Showing papers on "Operational transconductance amplifier published in 1990"

On the design of voltage-controlled sinusoidal oscillators using OTAs

Abstract: A unified systematic approach to the design of voltage-controlled oscillators using only operational transconductance amplifiers (OTAs) and capacitors is discussed. Two classical oscillator models, i.e. quadrature and bandpass-based, are employed to generate several oscillator structures. They are very appropriate for silicon monolithic implementations. The resulting oscillation frequencies are proportional to the transconductance of the OTA, and this makes the structures well-suited for building voltage controlled oscillators (VCOs). Amplitude stabilization circuits using both automatic gain control (AGC) mechanisms and limitation schemes are presented. The circuits are compatible with the transconductance amplifier capacitor oscillator (TACO). Experimental results from bipolar breadboard and CMOS IC prototypes showing the potential of OTA-based oscillators for high-frequency VCO operation are included. >

Biosensor electrode excitation circuit

Abstract: A circuit is described for applying a potential to an electrode of a biosensing test cell, which electrode, when properly inserted in a female connector, is contacted by a pair spaced apart contacts. The circuit includes a source of excitation potential and an operational amplifier having one input connected to the source of excitation potential. A switching circuit is coupled between the operational amplifier and a first one of the spaced apart contacts, with the switch means exhibiting an impedance. A feedback circuit is connected between the second of the spaced-apart contacts and another input to the operational amplifier, to feed back a potential appearing at the second contact. The feedback is for the purpose of maintaining the output of the operational amplifier at a level which compensates for impedance losses in the swtiching circuit. The feedback circuit enables the output of the operational amplifier to be varied so that the potential applied to the electrode is equal to the source of excitation potential. A further circuit is connected to the feedback circuit for sensing when an open or high impedance state exists between the spaced-apart contacts.

A CMOS large-swing low-distortion three-stage class AB power amplifier

Abstract: A CMOS power amplifier with a class AB rail-to-rail output stage is presented. By using a three-stage amplifier with double Miller compensation, the harmonic distortion of the output stage is suppressed by the internal feedback loops. This approach is thoroughly investigated, and it is shown that a three-stage amplifier has apparent advantages for DC gain, harmonic distortion, and power-supply rejection ratio (PSRR). A realized prototype for ISDN applications with a gain bandwidth (GBW) of 5 MHz and with -80-dB THD at 10 kHz for an output current of 20 mA in a load of 81 Omega is presented. >

Class AB CMOS amplifiers with high efficiency

Abstract: A new class AB CMOS operational-amplifier principle is presented. A transconductance amplifier based on this principle exhibits small-signal characteristics comparable to those of a conventional OTA. It has, however, a superior current efficiency and its settling time is not slew-rate limited. The new class AB principle can also be used in an output stage with a well-defined quiescent current, a rail-to-rail output swing, and a good driving capability. A two-stage amplifier with both the input and output stages based on the new principle has been realized. It features a rail-to-rail input and output common-mode range, a gain-bandwidth of 370-kHz, a settling time of less than 5 mu s independent of the applied step, and a power consumption of 247 mu W. It drives a resistive load of 3 k Omega in parallel with a capacitive load of 400 pF when operated on a 2.5-V/-2.5-V power supply. >

Modulation device with input signal modification for correction of amplifier nonlinearities

Abstract: In a modulation system using an amplitude and a phase of a carrier wave as information such as a QPSK system, a modulation device modifies an input signal series to compensate the nonlinear characteristics of an amplifier located at a later stage, and provides a carrier wave modulated by the modified signal series to the amplifier. A first arithmetic circuit obtains an amplitude and a phase of an input signal by calculation. A ROM is set with correction data corresponding to the calculated amplitude so as to compensate the nonlinearity of the amplifier. A modification value generating circuit and a RAM output an amount of compensation so as to further modify the correction data according to part of an output signal from the amplifier to compensate amplifier characteristic changes due to temperature variations and the like. A second arithmetic circuit provides a signal series produced from the modified amplitude and phase to a quadrature modulator.

Extending voltage-mode op amps to current-mode performance

Abstract: This paper reviews techniques for extending the output cababilities of conventional voltage-mode operational amplifiers to achieve current-mode performance. Tracing the development over the past two decades, a number of elegant and useful circuit topologies for realising amplifiers with controlled current output properties are described. In particular, the operational amplifier supply current sensing technique and its application to current follower and current conveyor circuit implementations is examined. The authors then review their work, based on enhancing the performance of conventional voltage-mode amplifier designs by application of these currentmode alternatives.A high performance follower based amplifier, a biquadratic filter section, a precision full-wave rectifier and an instrumentation amplifier based upon enhancement to the voltage operational amplifier are shown to outperform their conventional counterparts. The integrated circuit realisation of a seven terminal operational amplifier that allows direct access to the operational amplifier output current via its push-pull output stage is then presented. The integrated seven terminal operational amplifier is realised in CMOS technology and experimental results presented. Finally a current feedback, high precision, current gain cell is described that overcomes several of the drawbacks that exist with the supply current sensing technique.

Automatic gain control apparatus and method

Abstract: An automatic gain control apparatus and method which optimally adjusts the gain of an amplifier to compensate for time-varying energy levels of a received input signal. A control input signal for adjusting the gain of the amplifier is determined by the selective average energy level of a present input signal, the transfer function characteristic of the amplifier and a previous control signal. A fast loop response time maintains the energy level of the amplified output signal at a nominal level.

Error amplifier for use with parallel operated autonomous current or voltage regulators using transconductance type power amplifiers

Abstract: An error amplifier is disclosed for use in linear or switched-mode voltage or current regulators that use a transconductance type power-amplifier (32a, b, c), enabling easy modular parallel connection of said regulators by simply parallel wiring of normally externally accessible nodes of the individual regulators: power-input, power-output, error amplifier output (58), and error amplifier input (56), to boost the system's total output power by about equally sharing the total output power among the individual regulators, comprising of a. an amplifier with grossly asymmetric output current capability in sink and source directions; and b. a sense circuit to slightly modify the voltage on the reference input of the said amplifier when the lower value output current limit becomes active so that it causes positive feedback thereby ensuring that at any time only one of the plurality of parallel operated amplifiers is active and controls the system's output while all the other amplifiers are in current limit and thereby inactive.

Stored program controlled module amplifier bias and amplitude/phase compensation apparatus

Abstract: A stored program amplifier compensation apparatus utilizing sensing elements to provide the operational states of an RF power amplifier to a controller processor unit which utilizes the operational data to provide a bias control signal to the RF power amplifier. Look-up tables which are stored in the controlled processor unit, contain a bias control signal for all the possible operational combinations.

Amplifying with directly coupled, cascaded amplifiers

Abstract: A signal is amplified with a plurality of amplifiers (12-18), each amplifier having a reference port (22), a reference node (C) coupled to the reference port, and a signal port (22), and each amplifier being supplied by a power source (30-36) with operating potential with respect to the reference node that is coupled to the reference port of that amplifier. The amplifiers (12-18) are cascaded in a manner selected so that the output of a first amplifier (12) (which receives the signal to be amplified at its input port) drives the reference node (22) of a second amplifier (14), and the reference node (22) of the first amplifier (12) provides an input at the signal port (20) of the second amplifier (14), whereby the first and second amplifiers are directly coupled together to amplify the applied signal.

CMOS amplifiers incorporating a novel slew rate enhancement technique

Abstract: A novel technique for enhancing the slew rate in CMOS amplifiers is described. The enhancement is provided by an auxiliary circuit which is automatically activated during transients. The main amplifier is not stressed with large currents, thus minimizing power dissipation and avoiding signal swing problems. This technique is quite generic, and can be applied to a variety of amplifier structures. An experimental operational transconductance amplifier incorporating this technique has been fabricated. A slew rate of 1 V/ mu s with a 10000 pF load capacitance has been achieved, while requiring a quiescent power dissipation of less than 1.5 mW. >

Active compensation of operational transconductance amplifier filters using partial positive feedback

Abstract: An active compensation technique for improving high-frequency performance in OTA-C filters is presented. Each critical OTA is replaced by two OTAs connected in parallel with opposite polarity and with different transconductances. The novel feature of this technique is that it does not require tuning to reduce excess phase and yields filters with extended tuning ranges. It is demonstrated by a programmable bandpass filter from 1 to 9 MHz fabricated in 3- mu m CMOS technology. >

Amplifier having feed forward cancellation

Abstract: The present invention provides an amplifier arrangement to which feed forward correction is applied by a comparison loop including comparison means for comparing amplifier input with amplifier output to provide an error signal, a cancellation loop including secondary amplifier means for amplifying the error signal and combining means for combining said amplified signal with said amplifier output, a pilot generator coupled to said amplifier input to introduce a pilot tone therein, detector means for detecting a level of pilot tone in said amplifier output and correction means for correcting said cancellation loop performance as a function of said detection wherein said pilot generator is further coupled to a multiplier receiving said amplifier output, said multiplier producing an output signal arranged to control a loop parameter to effect said correction. The distortion performance of a feed forward amplifier is thereby improved, alternatively an amplifier of inferior distortion performance, but potentially higher efficiency may be used.

A 500-nA sixth-order bandpass SC filter

Abstract: A sixth-order bandpass switched-capacitor (SC) filter that requires only 500 nA of total supply current has been designed and fabricated in a 2- mu m CMOS technology. The filter is part of an implantable device powered by a +or-1.2-V battery; it can drive up to 30 pF of capacitive load and uses a 2-kHz sampling frequency. A substantial reduction in the power consumption has been achieved by using a novel amplifier time-sharing technique that allows the realization of an arbitrary number of biquadratic cells with only two amplifiers. Further power saving was obtained with the use of positive feedback in the amplifier input stage to enhance its transconductance. The prototype chip requires an area of 2200 mils/sup 2/. >

Multistage cascode radio frequency amplifier

Abstract: A cascode radio frequency amplifier in which a control amplifier stage is provided and any number of clone amplifier stages are connected in series (cascode) with the control amplifier. The cascode amplifiers provide equal voltage and power since each of the clone stages provides unity gain. The device can operate from low frequencies to high frequencies.

VLSI implementation of a reconfigurable cellular neural network containing local logic (CNNL)

Abstract: A new integrated circuit cellular neural network implementation having digitally or continuously selectable template coefficients is presented. Local logic and memory is added into each cell providing a simple dual computing structure (analog and digital). The variable-gain operational transconductance amplifier (OTA) is used as voltage controlled current sources to program the weighting factors of the template elements. A 4-by-4 CNN circuit is realized using the 2 mu m analog CMOS-process. The circuit with different template configurations has been simulated with HSPIC. >

Switched-capacitor circuit having a full-wave-rectifying and integrating function

Abstract: A switched-capacitor circuit is described, which performs the functions of a full-wave rectifier and of an integrator and has a single operational amplifier and a comparator. The circuit is insensitive to the stray capacitances and offsets of the comparator and the operational amplifier. In particular, the input signal is sampled during only one phase of the clock which pilots the operation of the switched-capacitance network.

Amplifier circuit with correction of amplitude and phase distortions

Abstract: A high frequency amplifier circuit comprises an amplitude characteristic correction circuit and a phase characteristic correction circuit for compensating the non-linearity of the input-output characteristics of the amplifier. The amplitude characteristic correction circuit varies the drain voltage or the collector voltage of the amplifier in accordance with the envelope level of an input signal in such a manner that the relationship between the amplitude of the output of the amplifier and the amplitude of the input signal has linearity. On the other hand, the phase characteristic correction circuit provides a quantity of phase shift to the input signal in accordance with the envelope level of the input signal, and the phase-shifted input signal is applied to the amplifier in such a manner that the phase of the output of the amplifier and that of the input signal coincide with each other.

High gain two-stage amplification with erbium-doped fibre amplifier

Abstract: Unsaturated net gain of 51 dB is obtained for 1.551 mu m signal light by using two-stage erbium-doped fibre amplifiers pumped by 1.48 mu m laser diodes. This is achieved by using both an optical bandpass filter to suppress amplified spontaneous emission from the first stage amplifier and a bidirectional pumping scheme in the second amplifier to increase saturation output power. >

Fully differential CMOS power amplifier

Abstract: Fully differential power amplifier comprising one high gain input stage (A1) and one AB class output stage (A2) realized in CMOS technology. Each of the two stages (A1, A2) is provided with a common mode feedback circuit (CMF1, CMF2) to set the working point thus optimizing the amplifier overall dynamic range. Besides a power dissipation reduction circuit (PWD) is provided to limit the power dissipated during the idle state of the power amplifier. In particular, the topology of the amplifier is fully symmetrical. In this way, a wide range output signal on a low resistive load, a very small harmonic distortion, as well as a low power consumption are achieved.

Multiple bandwidth crystal controlled oscillator

Abstract: A dual bandwidth crystal controlled oscillator (200) is described having a first transconductance amplifier (202) providing sufficient gain to maintain oscillation with an oscillator crystal (210) at a minimum current drain. A second transconductance amplifier (218) is provided which can be selectively coupled to the first transconductance amplifier (202), thereby augmenting the gain of the first transconductance amplifier (202) to provide the capability for rapid oscillator start-up following battery saver operation. The dual bandwidth crystal controlled oscillator (200) can be utilized in conventional oscillator and frequency synthesizer applications.

Wideband class AB (push-pull) current amplifier in CMOS technology

Abstract: A wideband class AB (push-pull) current amplifier realised with only ten MOS devices is described which provides very low input resistance, good large signal behaviour and large bandwidth. Detailed analysis of the proposed circuit is presented. The two amplifier circuits composed of simple and cascode current mirrors are simulated and their performance characteristics compared.

A novel CMOS linear transconductance cell for continuous-time filters

Abstract: A novel tunable transconductance cell with extended linearity is described. It is based on the use of the transconductance of an MOS transistor operated in the triode region. High linearity of the cell is achieved by maintaining both drain-to-source and source-to-body voltages of the transistor constant by means of a very simple feedback loop. The tuning of the transconductance cell is obtained by adjusting the current delivered by a current source. The cell also provides high operation speed. The circuit is suitable for the design of high-performance, high-frequency, continuous-time filters. It is shown that, when the cell is used in a fully differential configuration, harmonic distortion as low as 0.3% can be achieved for processed signals with a peak amplitude of 3 V. >

Feed-forward amplifier having increased compression point

Abstract: In order to improve the distortion performance of a feed forward corrected amplifier, an amplifier arrangement includes a distortion generator (312) which is coupled between an input (15) and a main amplifier (1). The amplifier arrangement is such that the input signal passes to the distortion generator (312) via a coupler (307). The signal passes via a delay network (310) which compensates for the delay of the distortion generator (312) and is tapped by a coupler (308) to be combined by a coupler (313) with the distorted signal from the distortion generator (312). In this way the output of the distortion generator is subtracted from a sample of the input signal so that only the distortion remains to pass via phase (314) and amplitude (315) correction networks to be amplifier by a gain element (316) before being coupled back into the main signal path by a coupler (309). The correction is active over a portion of the main amplifier characteristics such as the compression region of the main amplifier. Hence the main amplifier (1) compression point may be raised. Raising the compression point increases the overall power handling capability of the main amplifier by increasing the level at which the overall arrangement will saturate to cause distortion.

Sense amplifier for a memory device

Abstract: A MOS transistor sense amplifier employs cross coupled positive feedback for the load circuit of a differential amplifier with an equalizing switch at the amplifier output, and preferably also at the input. This basis amplifier circuit may be repeated in stages. When stages are employed, it is desirable that the first stage employs current mirror loading of the differential amplifier to reduce the data delay. Data delay is further reduced by providing strong amplification during the sense portion of the read cycle with a preamplifier, which preamplifier has its amplification reduced, preferably to unity by being turned off, when the sense portion of the cycle is finished, and most preferably when the input and output data lines are directly connected independently of the preamplifier, so that the preamplifier may be completely turned off to lower power consumption.

Amplifying compensation circuit for semiconductor

Abstract: A pressure sensor circuit has a bridge circuit of strain gauges formed on a silicon diaphragm with two output terminals. The difference in the voltage between the two output terminals is dependent on the pressure applied to the strain gauges. A differential amplifier circuit having an operational amplifier and a feedback circuit amplifies the difference between the two output terminals. A temperature dependent resistor in the feedback circuit provides temperature compensation. An adjustable resistor adjusts the sensitivity of the pressor sensor circuit. Temperature dependent resistors connected between the operational amplifier and reference voltages compensate for zero point temperature fluctuations, and adjustable resistors connected between the operational amplifier and the reference voltages adjust the zero point.

A high slew-rate CMOS amplifier for analog signal processing

Abstract: The performances of several types of analog VLSI circuits are limited by the setting behavior of CMOS amplifiers. An amplifier with a nonsaturated input stage which achieves a high slew-rate response is presented. The impact of this slew-rate amplifier on switched-capacitor circuits is described. Prototyping amplifier circuits were fabricated by the MOSIS service using a 2- mu m scalable CMOS technology. When biased at a DC power dissipation of 1 mW, the two-stage amplifier achieves a slew rate of 80 V/ mu s, a positive-supply rejection ratio of 73 dB, and a negative-supply rejection ratio of 57 dB and 50 kHz. >

Low-noise preamplifier for magneto-resistive heads

Abstract: A preamplifer for use with a magneto-resistive playback head in which a d.c. current source provides current through a field effect transistor and the magneto-resistive element to ground. An operational transconductance amplifier included in a feedback loop provides a bias voltage for the field-effect transistor, whereby the voltage across the said magneto-resistive element is held constant while the resistance of said element changes. The resulting a.c. current flowing through the magneto-resistive element flows only through the feedback loop and an output resistor connected across the inputs of the operational transconductance amplifier. The amplification of the circuit is approximately the resistance of the output resistor divided by the resistance of the magneto-resistive element.

Stabilized-feedback control device for semiconductor lasers

Abstract: A semiconductor laser control apparatus includes a semiconductor laser, a current driver connected to the semiconductor laser, a semiconductor p-i-n photodiode for generating a monitoring current, and an operational amplifier. The inverting input of the operational amplifier receives a modulated or control signal through a resistor and a feedback current based on the monitoring current. The non-inverting input of the operational amplifier receives a reference signal. When a variation in output light amount of the semiconductor laser occurs, the operational amplifier generates an error signal in accordance with the feedback current and supplies the error signal to the current driver, thereby compensating for the variation in output light amount of the semiconductor laser.

Splatter controlled amplifier

Abstract: An amplifier circuit uses a microprocessor to count occurrences of the output stage going into saturation to decide when to control input levels to the amplifier. When the output amplifier stage saturates too frequently, the microprocessor controls a scaling line that effectively attenuates input levels to the amplifier, eliminating saturation levels. When the output stage saturates too infrequently, input levels to the amplifier are increased.