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Emitter Coupled Logic to Either Long Line or Send Receive Mode Bidirectional Convert Circuit

IP.com Disclosure Number: IPCOM000085692D
Original Publication Date: 1976-May-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 76K

Publishing Venue

IBM

Related People

Williams, KR: AUTHOR

Abstract

The circuit, shown in Fig. 1, allows high-speed bidirectional communication between existing emitter-coupled logic (ECL) and either Long Line (LL) or Send/Receive (S/R) mode logic. As will be shown later, the receiver threshold for Long Line and for Send/Receive must be programmed externally but the driver will drive either mode without external programming. CIRCUIT OPERATION - DRIVER MODE

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Emitter Coupled Logic to Either Long Line or Send Receive Mode Bidirectional Convert Circuit

The circuit, shown in Fig. 1, allows high-speed bidirectional communication between existing emitter-coupled logic (ECL) and either Long Line (LL) or Send/Receive (S/R) mode logic. As will be shown later, the receiver threshold for Long Line and for Send/Receive must be programmed externally but the driver will drive either mode without external programming. CIRCUIT OPERATION - DRIVER MODE

The heart of the Fig. 1 circuit is transistors Q6 and Q7 and the two terminators (near and far end of the transmission line). The thevenin line impedance is always 4O-45 omega and when transistor Q7 is off, the line "floats" to the thevenin voltage of the two terminators; however, when Q7 turns on, current IC7 is about 24 mA which causes the line to drop about 1 volt (40 Omega x 25 mA) from the transistor Q7 off value. Thus for the two terminations the levels are (Long Line) ground to -1.0v, see equivalent circuits Figs. 2a and b, and (Send/Receive) -1.0v to -2.0v, see equivalent circuits Figs. 3a and b.

Transistors Q3, Q4 and Q5 form a current switch emitter-follower to clamp the Send/Receive uplevel up to -0.8v (so that loading will not pull the leveldown) and has no affect in any other case.

Transistors Q1 and Q2 serve as emitter-followers to shift the input levels and isolate the current switches from the line.

Again the heart of the circuit is transistors Q6 and Q7 shown in Fig. 1...