JPH03148986A - Chrominance signal processing circuit - Google Patents

Abstract

PURPOSE:To execute hue correction stably and extending over a wide band by demodulating a carrier chrominance signal whose phase variation component of low frequency is reduced by a closed loop phase correction system by a signal obtained by modulating the phase of a reference signal at high speed by a residual phase error component. CONSTITUTION:In a phase correction circuit 100, a closed loop is set up so that the phase of a color burst signal and the phase of the output signal of a reference signal generation circuit 6 synchronize always with each other. The comparatively low frequency component of the phase variation of the input signal of a terminal 30 is corrected by this closed loop. Next, the output signal of the phase correction circuit 100 is supplied to a chrominance signal demodulator DEM 38, and is demodulated by making the output signal of a phase modulator 37 a carrier, and color difference signals R-Y, B-Y are obtained. Further, actual variation is suppressed by the phase correction circuit 100 so as to be about + or -10 degrees. Accordingly, the dynamic range of the phase modulator 37 need not be made wide, and every stable operation is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color signal processing circuit, and more specifically, to a color signal processing circuit that can stabilize the hue after demodulation even for a carrier color signal that includes fast phase fluctuations. Regarding processing circuits.

(Prior Art) Fig. 6 is a diagram showing a conventional color signal processing circuit shown in, for example, pages 183 to 86 of NHK Home Video Technology edited by Japan Broadcasting Corporation, (1) is an input terminal for low-range color signals;
2) is a low pass filter (LPF) that removes unnecessary components other than the low range color signal, (3) is the first frequency converter that converts the low range color signal to the original frequency, and (4) is the frequency of 341 a first bandpass filter (BPF) that removes unnecessary components from the output signal of the converter (3); (5) a burst sampling circuit (Burst Sep) that extracts a color burst signal component from the first bandpass filter output signal; (li) is a reference signal generation circuit (REF OSC) that serves as a phase reference for the output of the first bandpass filter, and (a) is the output signal of the burst extraction circuit (5) and the output signal of the reference signal generation circuit (6). A phase detector (PD) that performs phase comparison of (8)
is a voltage I-controlled oscillator (hereinafter referred to as rVcOJ) controlled by the output signal of the phase detector (7), (9) the output signal of the reference signal generation circuit (6), and v c O (6).
), a second frequency converter which multiplies the output signals of (1
0) is a second bandpass filter (BPF) that removes unnecessary components from the output signal of the second frequency converter C9), (11)
is the color signal output terminal.

Next, the operation will be explained.

Low-range color signal fL that includes frequency fluctuations ±Δf caused by uneven running of the tape or uneven rotation of the rotating drum, etc.
is input to the terminal (1) and supplied to the low-pass filter (2). The low-pass filter (2) removes unnecessary frequency components other than the low-pass color signal input to the terminal (1). The output signal of the low-pass filter (2) is fed to a first frequency converter (3) and converted to the original color signal carrier frequency flAc. For example, in the NTSC system, the frequency is 3.58 MHz. Since the first frequency converter (3) generates many harmonic components in addition to the necessary color signals, the first bandpass filter (4) removes unnecessary components. The output signal of the first bandpass filter (4) is supplied to the output terminal (11) and becomes a color signal output signal, while the burst sampling circuit (
5), and only the color burst signal is extracted from the color signals. The output signal of the burst sampling circuit (5) is subjected to phase detection 11 (7) together with the output signal of the reference signal generation circuit (8) which generates the 3.58 MHz reference signal rsc.
The phase difference between the two is detected.

Next, the output signal of the phase detector (1), that is, the phase error signal, controls v c o (8), which generates the same frequency f, ±Δf as the low-frequency color signal input to the terminal (!). do. The output signal of the VCO (8) is generated by the reference signal generation circuit (
'M2 frequency converter (9) which is supplied together with the output signal of 'M2 to the second frequency converter (9) and multiplies both.
) output signals are f sc+ f L±Δf and f
Since it includes frequency components of sc-f , , ±Δf, the second bandpass filter (lO) removes f , , +
Only the components of f L±Δf are extracted. The output signal of the second bandpass filter (lO) is fed to the first frequency converter (3) as a carrier wave. tsc and f sc+2 as output signals of the first frequency converter (3)
A signal having frequency components of Cf L±Δf) is obtained, and the fo component is extracted by the first bandpass filter (4). Here, a first frequency converter (3), a first bandpass filter (4), a burst sampling circuit (5), a phase detector (7), a V CO (8), a reference signal generation circuit (6)
), the second frequency conversion circuit (9), and the second bandpass filter (10) constitute a phase-locked loop (hereinafter referred to as "rPLL circuit"), and the first bandpass filter (4
) A closed loop is constructed so that the color burst signal phase of the output signal of the reference signal generating circuit (6) is always synchronized with the phase of the output signal of the reference signal generating circuit (6).

Next, the dynamic characteristics of a general PLL circuit will be described.

Figure 7 is a block diagram of a general PLL circuit, with terminals (
A signal θS (S) (S nira plus operator) is input to 15), and is supplied to the phase detector (1). The phase detector (7) detects the phase θ of the input signal (S) and the phase θ of the output signal of the V CO (Jl), which will be described later. (S) and outputs a voltage according to the phase difference. Here, phase detection! ! The phase detector l(
Since the output signal of 7) contains many harmonic components,
In order to remove this and control the response of the system when a closed loop is formed, it is supplied to a loop filter (1B).

The output signal of the loop filter (16), where the transfer relationship of the loop filter (16) is denoted by F (s), is
control the oscillation frequency of m). The output signal of the VCO (8) is fed back to the phase detector (7) to form a closed loop. The oscillation frequency of VCO(a) is controlled according to the input voltage, but since the phase detector (7) detects the phase difference, the transfer function of VCO(8) is -. Also, if the ratio of the output frequency change to the input voltage change is 0, then V
The totally zero field transfer function of CO(8) can be expressed as □.

Next, v c O (8) output signal phase θ when the input signal phase θs (s) is changed. (s), that is, the closed-loop transfer function H(s), is as follows. Here, the transfer function F (s
), the transfer function of the commonly used active filter shown in FIG. 8 is F(s)-(Sτ, +1)/Sτ, (
Here, by substituting τ, = CR, , τ2: CR2, the closed loop transfer frequency H(s) becomes =, and if Kd (ωn: natural angular frequency, ζ: damping coefficient), then The above formula becomes.

Next, by substituting the function of S−Jω in equation (1)...
(2) becomes. If we look at the frequency response by taking the absolute value IH(jω)1 of H(jω) on the vertical axis and ω/ω on the horizontal axis, we get the characteristics shown in FIG. 9. As can be seen from the figure, the frequency characteristics vary greatly depending on the damping characteristics ζ, but the angular frequency ω is the natural angular frequency ω. 6 dB/
It is attenuated by the curve of oc t, and has a characteristic that it is difficult to respond to high frequencies. Even if the frequency characteristics were extended by increasing ζ, there would be no phase margin in the system, and the loop would become unstable.

Also, as an error rate, V for input signal phase θ, (S)
Phase θ of the output signal of CO(8). Defining the error of (S), i.e., formula (3) becomes, and further substituting the relationship s=jω into formula (4) yields.Here, the damping coefficient, which is commonly used as this value, becomes The absolute value of the error rate when 0.707 is 11-
When looking at the frequency response when H(jω)1 is plotted on the vertical axis and (ω/ωn) is plotted on the horizontal axis, the characteristics are shown in FIG. 10.

From the figure, the angular frequency ω is the natural angular frequency ω. If the error rate is approximately 1/10 of , the error rate is -40 dB, and the response is almost perfect. However, when ω becomes the same as ω, the error rate becomes approximately -3 dB, resulting in a considerable error. General household VT
Rf if, 6), Ha1800 (''/,) ω that can ensure an error rate of -30 dB or more at 8 degrees Tealz is:
Approximately 360 (''/,), frequency is approximately 60 (H,
)It turns out that.

The carrier color signal includes two color difference signals R-Y and B-Y.
It is amplitude modulated and summed by two orthogonal carrier waves cosωct and sinωct, and (R-Y)
It can be expressed as cos a) ct+ (B-Y) sin ωct. If this is expressed as a vector diagram, it will be as shown in FIG. 11(a). Further, the burst signal does not include any (RY) component, and the phase is the inverse of sinωct.

The fact that the phase of the color burst signal fluctuates with respect to the phase of the reference signal in such a state of the carrier color signal means that the amplitude of the demodulated color difference signal varies with the phase as shown in FIG. 11(b). This means that it changes in accordance with the variation θ, that is, that a hue change occurs.

As described above, when trying to make the vCO output frequency follow the input frequency using a PLL circuit, the response characteristics deteriorate and the error increases with respect to high frequency phase fluctuations, resulting in It appears as uneven hue.

[Problem to be solved by the invention]

Conventional color signal processing circuits are configured as described above, so they cannot respond to fast phase fluctuations in the input signal.As a result, the residual phase error component of the color signal causes hue unevenness on the TV screen, causing the color signal to become uneven. There was a problem in that the quality was extremely deteriorated.

The present invention was made to solve the above-mentioned problems, and it is an object of the present invention to provide a color signal processing circuit that can sufficiently respond even to fast phase fluctuations.

[Means to solve the problem]

A color signal processing circuit according to the present invention includes a reference signal generation circuit that serves as a phase reference for a color signal, a phase correction circuit that includes a closed loop that matches a color burst signal with the phase of this reference signal, and a phase correction circuit that A phase detector detects the phase difference between the color burst signal and the reference signal, a sample hold circuit detects and holds the burst potential of the output signal of the phase detector, and a sample hold circuit detects the phase difference of the reference signal. This device includes a phase modulation circuit that performs phase modulation using an output signal, and a demodulator that demodulates the output color signal of the phase correction circuit using the output signal of the phase modulator.

(Operation) The phase correction circuit according to the present invention is configured in a closed loop and corrects relatively low frequency components of the phase fluctuations of the input signal.The phase modulator modulates the phase of the reference signal and outputs it from the position correction circuit. High-speed synchronization with the phase of the output color burst signal.The demodulator demodulates the output signal of the phase correction circuit with the output signal of the phase modulator and outputs a demodulated color signal with hue fluctuations corrected up to high frequencies. do.

(Embodiment of the Invention) Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1st
The figure shows an example of application to a home VTR such as a VHS system. In the figure, the terminal (30) has f, which includes frequency fluctuations ±Δf caused by uneven running of the tape, uneven rotation of the rotating drum, and the like. Figure 2 (
The low-pass color signal shown in a) is input and supplied to the first low-pass filter (2). The first low-pass filter (2) removes unnecessary components other than the low-pass color signal. The output signal of the first low-pass filter (2) is supplied to the first frequency converter (3) and converted into a color signal having the original carrier frequency f3c. For example, in the NTSC system, the frequency is 3.58 MHz. In the first frequency converter (3).

Since many harmonic components are generated in addition to the necessary color signals,
Unnecessary components are removed by a first bandpass filter (4). The frequency spectrum of the output signal of the first bandpass filter (4) is shown in FIG. 2(b).
) output signal is passed through a comb filter (COM B) (3
1). The purpose of inserting the comb filter (31) is to eliminate crosstalk from adjacent tracks on the magnetic tape. In general, home VTRs have a recording/reproducing mode in which there are no gaps between recording tracks, or so-called guard bands, in order to increase the efficiency of magnetic tape use. For example, in the long-time mode of VHS system, the track width is 19 μm and the head width is 25 to 30 μm.
There is no guard band because recording and playback is performed using a magnetic head of about 100 kHz. Therefore, in home VTRs, the color signal carrier frequencies of adjacent tracks are interleaved with an offset of S4fn (fn: horizontal frequency). I have to. Therefore, by passing the signal through the comb filter C31), crosstalk from adjacent tracks can be efficiently removed. For color signals that do not include crosstalk from adjacent tracks, a comb filter (31) is used.
may be omitted.

Next, the output signal of the comb filter (31) is supplied to the burst sampling circuit (5) to extract only the color burst signal from among the color signals.
) is output from N1 along with the output signal of the reference signal generation circuit (6) which generates the 3.58MHz reference signal sc.
is supplied to the phase detector (1), and the phase difference between the two is detected.

Next, the output signal of the first phase detector (7), that is, the phase error signal, is passed through a loop filter (LPF) (32).
A VCO that generates the same frequency fL±Δf as the low-frequency color signal input to the terminal (30) by removing high frequency components at the terminal (30).
(II).

The output signal of v c o (a) is generated by the reference signal generation circuit (
It is supplied to the second frequency converter (9) together with the output signal of (6), and the two are multiplied. The output signal of the second frequency converter (9) is f sc + fL±Δt and fs
Since it includes the frequency components of c-fi and ±Δf, the second bandpass filter (1G) L therefore rgc+fL±Δ
Only the component of f is extracted. This second bandpass filter (
The output signal of lO) is fed as a carrier wave to the first frequency converter (3). The output signal of the first frequency converter (3) has frequency components of tsc and f, c+2 (f, ±Δf), but is filtered by the first bandpass filter (4) to
Only the sc component is extracted. Here, the first frequency converter (3), the first bandpass filter (4), the square filter (31), the burst sampling circuit (5), the first phase detector (7), and the loop 74JLI ( 32), VCO (8
), reference signal generation circuit (δ), second frequency converter (9
) and the second bandpass filter (10) to form a phase correction circuit (
100), and a closed loop is constructed so that the phase of the color burst signal of the output signal of the burst extraction circuit (5) and the phase of the output signal of the reference signal generation circuit (6) are always synchronized. Such a closed loop configuration corrects a relatively low frequency component of the phase fluctuation of the input signal of the terminal (3G).

Next, the output signal line of the burst extraction circuit (5), the second
The signal is supplied to a phase detector (PD) (33), and its phase is compared with the output signal of the reference signal generation circuit (6).

The output signal of the phase correction circuit (100) suppresses low frequency phase fluctuations, but suppresses phase fluctuations of high frequency components by suppressing the reference signal as shown in FIG. 3(a). It is fluctuating against. The second phase detector (33) detects the phase variation θ with respect to this reference signal. Since the output signal of the second phase detector (33) contains many unnecessary frequency components, it is filtered by the second low-pass filter (LPF) (
34) to remove high frequency components. As shown in FIG. 4(a), the output signal of the second low-pass filter (34) has a voltage corresponding to the phase variation at the color burst signal position at intervals of one horizontal period (IH). can get. The output signal of the second low-pass filter (34) is supplied to a sample and hold circuit (S/H) (35), which detects the potential of the color burst portion and holds that potential during IH.

FIG. 4(b) shows the output signal waveform of the sample-and-hold circuit (35). Also, since the output signal of the sample-and-hold circuit (35) also contains unnecessary high-frequency components, the third
Unnecessary components are removed by passing the signal through a low-pass filter (36). An example of the output signal waveform of the third low-pass filter (36) is shown in FIG. 4(C).

Next, the output signal of the reference signal generation circuit (6) is supplied to a phase modulator (PM) (37), and the phase of the reference signal is modulated by the output signal of the third low-pass filter (36). for example,
As shown in FIG. 3(b), when the reproduced burst phase has a phase error of θ with respect to the reference phase, the reference phase is rotated by θ by the phase modulator (37). Create a new orthogonal [J system based on the output signal of By performing such operations, the phase modulator (3
7) The relative phase fluctuation of the color burst phase with respect to the output signal phase can be removed.

Next, the output signal of the phase correction circuit (100) is supplied to a color signal demodulator (DEM) (38) and a phase modulator (38).
1) is demodulated using the output signal as a carrier, and the color difference signal R is
-Y and BY are obtained. Here, the phase modulator (3
If the output signal of step 7) is expressed in a vector diagram as a temporary reference signal, it will be as shown in FIG. 5, and the phase fluctuation θ will not affect the demodulated output.

Further, the phase of the output burst signal of the phase correction circuit (100) and the output signal phase of the reference signal generation circuit (6) are compared,
Since the process of modulating the reference signal phase according to the phase difference does not include a feedback loop, it is possible to respond quickly, and the high-frequency residual phase fluctuation component contained in the output signal of the phase correction circuit (100) is can be removed efficiently.

Furthermore, since the actual fluctuation is suppressed to about ±10 degrees by the phase correction circuit (100), the phase modulator (37
) It is not necessary to have a wide dynamic range, and very stable operation is possible.

In the above embodiment, the first phase detector (7) and the second phase detector (33) are provided separately, but either one may be used in common.

Further, in the sample and hold circuit (35), a zero-order hold circuit that holds detected potentials as they are is used, but a first-order hold circuit that connects detected potentials with a straight line may be used, and the order is not limited.

Furthermore, since the third low-pass filter (36) largely depends on the signal-to-noise ratio (S/N) of the input color signal, it can be omitted if the S/N is good.

Furthermore, in the above embodiment, the demodulated color difference signal was used as the output signal, but the demodulated color difference signal was used as the reference signal generation circuit (
The output signal of step 6) may be converted back into a carrier color signal, and there are no restrictions on the output signal format.

[Effects of the Invention] As described above, according to the present invention, a carrier color signal in which a low frequency phase fluctuation component is reduced by a closed-loop phase correction system that matches the phase of a color burst signal of a color signal with a reference signal. is configured so that the phase of the reference signal is demodulated using a signal that is modulated at high speed with the residual phase error component, so stable and broadband hue correction is possible, and the color signal can significantly reduce hue unevenness in the color signal. This has the effect of providing a processing circuit.

[Brief explanation of the drawing]

Fig. 1 is a block circuit diagram of an embodiment of the present invention, Fig. 2 is a diagram showing the frequency spectrum of the color signal in this embodiment, Fig. 3 is a diagram showing the color signal vector in this embodiment, and Fig. 4 is a diagram showing the frequency spectrum of the color signal in this embodiment. 5 is a diagram showing the signal waveform of each part of this embodiment, FIG. 5 is a diagram showing the demodulated output after hue correction in this embodiment, and FIG. 6 is a block circuit diagram of a conventional color signal processing circuit.
FIG. 7 is a block circuit diagram of the PLL in this conventional example,
FIG. 8 is a diagram showing the loop filter of this conventional PLL circuit, and FIG. 9 is a diagram showing the frequency response of this PLL circuit.
FIG. 10 is a diagram showing the error rate of the PLL circuit, and FIG. 11 is a vector diagram of phase fluctuation. (6)--Reference signal generation circuit, (33)--Phase detector, (35)--Sample and hold circuit, (37)
--- Phase modulator, (38) --- Color signal demodulator, (10
0) --- Phase correction circuit. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] (1) Regarding the color signal, this is a circuit that reproduces the color signal from a video signal in which a color signal that has been low-frequency converted to the low frequency band of an FM-modulated luminance signal is multiplexed, and is a signal that serves as a phase reference for the color signal. and a closed loop that converts the reproduced low frequency converted color signal to the original carrier frequency and simultaneously synchronizes the phase of the reproduced color signal with the phase of the reference signal. a phase correction circuit, a phase detector that detects the phase difference between the color burst signal extracted from the color signal output from this phase correction circuit and the reference signal, and a potential of the burst portion of the output signal of this phase detector. a sample-and-hold circuit that detects and holds it for one horizontal period; a phase modulator that phase-modulates the reference signal with the output signal of the sample-and-hold circuit; A color signal processing circuit comprising: a color signal demodulator that demodulates an output color signal.