filters from that used to evaluate active filters in discrete form. Where sensitivity was previously found to be an adequate and useful measure for Q stability of discrete active filters, the gain-sensitivity product gives an accurate measure of Q stability for hybrid-integrated circuits. Where negative feedback filter schemes were found to be preferable with respect to Q stability when realized in discrete form, positive feedback schemes with their very much lower gain- sensitivity product may be preferable in hybrid-integrated filter circuits. In addition, they require low-gain amplifiers than can be used up to higher frequencies. Q-stability measurements of hybrid- integrated positive feedback, or Sallen-Key-type circuits, which were realized with tantalum thin-film resistors and capacitors combined with beam-leaded operational amplifier chips agree very accurately with the predictions derived from gain-sensitivity calculations.

Receiver tuning system

Abstract: A harmonic generator produces simulated station signals which are heterodyned in the mixer stage of a receiver. A local oscillator of the receiver is swept through its frequency bandwidth, producing an IF pulse each time the receiver tunes one of the simulated stations. The IF pulses are counted, and upon reaching a number preset on station selection switches, convert the sweep circuit to an AFC amplifier, maintaining the receiver tuned to a desired station frequency.

Monolithic acoustic surface‐wave amplifier

Abstract: The characteristics of a monolithic surface‐wave acoustic amplifier are described. Using indium antimonide vacuum‐deposited on lithium niobate, electronic gain of 70 dB with a terminal gain of 24 dB has been obtained at 660 MHz.

High precision wide dynamic range viscous loss measuring apparatus

Abstract: A viscosity measuring system especially useful in pollution and chemical process control applications. A variable gain amplifier drives a magnetic coil which causes a torsion member to oscillate. The amplitude of the oscillations is sensed by a transducer, and converted to a DC voltage by an amplitude monitoring circuit. The DC voltage, which represents the instantaneous amplitude of mechanical oscillation, is compared to a reference DC voltage which represents the desired amplitude of oscillation. The resulting error signal is utilized to control the gain of the amplifier in such a manner that the amplitude of mechanical oscillation is maintained constant and equal to the desired amplitude. The viscosity of the fluid in which the torsion member is immersed is obtained by providing an output signal which is a measure of the power provided by the amplifier to the magnetic coil in order to maintain the desired constant amplitude of oscillation. Preferably, the output signal is obtained from the voltage developed across a resistor in series with the magnetic coil.

Josephson‐Junction Amplifier

Abstract: Positive feedback has been used within a double‐Josephson‐junction quantum interferometer to achieve a current amplification which can be adjusted from outside the cryostat over the range 1–100. The interferometer may be regarded as a three‐terminal amplifying device.

A Feedforward Experiment Applied to an L-4 Carrier System Amplifier

Abstract: As part of a test to determine its applicability to coaxial repeaters, a feedforward error-control system was applied to an L-4 coaxial system flat-gain amplifier operating in the frequency range of 0.5-20 MHz. The error amplifier was a duplicate to the main amplifier. With three test tones at 7.5 dBm output each applied within the last L-4 master group, modulation products in the uncompensated system were observed about 65 dB down from a single-tone level. With the error loop applied, modulation products dropped to greater than 100 dB over the range, often exceeding 110 dB. In particular, the third-order intermodulation product corresponding to A + B - C was reduced by 42 dB to - 108 dB.

Lumped-circuit elements at microwave frequencies

Abstract: Details are given of lumped capacitors, inductors, resistors, and gyrators. Active combinations of these components and encapsulated semiconductor chips include a 4-GHz tunnel-diode amplifier, a varactor-tuned X-band Gunn oscillator, a degenerate S-band parametric amplifier and an X-band Doppler radar. It is concluded that the techniques described here are useful at microwave frequencies up to X-band.

Double sideband modem with either suppressed or transmitted carrier

Abstract: An inexpensive, two-transistor modem wherein the first transistor is a high gain amplifier connected to receive the modulating signal, and the second transistor is connected as a shunt modulator driven by a carrier signal source. Individual resistors are connected with the collector and emitter electrodes of the first transistor and so proportioned that the input baseband (for modulation) and carrier (for demodulation) signals are cancelled at a common summing node. The circuit is useful for double sideband suppressed or transmitted carrier applications, especially where the desired sidebands are very near, or go down to, the baseband frequencies.

SSMA receiver with synchronous demodulation and variable gain control

Abstract: A receiver for electric oscillations modulated in SSMA technique with which, in an intermediate frequency position, a multiplier is provided for multiplying the intermediate frequency signal with a code which is to be received, and with which a synchronous demodulator for obtaining the information to be received is connected to the multiplier, wherein the receiver includes in a section preceding the multiplier a gain control amplifier having two control voltage derivation circuits assigned thereto for deriving control signals, one of the voltage derivation circuits operable to evaluate the output signal of the multiplier and other of the voltage derivation circuits operable to evaluate the output of a synchronous demodulator so that in an unsynchronized state of the synchronous demodulator the control signal which is derived from the multiplier output serves to control the gain control amplifier and in the case of synchronous operation the control signal derived from the synchronous demodulator is employed to control the gain control amplifier.

Capacitive pick-off transducer

Abstract: A capacitive pick-off transducer is disclosed in which small relative movement between aligned capacitive elements is utilized to provide an electrical output signal responsive to such movement. The capacitive elements include a fixed driven element having 2n driven sectors each connected to one of two sources of input electrical signals of opposite phase, a fixed receptor element including 2n 1 active areas connected to an electrical signal output circuit, and a moveable shield element between the driven and receptor elements and including 2n 1 shielding lobes. Circuit means including a high gain amplifier with a negative feedback circuit are provided for maintaining the signal levels of the shield element and the active areas substantially lower than the absolute values (ignoring polarity) of the input signals, and preferably at or near ground.

Three-terminal capacitive apparatus for remotely responding to a condition or dielectric properties of a material

Abstract: Three-terminal capacitive apparatus are disclosed which provide information concerning a condition of a material by responding to the dielectric properties of the material. A three-terminal capacitor, which may be a cell or probe, may be used, for example, to measure the dielectric constant of a material, to determine the level of a material in a container, to determine the interface between liquid materials in a pipeline, or the proximity of a material to the probe. Each cell or probe includes a conductive driven element connected to a regulated square wave source, and a conductive receptor element connected to the input of a high gain amplifier with a capacitor in the feedback loop which maintains the receptor element at virtual ground. The output of the feedback amplifier is proportional to the feed through capacitance of the capacitive probe or cell. A synchronous demodulator, synchronized by the drive signal or a signal in phase with it, is connected to the feedback amplifier output and is used to produce a DC output signal used for display or control. The cell or probe is connected to associated electronics through shielded cables and may be remotely located from the electronics. Suitable mechanical apparatus is associated with a particular three-terminal capacitor cell or probe for mounting it in position to respond to a particular condition being monitored.

Linear amplification using envelope feedback

Abstract: An envelope-feedback technique applicable for reducing the distortion of amplitude-modulated signals in transistor amplifiers is described. The basis of the technique is to compare the input and output signals, and to introduce a correction signal into the circuit. An analysis and experimental results are provided.

General energy relations for Josephson junctions

Abstract: The Josephson junction acts as a nonlinear lossless inductor and can be applied for mixing and parametric amplification in the microwave region. Since an alternating current can be generated in the junction by an applied dc voltage, a dc power flow must be taken into consideration. Energy relations for the Josephson junction are derived which are similar to the Manley-Rowe equations but with an additional term for the dc power. These equations show the possibility of realizing dc-pumped parametric amplifiers.

Pulse modulation motor control

Abstract: A typical alternating current servomotor has two windings displaced 90*; these windings are identified as a reference winding and a control winding. Rotational direction and speed of the motor may be controlled by applying AC voltages of the proper wave form, amplitude and phase relationship to these windings. When controlling the direction of rotation and speed of the motor in accordance with a DC error signal, pulse width modulation techniques are employed. The error signal is compared with a triangular wave function to generate a first and second series of pulses each having a width related to the magnitude of the error signal. These series of pulses are logically combined with a square wave function to produce first and second digital motor energizing signals. The motor energizing signals control a power amplifier switch connected to the windings of the motor to be controlled.

Noise reduction in bulk negative-resistance amplifiers

Abstract: The letter presents noise calculations for Gunn amplifiers with both uniform and nonuniform field distributions. The results indicate that amplifiers with an injection-limited cathode contact, and hence a uniform field distribution, exhibit significantly lower noise figures than those having an ohmic cathode contact, which yields a nonuniform field distribution. A further reduction of noise could be obtained by using materials with high negative mobility.

Microwave properties and applications of negative conductance transferred electron devices

Abstract: The transferred electron effect in epitaxial GaAs has been used to realize a semiconductor device which exhibits a stable negative conductance over a wide range of microwave frequencies and power levels. These devices have been used in conjunction with circulator coupled networks to design high-level wide-band transferred electron amplifiers which have a voltage gain bandwidth product in excess of 10 GHz for frequencies from 4.0 to about 16.0 GHz. Linear gains of 6-12 dB per stage and saturated output power levels in excess of ½ W have been realized. The physical and electrical properties of these devices are described with regard to the achievement of a stable negative conductance. The influence of several parameters (i.e., device temperature, bias voltage, circuit loading, etc.) is discussed with regard to device and circuit stability. Measurements of the terminal admittance of several typical devices as a function of the bias, input power, and frequency have been used to study their microwave properties. The large signal data are used to compute the relationship between the available device power and the magnitude of the negative conductance independent of the test circuit. This same measurement technique can provide a simulation of the performance of any nonlinear negative conductance, without the need for circuit design and load tuning. In addition, an analytical large signal model of the negative conductance has been used to predict the large signal performance of the active device (i.e., gain compression, conversion efficiency, etc.) in both oscillator and amplifier circuits.

Automatic light control for low light level television camera

Abstract: The video signal in a low light level television camera is fed to a first operational amplifier which continuously integrates this signal to produce an indication of the average value of the intensity of light in a viewed scene. The video signal is also applied to a pair of circuits that detect and store the peak values of the video signal in alternate fields formed by the scanning electron beam in the camera pick-up tube. During formation of one field, the peak value of the intensity of light in the viewed scene is detected and stored in one circuit while the stored indication of the peak intensity of the light detected by the other circuit during the preceding field is integrated in a second difference amplifier. The output voltage of the second amplifier is a measure of the difference between the stored peak voltage applied thereto and a reference voltage. This difference voltage is passed by a diode switch to a summing amplifier where it is combined with the average value signal from the first amplifier if the peak value signal indicates that the intensity of light from the viewed scene exceeds a prescribed peak reference light intensity. The combined signal is applied to a voltage translator which produces signal voltages of the correct polarities for varying the gains of image intensifier and vidicon pickup tubes of the camera inversely with respect to changes in the intensity of light from the viewed scene.

Analog to digital converter

Abstract: An analog to digital converter of the dual slope type, employing a high gain input amplifier as both a buffer and integrator and a second high gain amplifier as a comparator. The input voltage is coupled to the non-inverting input terminal of the integrator through a capacitor. A programmed switching circuit provides for switching of the coupling capacitor either to the input voltage or to an input common terminal and also provides for opening and closing a direct feedback loop from the comparator output and for switching the second input terminal of the integrating amplifier between a reference level and ground. The converter operates to charge the integrator capacitor for a fixed time at a rate proportional to the input voltage and then to discharge this capacitor at a rate proportional to the reference voltage, while a counter accumulates time base pulses, until the capacitor reaches its initial level, the accumulated counts being a digital representation of the input voltage.

Static electric field detector

Abstract: This apparatus is used to detect the presence of static or alternating electric fields. The electric field intensity is sensed with a probe by proximity capacitance coupling. It comprises an antenna which applies any signal it detects to the input of an amplifier. The output of the amplifier is applied to the input of a threshold circuit which conducts when an input signal of greater than a prescribed value is detected. Conduction of the threshold circuit energizes an oscillator which drives indicators of various types. Once a prescribed threshold level is exceeded, display is activated. Hence, the device of this invention provides a go-no-go presentation of field intensities.

Photomultiplier gain control circuit

Abstract: Automatic gain control circuit for controlling the gain of a photomultiplier. Successive pulsed reference light beams are directed onto the photomultiplier while a dc voltage is supplied thereto causing the photomultiplier to produce successive output current signals. Each current signal is transformed to a voltage signal which is then processed to derive a maximum-amplitude signal having a value related to the maximum amplitude of the signal. A differential operational amplifier circuit then compares the value of the maximum-amplitude signal with the value of a reference signal representative of a desired output current signal produced by the photomultiplier. When the value of the maximum-amplitude signal is less than the value of the reference signal, indicating that the photomultiplier requires an increasing value of dc voltage for increasing the value of its gain, an output signal of a first polarity and having a value proportional to the difference between the two compared signals is produced by the amplifier circuit. When the value of the maximum-amplitude signal is greater than the value of the reference signal, indicating that the photomultiplier requires a decreasing value of dc voltage for decreasing the value of its gain, an output signal of a second polarity and having a value proportional to the difference between the two compared signals is produced by the amplifier circuit. A dc voltage supply control circuit coupled to the amplifier circuit receives the output signals produced by the amplifier circuit and operates in response to an output signal of the first polarity to supply a dc voltage to the photomultiplier in an increasing direction and varying at a rate determined by the value of the output signal, and in response to an output signal of the second polarity to supply a dc voltage to the photomultiplier in a decreasing direction and varying at a rate determined by the value of the output signal. The supply of dc voltage to the photomultiplier is controlled until the value of a maximum-amplitude signal is equal to the value of the reference signal.

Differential doppler detection for rf intruder alarm systems

Abstract: An intruder detection system in which an RF transmitter is connected through a length of transmission line to a transmit/receive antenna, both transmitter and antenna are matched to the line. Diode detectors are connected in opposite directions to the line at points spaced a quarter wave length apart. The diodes connect through low-pass filters to the balanced inputs of an AC coupled amplifier which extracts the doppler sine wave from the oppositely traveling transmitted and received waves on the line. The doppler sine wave is squared and the pulses are integrated to trigger an alarm. A band pass filter is so positioned in the line to reduce false alarms by defining a specific radio frequency bandwidth and also allows the detectors to be used to time the transmitter oscillator.

Cross loop antenna

Abstract: Two orthogonal arrays of ferrite cores wound and connected in series. The arrays are insulated from each other to provide predictable inductance. The arrays preferably form a square inside of which a low-noise amplifier is connected directly to each array, the amplifiers forming a built-in part of the antenna assembly. A design for a small, narrow-band 10 KHz to 14 KHz antenna is described, having a large effective height.

Blood gas sensor amplifier and testing system

Abstract: The invention includes an amplifier for processing the output signal from an in vivo sensor for the partial pressure of gas in blood. Means are provided to protect the patient from excess currents and voltages. The first amplifying stage has a floating ground and is at substantially the same potential as the sensor. The output of this stage is chopped with a field effect transistor that derives its control voltage from a transformer which is driven at high frequency and which has high impedance or low leakage at power line frequencies. The chopped amplifier output signal is passed through another transformer which closely couples high frequencies. The amplified signal is demodulated by another field effect transistor in the secondary of this transformer after which the signal is further processed in circuitry that need not be isolated from ground. Means are provided for displaying the signal in terms of partial pressure of the gas in millimeters of mercury. The system includes means for testing the integrity of the sensor before and continuously after it is implanted in the body. Means are also provided for calibrating the sensor under known conditions which are conveniently established.

Possibility of a unidirectional laser amplifier produced by monochromatic optical pumping of a coupled Doppler-broadened transition

Abstract: Unidirectional gas laser amplifier using monochromatic optical pumping of coupled Doppler broadened transition