GB1012868A - Electrical switching circuit - Google Patents

Abstract

1,012,868. Pulse modulation systems. STANDARD TELEPHONES & CABLES Ltd. Feb. 18, 1964, No. 6704/64. Heading H4L. A switching circuit, e.g. in a P.C.M. system, comprises an input over which may be received an electrical signal of positive or negative polarity, a trigger circuit which is settable to its first or its second state dependent on whether its input signal is positive or negative, means under the control of the trigger circuit for producing an output from the switching circuit having an amplitude dependent upon the amplitude of the input signal and of one polarity only irrespective of the polarity of the input signal, the trigger circuit supplying a signal which is indicative of the polarity of the input signal to a further output of the switching circuit. As shown in Fig. 1, input signal samples from 1 are supplied via a channel gate 2 and load resistor 3 to a trigger circuit 4 and also to an amplifier 5 feeding a transformer 8 having a centre tapped output winding. The trigger 4 is set in one or the other state according to the polarity of the incoming signal and operates a circuit 9 or 10 to clamp the corresponding end of the output winding of transformer 8 to earth so that amplitude modulated pulses of the same polarity appear at the output 11. The polarity of the input is represented by binary one or binary nought appearing on the output 13. The transformer 8 may be replaced by a pair of capacitors, Fig. 2 (not shown), or by transistors, Fig. 3 (not shown).