Patent GB-1459045-A (GB)
Title: Recording and reproducing television signals
IPC: G11B23/00
Filed: 1974-03-14
Abstract: 1459045 Video recording and playback on discs SONY CORP 14 March 1974 [16 March 1973] 11469/74 Heading G5R A television signal, having line and field intervals, is recorded in substantially circular tracks on a rotatable record disc by pulse modulating a carrier signal with the television signal to form a pulse modulated video signal, generating an unmodulated pilot carrier signal during one or more portions of each line interval of the television signal for use in demodulating the video signal during playback, scanning successive scan lines on the record tracks, the scan lines crossing the record tracks transversely to the circumferential direction thereof, and recording in each said scan line a said pulse modulated video signal corresponding to one or more line intervals of the television signal and at least one said unmodulated pilot carrier signal. The scan lines may be radial to the disc or in a slant direction across the tracks. The signals may be recorded by a modulated light or electron beam as depressions 1 micron wide and 1 micron deep in a photoresist layer over a lacquer layer on an aluminium base, the photoresist then being hardened by a developing process and vinyl copies made from the so-formed master by conventional means. Alternatively the signals may be recorded magnetically, or optically to give bright and dark areas with playback being by transmitted light, or capacitatively. The tracks may be formed by a spiral or by concentric circles. For an NTSC system each scan line corresponds to one video line 1H, Fig. 4, and has a front pilot carrier part n 1 , a pulsewidth or pulse-phase modulated video part m, a back pilot carrier part n 2  and a pulse-width modulated audio part a, such parts being related to the video signal portion S V  and horizontal synchronizing signal S H  of the incoming signal S T  as shown in Fig. 4. One of the carrier signal parts n 1 , n 2  may alternatively be omitted. For a 525 line system, one frame F 1  or F 2  may occupy about 0À525 mm. length of track T, whereby the recording time per disc side is over one hour. A recording apparatus. Fig. 8, for producing recordings as said depressions has a disc turntable 101 rotated by a motor 105, drive from the spindle 108 of turntable 101 being transmitted to a carriage 107 whereby the disc 12 is gradually moved radially, H, whilst rotating at a speed varied from about 1 to 3 rpm to maintain a constant linear disc speed at the recording location. The video part of the signal to be recorded passes to a circuit 201 which eliminates the horizontal sync. signal and the front and back porches of the composite input signal, the remaining signal passing to a pulse modulator 202 wherein the video signal is pulse-phase modulated on to a 4 MHz carrier from an oscillator 203 locked by the horizontal sync. signal from a circuit 204, circuit 202 also giving unmodulated output periods forming the front and back pilot carrier signals n 1 , n 2 , Fig. 4. The pilot carrier signals may be at the video carrier frequency, or at a multiple or submultiple thereof. The audio part of the signal passes to a gate 205 controlled by generator 206, itself controlled by the horizontal sync. signal from circuit 204, so that the audio signal is sampled at the horizontal scanning frequency and then pulse-width modulated in modulator 207 on to a 15À75 kHz carrier from oscillator 206 locked by the horizontal sync. signal. The outputs of modulators 202, 207 pass to an electron gun 102 via a switch 209 switched at the horizontal scanning frequency. The beam from gun 102 is scanned transversely of the record track by a deflecting coil 103 supplied with the output of sync.- separator 204 via phase shifter 211 and sawtooth wave generator 212. The signal from switch 209 may alternatively be used to modulate the beam from a laser (300), Fig. 9 (not shown), the light beam width being equal to the recorded track width and the beam passing through 1À5 micron optical apertures in a rotating shutter disc (302) to scan the beam widthwise of the record track. A playback apparatus, Fig. 11, for a disc having data stored thereon by said depressions has a photo-detecting assembly 410 which is moved radially inwards as a motor 402 rotates the disc D, light from a laser 411 being scanned across the track width by a rotating apertured disc shutter 414 and the reflected light beam passing to a photo-sensor 417 giving outputs to audio and video signal demodulators 409, 408 respectively. A circuit 407 passes the vertical sync. signal from the demodulated video signal to a servo circuit 405 having an input from a reference signal generator 406 and giving an output to adjust the speed of motor 402 to maintain a constant linear speed of disc D at the playback point. If the beam from laser 411 is incident on disc D at other than 90 degrees the half-mirror 415 can be omitted. The shutter disc 414 may be formed by an apertured opaque layer (503), Fig. 17 (not shown), on one side of a glass disc (501) the other side of which is formed with an integral lens (502) under each aperture (504) of layer (503), whereby lens 416, Fig. 11, can be omitted. Use of a disc shutter having photodiodes at positions of the optical apertures of the other forms of shutter is also referred to. To playback a still picture rotation of disc D is stopped and the light beam is scanned across the successive lines of a recorded frame by means of a rotating shutter disc having optical apertures therein spaced apart along a spiral, the number of such apertures being equal to the number of horizontal lines in a frame. In the video demodulator 408, Fig. 15 (not shown) and Fig. 11, the replayed video input passes to a limiter (510) and to an envelope detector (511), the output of detector (511) going to a pulse shaper (512) giving the horizontal sync. signal or output. Gate circuits (513), (514) controlled by this sync. signal via a circuit (515) extract the front and back pilot carrier signals respectively from the output of limiter (510), which output is also supplied to a phase detector (516) which detects the video signals detector (516) being supplied with a carrier signal to effect the detection from a variable frequency oscillator (517) via a 90 degree phase shifter (519). Oscillator (517) receives the output of gate (513) and a control signal from a phase comparator (518), receiving inputs from gate (514) and oscillator (517), whereby the output of oscillator (517) is controlled in phase by the front pilot carrier signal and in frequency by the back pilot carrier signal. The output of detector (516) passes via a low pass filter (520) to be added in circuit (521) with the horizontal sync. signal from shaper (512) thereby giving a composite video signal at output (408a).