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Improved Video Interface Made by Pulse Transformer and Differential Receiver

IP.com Disclosure Number: IPCOM000059938D
Original Publication Date: 1986-Feb-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Ohtaka, Y: AUTHOR

Abstract

This article describes a solution to a problem in the CRT display terminal concerned with the radiated electromagnetic interference (EMI) (E-Field) from the interface between logic and monitor portions. Today, it is quite important for CRT display terminals, in particular for low-end ones, to comply with the regulation of radiated EMI (E-Field Strength), such as US FCC-EMI, GERMAN VDE-RFI, etc.. One of the main radiation sources is the interface portion between the logic and monitor portions, on which the high frequency video signal runs through a long way (for example, 100 cm). Fig. 1 shows the proposed new video interface which can improve the radiated EMI characteristics.

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Improved Video Interface Made by Pulse Transformer and Differential Receiver

This article describes a solution to a problem in the CRT display terminal concerned with the radiated electromagnetic interference (EMI) (E-Field) from the interface between logic and monitor portions. Today, it is quite important for CRT display terminals, in particular for low-end ones, to comply with the regulation of radiated EMI (E-Field Strength), such as US FCC-EMI, GERMAN VDE-RFI, etc.. One of the main radiation sources is the interface portion between the logic and monitor portions, on which the high frequency video signal runs through a long way (for example, 100 cm). Fig. 1 shows the proposed new video interface which can improve the radiated EMI characteristics. Following are the key advantages of this interface: (1) To separate the return path of the video signal between the logic portion and the monitor portion. This makes "shielding" of the interface cable more effective. (2) To enable a great reduction of the interface signal level. This works to reduce the source level of radiation. By the mutual effectiveness of the above, radiation from the video interface can be greatly reduced. Fig. 2 and Fig. 3 show the actual example of interface and operation. The pulse width is 40 nsec, which is equivalent to a 25 MHz video signal (100% duty). Also, it is found that the interface signal level is very small (Vinf < Å 0.2 V). In the actual application, a pull-up or -down resistor...