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Loop Connection of Unterminated Printed Circuit Wire Nets

IP.com Disclosure Number: IPCOM000061393D
Original Publication Date: 1986-Jun-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Timmer, MR: AUTHOR

Abstract

A method is described to curtail mismatches and reflections in transmission lines in high performance semiconductor systems. Addition of a parallel line from the driver effectively reduces the characteristic impedance to half the value and provides an a.c. termination at the far end of the line.

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Loop Connection of Unterminated Printed Circuit Wire Nets

A method is described to curtail mismatches and reflections in transmission lines in high performance semiconductor systems. Addition of a parallel line from the driver effectively reduces the characteristic impedance to half the value and provides an a.c. termination at the far end of the line.

The problem in the conventional system is due to a long main line segment with no load which results in a high impedance as compared to the loaded segment. Since the far end of the line is not terminated the open ended effect causes reflections. Objectionable overshoots occur at the far end of the l

Typical array cards use push-pull drivers of Fig. 1 on unterminated lines to power array inputs. The arrays 3 are lumped at the far end of the line with field effect transistor array loads indicated 4. In the case of a long mainline 2 and low array capacitance, the downgoing transition will overshoot 5 and then ring 7 past the down level threshold 6 to create a false switch, as indicated in the waveform
10.

In the improved loop connection a second printed circuit wire 8 of Fig. 2 is connected in parallel with the mainline 2 from the driver to the far end of the net, thereby providing a termination. This eliminates some of the reflection caused by the far end mismatch and is also a better impedance match at the driver. The improved waveform 10 does not overshoot past the threshold 6.

Disclosed anonymously.

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