JPH01236889A - Y/c separating circuit - Google Patents

Abstract

PURPOSE:To attain high resolution by allowing a comb-line filter circuit using a CCD delay element to handle a frequency component not subjected to the effect of loopback and allowing other system to handle the frequency component over the former frequency and synthesizing the frequency components. CONSTITUTION:A frequency component up to 5.5MHz in a luminance signal is fed to a base of a transistor(TR) Q1 and the frequency component in excess of 5.5MHz passing through a high pass filter 11 is fed to a base of a TR Q2. No color component is included in the frequency component in excess of 5.5MHz and is a substantially the luminance signal component. Thus, a broad band luminance signal component over a wide band in excess of 5.5MHz is outputted from a mixing circuit 9. After the phase of the luminance signal component is matched with the phase of a color signal by a delay element 12 and the result is amplified by TRs Q4, Q5 coupled in DC and a low impedance is outputted from a TR Q6 of emitter follower. Thus, the signal is reproduced up to high frequencies without being affected by the CCD delay element.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a Y/C separation circuit that is capable of extracting a luminance signal up to high frequency components.

[Conventional technology]

As a Y/C separation circuit, there is a comb filter circuit using a CCD delay element. FIG. 3 is a diagram showing an example,
When the output signal of the CCD delay element 31 which inputs the composite video signal and delays it by IH (one scanning line period) and the original signal are added by the adder 32, the Y component of the luminance signal is obtained according to the following equation. Note that C is a 3.58MHz chroma signal,
In the NTSC system, the horizontal synchronization signal frequency and 3.58MH
Since the cross carrier frequency of z has an interleaving relationship, the chroma signal signal phase for each IH is y+c.

It is reversed like Y-C.

Y=%((Y+C)+(Y-C))...(
1) Furthermore, when the subtracter 33 takes the difference, the color signal C component is obtained according to the following equation.

C=%-((Y+C) (Y-C))...
- (2) This CCD delay element has a much wider transmission band (~5 MHz) than the transmission band of a glass delay line (3 to 4 MHz for NTSC) and has good phase characteristics.

Furthermore, since transmission is possible from direct current, it is also possible to extract low-frequency line-to-line difference components, making it possible to perform vertical contour correction.

[Problem to be solved by the invention]

・However, when this CCD delay element receives a signal containing a frequency component higher than A of the clock frequency that drives it, the high-frequency components are folded back to the low-frequency side. There is a phenomenon in which the signal is converted into a low-frequency component.

For example, 10.7 MHz, which is three times the frequency of the color subcarrier, is normally used as the clock, but in this case, if a composite video signal component of 6 MHz is added,
．． It is converted into a beat component of 7-6 = 4.7 Mllz. Therefore, the frequency that can be handled is limited to about 5 MHz, for example, and the horizontal resolution in this case is about 400 lines if the scanning line equivalent is 80 lines per IM), and a higher resolution cannot be obtained.

The present invention has been made in view of these points, and its purpose is to make it possible to reproduce high frequencies without being influenced by CCD delay elements, thereby achieving high resolution.

[Means to solve the problem]

To this end, the present invention provides a comb filter circuit that inputs a composite video signal using a CCD delay element and extracts a luminance signal component, a low-pass filter connected to the input side of the comb filter circuit, and a low-pass filter that inputs the composite video signal. and a mixing circuit that mixes the luminance signal from the comb filter and the signal from the high-pass filter.

〔Example〕

Examples of the present invention will be described below. FIG. 1 is a diagram showing a Y/C separation circuit for extracting a luminance signal in one embodiment. A composite video signal having a positive polarity of a synchronizing signal is applied to the input terminal 1, and a high frequency component is cut off by a low pass filter 3 having a cutoff frequency of 5.5 Mllz via an amplifier 2. Then, a part of it is subjected to an IH delay through an inverting amplifier 4 and an IH delay circuit 5 made of a CCD delay element.

The driving clock for this IH delay circuit 4 is 10.7 MHz. Then, the clock signal of the delayed signal is removed by a low-pass filter 6 having a cutoff frequency of 4.2 MHz, and after being inverted by an inverting amplifier 7, the signal is input to an adder 8. The frequency components from the low-pass filter 3 are applied to this adder 8, and by being added here,
A luminance signal component is obtained from the above equation (1). The circuit from the output side of the low-pass filter 3 to the adder 8 constitutes a comb filter circuit.

The luminance signal component obtained from the adder 8 has 5.5
Frequency components above MHz are not included. Therefore, regarding this luminance signal component, the IH formed by the CCD delay element
It is not affected by the aliasing phenomenon in the delay circuit 4.

The luminance signal component from this adder 8 is applied to the base of one transistor Ql of the mixing circuit 9 via a DC cut capacitor C1. Furthermore, at this time,
A clamp circuit 10 including resistors R1 and R2, a capacitor C2, and a diode D1 clamps the leading value of the synchronizing signal to a predetermined level.

A part of the composite video signal applied to the input side 1 is as follows:
A high-pass filter 1 with a cutoff frequency of 5.5 MHz that is amplified by a transistor Q3 for level adjustment.
1 to the base of transistor Q2, and is mixed at the collectors of transistor Q2 and transistor Ql and output. The delay time of this high-pass filter 11 is set to be the same as the delay time of the low-pass filter 3, for example, 0.28 μs.

As mentioned above, the frequency component of the luminance signal up to 5.5 Mllz is applied to the base of the transistor Q1, and the frequency component exceeding 5.5 Mllz that has passed through the high-pass filter 11 is applied to the base of the transistor Q2. . This frequency component exceeding 5.5 MHz does not include a color component and is essentially a luminance signal component.

Therefore, the mixing circuit 9 outputs a broadband luminance signal component exceeding 5.5 MHz.

Therefore, it is possible to obtain a luminance signal up to a frequency component of about 7.5 MHz, for example. In this case, the horizontal resolution is 600 in terms of scanning lines.

After this luminance signal component is phase-matched with the color signal by the delay element 12, the transistors Q4 and Q5 directly connected to DC
The signal is amplified by the emitter follower transistor Q6 and output at low impedance.

FIG. 2 is a diagram showing the frequency characteristics of the above-mentioned low-pass filter 3 and high-pass filter 11, and both characteristic curves are
They cross at a level of dB and have a frequency of 5.5 MHz. and 5 Mllz at a level of -10 dB,
6 Mllz. It is preferable that the characteristics of both filters be complementary (symmetrical) between 5 and 6 M) Iz.

It is also desirable that the delay characteristics within the passband be constant.

〔Effect of the invention〕

As described above, according to the present invention, a comb filter circuit using a CCD delay element handles frequency components that are not affected by aliasing, and higher frequency components are processed in a separate system to synthesize frequency components. This makes it possible to separate and extract luminance signals in a wide range from low to high frequencies, and achieve high resolution.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a Y/C separation circuit according to an embodiment of the present invention,
FIG. 2 is a characteristic diagram of a low-pass filter and a high-pass filter, and FIG. 3 is a circuit diagram of a conventional Y/C separation circuit. Agent Patent Attorney Tsuneaki Nagao Figure 2 5. ”A I4.1 5.0 6.0 7.5
(MB2) 5.5 Figure 3

Claims (4)

[Claims] (1) a comb filter circuit that inputs a composite video signal using a CCD delay element and extracts a luminance signal component; a low-pass filter connected to the input side of the comb filter circuit;
A Y/C separation circuit comprising: a high-pass filter that inputs the composite video signal; and a mixing circuit that mixes a luminance signal from the comb filter and a signal from the high-pass filter. (2) The Y/C separation circuit according to claim 1, wherein the cutoff frequencies of the low-pass filter and the high-pass filter are substantially the same. (3) The Y/C separation circuit according to claim 1 or 2, wherein the low-pass filter and the high-pass filter have the same delay characteristics. (4) Claim 1, characterized in that a DC-coupled luminance signal delay circuit is connected to the output side of the mixing circuit.
Y/C separation circuit according to items 3 to 3.