RTB: A Full-Duplex ECL Transceiver For Wideband Digital Systems

This paper deals with the design of a low cost ECL bipolar compatible I.C performing the function of four balanced full-duplex transceivers particularly suitable for interconnections long up to several tens of meters in digital systems. One of the most interesting applications of this circuit is in the field of wideband digital switching (up to 100 Mbit/sec) where the amount of two-way internal connections can be very high, [1] More precisely when bidirectional video communications are concerned (as in the case of the digital switching of video telephony signals) the use of this component virtually halves the wiring cost. Other applications include narrow band (up to 2 Mbit/sec) digital switching systems where it is possible to achieve great saving in cabling cost or to allow the designers to implement interesting diagnosis and signalling schemes inside the exchange.[2] Obviously his application range is not bounded to these fields but covers all the situations where two-way communication implying the use of standard receiver/transmitter pairs is needed. The functional behaviour of RTB is shown in fig. 1: Ct is an ECL driver with a low output inpedance, Ip is a common mode current source, Ro is the line characteristic resistance, A1(A2) are linear amplifiers, Cr is a differential to single ended ECL translator. When two transceivers are sending data through the same line, the signal at both end of the line is a superposition of the one transmitted from the local terminal and the one received from the remote terminal.