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Regulated Driver Clamp Circuit for Lossy Unterminated Transmission Lines

IP.com Disclosure Number: IPCOM000045636D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Cavaliere, JR: AUTHOR [+3]

Abstract

This circuit is a push-pull driver that feeds a lossy unterminated transmission line that regulates the output signal against reflections and temperature variation.

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Regulated Driver Clamp Circuit for Lossy Unterminated Transmission Lines

This circuit is a push-pull driver that feeds a lossy unterminated transmission line that regulates the output signal against reflections and temperature variation.

Since the transmission line is unterminated, the push-pull transistor pair (Q5 and Q6) has to supply high transient current for positive/ negative-going transitions, but there is no steady-state current in the line. Consequently, transistors Q5 and Q6 turn on and off alternately for positive and negative charging of the line. Q3 and RI form the constant current source for the differential pair (Q1 and Q2). A resistor alone could be used in the emitter of Q1 and Q2. The logic section (QA to QH and R1 to R8) is shown as a 4-way OR but could be any logic block with two phase outputs Phi and Phi.

Transmission line reflections are flattened out by the use of a Schottky barrier diode clamp network composed of drodes D1 and D2 returned to ground. The reflections are dampened out by the D1, D2 network that clamp the signal only when it overshoots over a design value. At all the other times, the attenuated signal travelling down the line will still be able to double at the end point and restore its amplitude. There is a small DC current in the line due to the clamp which is much less than that which would be dissipated in a terminating resistor in a conventional lossless line.

The driver has to absorb the reflections at the driving end as...