NZ206205A

NZ206205A - Recorded colour tv: colour difference signal compressed in blanking periods: synchronisation

Info

Publication number: NZ206205A
Application number: NZ206205A
Authority: NZ
Inventors: E Meyer H Geiger
Original assignee: Thomson Brandt Gmbh
Priority date: 1982-11-11
Filing date: 1983-11-09
Publication date: 1987-05-29
Also published as: DK435684A; EP0111157B1; DK435684D0; KR850003490A; FI76661C; WO1984002047A1; FI76661B; EP0111157A2; EP0111157A3; FI843677A0; DE3377190D1; FI843677L; AU2260783A

Description

<div class="application article clearfix" id="description"> 206205 Priority Date(s): U:Jl\£/?... A /A:£2 Complete Specification Filed: Class: Publication Dote: Z. 9. MAY.1987.... P.O. Journal. No: . Patents Form No: 'NOVJ983' S iff NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "Process for recording and playback of TV-signals" We, DEUTSCHE THOMSON-BRANDT GmbH, of Hermann-Schwer-Strasse 3, D-7730 Villingen-Schwenningen, Federal Republic of Germany, a Germany Company, hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement - 1 - (followed by page 1A) 206205 The present invention relates to a method for recording and reproduction of television signals in analog form whereby the luminance . 'signal is recorded during the course of the line run and the colour ' signal is recorded time-compressed sequentially during the remainder of the line • run - within the blank time. Such a method has been described in U.S. Patent Specification No: 4245235. This method has been found reliable for colour television signals which are to be transmitted through channels with limited quality, for example, video recorders. In this method the luminance signal and colour difference signals are transmitted or recorded line-frequent serially. This occurs in such a way that the luminance signal is recorded during the line run period, whereas both colour difference signals are recorded or transmitted alternately time-compressed by a factor 5 during the blank time. In the blank intervals, the line synchronising pulse and a trap indicator must also still be transmitted. However, since the time is very limited for transmission of these signals by the provision of the colour difference signals, it has been proposed to transmit the line synchronising pulse and the trap pulse from line to line alternately. IK:-*. Consequently, a line pulse with a duration of l.ffi.]i s was transmitted line sequentially and within thefts 206205 line return an equally long trap pulse was transmitted. It has, however, been shown that such a short pulse leads to difficulties in synchronisation especially with picture recording and reproduction with video recorders for home use, and particularly if it is provided only every second line. It is known when recording colour signals ±0 record an additional control signal lying outside the transmission region of the colour signal and which varies the amplitude of the colour signal according to the amplitude variations of the control signal (U.S. Patent Specification No:3580990). It is moreover known to record a pulse alternating in amplitude from line to line together with a colour signal, which is recorded on the basis of a transmitted frequency modulation in the form of a frequency alternating from line to line and which serves for line synchronisation and also for differentiation between the two line sequentially recorded colour difference signals (U.S. Patent Specification No: 3717725). The invention has the object of ensuring line synchronisation in the reproduction of signals recorded in the Timeplex method According to the present invention a method for recording and reproducing colour television signals in analog form whereby a luminance signal is recorded during the course of the line period and a colour signal is recorded sequentially time compressed during the remaining time of the line periods in the blank time, whereby the colour signals are digitised Wid collected into and selected from a memory under.the control of beat pulses produced by a beat generator, characterised in that an oscillating synchronisation pulse 20G205 serving for synchronisation is coupled into the colour signal to be recorded, the oscillating synchronisation pulse frequency being switched at half the line frequency symmetrically about a middle frequency and the frequency and amplitude of the oscillating synchronisation pulse is so chosen as to avoid damage to the luminance information and colour information. In order that the invention may be more readily understood preferred embodiments thereof are described below in conjunction with the accompanying drawings, in which : Fig. 1 shows a voltage-time-diagram of the signal produced in the Timeplex method; Figs. 2 to 5 show block circuit drawings for performing the method of the invention; and Fig. 6 shows the frequency variation of the FM-transmission region of the magnetic head signal with the carrier frequencies of the additional pulse signal. Figure 1 shows the FBAS-signal produced according to the Timeplex method. It is recognised that the luminance signal Y occupies the greater part of the line period during the time T„ and the time compressed colour difference signals H (R-Y), (B-Y), are recorded in the blank gaps AT^ and AT2, whereby a trap pulse K is transmitted within the one blank gap AT^ and a synchronising pulse S is transmitted during the next blank gap AT^. Figures 2 and 3 elaborate the essential features of the invention in a block circuit diagram. The circuit component groups relating to the known Timeplex method are indicate!.: - 4 - © JtiQe&^LO 5 above the dotted line whereas the component gr< for the method according to the invention are shown below this line. Firstly, the Timeplex method will be briefly described. Figure 2 depicts the reception of a video signal on a magnetic tape. The Y signal passes via a colour carrier trap (filter) 1 to a switch 2, which is controlled by a beat generator 3 so that the Y signal is directed to a recording channel 4 during the line run, said channel consisting of the FM modulator of the pre-emphasis and the sound amplifier. During the line return time TA the R-Y signal or B-Y signal refined by PAL-Decoder 5, is connected alternately line frequent to the receiver channel 4 by the fH/2-beat after which they are collected in a store 6 with the help of a collection beat 15 produced by the beat generator 3 of, for example, 2 MHZ and are then again selected with the help of a selection beat of 10 MHZ, whereby time compression of about factor 5 results;' According to the invention an additional synchronising signal produced with the help of an oscillator 7 is received at the 20 receiver head of the magnetic tape apparatus 8, which is recorded together with the time compressed colour difference signals R-Y, B-Y and the Y signal. The carrier frequency of the synchronising signal lies preferably in the upper transmission range of the magnetic head signal. The amplitude of 25 the signal is so chosen that damage to the Y and chroma O signals is avoided. The characteristic necessary for the PAL-standard can be produced with the help of a controlled carrier frequency for the synchronising signal. To this end - 5 - 20t#05 control beat of the-oscillator 7 is switched over through a stage 9 by a / the half/line frequency .cojvfca?©!—beat taken from the beat generator 3 into a frequency symmetrical about a middle frequency, whilst the control beat of half the line frequency switches over the switch 9b via the switch 9a - here represented for simplicity as a mechanical switch. A condenser 23 is thus connected alternately to the oscillator. The effect of the control beat H is switched off by vertical 2 frequency switching of the contact 9a with the help of a control beat V produced by the beat generator 3. This step facilitates the reproduction of the vertical synchronising pulse on the reproduction side as will be explained later. With the aid of Figure 3 the refinement of the pulse serving for synchronisation will be explained. The signal emitted by the recording apparatus 8 is amplified in a reproduction channel 10 which consists of a reproduction amplifier, a drop-out compensator, a limiter, an FM demodulator and a de-emphasis, and the luminance signal Y passes from there to an adding stage 12 via a switch 11 controlled by a beat generator 3 during the line return time. In an adjacent branch the colour signal decompressed again through the adding stage is converted into an integrated FBAS-signal with the aid of a store 13a/13b controlled by a beat generator 3 and a PAL-Decoder 14, which signal is reproduced by a television receiver. Decompression occurs in such a way that the store 13 collects with a beat of 10 MHZ and again selects with a beat of 2 MHZ. The synchronising signal necessary for synchronisation of the television receiver is produced as follows and is likewise passed to the adding stage 12. - 6 - 206205 The 'carrier signal recorded during reception is connected to a phase discriminator 16 via a device 15 which limits and strengthens the signal. The phase discriminator 16 is set at a frequency which lies between the carrier frequencies of the synchronising signal. Signals of variable polarity are produced by the phase discriminator 16 or an equivalent circuit. The rectangular signal produced with half frequency serves as a reference frequency of a phase-locked-loop-circuit (PLL), consisting of the voltage-controlled oscillator 19 (VCO) oscillating with line frequency, the divider 20 halving the oscillator frequency, the phase comparator 17 and the low pass 18. The method of operation of such a circuit can be considered as known. A mono-stable rocker stage 21 connected to the oscillator 19 produces horizontal frequency synchronising pulses which pass to the adding .stage 12 via the beat generator together with the likewise re-generated vertical synchronising pulses. The vertical synchronising pulses are produced with the aid of a further mono-stable rocker stage 22, which receives trigger pulses from the phase comparator 17, which originate at the outlet of the phase comparator 17 through the previously described interruption of the pulse H of half the line frequency 2 during the picture return. Figure 6 depicts the FM transmission range of the head signal and the frequency position of the carrier of the transmitted synchronising pulse which can lie at the upper end of the transmission range. A further embodiment of the method according to the invention is described below with the help of Figures 4 and 5 ifs? 1 7NOVJ886; \ 206205 The Y signal passes via a colour carrier trap (filter) 1 to a switch 2 which is controlled by a beat generator 3 in such a manner that the Y signal is connected during the line run to the reception channel 4 which consists of the FM modulator of the pre-emphasis and the speaker amplifier. During the line return time TA the R-Y signal or B-Y signal refined by PAL-Decoder 5 is connected alternately line frequent to the receiver channel 4 by the fH/2 beat, after which they are collected in a store 6 with the help of a collection beat, for example, of 2 MHZ and are again selected with the aid of a selection beat of 10 MHZ whereby a time compression of factor 5 occurs. A carried pulse produced with the help of an oscillator 7 is passed to the receiving head of the magnetic tape apparatus 8 via a contact 9 closed during the line return time by the beat generator 3, so that this pulse is recorded together with the time compressed colour difference signals R-Y, B-Y, The carrier frequency of the transmitted pulse also preferably lies at the upper transmission range of the magnetic head signal. The amplitude of this pulse signal is so chosen that damage to the chroma signal is avoided. The characteristic required for the PAL-standard can be produced with the help of an associated carrier frequency for the pulse. To this end the oscillator 7 is switched over half line frequent into the frequency, for example with the help of a capacitance diode, by abeat fH/2 produced by the beat generator. " " 20t>205 With the aid of Figure 5 the refinement of the pulse serving for synchronisation will now be explained. The signal emitted by the recording apparatus 8 is amplified in a reproduction channel 10, which consists of a reproduction amplifier, a drop-out compensator, a limiter, an FM demodulator and a de-emphasis and during the line return time the luminance signal Y passes from there to an adding stage 12 via a switch 11 controlled by the beat generator 3. In an adjacent branch the colour signal again decompressed via the adding switch 12 is converted to an integrated FBAS signal with the aid of a store 13 controlled by the beat generator 3 and a PAL Coder 14, which FBAS signal is reproduced by a television receiver. Decompression takes place in such a way that the store 13 collects with a beat of 10 MHZ and selects again with a beat of 2 MHZ. The synchronising .signal necessary for synchronisation of the television receiver is reproduced in the following way and likewise passed to the adding stage 12. The signal given off during line return is connected to a phase discriminator 16 via a device 15 amplifying and limiting the signal. The phase discriminator 16 is set at a frequency which lies between the carrier frequencies of the transmitted pulses. Line frequent pulses of alternating polarity are produced by the phase discriminator 18 or an equivalent circuit. In a subsequent stage 23 the pulse is so converted that pulses of half the line frequency are removable at an outlet A, which serve to control the PAL flip-flop 24. Line frequent pulses at the other outlet B of stage 23 serve for synchronising the beat generator 3 during reproduction, which supplies the horizontal frequent pulses H and the vertical 206205 frequent pulses V serving for synchronisation of the television receiver, which pulses are added in the adding stage 12 to the Y signal and to the chroma signal for forming an integrated FBAS signal. </div>

Claims

<div class="application article clearfix printTableText" id="claims"> _ 10 _ 20*>S05 WHAT WE CLAIM IS:

1. A method for recording and reproducing colour television signals in analog form whereby a luminance signal is recorded during the course of the line period and a colour signal is recorded sequentially time compressed during the remaining time of the line periods in the blank time, whereby the colour signals are digitised and collected into and selected from a memory under the control of beat pulses produced by a beat generator, characterised in that an oscillating synchronisation pulse serving for synchronisation is coupled into the colour signal to be recorded, the oscillating synchronisation pulse frequency being switched at half the line frequency symmetrically about a middle frequency and the frequency and amplitude of the oscillating synchronisation pulse is so chosen as to avoid damage to the luminance information and colour information.

2. A method according to claim 1, characterised in that the coupling of the oscillating synchronisation pulse serving for synchronisation together with the existing colour information occurs during each blank time and the frequency and amplitude of the pulses are so chosen that damage of the colour information is avoided.

3. A method according to claim 1, characterised in that the carrier frequency of the synchronising carrier lies in the upper transmission range of the magnetic head signal of the recording apparatus.

4. A method according to claim 1, characterised in that the switching over of the carrier frequency is interrupted through a vertical frequency beat control during the picture return. 11 20t>'Sr05 © 5

5. A method according to any one of Claims 1 to 3, characterised in that during reproduction the coupled synchronising signal is switched over after amplification to a discriminator which operates in dependence upon the carrier frequency signals of different polarity.

6. A method according to Claim 5, characterised in that the middle frequency of the discriminator lies between both carrier frequencies of the oscillating synchronisation pulses.

7. A Method according to Claim 4 or 5, characterised in that the signal produced by the discriminator controls with fixed phase an oscillator with a control loop.

8. A method according to Claim 7, characterised in that the beats for the horizontal pulses, vertical pulses and the beat with half tfr,e line frequency is derive^, fjrom. the PLIc--loop and are added to the demodulated colour signal via the beat generator as a combined synchronising signal.

9. A. method according to Claim 2, characterised in that on reproduction, the coupled oscillating synchronisation pulse connected after amplification to a discriminator, which supplies pulses of different polarity in dependence upon the carrier frequency.

10. A method according to Claim 9, characterised in that the middle frequency of the discriminator lies between both carrier frequencies of the oscillating synchronisation pulses.

11. A method according to Claim 9 or 10, characterised in that the pulses produced by the discriminator are connected to an inverter stage, which supplies the pulses of half the line frequency for identifying the PA: \ ' - 12 - 2062 0^ connected with line frequent pulses as well as line frequent pulses for the time generator.

12. A method for recording and reproduction of colour television signals in analog form as hereinbefore described with reference to any one of the embodiments shown in the accompanying drawings. </div>