GB1118465A - Improvements relating to colour television receivers - Google Patents

Abstract

1,118,465. Colour television. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. 27 Sept., 1965 [8 Oct., 1964], No. 40962/65. Heading H4F. In a receiver for the PAL colour television system the chrominance carrier signal is modified in a stage 4 to produce a signal having a phase angle with respect to a reference axis <SP>1</SP>equal and opposite to that of the received signal, which modified signal is then compared in a phase comparator 7 with the unmodified signal from the preceding line, obtained via delay line 2, to obtain a signal U R to control the phase of a datum carrier oscillator 9. The control signal is proportional to undesired phase errors imparted to the carrier signal by transmission conditions and is independent of the phase modulation due to chrominance information. By transferring delay line 2 to the same path as modifier 4 an alternative arrangement is produced in which the modified signal is phase compared with signal in the next succeeding line. The modifier 4 comprises a modulator in which the chrominance carrier is modulated by a signal of twice the frequency and the lower side-band selected from the resulting signal. As illustrated the double frequency signal is obtained from oscillator 9 by way of frequency doubler 11. The control signal controls the phase of oscillator 9 by means of reactance stage 8. The effect of the arrangement is to cause the output of oscillator 9 to vary in phase in accordance with the phase error of the chrominance carrier signal so that the oscillator output is always of the correct phase to demodulate the carrier. Oscillator 9 is also synchronized by the colour synchronizing signals which produce a signal over lead 13 to control reactance stage 8. In another arrangement (not described in detail) oscillator 9 is synchronized by the colour synchronizing signals and the control signal U R controls a phase shifter connected to the output of the oscillator.