JP3371195B2 - Color synchronization circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color synchronizing circuit suitable for use in a color signal recording system in a VTR, for example.

[0002]

2. Description of the Related Art In a VTR such as an 8 mm VTR,
On the recording side, the luminance signal Y is converted to FM and, for example, a carrier color signal C having a color subcarrier frequency of 3.58 MHz.
Is converted into a carrier color signal CLo having a color subcarrier frequency of 743 kHz, for example, and both are added and recorded on a magnetic tape via a magnetic recording head.

On the reproducing side, the FM output signal YFM and the low-frequency conversion carrier color signal CLo are separated from the output signal of the head by a filter and subjected to demodulation processing and frequency conversion processing, respectively. Luminance signal Y and carrier color signal C
And is obtained.

In this case, in the color synchronizing circuit on the recording side, a necessary subcarrier is generated with reference to the color burst signal in the input carrier color signal. This color sync circuit is usually
An automatic phase control (APC) method is used.

FIG. 5 is a block diagram of an example of a conventional color synchronizing circuit. In FIG. 5, reference numerals 11 and 21 denote multiplication circuits, to which the carrier color signal C is supplied via the phase control circuit 12. Then, the signal of the color subcarrier frequency from the voltage control type variable frequency oscillation circuit (hereinafter referred to as VCO) 13 is supplied to the multiplication circuit 11 to perform the synchronous detection, and the red color difference signal RY is obtained.

Further, the carrier signal is supplied to the second multiplication circuit 21 through the phase control circuit 12, and 9
The output signal of the VCO 13 is supplied through the 0 ° phase shift circuit 22 to perform synchronous detection.
-Y is obtained.

The outputs of the multiplication circuit 11 and the multiplication circuit 21 are also supplied to the phase difference detection circuit 14. And
The burst gate signal Sbg is supplied to the phase difference detection circuit 14, and the phase difference detection circuit 14 outputs the color subcarrier of the carrier color signal and the VCO 13 from the output levels of the multiplication circuit 11 and the multiplication circuit 21 during the burst signal section. An error voltage corresponding to the phase difference with the output signal is detected.

That is, if the phase difference between the color subcarrier and the output signal of the VCO 13 is zero, the red color difference signal R-
The level of the Y burst signal section is zero, and the blue color difference signal B
Since the level of the -Y burst signal section is the maximum, the levels of these two are compared and weighed to accurately detect the error voltage corresponding to the phase difference between the color subcarrier and the output signal of the VCO 13. it can.

The detection output of the phase difference detection circuit 14 is fed back to the VCO 13 through a loop filter 15 consisting of a high-pass filter and an integrator and an amplification circuit 16, and the color subcarrier of the input carrier color signal and the output signal of the VCO 13 are fed. The phase error is controlled to be zero.

The phase control circuit 12 is provided when there is a large phase error between the color subcarrier of the input carrier color signal and the output signal of the VCO 13, and the carrier color signal is generated by a feedback loop as described below. When the phase difference between the color sub-carrier and the transmission output signal of the VCO 13 is large, the phase control circuit 12 inverts the phase of the input carrier color signal, for example.

That is, the multiplication circuit 11 and the multiplication circuit 2
The output of 1 is supplied to the phase difference detection circuit 17, and the burst gate signal Sbg is supplied to the phase difference detection circuit 17, so that the multiplication circuit 11 and the multiplication circuit 2 during the burst period are supplied.
The output voltage of 1, that is, the error voltage corresponding to the phase difference between the color subcarrier of the carrier color signal and the output signal of the VCO 13 is detected. Then, when the detection error voltage exceeds a predetermined magnitude, the phase control circuit 12 inverts the phase of the input carrier color signal by the output signal of the phase difference detection circuit 17 to improve the transient response. Is being done.

From the multiplication circuits 11 and 21, the phase difference detection circuit 14, the high-pass filter 15, the amplification circuit 16, and the VCO 1
In general, the first feedback loop reaching the multiplication circuits 11 and 21 through 3 generally has a relatively low loop gain in order to secure a good S / N in the color synchronization system for recording.

However, the phase error or the frequency error becomes large at the time of a transient response such as when the power is turned on or when the variable speed reproduction signal of another VTR is input, so that the APC becomes large.
The loop pull-in speed tends to be slow. Therefore,
As described above, the second feedback loop from the multiplication circuits 11 and 21 to the phase control circuit 12 through the phase difference detection circuit 17 is formed, and when the phase error is large, the second phase difference detection circuit 17 controls the phase. The circuit 12 is activated.

As a result, as in the transient response, the phase error between the burst signal in the input color signal and the output of the VCO is
For example, it is possible to deal with the case where it is larger than ± 90 °.

In FIG. 5, the portion for obtaining the color difference signal from the carrier color signal has been described for the sake of simplification, but in reality, it is so-called that the color difference signal is synchronized with the horizontal frequency of the input video signal. AFC loops are built in parallel.

The circuit configuration of FIG. 5 has been a configuration of an analog signal processing circuit in the past, but it may be a configuration of a digital signal processing circuit. That is, in recent consumer-use VTRs with built-in cameras, digital signal processing is performed in the camera system in order to realize multiple functions such as adaptive image quality control, electronic zoom using a memory, and image stabilization. In such a VTR system as well, digitalization of signal processing is being promoted in order to reduce power consumption and image quality. Therefore, the color synchronizing circuit as in the example of FIG. 5 is configured by digital hardware.

[0017]

As described above,
In the conventional color synchronizing circuit shown in FIG. 5, a phase control circuit (phase shift circuit) is also used to accelerate pull-in during a transient response such as power-on.

However, in the conventional color synchronizing circuit of FIG.
As described above, since the gain of the first loop is set to be relatively low in order to secure a good S / N, after the phase control circuit 12 operates, the gain of the first loop is set within ± 90 °. There is a problem that it takes a relatively long time to pull in, and deterioration of S / N and fading easily occur.

In view of the above point, an object of the present invention is to provide a color synchronizing circuit capable of achieving both S / N in a steady state and responsiveness in a transient state.

[0020]

In order to solve the above-mentioned problems, the color synchronizing circuit according to the present invention has a variable frequency oscillator 13 and a color sub-carrier of a carrier color signal, in correspondence with the reference numerals of the embodiments described later. In a color synchronization circuit including a first detection circuit 14 that detects a phase difference from the output of the variable frequency oscillator 13, and an amplifier circuit 16v that amplifies the output of the first detection circuit and returns the amplified output to the variable frequency oscillator 13. A second detection circuit 17m for detecting the phase difference between the color subcarrier of the carrier color signal and the output of the variable frequency oscillator 13;
And a determination circuit 18 for determining that the phase difference detected by the detection circuit exceeds a predetermined value, and the output of this determination circuit 18 causes the phase difference detected by the second detection circuit to reach a predetermined value. When it exceeds, the gain of the feedback loop is controlled to be increased.

[0021]

According to this structure, in the transient state, the second
When the determination circuit 18 determines that the output level of the multiplication circuit in the burst period detected by the detection circuit No. 2 exceeds the predetermined value Vth, the gain of the APC loop is increased and the response is improved. In the steady state, the APC
Since the loop gain can be set relatively low,
A high S / N color signal is obtained.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a VTR to which an embodiment of a color synchronizing circuit according to the present invention is applied will be described with reference to FIGS.

In FIG. 3, reference numeral 100 denotes a VTR recording system of this example, in which an analog luminance signal Y is supplied to an AD converter 111 and an AFC circuit 112, and an output of the AD converter 111 is output. It is supplied to the signal processing circuit 113. The signal processing circuit 113 includes a pre-emphasis processing circuit 11
4 and the FM modulation processing circuit 115, and the output from the signal processing circuit 113 is output by the DA converter 116.
The adder 11 is converted into an analog FM luminance signal YFM.
7 is supplied. A-D converter 111 to D-A converter 1
A clock that is synchronized with the horizontal synchronizing signal in the luminance signal Y is supplied to each of 16 from the AFC circuit 112.

Further, the carrier color signal C is transferred to the A / D converter 12
1 to the decoding circuit 122, and
The burst gate circuit 123 outputs the color burst signal extracted from the carrier color signal C to the clock generation circuit 124.
Is supplied to the A / D converter 121, the decoding circuit 122, and the signal processing circuit 125 to generate a pair of baseband color difference signals RY and BY. Formed, signal processing circuit 125
Is supplied to.

The output of the signal processing circuit 125 is supplied to the encoding circuit 126, and the low frequency conversion signal generating circuit 1
The output of 27 is supplied to the encoding circuit 126, and in the encoding circuit 126, the low-frequency conversion carrier color signal CLo is output.
The data corresponding to is generated. This data is DA
In the converter 128, the analog low-frequency conversion color signal CLo
And is supplied to the adder 117, together with the FM luminance signal YFM, through the recording amplifier 101.
2 and is recorded on the tape MT. In addition, the signal processing circuit 125 to the D-A converter 128 respectively include an AF
The clock from the C circuit 112 is supplied.

FIG. 4 is a block diagram of the reproducing system 200 of the VTR of this example. Tape M by magnetic head 201
The signal reproduced from T passes through the reproduction amplifier 202,
High pass filter 211 and band pass filter 22
1, the FM luminance signal YFM is obtained from the high pass filter 211, and the low-pass conversion carrier color signal CLo is obtained from the band pass filter 221.

The FM luminance signal YFM from the high pass filter 211 is supplied to the signal processing circuit 213 through the AD converter 212. This signal processing circuit 213 is
The demodulation processing circuit 214 and the de-emphasis processing circuit 215 are included, and the output from the signal processing circuit 213 is D-
The A converter 216 converts the analog luminance signal Y into an analog luminance signal Y, which is supplied to the adder 217 and the AFC circuit 2
18 are supplied. From the AFC circuit 218, the clock synchronized with the horizontal synchronizing signal in the reproduction luminance signal Y is A-
It is supplied to each of the D converter 212 to the D-A converter 216.

The low-frequency conversion carrier color signal CLo from the bandpass filter 221 is supplied to the decoding circuit 223 through the A / D converter 222 to form a pair of baseband color difference signals R-Y and B-Y. Then, the signal processing circuit 224
Is supplied to. The output of the signal processing circuit 224 is supplied to the encoding circuit 225, and the reference clock from the reference oscillation circuit 226 is supplied to the encoding circuit 225. In the encoding circuit 225, data corresponding to the carrier color signal C is generated. It This data is converted into an analog carrier color signal C in the DA converter 227, supplied to the adder 217, and superposed on the luminance signal Y to be derived.

The A / D converter 222 to the signal processing circuit 224 are respectively supplied with the clock from the AFC circuit 218. Note that, as shown in FIG. 4, the luminance signal Y and the carrier color signal C can also be derived independently.

[Description of Embodiment of Color Synchronous Circuit] Next, referring to FIG.
An embodiment of the color synchronizing circuit according to the present invention will be described with reference to FIG. The color synchronization circuit is, for example, the decoding circuit 122 of the recording system 100 described above.
(See FIG. 4).

The configuration of an embodiment of the present invention is shown in FIG.
In the example of FIG. 1, parts corresponding to those in the example of FIG.

In the example of FIG. 1, the phase control circuit of the conventional example of FIG. 5 is not provided, and the carrier color signal C is directly supplied to the pair of multiplication circuits 11 and 21. The carrier color signal C
The first detection circuit for detecting the phase difference between the color sub-carrier and the output of the VCO 13 is composed of the multiplication circuits 11 and 21 and the phase difference detection circuit 14, and the output signal of the phase difference detection circuit 14 is It is supplied to the VCO 13 via a loop filter 15m including a high pass filter and an integrator and an amplifier circuit 16v.

The loop filter 15m is obtained by sufficiently lowering the cutoff frequency of the high-pass filter constituting the loop filter 15m of the conventional example shown in FIG. The gain of the amplifier circuit 16v is variable.

The color subcarrier of the carrier color signal C and the VCO
The second detection circuit for detecting the phase difference from the output of 13 is composed of the multiplication circuits 11 and 21 and the phase difference detection circuit 17m, and the level detection output of the phase difference detection circuit 17m is supplied to the determination circuit 18. It When the output level of the phase difference detection circuit 17m is lower than the predetermined threshold value Vth, the determination circuit 18 sets the gain of the amplification circuit 16v to a low value as a steady state, and the output of the phase difference detection circuit 17m. When the level exceeds a predetermined threshold value Vth, the gain of the amplifier circuit 16v is set to a high value as a transitional state such as when the power is turned on or when a variable speed reproduction signal of another VTR is input.

Next, the operation of this embodiment will be further described with reference to FIG. As described above, in the steady state, the gain of the amplifier circuit 16v is set low, and the characteristic of the color synchronization circuit is as shown by the solid line in FIG. 2, for example. In this steady state, together with the characteristics of the loop filter 15m, the APC loop follows only the phase error component (phase error and constant frequency error) of the carrier color signal and the phase modulation error component such as various jitters. It becomes difficult and the S / N of the color can be improved.

Now, it is assumed that the phase error between the burst signal in the carrier color signal and the output of the VCO 13 is transiently larger than ± 90 ° from this steady state, as indicated by the point P in FIG.

Then, in this embodiment, the output level of the phase difference detecting circuit 17m exceeds the threshold value Vth of the judging circuit 18, and the control signal from the judging circuit 18 causes
The gain of the amplifier circuit 16v is switched to a relatively high level, and the characteristic of the color synchronization circuit becomes as shown by the chain line in FIG.

As a result, the loop gain is increased,
As indicated by the arrow in FIG. 2, from the state indicated by the point P,
Since the pull-in time after entering the range of 90 ° and after entering the range of ± 90 ° is shortened, the transient response is improved, and it is possible to reduce the occurrence of color fading as in the conventional case.

After the color synchronizing circuit is pulled in the input carrier color signal, the threshold level V of the decision circuit 18 is reached.
Without exceeding th, the gain of the amplifier circuit 16v is returned to a relatively low set value by the control signal from the determination circuit 18, and the above-mentioned steady state is restored.

In the above embodiment, the amplifier circuit 16v
In the configuration of the variable gain amplifier, the loop gain of the APC loop is increased by increasing the gain during the transient response, but the loop gain of the APC loop is increased by increasing the input sensitivity of the VCO 13. Alternatively, the gain control of the amplifier circuit 16v and the input sensitivity control of the VCO 13 may be performed together to control the APC loop gain.

Since the phase difference detection circuits 14 and 17 detect the phase difference between the color subcarrier and the output signal of the VCO 13 more accurately, the output signals RY and B of the two multiplication circuits 11 and 21 are detected. Although the level of the -Y burst signal section is compared and weighed, an error voltage corresponding to the level of the burst signal section of one output of the multiplication circuits 11 and 21 may be used as the phase difference detection output. .

In the above embodiment, the phase difference between the color subcarrier of the carrier color signal and the output signal of the VCO is obtained by obtaining the phase difference between the color burst signal in the carrier color signal and the output signal of the VCO 13. However, in the case of an apparatus for recording and reproducing by inserting a reference signal for color synchronization into the carrier color signal, the reference signal for color synchronization and VC
The phase difference from the O output signal is detected.

Further, although the above-described embodiment has the configuration of the digital signal processing circuit, as described above, the present invention can have the configuration of the analog signal processing circuit.

The above-described embodiment applies the present invention when the APC circuit is used as a circuit for generating a synchronous detection signal when the carrier color signal is a baseband signal, that is, a color difference signal. However, the present invention can be similarly applied to the case where the APC circuit is used as the low frequency conversion signal generation circuit in the case of performing the low frequency conversion of the carrier color signal.

[0045]

As described above, according to the present invention, the APC loop follows only the phase error component of the carrier color signal, and it becomes difficult to follow the phase modulation error component such as various jitters. / N can be improved and
If a large error occurs during transient response, A
Since the gain of the PC loop is increased, the transient response characteristic can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a color synchronizing circuit according to the present invention.

FIG. 2 is a diagram showing characteristics of an embodiment of the present invention.

FIG. 3 is a block diagram for explaining the present invention.

FIG. 4 is a block diagram for explaining the present invention.

FIG. 5 is a block diagram showing a configuration example of a conventional color synchronization circuit.

[Explanation of symbols]

11, 21 Multiplication circuit (Synchronous detection circuit) 13 Variable frequency oscillator 14,17m Phase difference detection circuit 15m loop filter 16v variable gain amplifier circuit 18 Judgment circuit 100 recording system 200 playback system Sbg Burst gate signal

Claims (2)

(57) [Claims] 1. A variable frequency oscillator, a first detection circuit for detecting a phase difference between a color subcarrier of a carrier color signal and an output of the variable frequency oscillator, and an amplifier for amplifying an output of the first detection circuit. An amplification circuit b that feeds back to the variable frequency oscillator, a second detection circuit that detects the phase difference between the color subcarrier of the carrier color signal and the output of the variable frequency oscillator, and the second detection circuit. And a judgment circuit for judging that the detected phase difference exceeds a predetermined value, and when the phase difference detected by the second detection circuit exceeds the predetermined value by the output of the judgment circuit, the feedback loop A color synchronization circuit characterized by controlling to increase the gain. 2. The carrier color signal is a signal to be recorded in a recording / reproducing apparatus, and the first detection circuit comprises a multiplier of a color subcarrier of the carrier color signal and an output of the variable frequency oscillator, A first circuit for obtaining an output of the burst signal section of the output of the multiplier, and the second detection circuit includes the multiplier and an output of the burst signal section of the output of the multiplier. The color synchronization circuit according to claim 1, further comprising a second circuit for obtaining a color difference signal output from the multiplier.