JPH04282992A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To realize the video signal processing circuit whose hue is unchanged even when the gain of an AGC circuit is changed. CONSTITUTION:Sample-and-hold circuits 2, 3 of a color signal system are provided to a pre-stage of a luminance signal system AGC circuit 5 and sample and hold directly an output of a CDS(correlation dual sampling) circuit 1 to separate color information. Moreover, color signal system AGC circuits 6, 7 receiving respectively the output of the sample-and-hold circuits 2, 3 are provided to the processing circuit. Through the constitution above, AGC is applied separately in each of the luminance system and the color information.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing circuit, and more particularly to a color separation circuit for an image sensor.

0002

2. Description of the Related Art A conventional video signal processing circuit has a configuration shown in FIG. In FIG. 2, the output of the CDS (correlated double sampling) circuit 1 is an AGC common to the luminance system and the color system.
A luminance signal processing section that receives the output of the AGC circuit 15 and samples the output of the same AGC circuit 15 at different timings supplied from the outside, and separates different color information. The color signal processing section includes sample and hold circuits 2 and 3 of the system, and a color separation circuit 4 that performs arithmetic processing using the outputs of the sample and hold circuits 2 and 3 as input.

Currently, complementary color filter type CCDs widely used in video cameras and the like use Mg (magenta), Cy
(cyan), Ye (yellow), and G (green) filters are arranged in one horizontal period (1 horizontal period) corresponding to a scanning line.
In H), two types of color information are output alternately at every other pixel period. For example, the two types of color information are (Mg+Ye)
and (Cy+G).

[0004] In this example, the color information that is alternately output at every other pixel is sampled at the output of the AGC circuit by two sample and hold circuits at every other pixel at timings shifted by one pixel from each other. , two consecutive color information signals, e.g. (Mg+Ye), (Cy+G)
It is separated into

The color separation circuit appropriately calculates the two separated color information signals to obtain a color signal. An example of the calculation is shown below.

[0006]

【number】

[2×(Mg+Ye)-(Cy+G)]÷4≒RAGC
Regarding luminance signal processing after color separation and color signal processing after color separation,
Since it has little relevance to the present invention, a description thereof will be omitted.

[0007]

SUMMARY OF THE INVENTION In the conventional video signal processing circuit described above, the AGC circuit output is sampled and held in order to obtain color information necessary for color signal calculation.

However, if the AGC circuit does not have a sufficiently wide band, especially when the gain increases and the frequency characteristics deteriorate, the output of the AGC circuit will have a large phase lag (the phase lag) as well as a change in the waveform due to the loss of high frequency components. Figure 3g)
, the output obtained by sampling and holding this at a fixed timing will have a large error (Fig. 3h). In other words,
A problem arises in that when the AGC gain changes, even the hue changes.

[0009] Regarding AGC circuits, it is technically difficult to further widen the band while satisfying the market requirements of high S/N, low power consumption, and large gain change range (several dB to 30 dB or more). There is also.

The present invention has been made in view of the above-mentioned conventional circumstances, and therefore, an object of the present invention is to provide a novel video signal processing circuit capable of solving the above-mentioned problems inherent in the conventional technology. It's about doing.

[0011]

[Means for Solving the Problems] In order to achieve the above object, a video signal processing circuit according to the present invention includes a circuit that performs correlated double sampling (CDS) on the output of a CCD image sensor, and a circuit that performs correlated double sampling (CDS) on the output of a CCD image sensor. A luminance signal processing unit including an AGC circuit as an input, a plurality of sample and hold circuits that sample the output of the CDS circuit according to timing supplied from the outside and separate color information, and input each of the outputs of the sample and hold circuits. and a color signal processing section including a plurality of AGC circuits, and a color separation circuit that performs arithmetic processing with the outputs of the plurality of AGC circuits as input, and the luminance signal processing section and the color signal processing section. multiple AGs
The C circuits are controlled by a common gain control signal.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a preferred embodiment of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

Referring to FIG. 1, one embodiment of the present invention includes:
The output of the CCD image sensor is subjected to correlated double sampling (CDS).
), a luminance signal processing unit including an AGC circuit 5 that receives the output of the CDS circuit 1 as input, and two systems that sample the output of the CDS circuit 1 according to the timing supplied from the outside and separate color information. sample-and-hold circuits 2 and 3, two AGC circuits 6 and 7 that receive the outputs of these sample-and-hold circuits 2 and 3 as inputs, and perform arithmetic processing using the outputs of these two AGC circuits 6 and 7 as inputs. A total of three AGC circuits, one for the luminance system and two for the color system, are controlled by a common gain control signal.

The difference from the conventional operation is that the color sample and hold circuits 2 and 3 are located before the AGC circuit 5, and the CD
The output of the S circuit 1 is directly sampled and held, color information is separated, and then AGC is applied separately to the luminance system and the two color information systems.

The other operations are the same as those of the conventional example and will therefore be omitted.

FIG. 3 is a timing chart showing the operation of the present invention in comparison with a conventional example.

[0018]

[Effects of the Invention] As explained above, according to the present invention,
A color sample and hold circuit is placed in front of the AGC circuit to separate color information before waveform and phase deterioration occurs, so the hue does not change even if the gain of the AGC circuit changes. Effects can be obtained.

Furthermore, since the AGC circuit requires a narrower band than the conventional configuration (about 20 MHz in the conventional case, about 10 MHz in the case of the present invention), the circuit design is relatively simple.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional example.

FIG. 3 is a signal waveform diagram at each part in the block diagrams of FIGS. 1 and 2;

[Explanation of symbols]

1...CDS (correlated double sampling) circuit 2...Sample hold circuit 3...Sample hold circuit 4...Color separation circuit 5...AGC circuit 6...AGC circuit 7...AGC circuit 15...AGC circuit

Claims (1)

[Claims] 1. A video signal processing circuit that extracts a color signal from the output of an image sensor having a color filter by sample-holding using a plurality of sampling pulses at different timings, comprising: a plurality of sample-and-hold circuits that receive the output of the image sensor as input; , and a plurality of AGC circuits whose inputs are respective outputs of the sample and hold circuits.