GB1499409A - Processing circuit for colour television signals - Google Patents

Abstract

1499409 Colour television receivers INDESIT INDUSTRIA ELETTRODOMESTICI ITALIANA SpA 5 May 1975 [8 May 1974] 18813/75 Heading H4F A circuit for separating the colour difference signals in a received PAL or ISA chroma signal includes means for forming the sum and difference between a first signal, which has colour difference components having the same phase relationships as the colour difference components of the chroma signal but a reference burst at 90 degrees to the burst in the chroma signal, and a second signal which is the chroma signal delayed relative to the first signal by n lines (n odd). The ISA signal is similar to the PAL signal but the burst occurs in alternate lines only and is of fixed phase. As illustrated the delay 12 receives the chroma signal C via an inverter 11 and delivers the signal in true and inverted form to a coil 13 connected across its output terminals. The coil has a centre tap to which is applied the received chroma signal which has had its burst shifted by + 90 degrees, this signal being derived by way of gates 15, 18, controlled by line frequency pulses H. The colour difference components B-Y and Œ(R-Y) appear at B and ŒR respectively. The signal on the output ŒR passes to gate 22, controlled by pulses H to pass only the reference burst to a crystal sub-carrier generator 24 which provides a reference subcarrier REF.R and, via 90 degree phase shifter, a sub-carrier REF.B. When a PAL signal is being received phase shifter 23 introduces a + 45 degree shift to the bursts passed by gate 22.