Browse Prior Art Database

EMI Reduction by Optical Barrier Computer/ Peripheral Interface

IP.com Disclosure Number: IPCOM000122462D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 79K

Publishing Venue

IBM

Related People

Sawdon, D: AUTHOR [+2]

Abstract

Disclosed is a technique to overcome some EMI (electro-magnetic interference) problems associated with the interface between a computer system adapter and a display monitor, by inserting an optical barrier in the interface.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

EMI Reduction by Optical Barrier Computer/ Peripheral Interface

      Disclosed is a technique to overcome some EMI
(electro-magnetic interference) problems associated with the
interface between a computer system adapter and a display monitor, by
inserting an optical barrier in the interface.

      Computer monitors are usually attached to a video adapter which
resides in a separate computer system unit. Connection between the
adapter and monitor is usually by a cable containing a mixture of
coaxial cables for the higher frequency signals and individual wires
for the DC and low frequency signals.  Typically, the length of this
cable can vary from one to twenty meters.

      EMI Units limits stipulated by the various national standards
regulatory bodies have caused considerable difficulty making systems
comply with their limits, leading to product and development cost
increases and schedule overruns.  A major contribution to the EMI
problem is made by common mode currents flowing along the interface
cable. A partial success results from fitting ferrites to the cable.
Described is an alternative to present practice by the use of fiber-
optic link techniques to form a highly effective optical common mode
barrier.

      This description is in terms of a monitor attachment, but it is
applicable to any peripheral.  The technique is to provide a high
series impedance in the common mode signal paths between the monitor
and adapter, while retaining a well-controlled impedance for
differential signals to allow correct termination and elimination of
unwanted reflections. Mandatory safety ground connections are
unaffected by this proposal.  Compatibility with other monitors
and/or system units which do not co...