GB1172486A - Chrominance Signal Routing Circuit - Google Patents

Abstract

1,172,486. Colour television. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 23 Aug., 1968, No. 40359/68. Heading H4F. In a circuit for separating the chrominance signal of a colour television system N.T.S.C. or PAL, into colour information signals and phase reference signals, the chrominance signal is fed into a multivibrator arrangement which switches the signal to a phase comparator 10 during the colour burst period and to synchronous demodulators 12 during the colour information period. The chrominance signal is fed via a transformer 2 to a push-pull amplifier comprising transistors 3 and 4. From this outputs are taken from transistor 3 to transistors 5 and 8 and from transistor 4 to transistors 6 and 7. The two pairs of transistors 5, 6 and 7, 8 form a multivibrator which may be triggered or synchronized at terminal 51. In the embodiment illustrated the multivibrator is of the monostable type, due to the presence of capacitor 14 and hence requires trigger pulses at 15. These pulses are arranged to switch transistors 5 and 6 on, and 7 and 8 off, during the colour burst interval so that a signal passes from transistors 3 and 4, through transistors 5 and 6 to a pushpull transformer 9 from which the signals are fed to a phase comparator 10. Similarly during the colour information period, transistors 5 and 6 are switched off while transistors 7 and 8 are on.