Patent GB-1424314-A (GB)
Title: Video signal processing system
IPC: H04N9/85
Filed: 1974-02-18
Abstract: 1424314 Colour television MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 18 Feb 1974 [20 Feb 1973 22 Feb 1973 31 May 1973 (4) 23 July 1973 2 Aug 1973] 7304/74 Heading H4F A recorded colour television signal including a luminance signal and a chrominance signal having a subcarrier frequency of 1À53 MHz is reproduced at 1, the resulting signal being demodulated at 3 and passed via a band-rejection filter 30 centred at 1À53 MHz, adders 32 and 38 and trimming delay lines 31, 33 to an output amplifier 25; the demodulated signal is also passed to a band-pass filter 7 centred at 1À53 MHz and then to a balanced modulator 27 and band-pass filter 23 to derive a signal at NTSC subcarrier frequency of 3À58 MHz, this signal being passed to chrominance and luminance comb filters 28, 29 each including a one-line delay line, the output of comb filter 28, which is the chrominance signal on a subcarrier at 3À58 MHz being supplied to adder 32 and the output of luminance comb filter 29 being converted, by balanced modulator 34 and band-pass filter 37, to a luminance signal in the pass-band of filter 7 (and rejection band of filter 30) which is passed to adder 38, the output of adder 38 being an NTSC colour television signal. The reference signal input to balanced modulators 27 and 34 is derived from a band-pass filter 21 receiving the output from a balanced modulator 19 receiving inputs from a fixed frequency oscillator 20 operating at 3À58 MHz and a variable frequency oscillator 16 operating at the frequency of the received bursts. In alternative embodiments the phase detector 15 controlling oscillator 16 receives inputs at 5À11 MHz in which case the burst gate 12 may receive the input to or output from band pass filter 7 and feed a balanced modulator (39, Figs. 6, 7, not shown) receiving an input from reference oscillator 20; alternatively this balanced modulator (39) may receive the input to or output from band-pass filter 7, the output of the balanced modulator being connected, via a band pass filter centred at 5À11 MHz, to the burst gate 12 (Figs. 8, 9, not shown) in any of these alternative embodiments the variable oscillator may operate at a fraction of the received burst signal frequency, the oscillator output being connected to a frequency multiplier to provide a signal at the received burst signal frequency (Figs. 10-13, not shown). The separate comb-filters 28, 29 may be replaced by a single delay line an adder and a subtractor (Fig. 14, not shown). Alternatively the chrominance signal from comb-filter 28 may be supplied to adder 38 and the luminance signal from 37 may be supplied to adder 32 (Fig. 15, not shown). In alternative embodiments the band-rejection filter 30 and luminance comb-filter are omitted. The output of the chrominance filter 28 may, after balanced modulation and bandpass filtering, be subtracted from the received signal to remove the chrominance signal having a subcarrier frequency 1À53 MHz (Fig. 20, not shown). Alternatively the output of band-pass filter 23 may be passed via a one-line delay line (which may be part of chrominance comb-filter 28) a balanced modulator and a band-pass filter and added to the received signal (Figs. 16, 17, not shown). In this arrangement the received signal may be passed through an amplifier having a reduced amplification factor in the pass-band of band-pass filter 7 to compensate for the effect of this addition on the amplitude of the luminance signal in this band.