JPH0666955B2 - Y / C separation circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a Y / C separation circuit capable of extracting a luminance signal up to a high frequency component.

[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 thereof, in which a composite video signal is input and delayed by 1H (one scanning line period).
When the output signal of the CCD delay element 31 and the original signal are added by the adder 32, the luminance signal Y component is obtained by the following equation. Note that C is a 3.58 MHz chroma signal, and in the NTSC system, the horizontal sync signal frequency and the 3.58 MHz cross carrier frequency have an interleaving relationship, so the chroma signal signal phase is Y + C, Y-C every 1H. And so on.

Y = 1/2 [(Y + C) + (Y-C)] (1) When the subtracter 33 takes the difference, the color signal C component is obtained by the following equation.

C = 1/2 [(Y + C)-(Y-C)] (2) This CCD delay element is much wider (~ 4MHz for NTSC) (~ 4MHz for NTSC). 5MHz) and good phase characteristics. Further, since almost direct current can be transmitted, it is possible to extract a low-frequency line difference component, so that vertical contour correction can be performed.

[Problems to be Solved by the Invention]

However, in this CCD delay element, when a signal including a frequency component of ½ or more of the clock frequency for driving the CCD delay element is added, the high frequency component is folded back to the low frequency side, that is, the high frequency component is the signal and the clock. There is a phenomenon that it is converted to the low frequency component of the beat.

For example, 10.7 MHz, which is three times the frequency of the color subcarrier, is usually used as the clock, but in this case, for example, if a composite video signal component of 6 MHz is added, 10.7-6 = 4.7M.
It is converted to the beat component of Hz. Therefore, the maximum frequency that can be handled is about 5 MHz, and the horizontal resolution in this case is
It is about the same level, and it is impossible to obtain higher resolution.

The present invention has been made in view of such a point, and an object thereof is to realize high resolution by enabling reproduction up to a high frequency without being affected by a CCD delay element.

[Means for Solving the Problems]

To this end, the present invention inputs a composite video signal, allows a color subcarrier to pass therethrough, and has a first low-pass filter having a cutoff frequency of 3/2 or less of the color subcarrier and a frequency three times that of the color subcarrier. A CCD delay element driven by the clock, a second low-pass filter connected in series to the output side of the CCD delay element, which passes the color subcarrier but removes the clock component, A comb filter circuit connected in a subsequent stage, a high-pass filter having the same cut-off frequency and delay characteristics as the first low-pass filter that receives the composite video signal, and the low-frequency luminance signal component obtained from the comb filter circuit. And a mixing circuit for mixing the high-frequency luminance signal component obtained 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 of the embodiment. A composite video signal having a positive sync signal is applied to the input terminal 1, and the cutoff frequency is passed through the amplifier 2.
The low-pass filter 3 of 5.5MHz cuts high frequency components. Then, a part thereof is delayed by 1H by the 1H delay circuit 5 composed of a CCD delay element via the inverting amplifier 4. This 1H
The drive clock of the delay circuit 4 is 10.7 MHz. And
The delayed signal is input to the adder 8 after the clock is removed by the low-pass filter 6 having a cutoff frequency of 4.2 MHz and inverted by the inverting amplifier 7. The frequency component from the low pass filter 3 is applied to the adder 8,
The addition is performed here to obtain the luminance signal component from the equation (1). The above 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 does not include a frequency component of 5.5 MHz or higher. Therefore, the luminance signal component is not affected by the folding phenomenon in the 1H delay circuit (5) including the CCD delay element.

Then, the luminance signal component from the adder 8 is applied to the base of one transistor Q1 of the mixing circuit 9 via the DC cut capacitor C1. At this time, the resistance
The leading value of the synchronization signal is clamped to a predetermined level by the clamp circuit 10 including R1, R2, the capacitor C2, and the diode D1.

A part of the composite video signal applied to the input terminal 1 is
Through the high-pass filter 11 whose cutoff frequency is 5.5 MHz, which is amplified by the transistor Q3 for level adjustment,
Applied to the base of transistor Q2, this transistor Q2
And are mixed in the collector of the transistor Q1 and output. The delay time of the high-pass filter 11 is the same as the delay time of the low-pass filter 3, for example, 0.28 μs.
Is set to.

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

Therefore, the wide band luminance signal component exceeding 5.5 MHz is output from the mixing circuit 9. So, for example, 7.
It is possible to obtain a luminance signal up to a frequency component of about 5 MHz. In this case, the horizontal resolution is 600 lines in terms of scanning lines.

The luminance signal component is phase-combined with the color signal by the delay element 12, amplified by the direct-current-coupled transistors Q4 and Q5, and output from the emitter follower transistor Q6 with low impedance.

FIG. 2 is a diagram showing frequency characteristics of the low-pass filter 3 and the high-pass filter 11 described above, and both characteristic curves are −3 dB.
Cross at the level of and its frequency is 5.5MHz. And it is 5MHz and 6MHz at the level of -10dB. This 5-6MHz
It is preferable that the characteristics of both filters are complementary (symmetrical) during the period. Further, it is desirable that the delay characteristic within the pass band is also constant.

〔The invention's effect〕

As described above, according to the present invention, in the comb filter circuit using the CCD delay element, the frequency components that are not affected by the folding phenomenon are handled, and the frequency components higher than that are processed by another system to synthesize the frequency components. By doing so, it is possible to separate and extract luminance signals in a wide range from the low range to the high range, and it is possible to realize high resolution.

[Brief description of drawings]

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.

Claims (1)

[Claims] 1. A first low-pass filter having a cut-off frequency of 3/2 or less of the color sub-carrier and a color sub-carrier of which a composite video signal is input, and a cut-off frequency of 3 times the frequency of the color sub-carrier. A CCD delay element driven by a clock, having a second low-pass filter connected in series to the output side of the CCD delay element and allowing the color subcarrier to pass but removing the clock component, and the latter stage of the first low-pass filter. A high-pass filter having the same cut-off frequency and delay characteristics as the first low-pass filter, the low-pass luminance signal component obtained from the comb filter circuit, And a mixing circuit for mixing with a high-frequency luminance signal component obtained from the high-pass filter. / C separation circuit.