Browse Prior Art Database

Digitally Controlled Precision Current Source

IP.com Disclosure Number: IPCOM000089023D
Original Publication Date: 1977-Sep-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Olsen, FW: AUTHOR

Abstract

This circuit provides a low noise, very fast response, electrically floating, and low capacitance current source for use in an analog test system which has critical precision test requirements.

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Digitally Controlled Precision Current Source

This circuit provides a low noise, very fast response, electrically floating, and low capacitance current source for use in an analog test system which has critical precision test requirements.

The circuit makes use of matched binary weighted current sources 10 and sinks 11, with their individual weighted source and sink outputs being digitally switched by FET analog switches 12 from a preload short condition to a load condition. Digital logic level input signals to program the total load output current are provided and are fed through inverters 13 and buffers 14 which are connected in series to the individual switches. A load 15 is multiplexed across the current sources and sinks by way of diodes 16. The individual current weights of the sources and sinks are on at all times and are electronically switched.

A down-level logic input signal on a line is inverted and effects a preload short condition wherein the switches 12 for that line are closed and the associated diodes 16 are reverse-biased. In this condition, current is fed from the positive terminal of current source 10 to the negative 5-volt bus and from the negative terminal of sink 11 to the positive 5-volt bus. An up-level logic input signal on a line is inverted to effect a load condition wherein the switches 12 for that line are open and the associated diodes 16 are forward-biased. In this condition, current is fed from the current source 10 through diode 1...