US 4,374,362 AGranted

Instrument zeroing circuit

AssigneeSys-Tec, Inc.

InventorsGeorge K. Sutherland, Thomas J. Thielen

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Abstract

An electronic interface circuit for coupling a source of analog signals to a measuring and/or recording device whereby the time varying component of the analog signal can be separated from any steady-state component, such as a DC bias, which may be present, allowing further signal processing on the time varying component only. The interface circuit comprises a servo control device having both a digital feedback loop and an analog feedback loop. Upon closure of a manually operable switch, a timer is initiated which first actuates the digital feedback loop wherein a digital number is generated which is proportional to the deviation of the signal output from a summing amplifier from a zero volt level. This digital number is applied through a digital-to-analog converter to the summing amplifier along with a second feedback signal obtained by sampling the output from the summing amplifier at a time subsequent to the digital correction operation. As a result, the deviation of the steady-state signal from zero occasioned by the inherent granularity in the analog-to-digital conversion process is eliminated.

Claims4

Dependent claims

Electronic apparatus for removing a direct current bias level from a composite input signal of the type having a time varying component superimposed on said direct current bias level, comprising:

(a) input means for receiving said composite input signal;
(b) summing amplifier means having an input terminal and an output terminal, said input terminal being coupled to said input means and first and second negative feedback loops adapted to be selectively coupled from said output terminal of said summing amplifier means to said input terminal thereof;
(c) said first feedback loop including means for generating a digital number proportional to the deviation of said output signal of said summing amplifier means from a zero voltage reference value, means for converting said digital number to an analog voltage, and means coupling said analog voltage to said input terminal of said summing amplifier;
(d) said second negative feedback loop including means for sampling the output from said summing amplifier means and for holding a voltage value proportional to the deviation of said output signal from said summing amplifier from a predetermined reference for a predetermined time and applying said voltage value to said input terminal of said summing amplifier;
and
(e) control means for effectively connecting said first feedback loop in circuit with said summing amplifier for a first predetermined time and for subsequently disconnecting said first feedback loop while coupling said second feedback loop in circuit with said summing amplifier for a second predetermined time.

3 more elements

Dependencies are inferred from the claim text.