GB1074295A - Improvements in and relating to transmission circuit arrangements for inverting the polarity of a signal - Google Patents

Abstract

1,074,295. Phase - reversible amplifiers. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. Feb. 17, 1965 [Feb. 19, 1964 (2)], No. 6858/65. Heading H3T. A transistor amplifier may be converted into a non-inverting unity gain stage by biasing the collector-base junction so that it acts as a shortcircuit. As applied to the post-detector stage of a dual-standard T.V. receiver (Fig. 2), the transistor 22 acts as a normal amplifier on one standard with switch 20 open, and as a non- inverting stage with switch 20 closed when the vision signal is of opposite polarity. The resistors 34 and 35 can be chosen so that the amplification is unity for both polarities. The collector-base junction also functions as a limiter for suppressing interference since, when forward biased, it will not pass negative signals large enough to overcome the bias. The preceding stage 21 acts as an emitter-follower for the video signals and a tuned commonemitter stage for the sound-carrier which is taken off at 24. Sound-rejection in the video channel is assisted by the rejector circuit 25. The switch 20 may apply a negative bias to the base instead of a positive bias to the collector. One or both transistors may be NPN. The arrangement is also applicable to logic circuits, computers and control systems.