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Signal Spectrum Reduction by Phase-Difference Transmission

IP.com Disclosure Number: IPCOM000059972D
Original Publication Date: 1986-Feb-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Aruga, N: AUTHOR [+2]

Abstract

This article describes a solution to a problem concerned with the signal transmission of high frequency through a long path, which frequently causes a radiated Electromagnetic Interference (EMI) problem or several signal distortion problems, etc. Today, it is quite important for CRT display terminals, in particular for the low-end, to comply with the regulation of radiated EMI, such as US FCC-EMI, German VDE-RFI, etc. The radiated E-field is sourced from base-clock and video signal, especially video signal due to running through a long path from the logic portion to the CRT. It is also known that E-field radiation is related to the spectrums contained in the video signal. Fig. 1 shows the principle of the new video interface circuit.

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Signal Spectrum Reduction by Phase-Difference Transmission

This article describes a solution to a problem concerned with the signal transmission of high frequency through a long path, which frequently causes a radiated Electromagnetic Interference (EMI) problem or several signal distortion problems, etc. Today, it is quite important for CRT display terminals, in particular for the low-end, to comply with the regulation of radiated EMI, such as US FCC- EMI, German VDE-RFI, etc. The radiated E-field is sourced from base-clock and video signal, especially video signal due to running through a long path from the logic portion to the CRT. It is also known that E-field radiation is related to the spectrums contained in the video signal. Fig. 1 shows the principle of the new video interface circuit. Two 1/2f input signals run through the interface in different phase, and at the receive side (monitor input) the input signal is regenerated by exclusive OR logic. The timing chart is shown in Fig. 2. This new interface has the following advantages: 1) Reduces radiated EMI (E-field) from the interface.
2) Reduces interface troubles such as waveform distortion, component selection, etc., by enabling the use of lower frequency. Fig. 3 through Fig. 5 show an example of this new interface. In this example, a 45 nsec. pulse width signal, which is equivalent to the 22 MHz dotclock for a 100% duty video signal, can be transmitted satisfactorily.

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