H - Electricity – 04 – L
Patent
H - Electricity
04
L
330/13, 340/72
H04L 25/08 (2006.01) H04B 15/00 (2006.01)
Patent
CA 1268226
ABSTRACT OF THE INVENTION A data processing system has a plurality of stations or terminals linked to a star coupler over cables comprising separate sending and receiving transmission lines, the cable shield being connected to system ground. To mini- mize bit error rate when a station is powered down, the transmitting differential amplifier at each terminal sta- tion is connected between a bias voltage and a virtual ground created by a pair of diodes connected in parallel, their anodes being connected to a voltage source through a current limiting resistor, the cathode of one diode be- ing connected to system ground, the cathode of the other diode being connected to one side of the transmitting amplifier to define the virtual ground. To further en- hance noise rejection, a balanced differential network is connected to the outputs of a transistor pair at the amp- lifier output to the differential wire transmission line. The network comprises a resistor and diode connected in series between each transistor's emitter output and the amplifier bias voltage source, the combined resistance and dynamic impedance of each portion of the balanced differential network being equal. At the receiver end of the star coupler cabinet, a series resistor network is coupled from a bias voltage source for a differential re- ceiver amplifier to the system ground. The receiver amp- lifier has two input transistors; the resistor network includes a resistor coupled across the transistor inputs of a resistance matched to the characteristic impedance of the cable; two additional resistors are connected in series between the ends of this resistor and the inputs to the amplifier transistors to define a relatively high offset voltage across the input to the receiver ampli- fier.
533915
Ncr Corporation
Singh Amar J.
Smart & Biggar
LandOfFree
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