JPH0761164B2 - Carrier color signal frequency conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Industrial Field B Outline of the Invention C Conventional Technology D Problems to be Solved by the Invention E Means for Solving Problems F Action G Example G-1 Configuration (Fig. 1) G-2 Operation (FIGS. 1 and 2) H Effect of Invention A Field of Industrial Application The present invention relates to a carrier color signal frequency for performing a process of converting the frequency of a carrier color signal forming a color video signal based on the PAL system. Regarding the conversion circuit.

B Outline of the Invention The present invention converts a low-frequency carrier color signal obtained by frequency-converting a carrier color signal forming a color video signal based on the PAL system to a low frequency band side into a carrier color signal of an original frequency. In the carrier color signal frequency conversion circuit for performing frequency conversion as much as possible, the frequency conversion signal used for frequency conversion of the low-frequency carrier color signal is equal to the carrier frequency of the original carrier color signal before being converted into the low-frequency carrier color signal. It is formed based on the oscillation output of the reference oscillator that generates the frequency signal and the oscillation output of the voltage controlled oscillator that should generate the signal of the frequency proportional to the line frequency. Is provided with a reference signal phase shift extraction unit that takes out the first and second phases determined by the mutual phase difference alternately for each line period, and the voltage controlled oscillator is obtained from the reference signal phase shift extraction unit. To be Signal and the burst signal in the carrier color signal obtained by frequency-converting the low-frequency carrier color signal are controlled based on the comparison output obtained by phase-shift comparison, and the low-frequency carrier color signal is frequency-converted and obtained. The burst signal in the carrier color signal is synchronously detected based on the signal obtained by 90-degree phase shifting of the signal from the reference signal phase shift extraction unit, and the output obtained by holding the negative peak level in the detected output When the signal level exceeds a predetermined value, the reference signal phase shift extraction unit is controlled by reversing the signal extraction mode for each line period in the reference signal phase shift extraction unit, whereby the reference signal phase shift extraction unit is controlled relatively easily. With such a configuration, it is possible to stably control the voltage-controlled oscillator according to the burst signal in the carrier color signal obtained by frequency-converting the low-frequency carrier color signal. The frequency stability of the number conversion signal can be improved, and the time base fluctuation of the carrier color signal obtained by frequency conversion of the low frequency carrier color signal caused by the frequency instability of the frequency conversion signal. It is possible to reduce.

C Conventional Technology When a color video signal is recorded on a magnetic tape,
The luminance signal forming the color video signal and the carrier color signal are separated from each other, and the separated luminance signal is frequency-modulated luminance signal frequency-modulated on the high frequency side, and the carrier color signal is frequency-shifted on the low frequency side. A recording method in which after being converted, that is, converted into a low-frequency-converted low-frequency carrier color signal, both are mixed and supplied to a rotary magnetic head and recorded on a magnetic tape by the rotary magnetic head. Is widely adopted.

When a color video signal is reproduced from a magnetic tape recorded under such a recording system, for example, a large number of recording inclined tracks arrayed on the magnetic tape may have two rotating magnetic fields. The head is alternately scanned, and the frequency-modulated luminance signal and the low-frequency carrier color signal for one field period recorded on each inclined track are sequentially read. Then, the frequency-modulated luminance signal and the low-frequency carrier color signal that have been read are supplied to the luminance signal processing system and the color signal processing system, respectively, and processed to obtain a reproduced color video signal.

At the time of reproducing such a color video signal, in the color signal processing system, frequency conversion is performed to convert the low-frequency carrier color signal read from the magnetic tape into the carrier color signal of the original frequency. A conventional carrier color signal frequency conversion circuit proposed for performing such frequency conversion is shown.

In the circuit shown in FIG. 3, the low-frequency carrier color signal C _L , which has the low-frequency converted carrier component of the frequency f _L , is supplied to the frequency conversion unit 12 through the terminal 11. Then, the frequency conversion unit 12
Sx is also supplied from the conversion signal forming unit 13. Further, a constant voltage is applied to the conversion signal forming unit 13 to operate,
Reference crystal oscillator (VXO) 1 for generating a stable signal having the carrier frequency f _sc of the original carrier color signal before low frequency conversion 1
4 and a voltage controlled oscillator (VC) that should generate a signal having a frequency f _aH proportional to the line frequency f _H.
O) 15 oscillating output signal Sb is frequency-divided by frequency divider 16 by 1 / N, and signal Sc that should have frequency f _L = 1 / N · _faH is supplied.

The voltage controlled oscillator 15 is supposed to be subjected to frequency comparison control and phase comparison control.The frequency comparison control for the voltage controlled oscillator 15 is performed by the oscillation output signal Sb of the voltage controlled oscillator 15.
Is divided by 1 / M in the frequency division section 20 to obtain the signal Sd and the terminal 21
And a horizontal synchronizing signal S _H having a line frequency f _H in a luminance signal forming a color video signal together with the original carrier color signal before low frequency conversion, which are frequency-compared in a frequency comparison unit 22, The comparison output obtained from the comparison unit 22 is supplied to the low-pass filter (LPF) 23, whereby the comparison is performed based on the control signal Sfc obtained at the output side of the low-pass filter 23. Further, the phase comparison control for the voltage controlled oscillator 15 is a conversion carrier which is taken out through the burst gate unit 17 and has a carrier component of the frequency f _sc obtained at the output side of the frequency conversion unit 12 as described later. The burst signal St in the color signal C _c and the oscillation output signal Sa of the reference crystal oscillator 14 are combined into a phase comparison unit 18
The phase-shifted comparison is performed and the comparison output obtained from the phase comparison unit 18 is supplied to the low-pass filter 19 to be performed based on the control signal Spc obtained at the output side of the low-pass filter 19. The oscillation output signal of the voltage controlled oscillator 15 for which the frequency comparison control and the phase comparison control are performed in this way
The signal Sc from the frequency divider 16 obtained by dividing Sb by 1 / N is
It has a frequency f _L set based on the frequency f _H of the horizontal synchronizing signal S _H in the above-mentioned luminance signal, and its phase is set based on the phase of the burst signal St in the converted carrier color signal C _c . To be taken.

Then, in the conversion signal forming unit 12, the oscillation output signal Sa of the frequency f _sc from the reference crystal oscillator 14 and the frequency _dividing unit 16 are provided.
From the signal Sc of frequency f _L from the frequency f _sc + f _L =
A frequency conversion signal Sx having f _x is formed, and the frequency conversion signal Sx is supplied to the frequency conversion unit 12. Thus, the frequency converter 12, the low-band carrier color signal C _L which is supplied through the terminal 11, based on the frequency conversion signal Sx, the frequency carrier component of the frequency f _L is f _x -f _L =
The frequency is converted to be f _sc, and the converted carrier color signal C _c having the carrier component of the frequency f _sc is obtained from the frequency conversion unit 12 and is derived at the output terminal 24.

In this way, the converted carrier color signal C _c obtained from the frequency converter 12 is the original carrier color signal from which the low-frequency carrier color signal C _L is obtained.

D Problems to be Solved by the Invention As described above, in the conventionally proposed carrier color signal frequency conversion circuit shown in FIG. 3, the low-frequency carrier color signal C _L is the original carrier color signal (converted). The carrier color signal C _c is frequency-converted, but the low-frequency carrier color signal C _L is
A carrier color signal that forms a color video signal based on the L system,
That is, when the PAL carrier color signal is obtained by low-frequency conversion, the phase comparison control in the voltage controlled oscillator 15 may become unstable.

The burst signal included in the PAL carrier color signal is 90
Two phases defined by the mutual phase difference of degrees, for example, the phase of the modulation axis of the (BY) color difference signal is used as a reference,
The phases of 135 degrees and 225 degrees are alternately taken every line period.

Therefore, in the circuit shown in FIG. 3, when the low-frequency carrier color signal C _L is obtained by low-frequency converting the PAL carrier color signal, it is obtained at the output side of the frequency conversion unit 12. The converted carrier color signal C _c becomes the PAL carrier color signal. Therefore, the burst signal St included in the converted carrier color signal C _c alternately takes two phases defined with a mutual phase difference of 90 degrees for each line period, and as shown in FIG. In the second line period, (B-
Y) It has a phase advanced by 135 degrees with respect to the phase of the modulation axis of the color difference signal, and in the next (n + 1) th line period,
(BY) The phase has a phase advanced by 225 degrees with respect to the phase of the modulation axis of the color difference signal. Then, the burst signal St having such a phase change for each one line period is supplied from the burst gate unit 17 to the phase comparison unit 18.

On the other hand, the oscillation output signal Sa of the reference crystal oscillator 14 has a fixed phase, for example, as shown in FIG.
-Y) It has a phase advanced by 180 degrees with respect to the phase of the modulation axis of the color difference signal. Therefore, the phase comparison unit 18
In the normal state, as shown in FIG. 4B, the phase difference of +45 degrees and −45 degrees is alternately detected every one line period, and the detection output corresponding to ± 45 degrees is detected. As an error signal, there is a possibility that the phase comparison control in the voltage controlled oscillator 15 will not be properly performed due to the error signal.

In view of such a point, the present invention, the low-frequency carrier color signal obtained by low-pass conversion of the PAL carrier color signal, in the frequency conversion to the PAL carrier color signal of the original frequency, low-frequency carrier color The signal for frequency conversion to the signal is controlled to generate the oscillation output of the reference oscillator that generates a signal whose frequency is equal to the carrier frequency of the original PAL carrier color signal and the signal whose frequency is proportional to the line frequency. The phase comparison control is appropriately performed according to the burst signal in the converted carrier color signal, which is formed based on the oscillation output of the oscillating unit and is obtained by frequency conversion of the low-frequency carrier chrominance signal in the voltage control oscillating unit. As a result, the frequency conversion signal is made excellent in frequency stability, and the time base fluctuation of the conversion carrier color signal caused by the frequency instability of the frequency conversion signal is reduced. Done , And to provide a carrier chrominance signal frequency conversion circuit.

E Means for Solving the Problems In order to achieve the above object, the carrier color signal frequency conversion circuit according to the present invention comprises a reference oscillating unit for generating a signal having a frequency equal to the carrier frequency of the PAL carrier color signal, and a line. A voltage controlled oscillator that should generate a signal of a frequency proportional to the frequency,
A conversion signal forming section that obtains a frequency conversion signal based on the oscillation output of the reference oscillation section and the oscillation output signal of the voltage control oscillation section, and a low-frequency carrier color signal obtained by low-frequency conversion of the PAL carrier color signal. Is provided, the low-frequency carrier color signal, based on the frequency conversion signal, with a frequency conversion unit for frequency conversion to be a PAL carrier color signal of the original frequency, and to the voltage control oscillation unit, A reference signal phase shift extraction unit that extracts the oscillation output of the reference oscillation unit as alternating first and second phases determined with a mutual phase difference of 90 degrees for each line period, and a reference signal phase shift extraction unit. An oscillation control unit that controls the voltage control oscillation unit based on a comparison output obtained by performing a phase comparison between the signal obtained from and the burst signal in the converted carrier color signal obtained at the output side of the frequency conversion unit is provided, Furthermore, frequency conversion Synchronously detects on the basis of the burst signal in the converted carrier chrominance signal obtained at the output side to the signal obtained by the signal from the reference signal phase extraction section 90-degree phase,
When the level of the output signal obtained by holding the negative polarity peak level in the detected output exceeds a predetermined value, the reference signal phase shift extraction unit reverses the signal extraction mode for each line period to shift the reference signal transfer. A reference signal extraction state control unit for controlling the phase extraction unit is provided and configured.

F action In the carrier color signal frequency conversion circuit according to the present invention having such a configuration, the reference oscillating unit sets the carrier frequency of the PAL carrier color signal which is the source of the low-frequency carrier color signal supplied to the frequency converting unit. The oscillation output of the same frequency is transmitted, and the voltage control oscillation unit transmits the oscillation output of the predetermined frequency proportional to the line frequency under the phase comparison control by the oscillation control unit. Then, the conversion signal forming unit forms a frequency conversion signal based on the oscillation outputs of the reference oscillation unit and the voltage control oscillation unit, and supplies the frequency conversion signal to the frequency conversion unit. In the frequency converter, the low-frequency carrier color signal supplied thereto is frequency-converted based on the frequency conversion signal, and the low-frequency carrier color signal is converted into a carrier of the original frequency as the converted carrier color signal from the frequency converter. A PAL carrier color signal obtained by frequency conversion to be a color signal is derived.

At this time, phase comparison for phase comparison control in the oscillation control unit is performed between the burst signal in the PAL carrier color signal derived from the frequency conversion unit and the signal obtained from the reference signal phase shift extraction unit, The signal obtained from the reference signal phase shift extraction unit is extracted by taking the first and second phases, in which the oscillation output of the reference oscillation unit is determined with a mutual phase difference of 90 degrees, alternately for each line period. If the signal extraction mode in the reference signal phase shift extraction unit is appropriate, it is assumed that the phase has a phase that matches the burst signal in the PAL carrier color signal derived from the frequency conversion unit. Therefore, when the signal extraction mode in the reference signal phase shift extraction section is appropriate, under the normal state, the phase comparison in the oscillation control section results in no error signal.

Further, when the signal extraction mode in the reference signal phase shift extraction section becomes improper, the state is changed by the reference signal extraction state control section to the reference signal phase shift to the burst signal in the PAL carrier color signal derived from the frequency conversion section. It is detected through synchronous detection based on the signal obtained from the extraction unit, and the signal extraction mode in the reference signal phase shift extraction unit is corrected so that the signal extraction mode in the reference signal phase shift extraction unit is properly maintained. Done

Therefore, the phase comparison control in the voltage controlled oscillator is always performed properly, and the frequency conversion signal has excellent frequency stability. As a result, the frequency conversion signal has a relatively simple structure. The time-axis fluctuation of the PAL carrier color signal derived from the frequency conversion unit caused by the frequency instability of the signal is reduced.

G Embodiment G-1 Structure (FIG. 1) FIG. 1 shows an example of a carrier color signal frequency conversion circuit according to the present invention. In FIG. 1, a part corresponding to each part in FIG. 3 described above and a third part obtained in each part in FIG.
Signals corresponding to the signals obtained in the figure are denoted by the same reference numerals as those in FIG. 3, and duplicate description of each of them is omitted.

In this example, in addition to the configuration similar to that shown in FIG. 3 described above, the first and second oscillation output signals Sa of the reference crystal oscillator (VXO) 14 are determined with a mutual phase difference of 90 degrees. The reference signal phase shift extraction unit 30 which supplies the phase comparison unit 18 with the phase of the signal alternately taken every line period, and the reference signal which controls the signal extraction mode in the reference signal phase shift extraction unit 30. An ejection state control unit 40 is provided.

The reference signal phase shift extraction unit 30 includes a 90 ° phase shift unit 31 that shifts the oscillation output signal Sa of the reference crystal oscillator 14 by 90 degrees, and an oscillation output signal Sa of the reference crystal oscillator 14 and a 90 ° phase shift unit 31.
And a signal from the movable contacts which are supplied to the selective contacts 32a and 32b, respectively, and are selectively connected to these selective contacts 32a and 32b.
The switch 32 has a switch 32c and a flip-flop (FF) 33 that drives the switch 32. Then, the flip-flop 33 has a terminal 21
From the supply of the horizontal sync signal S _H, the horizontal synchronizing signal S _H
The switch control signal Ss having a frequency of 1 / 2f _H is generated at the output side of the switch contact signal Ss based on the switch control signal Ss.
The selection contact 32a and the selection contact 32b are alternately connected every line period. As a result, the oscillation output signal Sa of the reference crystal oscillator 14 is output from the switch 32 as a signal Sa 'that alternately takes the original phase and the phase shifted by 90 degrees from the original phase for each line period. Taken out.

Further, the reference signal extraction state control unit 40 shifts the signal Sa ′ obtained from the switch 32 in the reference signal phase shift extraction unit 30 by 90 degrees and sends it as a signal Se.
° Burst gate section by signal Se obtained from phase shift section 41
The synchronous detection unit 42 that synchronously detects the burst signal St obtained from 17 to generate the detection output signal Sf, the peak hold unit 43 that holds the negative peak level in the detection output signal Sf of the synchronous detection unit 72, and the peak hold unit And a level detector 44 for detecting the level of the output signal of 43. Then, the level detection unit 44 includes a peak hold unit 43.
When the output signal level of exceeds the specified value,
Generates the detection output signal Sg and outputs it to the reference signal phase shift extraction unit.
Supply to the control terminal of the flip-flop 33 in 30
The inversion mode of the flip-flop 33 is changed.

G-2 Operation (FIGS. 1 and 2) In the example shown in FIG. 1, the low-frequency carrier color obtained by the low-frequency conversion of the PAL carrier color signal based on the above-described configuration. The signal is frequency-converted to be a PAL carrier color signal of the original frequency, and the low-frequency carrier color is assumed to have a carrier component of frequency f _L obtained by low-frequency conversion of the PAL carrier color signal. The signal C _L is transmitted through the terminal 11 to the frequency conversion unit.
Supplied to 12.

From the reference crystal oscillator 14, a stable oscillation output signal Sa having a frequency equal to the carrier frequency f _sc of the PAL carrier color signal is obtained, and this oscillation output signal Sa is supplied to the conversion signal forming unit 13 and is supplied as a reference signal. It is supplied to the signal phase shift extraction unit 30. Further, the voltage controlled oscillator (VCO) 15 performs frequency comparison control in the same manner as in FIG. 3 in order to generate a signal having a frequency f _aH proportional to the line frequency f _H of the color video signal based on the PAL system. In addition, the phase comparison control is performed. Then, the voltage controlled oscillator 15
The oscillating output signal Sb is divided by 1 / N in the frequency dividing section 16 to form a signal Sc having a frequency f _L , and the signal Sc is supplied from the frequency dividing section 16 to the conversion signal forming section 13.

In the conversion signal forming unit 13, the reference crystal oscillator
A frequency conversion signal Sx having a frequency f _sc + f _L = f _x is formed from the oscillation output signal Sa having the frequency f _sc from 14 and the signal Sc having the frequency f _L from the frequency dividing unit 16. The signal Sx is supplied to the frequency conversion unit 12. Thereby,
In the frequency converter 12, the low-band carrier color signal C _L which is supplied through the terminal 11, based on the frequency conversion signal Sx, the frequency carrier component of the frequency f _L is f _x -f L ₌ f _sc
And the converted carrier chrominance signal C having the carrier component of the frequency f _sc from the frequency converter 12.
_c is obtained as a PAL carrier color signal, which is output terminal 24
Be derived to.

In this example, in the phase comparison control in the voltage controlled oscillator 15 at the time of the frequency conversion operation, the PAL carrier color signal (converted) having the carrier component of the frequency f _sc obtained at the output side of the frequency converter 12 is converted. Carrier color signal C
The burst signal St in ( _c ) is taken out by the burst gate unit 17 and supplied to one input terminal of the phase comparison unit 18. Also, the oscillation output signal Sa of the reference crystal oscillator 14
In the reference signal phase shift extraction unit 30, the switch 32 is driven by the flip-flop 33 as described above, whereby the oscillation output signal of the reference crystal oscillator 14 is output from the reference signal phase shift extraction unit 30. Sa is taken out as a signal Sa 'that alternately takes the original phase and the phase shifted by 90 degrees from the original phase for each line period, and the signal Sa' is taken out from the other side of the phase comparison unit 18. Is supplied to the input terminal of.

Then, with the burst signal St from the burst gate unit 17,
The signal Sa ′ from the reference signal phase shift extraction unit 30 is compared with the phase comparison unit.
The phase comparison is performed at 18, and the comparison output obtained from the phase comparison unit 18 is supplied to the low-pass filter (LPF) 19, so that the voltage-controlled oscillator 15 in the voltage-controlled oscillator 15 is generated based on the control signal Spc obtained at the output side of the low-pass filter 19. Phase comparison control is performed. Such a phase comparison control is performed in addition to the frequency comparison control based on the control signal Sfc obtained from the low-pass filter 23, and the oscillation output signal Sb of the voltage controlled oscillator 15 is divided by 1 / N to obtain a frequency division unit. Signal Sc from 16
Has a frequency f _L set based on the frequency f _H of the horizontal synchronizing signal S _H , and its phase is based on the phase of the burst signal St in the PAL carrier color signal obtained at the output side of the frequency conversion unit 12. It is assumed that it has been set.

In such a case, the burst signal St from the burst gate unit 17
Takes two phases defined with a mutual phase difference of 90 degrees alternately for each line period, and in the normal state,
As shown in FIG. 2A, for example, in the nth line period, it has a phase advanced by 135 degrees with respect to the phase of the modulation axis of the (BY) color difference signal, and the next n + 1th line period. , The phase has a phase advanced by 225 degrees with respect to the phase of the modulation axis of the (BY) color difference signal. On the other hand, the signal Sa ′ from the reference signal phase-shifting / extracting section 30 also takes two phases defined with a mutual phase difference of 90 degrees alternately for each line period, so that the reference signal phase-shifting / extracting section 30 can properly take out the signal. , As shown in FIG. 2B,
In the nth line period, the original phase of the oscillation output signal Sa has a phase advanced by 135 degrees with respect to the phase of the modulation axis of the (BY) color difference signal, and the next n + 1th line period At 90 degrees from the original phase of the oscillation output signal Sa.
The phase is shifted by 225 degrees with respect to the phase of the modulation axis of the (BY) color difference signal. Therefore, under such a state, in each line period, the phase of the burst signal St from the burst gate unit 17 and the phase of the signal Sa ′ from the reference signal phase shift extraction unit 30 match and the phase comparison unit No detection output as an error signal can be obtained from 18. Therefore, the phase comparison control in the voltage controlled oscillator 15 is stably performed.

At this time, 90 in the reference signal extraction state control unit 40
As shown in FIG. 2C, the signal Se obtained from the phase shifting section 41 and having a phase shifted by 90 degrees with respect to the signal Sa 'is transmitted from the burst gate section 17 to the burst signal St. The phase also has a phase shifted by 90 degrees. Therefore, the detection output signal Sf cannot be obtained from the synchronous detection unit 42, and accordingly, the detection output signal Sg from the level detection unit 44 is obtained.
And the flip-flop in the reference signal phase shift extraction unit 30
The inversion mode of the flop 33 is maintained as it is.

On the other hand, when the signal extraction by the reference signal phase shift extraction unit 30 is made improper, the reference signal phase shift extraction unit 30
As shown in FIG. 2D, the signal Sa 'from the (BY) color difference signal is a phase shifted by 90 degrees from the original phase of the oscillation output signal Sa in the nth line period. The phase of the modulation axis of the (BY) color difference signal, which is the original phase of the oscillation output signal Sa in the next (n + 1) th line period, has a phase advanced by 225 degrees with respect to the phase of the modulation axis of It has a phase advanced by 135 degrees with respect to. Therefore, in such a case, the signal from the reference signal phase shift extraction unit 30
Sa 'has a phase difference of 90 degrees with respect to the burst signal St from the burst gate unit 17 in the nth line period,
In addition, a phase difference of 270 degrees will occur in the (n + 1) th line period. However, such a state is automatically switched by the operation of the reference signal extraction state control unit 40 to a state in which signal extraction in the reference signal phase shift extraction unit 30 is properly performed.

That is, in such a state, the reference signal extraction state control unit
The signal Se obtained from the 90 ° phase shifter 41 at 40 has a phase which is 90 ° phase shifted from the phase of the signal Sa ′ shown in FIG. 2D, as shown in FIG. With respect to the burst signal St from the burst gate unit 17, there is a phase difference of 180 degrees in the n-th line period and the same phase in the (n + 1) -th line period. Therefore, as shown in FIG. 2F, the synchronous detection unit 42 obtains a negative-polarity detection output signal Sf having a large level in the nth line period and a large negative output signal Sf in the (n + 1) th line period. A positive polarity detection output signal Sf having the following level is obtained. Then, of these, the peak level of the negative-polarity detection output signal Sf is held by the peak hold unit 43, and further, the level detection unit 44 detects that the level held by the peak hold unit 43 exceeds a predetermined value. As a result, the detection output signal Sg is obtained from the level detector 44. Then, the detection output signal Sg causes the inversion mode of the flip-flop 33 in the reference signal phase shift extraction unit 30 to change, for example, to be inverted, and as a result, the signal extraction in the reference signal phase shift extraction unit 30. The state is switched to a state in which the extraction of the signal Sa 'is properly performed.

In this way, in the example of FIG. 1, when the low-frequency carrier color signal obtained by low-frequency conversion of the PAL carrier color signal is frequency-converted to be the PAL carrier color signal of the original frequency, The phase comparison control in the controlled oscillator 15 is always stably performed.

H Effect of the Invention As is clear from the above description, according to the carrier color signal frequency conversion circuit of the present invention, the PAL carrier color signal is frequency-converted to obtain the low-frequency carrier color signal, In obtaining the PAL carrier color signal of the original frequency, the frequency conversion signal for the low-frequency carrier color signal is generated by the oscillation output of the reference oscillator that generates a stable signal with a frequency equal to the carrier frequency of the PAL carrier color signal, and the line. It is formed based on the oscillation output of the voltage controlled oscillator that is controlled to generate a signal of a frequency proportional to the frequency. The PAL carrier color signal obtained by conversion can be in a state in which it is properly performed according to the burst signal in the color signal.
The frequency stability of the frequency conversion signal can be improved. With a relatively simple configuration, the time-axis fluctuation of the PAL carrier color signal, which is generated by frequency conversion of the low-frequency carrier color signal, caused by the frequency instability of the frequency conversion signal is significantly reduced. You will be able to

[Brief description of drawings]

FIG. 1 is a block connection diagram showing an example of a carrier color signal frequency conversion circuit according to the present invention, FIGS. 2A to 2F are signal vector diagrams used for explaining the operation of the example shown in FIG. 1, and FIG. Is a block connection diagram showing a conventional carrier color signal frequency conversion circuit,
4A and 4B are signal vector diagrams provided for explaining the operation of the conventional circuit shown in FIG. In the figure, 12 is a frequency conversion unit, 13 is a conversion signal forming unit, 14 is a reference crystal oscillator, 15 is a voltage controlled oscillator, 16 is a frequency dividing unit, 17 is a burst gate unit, 18 is a phase comparison unit, and 30 is a reference. Signal phase shift extraction unit, 31 and 41 are 90 ° phase shift unit, 32 is a switch, 40 is a reference signal extraction state control unit, 42 is a synchronous detection unit, 43
Is a peak hold unit, and 44 is a level detection unit.

Claims (1)

[Claims] 1. A reference oscillator for generating a signal having a frequency equal to a carrier frequency of a carrier color signal forming a color video signal based on the PAL system, and a signal having a frequency proportional to a line frequency related to the carrier color signal. A voltage controlled oscillator to be generated, a conversion signal forming unit that obtains a frequency conversion signal based on the oscillation output of the reference oscillator and the oscillation output signal of the voltage controlled oscillator, and the carrier color signal has a low frequency. A low-frequency carrier color signal obtained by frequency conversion to the band side is supplied, and a frequency for converting the low-frequency carrier color signal to a carrier color signal of the original frequency based on the frequency conversion signal. A conversion unit; and a reference signal phase shift extraction unit that extracts the oscillation output of the reference oscillation unit by alternately taking first and second phases determined with a mutual phase difference of 90 degrees for each line period, Basis Oscillation control for phase-comparing the signal obtained from the quasi-signal phase shift extraction unit and the burst signal in the carrier color signal obtained at the output side of the frequency conversion unit, and controlling the voltage controlled oscillation unit based on the comparison output. Section, the burst signal in the carrier color signal obtained at the output side of the frequency conversion section, the signal from the reference signal phase shift extraction section 90
When the level of the output signal obtained by carrying out synchronous detection based on the signal obtained by phase shifting and holding the negative peak level in the detected output exceeds a predetermined value, one line in the reference signal phase extraction section A carrier color signal frequency conversion circuit comprising: a reference signal extraction control unit that controls the reference signal phase shift extraction unit so as to reverse the signal extraction mode for each period.