GB1213196A - Improvements in or relating to circuit arrangements for modifying television signals - Google Patents

Abstract

1,213,196. Television. FERNSEH G.m.b.H. 11 March, 1968 [11 March, 1967], No. 11813/68. Heading H4F. A circuit is provided which enables colour or black and white television signals to be mixed, faded in and out, or to have correction applied with out affecting the synchronizing or test signal components. As shown, a composite television signal selected by a switch 12 is supplied to an amplifier 2 whose gain is continuously or stepwise adjustable and to an amplifier 3 whose gain is preset to the maximum value of the gain of amplifier 2. After the black levels have been adjusted to the same value by stages 5, 6, the outputs of the amplifiers are supplied via an electronic changeover switch 4 to the output amplifier 7. The switch 4 is controlled by pulses U consisting of pulses (U H ) extending over each horizontal flyback time and pulses (U V ) extending over each vertical blanking interval, Fig. 1 (not shown), which are derived by a circuit 9 from the input signal, or alternatively, from a separate source S via switch 10. By this means the switch 4 is timed to connect the amplifier 2 to the output while the picture information is being transmitted and the amplifier 3 to the output when synchronizing or test signals are being transmitted. A switch 11 may be arranged to select a constant potential to provide a blanked video signal at the output 7 or alternatively may be switched to introduce an external source S of sync. signals. A plurality of these circuits may be combined through a common adding circuit Fig. 3 (not shown). In a modification of Fig. 2, a gamma control stage and a colour matching circuit are included in series with the amplifier 2 thus necessitating a compensating delay circuit in series with the amplifier 3. Means are also provided for independent adjustment of the black level at the output of amplifier 2.