Browse Prior Art Database

Connectorless Video Interface for Display Terminals

IP.com Disclosure Number: IPCOM000099893D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Hubing, TH: AUTHOR

Abstract

High resolution video displays often have a difficult time meeting government radiated electromagnetic interference (EMI) requirements. This is often primarily due to the high frequency video signals that are inadvertently induced on the external surfaces of the display's power and I/O cables. The cable that carries the video signals from the logic card to the video amplifiers on the neck of the CRT is usually a critical component contributing to the unwanted radiation (*).

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Connectorless Video Interface for Display Terminals

       High resolution video displays often have a difficult
time meeting government radiated electromagnetic interference (EMI)
requirements.  This is often primarily due to the high frequency
video signals that are inadvertently induced on the external surfaces
of the display's power and I/O cables. The cable that carries the
video signals from the logic card to the video amplifiers on the neck
of the CRT is usually a critical component contributing to the
unwanted radiation (*).

      The video interface illustrated in the figure eliminates the
need for this cable.  Instead of conducting the signal on wires
between the logic card and the CRT, the signal is coupled through the
covers using two coils.  The transmit coil and receive coil work
together like an air-core transformer, providing a high degree of
common-mode rejection.  This reduces the amount of video signal
coupling to the external cables making it easier to meet the FCC
(Federal Communications Commission) EMI requirements without
expensive filters and shields.

      The emanations from a properly designed transmit coil are well
below the FCC limits, and with the proper receiving circuit, this
interface can be designed with a high level of immunity to ambient
electromagnetic fields.  The simple interface circuitry shown on the
preceding page was used in a display terminal that operated with a
video frequency of 56 MHz.  This nonlinear rece...