Patent GB-1522339-A (GB)
Title: Apparatus for reproducing a video signal
IPC: H04N9/83
Filed: 1975-11-07
Abstract: 1522339 Magnetic video recording and playback SONY CORP 7 Nov 1975 [11 Nov 1974 16 Jan 1975] 46242/75 Heading G5R [Also in Division H4] The Specification discloses video recording and reproducing apparatus but the claims relate only to reproducing apparatus for replay of a video signal magnetically recorded with the recorded video signal comprising a modulated signal sideband having its carrier frequency at or near the low frequency end of the sideband, the reproducing apparatus having a magnetic replay head 51, Fig. 9, a frequency converter 53 connected to the output of head 51 to frequency convert the modulated sideband signal and the carrier thereof to dispose the converted carrier at or near the upper end of the converted modulated signal sideband, and a detector 60 for detecting the frequency converted sideband signal. The video signal may be recorded on a magnetic sheet, card or disc, or as skew tracks on a magnetic tape, Fig. 2 (not shown). In a RECORDING circuit, Fig. 7, a low pass filter 32 passes the luminance signal Y A , Fig. 8A, of a colour video signal at input 31, and the balanced modulated (carrier suppressed AM) luminance signal Y B , Fig. 8B, is formed by modulator 33 receiving a carrier signal f B = 2À99 MHz from filter 37. Vestigial side band filter 39 forms the signal Y C , Fig. 8C, from Y B , and C C  is combined in mixer 40 with the chrominance signal C S , Fig. 8C, on a carrier f s  = 3.58 MHz and passed by filter 41. Frequency converter 42 combines the composite signal Y C +C S  with a signal f C  = 4À17 MHz to form the sum and difference signals C L , C H , with carrier f L =0.59 MHz and f H =7.75 MHz, and Y D  and Y E  with suppressed carrier f D  = 1À18 MHz and f E =7.16 MHz, only the lower frequency parts C L , Y D , Fig. 8E, passing via filter 43 to magnetic recording head 45. A frequency converter 36 receives signals from oscillators 34, 35 at 0.59 MHz and 3.58 MHz respectively to form the sum f C  and difference f B  signals which are passed by filters 38, 37 to converter 42 and modulator 33. Oscillator 34 is controlled by a comparator 47 which compares the phase of the output of oscillator 34 via frequency divider 48 with the horizontal sync. signal from separator 46. The sync. signal is modified by waveforming circuit So to form a gating signal input to gate 49 which gates the chrominance biases and applies them to control oscillator 35 having the same frequency as the bursts. The circuits of Fig. 7 may be modified so that the luminance and chrominance signals are separately frequency converted and then combined, Fig. 14 (not shown). In a PLAYBACK circuit, Fig. 9, for recordings made by the circuit of Fig. 7, the replay signal C L , Y D , Fig. 8E, from head 51 is frequency converted by circuit 53, receiving an input f C  = 4À17 MHz, into luminance components Y F , Y G , Fig. 8F, with suppressed carriers f B =2.99 MHz and f G =5.35 MHz, and chrominance components C S , C I  with carriers f s =3-58 MHz and f I  = 4À76 MHz. The lower luminance band Y F  is passed by filter 59 and synchronously detected in detector 60, receiving an input signal f B  = 2À99 MHz, the output of detector 60 being combined in mixer 61 with the lower chrominance band C S  passed by filter 62. Frequency converter 56 forms the sum f C  = 4À17 MHz and difference f B =2.99 MHz of the 0.59 MHz output of oscillator 54 and the 3.58 MHz output of oscillator 55, filters 57, 58 passing f B  and f C  respectively as the synchronous detection signal input to detector 60 and the frequency conversion input to converter 53. Oscillator 54 is controlled by a circuit 25 comparing the phase of the output f B  of filter 57 with a signal from gate 22. An envelope detector 23 and sync. separator 24 extract the horizontal sync. pulses from the luminance output Y F  of filter 59 so that gate 22 passes to comparator 25 a gated signal at f B =2.99 MHz at each sync. pulse. The playback circuit of Fig. 9 is said to eliminate jitter due to fluctuations of the record medium drive motor. Modified forms of the circuit of Fig. 9 are described with reference to Figs. 10 and 17 (not shown). In a further PLAYBACK circuit, Fig. 11, the replayed luminance signal Y D , Fig. 8E, passed by filter 64 is frequency converted in a circuit 65 the output of which is filtered to give signal Y F , Fig. 8G, which is synchronously detected 60 with a signal of 3.58 MHz from oscillator 69, and the replayed chrominance signal C L , Fig. 8E, passed by filter 72 is frequency converted 73 to form via filter 77 the signal C S  which is combined with luminance signal Y F  in mixer 61. The 4.76 MHz and 4.17 MHz signals to converter 65, 73 respectively are extracted by filters 70, 76 from the outputs of frequency converters 68, 75 each of which receives or one input the 3.58 MHz output of oscillator 69. The other input of converter 68 is a 1.18 MHz signal from oscillator 67 controlled by limiter 66 receiving the replayed luminance signal Y D  from filter 64, and the other input of converter 75 is a 0.59 MHz signal provided by divide-by-two 74 from oscillator 67 output. In a PLAYBACK circuit, Fig. 13, for phase or frequency modulated recordings, the replayed chrominance signal having a 0.59 MHz carrier and the replayed luminance signal frequency or phase modulated on a 1.18 MHz carrier are frequency converted in circuit 53 receiving a 4.17 MHz input from filter 58. Filter 59 passes the frequency converted luminance signal on a 2.99 MHz carrier via limiter 78 to a frequency or phase demodulator 79 the output of which is combined in mixer 61 with the output of filter 62 which is the frequency converted chrominance signal on a 3.58 MHz carrier. The 4.17 MHz input to converter 53 is obtained from the output of converter 56 receiving 3.58 MHz from oscillator 55 and 0.59 MHz from oscillator 54 which is controlled by phase comparator 83 comparing the output of oscillator 55 and the frequency converted colour bursts gated by gate 80 controlled by a signal formed by waveforming circuit 82 from the horizontal sync. signal extracted by separator 81 from the demodulated luminance signal. A frequency modulation luminance signal recording circuit is described with reference to Fig. 15 (not shown).