Output Offset Voltage Research Articles

Mind the gap [electric trains

Engineers working on electric trains have struggled with the problem of ensuring that the pantographs keep as much contact with the overhead line as possible without damaging it in one of the harshest environments for electronics known. One system has stepped into the breach. Experience of electronics on trains dictates that both input circuit protection and galvanic isolation are essential (RIA 13 & EN50155). PanChex and the original pantograph telemetry developed by BR Research had used voltage to frequency and voltage to frequency conversion to enable digital transmission of analogue signals over a fibre optic cable. Although this method is useful for simple systems, it suffers from thermal drift. A small change in gain inherently creates a large change in output offset voltage. It was decided from the outset of this project that a standard analogue-to digital converter (ADC) preceded by a high performance instrumentation amplifier would be used to digitise the analogue signals from the sensors.

Prediction of High-Power EMI Effects in CMOS Operational Amplifiers

In this paper, a new analytical model for the prediction of the effects of high-power electromagnetic interference in CMOS operational amplifiers is presented. This model provides a closed-form expression of the operational amplifiers (opamp) output offset voltage that is induced if radio frequency interference (RFI) is superimposed onto the opamp input voltages in terms of technology and design parameters. Such a model is very useful both to predict the susceptibility of a given opamp circuit and to design opamp topologies with a high immunity to RFI. Model predictions are compared with experimental results

Prediction of EMI effects in operational amplifiers by a two-input Volterra series model

The authors present a new analytical model that describes the nonlinear behaviour of common CMOS operational amplifiers excited by radio-frequency interference (RFI) added to the input nominal signals. The new model is a valid support to analogue integrated circuit designers since it expresses a relationship between circuit parameters, parasitic elements and the amplitude of the RFI induced output offset voltage of a feedback CMOS operational amplifier. The validity of model prediction has been verified through a comparison with experimental and computer simulation results.

CMOS interface circuitry for a low-voltage micromachined tunneling accelerometer

This paper describes the design and development of three types of complementary metal-oxide-semiconductor (CMOS) interface circuitry for low-voltage micromachined tunneling accelerometers. Using a simple inductance-capacitance-resistance (LCR) circuit as well as two nonlinear current/voltage-controlled current sources, an electromechanical model enables simulating and predicting the performance of the accelerometer with CMOS interface circuitry. Of the three types of interface circuitry, the one utilizing a pn-junction diode as a logarithmic current-to-voltage converter has the best performance. The hybrid sensor-circuit module can be incorporated into a portable battery-operated multisensor instrumentation microsystem. Only one 12-V power supply is required for device operation with a power dissipation of 2.5 mW. The accelerometer has a sensitivity of 125 mV/g and bandwidth of 2.5 kHz with a measurement range of 30 g. The noise spectral density with a 1/f behavior drops from 4 mg//spl radic/(Hz) (at 0.5 Hz) to 0.1 mg//spl radic/(Hz) (at 2.5 kHz). The accelerometer in turn provides a dynamic range over 71 dB with a minimum detectable acceleration of 8 mg in a bandwidth of 2.5 kHz. In continuous operation over 720 h, the long-term variations of the output offset voltage and device sensitivity are /spl plusmn/10 mV (0.12%) and /spl plusmn/0.2 mV/g (0.15%), respectively.

Switched capacitor circuits with compensator for clock feedthrough effects

AbstractWhen a switched capacitor circuit is constructed, a provision for output offset voltage generation by the effect of the clock feedthrough charge is indispensable. Especially in the circuit made of individual components using commercially available analog switches, this effect is significant.In this paper, the generation mechanism of the feedthrough charge in an analog switch is analyzed and a circuit configuration method is proposed for compensation of the feedthrough effect for the integrator as the most fundamental switched capacitor circuit. Also, by a comparison experiment, with the conventional method, the effectiveness of the proposed circuit is confirmed.The circuit size is larger as an integrator itself than the one by the conventional method. However, even in the case with a multiple cascading of the integrators such as in a higher‐order filter, the feedthrough compensation is possible with only one feedback loop so that the overhead for the increased circuit size can be reduced. According to the trial circuit, the output offset voltage can be suppressed to the level of several millivolts. Hence, the present method can be applied to various operating circuits with high accuracy.

Truly temperature independent current conveyor precisionrectifier

A current conveyor based rectifier circuit with very low temperature sensitivity is presented. The use of a current mirror arrangement to bias the rectifying diodes provides higher temperature stability than previously reported designs. The output offset voltage is easily adjustable to the desired optimum level.

Ultralow-frequency design of the Wien bridge oscillator using switched capacitors

An ultralow-frequency Wien bridge oscillator, in which resistors are replaced by switched capacitors and automatic gain controller circuitry, is reported. The oscillation frequency f is varied only by adjusting the SC clock frequency f/sub c/ without changing any element values. Experimental results show that the oscillator is stable over the oscillation frequency range from 10 /spl mu/Hz to 100 Hz. The linearity between f and f/sub c/ agrees with theoretical results. The device exhibits output voltage distortion of less than -40 dB within the frequency range from 100 /spl mu/Hz to 100 Hz. The distortion increases at frequencies below 100 /spl mu/Hz, resulting from an increase in output offset voltage. Very short rise times for stable oscillation is achieved by lowering the clock frequency after achieving stable oscillation at a higher clock frequency. Experiments and computer simulations are also discussed. >

Temperature independent current conveyor precisionrectifier

A dual current conveyor based rectifier circuit with low temperature sensitivity is presented. The use of a DC current source to bias the rectifying diodes provides higher temperature stability than previously reported designs. In addition the output offset voltage is easily controlled and adjusted to a minimum low value.