Showing papers on "Operational transconductance amplifier published in 1976"

A Feedback Receive Amplifier for Optical Transmission Systems

Abstract: We consider the design and implementation of a lownoise feedback receive amplifier for use in optical communication systems. The feedback amplifier configuration is advantageous in that it offers a wide bandwidth with good signal to noise ratio.

Amplifier for fiber optics application

Abstract: An amplifier for use with a photodiode in an electro-optical transmission ne. A transimpedance amplifier is connected to an output port of a photodiode and a T-network feedback circuit is provided as a feedback element in order to provide a significant increase in the transimpedance gain-bandwidth product.

Discrete-gain output limiter

Abstract: An improved gain control circuit for an amplifier having a plurality of parallel connected resistors each having a series switch to selectively switch the resistor into the control circuit to vary the gain incrementally as some continuous function of amplifier input voltage. In one embodiment, the parallel resistors are connected between the amplifier input and output. Alternatively, the parallel resistors may be connected as the amplifier input resistance. A peak follower circuit monitors the amplifier input and applies an output control voltage to a plurality of comparators each having a separate reference voltage. Each comparator generates an output signal when the control voltage exceeds its associated reference and this output is connected to one of the resistor switches to change the parallel resistance incrementally generating a corresponding incremental gain variation. In an alternative embodiment, the comparator outputs are connected to data flip flops having complementary outputs triggered by pulses from a clock pulse circuit. The pulse circuit generates a pulse upon each zero crossing of the amplifier input so that incremental gain changes occur only at zero crossings of the amplifier input.

Amplifier improvements for limiting clipping

Abstract: A differential amplifier is connected to an amplifier for comparing an amplifier input signal with the signal fed back by the amplifier feedback circuit. The output of the differential amplifier is coupled to a full wave rectifier the output of which controls an attenuator connected between a source of electrical input signals and the amplifier. When the amplifier is operating in its linear range, the differential amplifier inputs are identical and it does not produce an output. Under this condition, the input signal is not attenuated. However, in the presence of amplifier clipping, the differential amplifier produces an output which, after full wave rectification, operates to increase the attenuation, and thus reduce the amplitude of the signal applied to the amplifier; clipping is limited.

Monolithic operational amplifier design with improved HF behaviour

Abstract: The design of a monolithic operational amplifier, which combines a large bandwidth and a high output current, is described. The output stage is equipped with n-p-n transistors only, biased in class-AB by an internal common-mode feedback loop. The intermediate stage consists of a unity-current-gain split-frequency-band voltage level shift. An integrated version, intended for driving 50-/spl Omega/ coaxial line systems, achieves a bandwidth of 25 MHz and 100-mA output current. The principle described provides the possibility for achieving higher output currents.

Instantaneous floating point amplifier

Abstract: An improved instantaneous floating point amplifier is provided having a plurality of cascaded amplifier stages, wherein the gain of a given stage of the amplifier is the square of the gain of the immediately succeeding stage of the amplifier. The number of amplifier stages which are required to implement the amplifier is minimized, and the control logic which is required to decide if a given stage is needed to amplify the input signal to a level within preselected limits is simplified. The amplifier has an automatic nulling feature which permits nulling of the amplifier without loss of data.

Digitized AGC amplifier with gain hysteresis circuit

Abstract: A digitized automatic gain controlled amplifier and gain hysteresis circuit is disclosed for preserving a low frequency, low level modulation at the output of an AGC amplifier while also providing for rapid correction of amplifier gain for large variations in the amplifier input signal level. The described amplifier is particularly adapted to satellite communications systems in which ionospheric changes produce rapid power fades and wherein satellite tracking is accomplished by dithering a high-gain antenna on the satellite to produce a low-frequency power amplitude control signal at the input to the AGC amplifier, which control signal is allowed to pass through to a control system while the larger input signal variations are gain-controlled out.

Closed-loop mixture control system for an internal combustion engine using a differential amplifier with a reference voltage variable according to engine operating parameters

Abstract: A closed-loop mixture control system for an internal combustion engine comprises an exhaust composition sensor generating an output whose waveform is nonlinear and substantially symmetrical with respect to a predetermined air-fuel ratio, a differential amplifier connected to the composition sensor for comparison with a reference voltage which is variable in accordance with the engine operating parameters, and an integral controller for integrating the output from the differential amplifier. The differential amplifier output is normally symmetrical with respect to a predetermined value of the reference voltage to control the air-fuel ratio at a desired value that corresponds to the maximum conversion efficiency of a catalytic converter. Under transient conditions, the reference voltage is varied so that the differential amplifier generates an unsymmetrical voltage which, when integrated, produces a bias voltage that shifts the air-fuel ratio to a value preferable for the transient engine operating conditions.

Method and a device for eliminating the residual error voltage of an amplifier

Abstract: The connections between the two inputs of an amplifier and the two outputs of a signal source as well as between the outputs of the amplifier and the inputs of a downstream output element into which the amplifier delivers a signal are inverted periodically and simultaneously and integration is carried out between the outputs of the amplifier and the inputs of the output element. In addition, the inputs of the amplifier are short-circuited periodically, the frequencies of inversion and of short-circuiting being multiples of each other.

Offset adjustment circuit

Abstract: An offset adjustment circuit for a differential amplifier includes a current source connected in series with a resistor for establishing a biasing voltage for a pair of field effect transistors (FET) having variable resistors in their biasing circuits. These FET's are connected to introduce currents respective connections between an input stage and a second stage of the differential amplifier. The difference of the currents supplied by the FET's divided by the transconductance of the input stage of the differential amplifier corresponds to an offset which remains fixed with changes in temperature. The offset introduced by the FET's, as determined by the adjusted values of the resistors in their biasing circuits, may be in opposition to the offset of the differential amplifier to either reduce it partially or completely, or it may be additive to the offset of the differential amplifier, as desired.

Amplifier with controllable transmission factor and switchable control characteristic

Abstract: An amplifier circuit whose gain bears a desired relation to a control voltage, including a differential amplifier, a plurality of impedances interconnected between the amplifier terminals and switches interconnected with the impedances and switchable between two states which create two impedance configurations that give the circuit mutually complementary gain vs. control voltage control characteristics.

Test apparatus circuit

Abstract: A circuit and apparatus combination for maintaining a balanced or regulated operational condition in test apparatus that includes mechanical drive and sensor elements as the sensor is exposed to the changing conditions experienced in a test sample or a sampled environment. The circuit automatically drives mechanical elements of the system at a resonant frequency or at other prescribed conditions with voltage changes at an output section of the circuit being indicative of changes in the sample tested or in the sensors environment. Drive elements of the circuit are powered by a drive voltage to cause movement of the sensor and the changing power thus used is evaluated and cancelled out, while a separate input or response voltage that is derived from the resulting movement of the same drive elements is introduced to an Operational Transconductance Amplifier together with an input control current likewise derived from such response voltage. The output current therefrom, which is a product of the separate input voltage times the input control current times a constant related to the transconductance amplifier, provides the changing drive voltage that is necessary to maintain the mechanical elements and sensor at their resonant or otherwise regulated and desired condition as the sensor environment changes. The changing drive voltage as the sensor is exposed to changing conditions provides a readout at an output section of the circuit that is indicative of changes in the sample or the sensor environment.

Audio power amplifier

Abstract: An audio power amplifier can be operated in either class A, class B or class AB amplifier modes by selectively switching bias values set in a bias setting circuitry provided for a driver stage which drives the main power amplifier stage.

Variable impedance circuit

Abstract: A variable impedance circuit comprises an amplifier with a high input impedance and a high output impedance whose gain is variable in response to a control voltage, an emitter-follower transistor, and an impedance element adapted to feedback an output signal to an input terminal of the amplifier. The input terminal of the amplifier and the input terminal of the emitter-follower transistor are connected in common. The emitter-follower transistor has its output terminal connected in series with the output terminal of the amplifier through a load resistor. An impedance of the amplifier as viewed from its input terminal is multiplied by Miller effect and varied in value by the control signal to a great extent.

Limiting amplifier with adjustable limits

Abstract: A limiting amplifier includes an operational amplifier with three feedback loops. One loop controls the gain of the amplifier when the output signal is between the upper and lower limit. Each of the other two feedback loops comprises the high gain summing amplifier in series with a diode, each summing amplifier comparing the output signal with one of the limit signals. The summing amplifiers insure hard limiting when the output signal tends to exceed the upper or lower limit.

Gain ranging amplifier system

Abstract: The compression portion of an instantaneous companding (compressing-expanding) system includes at least two and preferably four "bi-gain" amplifiers connected in cascade. Each bi-gain amplifier normally has a low-gain state and can be switched to a discrete high-gain state. A discrete reference voltage is provided to compare with the output of each amplifier. The amplifiers are initially switched to their low-gain states and the reference voltage corresponding to the first amplifier is selected. A comparator means makes a comparison between the system's output voltage and the selected reference voltage. The control means switches the first amplifier to its high-gain state or holds it in the low-gain state depending on the result of the comparison. By utilizing a different variable reference voltage and bi-gain amplifiers with two different amplification factors, the number of amplifiers and comparisons is significantly reduced. Noise-cancelling means are also associated with each amplifier to remove undesired DC noise signals from each amplifier.

Difference amplifier having extended common mode range

Abstract: A difference amplifier, the construction of which includes operational amplifier, has an extended amplitude range of common mode signal. The input of the circuit which is applied to the inversion input of the operating amplifier is applied to the latter through an attenuation network. An adjustment of the other resistor values in the circuit is made to appropriately retain the desirable characteristics of keeping common mode rejection.

Automatic range selection circuit

Abstract: The automatic range selection circuit is particularly useful with a photomultiplier tube linear microphotometer and includes an amplifier, adjustable and switchable impedances coupled between an input and an output of the amplifier for adjusting the gain thereof, two comparators for comparing the output from the amplifier with upper and lower reference voltage levels, an integrator for integrating the output of the comparators, and an analog control circuit responsive to the output signal level at the output of the integrator for controlling the amount of impedance coupled between the input and output of the amplifier thereby to automatically adjust the gain thereof.

Digitally controlled amplifying equipment

Abstract: A digitally controllable amplifier unit and musical instrument amplifier incorporating such a unit. Digital control of the transfer function of a high-gain virtual-earth amplifier is effected by switching input and feedback impedances by means of transistor switches. Digital storage means are used to control the transistor switches.

Semiconductor gas detector circuit

Abstract: In a gas detector circuit a semiconductive detector, such as a Taguchi detector, is disposed in gas communication with the gas to be detected. The detector has a sensing resistor incorporated therein with a value of resistance that changes in accordance with the concentration of the gas constituent being detected. This type of detector provides an output signal with a temperature dependence caused by the temperature coefficient of the resistance of the resistive detector with a negative sign. The temperature dependent output signal derived from the detector is fed to one input of a differential amplifier for comparison against a second input to derive an output signal which is fed to an alarm and/or meter and/or recorder. A feedback signal portion of the output of the differential amplifier is fed back to the second input of the differential amplifier, as a feedback component of the second input, via the intermediary of a gain control resistor. The supply current drawn by the differential amplifier has a positive temperature coefficient and the supply current is passed through a resistor to derive a correction voltage which is superimposed on the feedback voltage of the differential amplifier to compensate for the temperature coefficient of the semiconductive detector.

Time division multiplexing amplifier

Abstract: A time division multiplexing amplifier having a differential amplifier, such as a dynamic bridge amplifier, which has a predetermined gain accurately provided by means of operational network resistors. The differential amplifier is used to amplify differential signals containing a common-mode voltage. Prior to amplification of the differential signals, a common-mode voltage is applied in common to two input terminals of the differential amplifier, and then the differential amplifier is adjusted to provide a zero offset voltage. After that, the differential signals are applied to the differential amplifier, so that the differential signals can be amplified without having any adverse effect of a common-mode voltage.

Current mirror amplifier augumentation of regulator transistor current flow

Abstract: A NMOS transistor in the input current path of a PMOS current mirror amplifier senses any tendency to change of the voltage across a load driven by the output current of the amplifier. In response thereto, the NMOS transistor changes the input current of the amplifier to thereby vary its output current in a sense to maintain the voltage across the load constant.

Synthesis of transfer functions using the operational amplifier pole

Abstract: A transfer-function synthesis which takes into account the frequency dependence of the operational amplifier gain is described. Apart from improving the useful frequency range of operational amplifiers, the method eliminates the external capacitors, thus making the resulting circuits suitable for microelectronic fabrication. Examples of realizations of different types of filters are presented along with a few experimental results.

Electric welder output control device

Abstract: A welding control circuit comprises a differential type operational amplifier preferably having at least first, second and third input terminals A signal S 1 corresponding to the desired output of an electric welder to be controlled is applied to the first input terminal of the amplifier; a signal S 0 for setting the output of the welder to initially approximate the desired output is applied to the second input terminal of the amplifier; and a feedback signal S 2 is applied from the welder to the third input of the amplifier The circuit constants of the adder-subtractor circuit are selected so that the ratio of the output S of the adder-subtractor circuit to the input signal S 0 is a (in the absence of other input signals) whereas the ratio of the output S to the input signals S 1 and S 2 is b (in the absence of other input signals) The adder-subtractor circuit is connected so that its output is given by S = aS 0 + b(S 1 - S 2 )

Bidirectional radio frequency amplifier with receiver protection

Abstract: A bidirectional radio frequency amplifier which includes a power amplifier and a receiver amplifier connected to a common antenna. A pair of parallel diodes coupled across the input of the receiver amplifier provides a high impedance path for a received signal and a low impedance path during transmission thereby eliminating the need for mechanical or semiconductor switching.

Protective network for an insulated-gate field-effect (IGFET) differential amplifier

Abstract: The input stage of an amplifier includes two input terminals to which are connected the gates of two, differentially connected, IGFETs protected by two diodes connected back-to-back (in series) between the gates. The amplifier also includes means for applying an external signal source to one input terminal, means for shorting the diode connected to the other input terminal, and means for negatively feeding back the output of the amplifier to its input. This maintains the potential difference across the diode connected to the input terminal to which the external signal source is connected close to zero volt thereby substantially eliminating any leakage current through it.

Amplifier with variable gain

Abstract: An amplifier circuit having a variable transmission factor and an effective transmission frequency band delimited by a lower limit frequency is arranged to enable the value of the lower limit frequency to be varied as a function of a control voltage, by including in the circuit an amplifier member and circuit components defining a feedback path connected between the output of the amplifier and an input thereof which is inverting with respect to the output signals of the amplifier, the components defining the feedback path including an electronically voltage-controllable resistor having a control voltage input and a first frequency dependent impedance connected in parallel with the resistor, and the circuit further including a second frequency dependent impedance connected between the inverting input of the amplifier and a point at the circuit reference potential, and a line for supplying the control voltage to the control voltage input of the controllable resistor.

Communication transmitting apparatus with carrier level control

Abstract: Low level amplitude modulated radio transmitting apparatus employing a DC control loop from the output amplifier to the audio modulating stage for maintaining the carrier output level constant. The audio signal to be transmitted is superimposed on the DC control signal and the resulting signal is applied to an operational amplifier that controls a current driver supplying operating potential to the modulating stage. A DC limiter at the input to the operational amplifier limits the DC control signal to the operational amplifier thus preventing continuous overdriving of the RF elements in the event of a disruption in the DC control loop. An audio by-pass permits the audio signal to by-pass the DC limiter and be summed with the limited DC control signal at the input to the operational amplifier.

Vertical deflection circuit

Abstract: A vertical deflection circuit having a vertical amplifier stage bias voltage stabilizing circuit including a differential amplifier circuit which operates only during the retrace period. One input of the differential amplifier circuit receives a D.C. bias voltage and the other input receives the mean voltage of an output signal. The output of the differential amplifier circuit is fed back to a drive stage to stabilize the bias voltage.

Design of the HEAO Main Bus Shunt Regulator

Abstract: The High Energy Astronomy Observatory (HEAO) main bus regulator contains a redundant error amplifier (REA) and a 12-section sequenced shunt transconductance amplifier (STA) in which not more than three and not less than one shunt section are in an active control mode regardless of a failure in any one of the twelve sections. The part of the work concerned with the shaping of the frequency response of the REA and STA minor feedback loops and of the teolator major feedback loop is described. Emphasis is on the application of a general design technique embodying a "design-analyze-measure iteration loop," in which a first-cut design and analysis is corrected ard improved after experimental observation of discrepancies and deficiencies. In particular, an incipient high-frequency oscillation was thereby reliably eliminated. It is demonstrated that analysis techniques involving a minimum of algebra can provide full quantitative information on an efficient and reliable system design.