Patent EP-0067899-A1 (EP)
Inventor: FLAMM PETER ING GRAD
IPC: H04N9/44
Filed: 1981-06-24
Abstract: 1. Colour-television receiver with at least one digital integrated circuit for processing the composite colour signal, comprising - a square-wave clock generator used as a chrominance-subcarrier oscillator and generating at least three clock signals (F1, F2, F3) the first of which (F1) is at four times the chrominance-subcarrier frequency, and the second and third of which (F2, F3) is at the chrominance-subcarrier frequency, the first and the second clock signal having a mark-space ratio of 1:1, - an analog-to-digital converter (AD) which is clocked by the first clock signal (F1), is fed with the composite colour signal (F) through its analog input, and forms a parallel binary word from the amplitude of composite colour-signal (F) at the instance respective amplitudes of the undemodulated chrominance signal are equal to the amplitudes of the respective colour-difference signal, - a subcircuit (DC) producing the digital Red-minus-Luminance difference signal (R-Y) and the digital Blue-minus-Luminance difference signal (B-Y), and - binary computing stages and buffer memories for digital signal processing, characterized by the following subcircuits and features serving to digitally synchronize the chrominance-subcarrier oscillator with the burst (B) contained in the composite colour signal (F) : - the chrominance-subcarrier oscillator (VCO) is a phase locked loop whose control signal is generated digitally, however ; - the positive digital Red-minus-Luminance difference signal (R-Y) is applied to the first input of a first parallel adder (A1) whose output feeds a first buffer memory (PS1) having its output coupled to the second input of the first parallel adder (A1) and to the input of a second buffer memory (PS2) ; - the positive digital Blue-minus-Luminance difference signal (B-Y) is applied to the first input of a second parallel adder (A2) whose output feeds a third buffer memory (PS3) whose output is coupled to the second input of the second parallel adder (A2) and whose sign output is coupled to the input of a fourth buffer memory (PS4) ; - the output of the second buffer memory (PS2) is coupled to the first input of a third parallel adder (A3) whose second input is connected to the output of a memory (S) and whose output is coupled to the input of a digital limiter (BG) having its output connected to the input of a switching stage (SS) with three switch positions and two switch inputs ; - the sign output of the second buffer memory (PS2) is coupled to the first switch input of the switching stage (SS), and the output of the fourth buffer memory (PS4) is coupled to the second switch input of the switching stage (SS) ; - the output of the switching stage (SS) is connected to the input of a digital-to-analog converter (DA) either directly, in which case the output of the digital-to-analog converter (DA) is coupled to the voltage-control input of the chrominance-subcarrier oscillator (VCO) through an analog low-pass filter (TP), or through a digital low-pass filter (DP), in which case the output of the digital-to-analog converter (DA) is connected directly to the voltage-control input of the chrominance-subcarrier oscillator (VCO) ; - the enable input of the first buffer memory (PS1) is connected to the output of a first AND gate (U1) whose first and second inputs are fed with the keying signal (K) and the third clock signal (F3), respectively ; - the enable input of the third buffer memory (PS3) is connected to the output of a second AND gate (U2) whose first and second inputs are fed with the keying signal (K) and the second clock signal (F2), respectively ; - the third clock signal (F3) leads the second clock signal (F2) by 90 degrees and has a 1:1 mark/space ratio ; - the enable inputs of the second buffer memory (PS2) and the fourth buffer memory (PS4) are fed during each line with an enabling pulse (U) following the keying pulse (K), and - the clear inputs of the first buffer memory (PS1) and the third buffer memory (PS3) are fed during each line with a clearing pulse (L) following the enabling pulse (U).