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Browse Prior Art Database

Active Terminator for Transmission Line

IP.com Disclosure Number: IPCOM000060156D
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Feth, GC: AUTHOR

Abstract

This article relates generally to transmission line termination and, more particularly, to the incorporation of active circuit devices to reduce power dissipation. Active switching devices in place of the usual resistive characteristic impedance terminators for transmission lines for binary signals can greatly decrease the average standby power dissipation. In the schematic binary circuit of Fig. 1, transmission line ZO is driven by push-pull driver Pu-Pd and terminated by the addition of controlled switches Su and Sd in series with respective resistors Ru and Rd on either side of node NR. Switch Su closes and switch Sd opens when node voltage is high. The switches function in the opposite manner when voltage is low.

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Active Terminator for Transmission Line

This article relates generally to transmission line termination and, more particularly, to the incorporation of active circuit devices to reduce power dissipation. Active switching devices in place of the usual resistive characteristic impedance terminators for transmission lines for binary signals can greatly decrease the average standby power dissipation. In the schematic binary circuit of Fig. 1, transmission line ZO is driven by push-pull driver Pu-Pd and terminated by the addition of controlled switches Su and Sd in series with respective resistors Ru and Rd on either side of node NR. Switch Su closes and switch Sd opens when node voltage is high. The switches function in the opposite manner when voltage is low. This action retains the new level of node voltage until changed to the opposite state by the driver, but opens the direct current path to ground in the standby state, eliminating power dissipation. The push-pull driver provides pull-up and pull-down for the high and low levels. An example of an implementation of an active termination circuit is shown in Fig. 2 using npn bipolar transistors for switches Su and Sd and logic gates for the controls. Transistors Q1 and Q2 together with Rb provide a logical inversion of the binary output signal B at the receiving end of the transmission line. Qd inverts again, consistent with the value B at its collector. Moreover, transistor Q3 inverts the output of Q2 again, which drives the base of Qu and then the emitter of Qu with the same sense as the signal B. T...