PubMed · 5146942
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E Greenstein, J Hynecek. 1971. A monolithic electrode amplifier.. https://pubmed.ncbi.nlm.nih.gov/5146942/
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We have developed a signal amplifier for the detection of weak repetitive pulsed signals superimposed on a large background. It is based on a double gated integrator principle with two channels locked to a sequence of alternate signal and background pulses. The circuit is compact and cost effective, and thus suitable for use in large numbers with detector arrays, for example in terahertz imaging. The performance was verified in terahertz time-domain spectroscopy based on an amplified femtosecond laser and found to be better than that of a commercial lock-in amplifier.
A circuit is proposed for a non-differential two-electrode biopotential amplifier, with a current source and a transimpedance amplifier as a potential equaliser for its inputs, fully emulating a differential amplifier. The principle of operation is that the current in the input of the transimpedance amplifier is sensed and made to flow with the same value in the other input. The circuit has a simple structure and uses a small number of components. The current source maintains balanced common-mode interference currents, thus ensuring high signal input impedance. In addition, these currents can be tolerated up to more than 10 microA per input, at a supply voltage of +/- 5 V. A two-electrode differential amplifier with 2 x 10 Mohm input resistances to the reference point allows less than 0.5 microA per input. The circuit can be useful in cases of biosignal acquisition by portable instruments, using low supply voltages, from subjects in areas of high electromagnetic fields. Examples include biosignal recordings in electric power stations and electrically powered locomotives, where traditionally designed input amplifier stages can be saturated.
A circuit was developed for a differential two-electrode biopotential amplifier. Current sources at the amplifier inputs were controlled by the common-mode voltage. This principle is well known in telephony for interfacing the telephone line with analogue-type phones. A low impedance of about 1 k(ohm) was obtained between each input and the common point of the circuit. The differential input impedance of 60 M(ohm) was obtained with the use of precision resistors. Considerable reduction in the common-mode voltages of more than 200 times resulted. The circuit can be useful for biosignal acquisition from subjects in areas of very high electromagnetic fields, where high common-mode voltages could saturate the input amplifier stages.