Browse Prior Art Database

Signal Isolating Means

IP.com Disclosure Number: IPCOM000074477D
Original Publication Date: 1971-Apr-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Chapman, NC: AUTHOR [+2]

Abstract

A variable voltage or current signal is sensed or measured despite the presence of large interfering common mode voltages by applying that signal so as to control the impedance across the secondary of a continuously energized transformer. The circuit is capable of fast response speeds and requires relatively small voltage or current for reliable operation.

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Signal Isolating Means

A variable voltage or current signal is sensed or measured despite the presence of large interfering common mode voltages by applying that signal so as to control the impedance across the secondary of a continuously energized transformer. The circuit is capable of fast response speeds and requires relatively small voltage or current for reliable operation.

Oscillator 10 operating at a frequency slightly larger than the desired response speed of the circuit is connected to one terminal of the primary winding 11 in closely coupled transformer 12. The other side of 11 is connected to amplitude detector 13. The output of 13 can be shifted, amplified or clamped as desired and is particularly well suited for producing proper voltage levels for driving binary logic circuit 15. Secondary winding 16 of 12 contains a variable impedance load consisting of three element transistor 17 which can be either unipolar or bipolar and operates without a DC power source for the collector circuit by direct AC energization from 16. In its simplest form, the circuit can be arranged so that the base of 17 is connected through current limiting resistor 18 directly to the isolated unknown input source 19, with the other terminal of the source being referenced to the common connection between 16 and the emitter of 17, as shown, or alternatively with the collector of 17.

A continuous range of input voltages at 19 can be produced at the output of
13. The sensing and utilization of the extremes of input voltages on either side of this continuous range is particularly well suited for binary-to-binary coupling purposes with extremely high-common mode rejection. That is, one polarity of the two extremes occurs when the base of 17 is nearly zero or negative, at which time 17 effectively causes a relatively large impedance to appear in circuit with secondary winding 16. This impedance is reflected to 11, thus causing a similarly high impedance to appear between 10 and 13 so that the output of 13 will be zero or of a small magnitude. For the other extreme of input signal at 19, 17 will be driven into saturation for both half-cycles of the voltage on 16, loading 16 wi...