GB1067049A - Demodulator circuit for signals of a colour television system - Google Patents

Abstract

1,067,049. Colour television. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. April 24, 1964 [April 24, 1963], No. 17159/64. Heading H4F. N.T.S.C. type colour sub-carrier signals which are modified in accordance with the P.A.L. method of operation (i.e. the modulation phase of " I " component is reversed during alternate lines) are separated into the " I " and " Q " components by adding and subtracting successive line signals by means of system 6-10 which includes a one-line-duration delay line 10 whereby the video signals may be derived by simple amplitude demodulators 11 and 12. The signals are transmitted in suppressed carrier form and in accordance with the invention the carrier is reinserted in common to both the " I " and " Q " components by an adder 2 which is placed before the delay line system 6-10 and to which the local sub-carrier oscillator 3, which is synchronized by the sub-carrier synchronizing " burst " over line 5, is connected. The local signal is set in phase at 45 degrees to the " I " and " Q " axis and is switched back and forth between + 45 degrees and- 45 degrees in successive lines as illustrated vectorally in Figs. 3 and 4 (not shown). In one arrangement (that shown in Fig. 1) the synchronizing " bursts " are at an invariable phase and the phase shift is introduced by a phase-shift circuit 4 controlled by line synchronizing pulses 15. In another arrangement (not illustrated) the synchronizing "bursts" change in phase appropriately and the local oscillator 3 is controlled on a start-stop basis so that it commences operation with the proper phase at the commencement of each line.