JPH02288490A - Color signal processing unit - Google Patents

Abstract

PURPOSE:To obtain the unit with fast response with simple circuit constitution by varying an output phase of a phase synchronizing circuit proportional to an output of a low pass filter and using its output as a carrier of a demodulation circuit. CONSTITUTION:A burst of R-Y axis is extracted by a burst gate circuit 8 and when the axis is a correct demodulation axis, the value is zero. Thus, an output of a burst gate circuit 8 is supplied to a low pass filter 9 to control the phase change in a variable phase circuit 5, then the demodulation axis is rotated and correct R-Y, B-Y axes are obtained through feedback and the feedback loop is an APC loop. In the case of special reproduction, just after a reproducing head is switched, since the period of a horizontal synchronizing signal is often disturbed, the response of the AFC 17 sufficiently slows down and since the APC loop responds to a signal even when the response of the AFC is slow, correct demodulation is applied. Then a linear APC loop is attained and the response is quickened.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color signal processing device for demodulating carrier color signals used in VTRs and the like.

Conventional technology Consumer video tape recorders (hereinafter referred to as VTR) often use a method called color under, which converts the carrier color signal to a low frequency signal when recording color signals. . In this method, a carrier for frequency conversion is generated using a phase-locked loop called APC in order to return the recorded carrier color signal to its original frequency while removing jitter during reproduction. After returning the frequency to its original value, the carrier color signal was demodulated and a color difference signal was output to facilitate various image processing. A conventional color signal processing device will be described below with reference to FIG.

FIG. 2 is a block diagram showing the configuration of a conventional color signal processing device. In FIG. 2, the reproduced low-pass conversion carrier color signal is inputted to the multiplier 10 via the input terminal 25, multiplied by the output of the bandpass filter (BPF) 11, returned to the original frequency, and then passed through the bandpass filter (BPF) 11. Filter (BPF) 40
The signal F/() is removed, and the demodulation circuit 19 demodulates the two color difference signals, the R-Y signal and the B-Y signal, and outputs them from the output terminals 26 and 27.The output of the bandpass filter 40 is a burst signal. The gate circuit 12 extracts the burst period signal, the phase comparator 13 compares the phase with the output of the reference frequency oscillator 30, and the error is filtered through the low-pass filter (L
PF) 14 to control vCO (voltage controlled oscillator). On the other hand, the horizontal synchronization signal input from the input terminal 29 is multiplied by a phase synchronization circuit called an AFC circuit 17. For example, in the case of an NTSC VH3” VTR, AFC
The output frequency of the circuit 17 is 40f'h (where fh is the horizontal synchronizing signal frequency). The phase of the output of the AFC circuit 17 is advanced or delayed by 90 degrees every IH (H is a horizontal synchronization period) by a 90 degree rotation oscillation circuit 18.

Whether it advances or lags is determined by the polarity of the head switch signal input from the input terminal 28. The head switch signal is a signal indicating the azimuth of the head of the azimuth recording VTR, and is at a high level or a low level depending on the azimuth angle. The output signal of the 90 degree rotation circuit 18 having a frequency of 40 fh that has been processed in this way is multiplied by the output of the VCO 15 in a multiplier 1G, sidebands are removed in a band pass filter 11, and the signal is sent to a multiplication circuit 10. . As a result, the carrier color signal at the output of bandpass filter 40 is synchronized with the output of reference frequency oscillator 30. Therefore, the carrier color signal obtained at the output of the bandpass filter 40 can be synchronously detected by the demodulation circuit 19 using the output of the reference frequency oscillator 30 as a carrier to obtain a color difference signal.

In the above configuration, the multiplier 10, the bandpass filter 40, the burst gate circuit 12, the phase comparator 13, the low-pass filter 14, the vCO 15, the multiplier 16,
The loop made up of the bandpass filter 11 is an APC loop.

An example of the above configuration is described in detail on pages 93 to 96 of Home Video Technology, published by Japan Broadcasting Corporation.

Problems to be Solved by the Invention However, in the conventional configuration described above, when the VTR is played back at a speed different from that during recording, which is called special playback, the playback head switches in the middle of the screen and the phase of the carrier color signal becomes discontinuous. However, there was a problem in that the APC loop was disrupted each time the head was switched, and the colors on the playback screen were disrupted until the pull-in was completed. Furthermore, if the loop gain of the APC is increased in order to speed up the pull-in time, the response becomes unstable and vibrations or oscillations occur, making it difficult to speed up the response.

FIG. 3a shows an example of a step response of a conventional APC loop. The horizontal axis represents time, and the vertical axis represents the output phase of the VCOI 5. When the response is made faster, vibrations as shown in the figure occur.

In view of the above problems, it is an object of the present invention to provide a color signal processing device with a simple APC loop circuit configuration and fast response.

Means for Solving the Problems In order to solve the above problems, the color signal processing device of the present invention includes a demodulation circuit that demodulates a carrier color signal into two color difference signals, and a demodulation circuit that multiplies a horizontal synchronization signal and synchronizes with the horizontal synchronization signal. a phase-locked circuit that generates a carrier; a burst gate circuit that extracts a burst signal from one of the two color difference signals; a low-pass filter that filters the output of the burst gate circuit; The variable phase shift circuit changes the output phase of the phase synchronization circuit and uses the output as the carrier of the demodulation circuit.

Effect: With the above configuration, the present invention can speed up the response of the APC loop without causing vibration.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIG. The low-pass conversion carrier color signal input from the input terminal 2o is sent to multipliers 2 and 3, and low-pass filters 41 and 42.9.
The signal is input to a demodulation circuit 1 composed of a 0 degree phase shift circuit 4. The input signal is multiplied by carriers having phases different by 90 degrees from each other in multipliers 2 and 3, and then passed through a low-pass filter 4.
1 and 42, the sideband is removed and the R-Y signal and B-
The Y signal is demodulated into two color difference signals. The 90 degree phase shift circuit 4 shifts the phase of the input by 90 degrees. As for the color difference signals obtained in this way, the B-Y signal is outputted to the output terminal 21 and the R-Y signal is outputted to the output terminal 22. The RY signal is also sent to the burst gate circuit 8, and a signal during the burst period is extracted, integrated by a low pass filter (LPF) 9, and input to the phase control input of the variable phase circuit 5.

On the other hand, the horizontal synchronization signal input from the input terminal 29 is
C circuit 17. The 90 degree rotation circuit 18 performs the same processing as in the conventional example. In the drawings, the same components as in the conventional example are given the same numbers.

In the case of VH8-VTR, the low frequency conversion carrier color signal input from the input terminal 20 has a frequency of 40fh, so
The AFC circuit 17 multiplies the horizontal synchronization signal by 40. The phase of the output is shifted in proportion to the output of the low-pass filter 9 by the variable phase shift circuit 5, and then input to the demodulation circuit 1 as a carrier for demodulation.

The above operation will be explained in more detail. The color subcarrier of the low-pass conversion carrier color signal is recorded in synchronization with the horizontal synchronization signal. In the case of VH3ΦVTR, it is 40fh as mentioned earlier. Therefore, in this embodiment, AI? Since the 'C circuit generates a carrier of 40 fh, the frequency is equal to that of the low frequency converted carrier color signal input from the input terminal 20. Therefore, a color difference signal can be obtained by performing a 90 degree rotation operation on this carrier and performing synchronous detection using it as a carrier. However, in this case, the phase of the demodulation axis cannot be determined because the relationship between the phase of the color subcarrier of the input low-pass converted carrier color signal and the phase of the horizontal synchronization signal is not defined. Therefore, the burst gate circuit 8 extracts the burst on the RY axis.

Since the RY axis is perpendicular to the burst, its value will be zero if it is the correct demodulation axis. Therefore, if the output of the burst gate circuit 8 is passed through the low-pass filter 9 and the phase change (2) of the variable phase shift circuit 5 is controlled, the demodulation axis is rotated and feedback is applied to obtain the correct RY and BY axes. This feedback loop is the APC loop of this embodiment. Furthermore, during special playback, the period of the horizontal synchronizing signal may be disturbed immediately after the playback head is switched, so the response of the AFC 17 may be made sufficiently slow. Even if the AFC response is slow, the APC loop responds, so correct demodulation is performed.

If we consider this kind of operation as a control system, the conventional AP
The difference from the C loop is that there is no VCO 15 in the control loop. Conventionally, VC015 was used for phase control, but in the present invention, a variable phase shift circuit 5 is used. When considered in terms of a transfer function, a VCO is an integrator, whereas a variable phase shift circuit is a proportional constant. In other words, the order in the comparison loop is one order lower than in the conventional case. Since the conventional APC had two integrating circuits, the low-pass filter 14 and the VCO 15, in the loop, the order of the loop was second order. In this embodiment, only the low-pass filter 9 is used, and the order is first-order, and its response does not oscillate in principle, so the loop gain can be increased to speed up the response. Note that the conventional bandpass filter 11
and 401 The low-pass filters 41 and 42 of this embodiment are not related to the order of the loop. An example of the step response of this embodiment is shown in FIG. The horizontal axis is time and the vertical axis is the output phase of the variable phase shift circuit, and no vibration occurs even if the loop response is made faster.

Effects of the Invention As is clear from the above description, since the present invention does not include a VCO in the APC loop, the order of the loop can be set to 1, and the response can be made faster than in the prior art.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of the embodiment of the present invention, Fig. 2 is a block diagram showing the configuration of the conventional example, and Fig. 3 is a characteristic diagram showing the response of the APC loop of the conventional example and the present invention. It is. 1... Demodulation circuit, 5... Variable phase shift circuit, 1
7... AFC circuit, 18... 90 degree low chiron circuit, 19... demodulation circuit, 30... reference frequency oscillator. Name of agent: Patent attorney Shigetaka Awano, 1 person Law 10
-) l! ! 1 Concave Cr-Φ

Claims (1)

[Scope of Claims] A demodulation circuit that demodulates a carrier color signal into two color difference signals; a phase synchronization circuit that multiplies a horizontal synchronization signal and generates a carrier synchronized with the horizontal synchronization signal; and one of the two color difference signals. a burst gate circuit for extracting a burst signal from one of the signals; a low-pass filter for filtering the output of the burst gate circuit; and a low-pass filter for changing the output phase of the phase-locked circuit in proportion to the output of the low-pass filter; A color signal processing device comprising a variable phase shift circuit that serves as a carrier for a demodulation circuit.