GB2157118A

GB2157118A - Data reproducing device

Info

Publication number: GB2157118A
Application number: GB08508232A
Authority: GB
Inventors: Toru Akiyama
Original assignee: Pioneer Electronic Corp
Current assignee: Pioneer Corp
Priority date: 1984-03-30
Filing date: 1985-03-29
Publication date: 1985-10-16
Also published as: GB2157118B; FR2562367A1; DE3511613A1; GB8508232D0; JPH0519877B2; JPS60206293A; FR2562367B1; DE3511613C2

Abstract

A data reproducing device has a phase correcting means (5) using a reference signal synchronous with a color burst signal in a PAL system color video signal read out of a recording medium eg a video disc recorder, to correct the phase of one of the chrominance signals in the PAL system color video signal. Oscillating means (25) is provided for oscillating at a frequency corresponding to an input signal. Signal selecting means (15) are provided for selecting, in response to an instruction, an output of the oscillating means (25) or an external reference colour sub-carrier signal, as a reference to the phase correcting means (5). Phase difference signal generating means (6,16) produces a signal corresponding to a phase difference between an output of the signal selecting means (15) and the color burst signal. The arrangement is such that, when the signal selecting means (15) selects the oscillating means (25), an output of the phase difference signal generating means (6,16) is supplied to the oscillating means to form a phase-locked loop, and when the signal selecting means (15) selects the reference colour sub-carrier signal, the output of the phase difference signal generating means (6,16) is utilized to perform time axis error correction (21,22,23) to make the color burst signal synchronous with the reference color sub-carrier signal. <IMAGE>

Description

SPECIFICATION Data reproducing device This invention relates to data reproducing devices, and more particularly to a data reproducing device for reproducing a PAL system color video signal.

A PAL system color video signal Ep can be represented by the following equation (1); Ep = Y + (B - Y)sin cost + (R - Y) cos & St (1) Where Y is the luminance signal, B is a blue signal, R is a red signal, and s is the color sub-carrier's angular frequency, about 4.43 MHz.

In equation (1), the sign (+) means that phase alternation (or inversion) is effected every horizontal scanning line. For the chrominance signal, the (R - Y) component is provided by amplitude modulating a sub-carrier signal + cos out having a 1500 phase difference every horizontal scanning line. Therefore, the color burst signal should have data for inverting the phase of an (R - Y) component demodulating subcarrier every line on the television set screen. Therefore, the color burst signal is provided as a signal sin (o) + 1350), in which the phase is inverted to +135 about the (B - Y) axis for every line.

In order to demodulate such a PAL system colour video signal into correct colors on the screen of the television set, it is necessary that the phase inversion condition of the color burst signal is detected and the polarity of the (R - Y) component demodulating sub-carrier signal is changed in a predetermined direction every other horizontal scanning period. For this purpose, a burst phase discriminator is provided to discriminate the phase inversion condition of the color burst signal, and when the inversion of the sub-carrier signal is opposite, thus demodulating - (R - Y), the sub-carrier phase inverting circuit is reset, so that the demodulation is carried out correctly.

However, if the response speed of the burst phase discriminator is increased, then when a noise signal is superposed on the input colour video signal, an erroneous reset pulse may be produced in response to the noise signal. Therefore, in general, a time constant is provided, so that, only when an erroneous demodulation has been effected to a certain period of time, is a reset pulse produced, whereby erroneous reset pulses are not produced in response to such a noise signal.

The above-described method utilizing a time constant is effective when receiving a broadcast television signal. However, it suffers from the following difficulties in the case where color video data recorded in a video disk is reproduced with a VDP (video disk player) and the data thus reproduced is input to the television set.

In general, a VDP can be operated in an ordinary reproduction mode, and in a special reproduction mode such as a still picture reproduction mode, a double fast speed reproduction mode, a triple fast speed reproduction mode, or a slow speed reproduction mode. In such a special reproduction mode, it is always required to perform a so-called "jumping operation" to cause the data detecting point of the pickup to jump instantaneously from the presently traced track over to another track. When this jumping operation is effected, the inversion state of a PAL phase (i.e., the phase of the color burst signal and the phase of the signal (R - Y) cos ct)st) is changed.Then, as the reaction of the color burst phase discriminator is slow as was described before, color killing is effected so that a color picture is changed into a monochromatic (black-and-white) picture or color demodulation is not correctly carried out.

Therefore, a VDP for reproducing a PAL system color video signal is provided with a PAL phase connecting circuit for correcting a PAL phase during jumping. It has been proposed that a so-called "external synchronization function", to synchronize a color burst signal with a reference color sub-carrier supplied from outside, be given to such a VDP when a plurality of such VDPs supply PAL system color video signals to a single color monitor in such a manner that the color video signals are switched in the same horizontal scanning period, so that picture composition is performed.

An object of this invention is to provide a data reproducing device for PAL color video signal reproduction which has an external synchronization function and which is simple in construction.

The data reproducing device according to the invention comprises; a phase difference signal generating means for producing a signal corresponding to that phase difference between a signal supplied thereto and a color burst signal, so that, when an external synchronization mode is effected, by utilizing an output obtained by supplying a reference color sub-carrier supplied from outside to the phase difference signal generating means the time axis error correction is carried out, while the PAL phase correction is performed by using the reference colour sub-carrier, and when the external synchronization mode is not effected, the phase difference signal generating means and an oscillating means which oscillates at a frequency corresponding to the output of the phase difference signal generating means form a PLL (phase locked loop), and the output of the oscillating means corrects the PAL phase.

One embodiment of a circuit in accordance with the invention will now be described with reference to the single block diagram figure of the accompanying drawings.

As shown in the figure, an RF (radio frequency) signal, read by a pick-up (not shown) off a recording disk (not shown) on which a PAL system color video signal is recorded, is applied to an FM demodulator 1. The PAL system color video signal, after being demodulated by the FM demodulator 1, is applied to a Y/C separator 2, in which it is separated into a luminance signal and a chrominance signal. At the same time, the demodulated PAL system color video signal is further applied to a horizontal synchronizing sig nal separator 3, which outputs a horizontal synchronizing signal.

The luminance signal output by the Y/C separator 3 is applied to an adder 4 and the chrominance signal provided by the Y/C separator 2 is supplied to a PAL phase correcting circuit 5 and a phase comparator 6. In the phase correcting circuit 5, the chrominance signal is applied to one injput terminal of a change-over switch circuit 7 and to a PAL phase converter 8 made up of a multiplier, etc. The PAL phase converter 8 is so designed as to extract only a component whose frequency is equal to the frequency of the chrominance signal out of the signal, obtained by subjecting the output of a doubler 9 and the chrominance signal to multiplication. The output of the PAL phase converter 8 is applied to the other input terminal of the change-over switch circuit 7, to the control terminal of which the output of a switching control signal generator 10 is supplied.The switching control signal generator 10 produces a signal whose state is changed whenever a jump instruction signal is provided, so that the input and output of the PAL phase converter 8 are selectively output through the switch circuit 7. The output of the switch circuit 7 is applied, as the output of the phase correcting circuit 5, i.e., the phase-corrected chrominance signal, to the adder 4, where it is added to the luminance signal.

The horizontal syncrhonizing signal output by the horizontal synchronizing signal separator 3 is applied to a burst gate signal generator 11 and another phase comparator 12. In the phase comparator 12, the horizontal synchronizing signal and an output signal from an external internal synchronizing change-over switch 13 are subjected to phase comparison. An external reference horizontal synchronizing signal is supplied to one input terminal of the change-over switch 13 and an internal reference horizontal synchronizing signal provided by an internal reference horizontal synchronizing signal generator 14 is applied to the other input terminal of the change-over switch 13. The output of the phase comparator 12 is applied to an adder 15.

An output signal from an external internal synchronization switching change-over switch 15 is supplied to the doubler 9 in the phase correcting circuit 5 and at the same time, the output signal from the change-over switch 15 and the chrominance signal output by the Y/C separator 2 are subjected to phase comparison in the phase comparator 6. In an S/H (sample or hold) circuit 16, the output of the phase comparator 6 is sampled every horizontal scanning period (1H) with a sampling pulse output by the burst gate signal generator 11. The hold output of the S/H circuit is applied to an input terminal of an external/ internal synchronization switching change-over switch 17. A signal from one output terminal of the change-over switch 17 is applied through an LPF (iow-pass filter) 18 to the adder 15.The output of the adder 15 is applied, as a time base error signal, through an equalizer amplifier 19 to a drive coil 22 for driving a tangential mirror 21 and through an equalizer amplifier 20 to a spindle motor 23. This drive signal determines the relative speed in the direction of a tangent which touches a recording track on a recording disk's recording surface at the data detecting point of the reading pickup.

A signal provided from the other output of the change- over switch 17 is applied through an LPF 24 to the control input terminal of a VCO (voltage-controlled oscillator) 25. The output of the VCO 25 is supplied to one input terminal of the change-over switch 15 to the other input terminal of which an external reference color sub-carrier is supplied.

The armatures of the change-over switches 13, 15 and 17 are tripped simultaneously by operating for instance an operating button (not shown). When the armatures of the change-over switches 13, 15 and 17 are tripped over to the first position contacts, the external reference color sub- carrier signal is supplied to the doubler 9 and the phase comparator 6, as a result of which the phase comparator 6 outputs a signal corresponding to the external reference color sub-carrier and the phase differences between the chrominance signal output by the Y/C separator 2 and the color burst signal.When the output of the phase comparator 6 is applied to the S/H circuit 16, in the latter circuit 16 the output of the phase comparator 6 is sampled and held with the aid of the output of the burst gate signal generator 11, i.e., a pulse signal generated in the period in which the color burst exists, as a result of which the signal corresponding to the phase difference between the external reference colour sub-carrier and the color burst is output. The output of the S/H circuit 16 is applied through the LPF 18 to the adder 15, to which the output of the phase comparator 12 is supplied. The external reference horizontal synchronizing signal is applied through the change-over switch 13 to the phase comparator 12, where it is compared with a regenerated horizontal synchronizing signal provided by the horizontal synchronizing signal separator 3.

Accordingly, a signal corresponding to the phase difference between the external reference colour subcarrier and the color burst signal, and a signal corresponding to the phase difference between the external reference horizontal synchronizing signal and the regenerated horizontal synchronizing signal are subjected to addition, thus forming the time base error signal. The relative movement speed of the reading pickup in the direction of the tangent of the recording tack at the data detecting point is controlled to eliminate the phase differences.

If the external reference color sub-carrier supplied to the doubler 9 in the phase correcting circuit is represented by cos st, then the output of the doubler 9 can be represented by cos 2 cast Furthermore, if the chrominance signal including the color burst signal outputted by the Y/C separator 2 is represented by sin (cast + Ci), then a multiplication output M represented by the following equation (2) is formed by the PAL phase converter 8:: M = cos 2 cast.sin (cast + ~) = (1/2 sin (3 cast + ~) + sin (cast - ~) ---(2) The first component, whose frequency is equal to that of the chrominance signal, is extracted out of the multiplication output M. Therefore, the output of the PAL phase converter 8 is sin (cast - ~). Accordingly, in the chrominance signal, the B-Y component is not subjected to phase inversion because ~ = 0, while the R-Y component and the color burst signal are subjected to phase inversion because ~ = 0.

Whenever the jump instruction signal is produced, the input and output of the PAL phase converter 8 are alternately and selectively applied, as the chrominance signal, to the adder 4 by means of the change-over switch 7, thus forming a PAL color vidw signal. Therefore, even after the jumping operation, the PAL phase inversion regularity is maintained unchanged.

When the armatures of the change-over switches 13, 15 and 17 are tripped over to the second position the phae comparator 6, the S/H circuit 16, the LPF 24 and the VCO 26 form a PLL (phase-locked loop) 26, and the VCO 25 outputs the color sub-carrier which is produced according to the chrominance signal outputted by the Y/C separator 2. At the same time, only the output of the phase comparator 12 is applied to the adder 15. The internal reference horizontal synchronizing signal provided by the internal reference horizontal synchronizing signal generator 14 is applied to the phase comparator 12, in which it and the regenerated horizontal synchronizing signal are subjected to phase comparison.Accordingly, only the signal corresponding to the phase difference between the internal reference horizontal synchronizing signal and the regenerated horizontal synchronizing signal forms the time base error signal, and the relative movement speed of the reading pickup in the direction of the tangent of the recording track at the data detecting point is so controlled that the phase difference becomes zero.

In this operation, the color sub-carrier output by the VCO 25 is applied through the change-over switch 15 to the doubler 9. Therefore, similarly as in the external synchronization mode, the PAL phase inversion regularity is maintained unchanged even after the jumping operation.

In the above-described embodiment, the LPFs 18 and 24 are provided in the rear stage of the changeover switch 17. However, if an LPF is provided in the front stage of the change-over switch 17, then the one of the two LPFs 18 and 24 can be eliminated; i.e., the circuit can be simplified. In the external synchronization mode, the synchronization of the regenerated horizontal synchronizing signal and the external reference horizontal synchronizing signal can be obtained by tripping the armature of the changeover switch 13 to the first position and by tripping the armature of the change-over switches 15 and 17 to the second position. In the above-described embodiment, the time base error signal is supplied through the equalizer amplifier 19 to the drive coil 22 adapted to drive the tangential mirror 21 and through the equalizer amplifier 20 to the spindle motor 23. However, the technical concept of the invention is applicable to the case also where a variable delay circuit such as a COD (charge coupled device) for time base error correction is provided instead of the tangential mirror 21 and the time base error signal is supplied to the control input terminal of the variable delay circuit.

Claims

1. A data reproducing device having a phase correcting means for using a reference signal synchronous with a colour burst signal in a PAL system color video signal read out of a recording medium, to correct the phase of one of the chrominance signals in said PAL system color video signal which are phase-inverted every other horizontal scanning period, and the phase of a color burst signal therein, the device comprising oscillating means 25 for oscillating at a frequency corresponding to an input signal; signal selecting means 15 for selecting, in response to an instruction, an output of the oscillating means 20 or a reference color sub-carrier signal supplied from outside, and supplying the output or the reference color sub-carrier signal as a reference signal to the phase correcting means 5; and phase difference signal generating means 6 for producing a signal corresponding to a phase difference between an output of the signal selecting means 15 and the color burst signal, the arrangement being such that, when the signal selecting means selects output of the oscillating means, an output of the phase difference signal generating means is supplied to the oscillating means to form a phase-locked loop, and when the signal selecting means selects the reference color sub-carrier signal, the output of the phase difference signal generating means is utilized to perform time axis error correction to make the color burst signal synchronous with the reference colour sub-carrier signal.

2. A data reproducing device comprising a phase difference signal generating means 6 for producing a signal corresponding to the phase difference between a signal supplied thereto and a color burst signal, so that, when an external synchronization mode is effected, by utilizing an output obtained by supplying a reference color sub-carrier supplied from outside to the phase difference signal generating means the time axis error correction is carried out, while the PAL phase correction is performed by using the reference color sub-carrier, and when the external synchronization mode is not effected, the phase difference signal generating means and an oscillating means which oscillates at a frequency corresponding to the output of the phase difference signal generating means form a PLL (phase locked loop), and the output of the oscillating means corrects the PAL phase.

3. A data reproducing device substantially as described with reference to the accompanying drawings.