Browse Prior Art Database

Isolating Digital or Analog Interface Circuit

IP.com Disclosure Number: IPCOM000090886D
Original Publication Date: 1969-Aug-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Keller, WL: AUTHOR

Abstract

The problem of ground loops frequently presents itself where precision AC, analog, or low-frequency signals are to be measured or transferred. The complex wiring of most equipment generally renders it impractical to modify the internal ground wires to eliminate ground loop currents between the source and the load.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 63% of the total text.

Page 1 of 2

Isolating Digital or Analog Interface Circuit

The problem of ground loops frequently presents itself where precision AC, analog, or low-frequency signals are to be measured or transferred. The complex wiring of most equipment generally renders it impractical to modify the internal ground wires to eliminate ground loop currents between the source and the load.

In A, there is shown an illustration of the ground loop problem. IGL represents ground loop current, VG1 and VG2 represent ground loop voltages, and R6 represents the impedance of the ground current path. In B, there is shown a circuit which overcomes the ground loop problem. The solution essentially employs switching devices such as a chopper, relay, semiconductor, insulated gate field effect transistor, etc., depicted as ordinary switches, and a storage capacitor CS, connected as shown.

In the operation of the circuit shown in B when switches 10 and 10' are closed, switches 12 and 12' are open and CS charges to a value substantially equal to the full source voltage. When CS becomes fully charged, switches 10 and 10' open with CS having the full source voltage across it. At this juncture, switches 12 and 13' close and the voltage across CS is measured using the measuring device's ground as a reference. The operation of the switches is break-before-make in order to provide full isolation between the load and the source. Since in the circuit, there is no conductive ground, there is therefore no ground loop or...