GB1077946A - Improvements in and relating to special effects apparatus for television - Google Patents

Abstract

1,077,946. Colour television. COMPAGNIE FRANCAISE DE TELIVISION. May 26, 1965 [May 28, 1964], No. 22463/65. Heading H4F. The invention relates to a fade-over or signal combining apparatus for use with SECAM (R.T.M.) signals in which the luminance components of two signals applied at terminals 101 and 201 are applied through circuits 112, 212 to a first fadeover or combining circuit 5, whilst the subcarrier components are separated by filters 105, 205 and applied through demodulators 106, 206 to a second fade-over or combining circuit 6, a resultant or composite signal being obtained via a circuit 7. The two original signals are synchronized as regards their line and frame blanking, but may not be in phase as regards the line frequency alternation of the two colour signals modulated on each subcarrier. It is the object of the invention automatically to remove any such phase difference. To this end each colour signal channel between filter and demodulator includes a pair of switches 113, 115 and 213, 215 whereby the signal may be sent through a one-line-duration delay circuit 4 instead of a direct non-delay circuit 114, 214. A circuit 107, 207 associated with each channel is driven by line blanking pulses from connection 3 and responds to the normal colour identification signals included in the blanking intervals to produce a square wave signal of half line frequency whose phase indicates the phase of colour alternation. A reference square wave is generated by a circuit 2 in response to local colour control signals obtained from connection 1. This wave is then compared with the waves from circuits 107 and 207 in adders 108 and 208. The square waves are arranged to be of equal amplitude whereby an adder output is zero if the associated colour signal phase is incorrect. The adder outputs are applied through diodes 109, 209 to integrator circuits 110. 111; 210, 211 whose outputs control the switches in the respective channels. The operation is such that the delay circuit 4 is introduced in response to zero output from an adder. Due to the use of a common delay circuit 4, the arrangement may correct the phase of only one colour signal, although the correction may be applied to either signal. A modification, Fig. 2 (not shown), employs a separate delay for each channel so that both signals may be corrected. With this modification, signals for circuits 107 and 207 may be obtained from the outputs of the associated direct and delayed channels to avoid the use of delay elements in the circuits. Where one signal source is synchronized locally and therefore has the correct phase of colour alternation, one half of the arrangement shown in block A, Fig. 1, may be dispensed with.