GB1530432A - Integrated circuit for connecting the audio channel of video recorders to television receivers - Google Patents

Abstract

1530432 Directional switching ITT INDUSTRIES Inc 25 Jan 1977 [29 Jan 1976] 02947/77 Heading H4R A circuit for connecting the audio channel of a radio or TV receiver to a record/playback machine by a single line, comprises a pair of emitter followers 11, 12, arranged parallel opposed in the line between the audio channel, connected at 4, and the record/playback machine, connected at 9, together with a switching circuit which includes a pair of transistors 101, 131 arranged in a long-tailed pair configuration with a reference voltage applied to the base of one, 131, and a control voltage applied to the base of the other, 101, to effect switching of conduction of the transistors. As described the switching of the transistors 101 and 131 is used to switch transistors 103 and 133 to enable or inhibit a respective one of the emitter followers 11, 12, to allow conduction of signals in one direction or the other between terminals 4 and 9. A current mirror circuit 25 supplies a constant current to the long-tailed pair, and the D.C. conditions at terminals 4 and 9 are maintained constant by the use of the second opposite conductivity emitter follower 12' and the current source 19 which is switched by transistor 134 when 131 is switched. During replay the de-emphasis capacitor 5 for the receiver is rendered ineffective by the low impedance presented by the output of emitter follower 12.