JPH06225314A - Signal processing circuit for color ccd imaging device - Google Patents

Abstract

PURPOSE: To provide a signal processing circuit for a color CCD image pickup element which has simple constitution and can have characteristics improved. CONSTITUTION: This circuit is equipped with a Y/C signal separating circuit 2 which separates a luminance signal Y and a color difference signal C from a CCD signal by using sample holding circuits. In this signal processing circuit, a single sampling circuit 3 consisting of a sample holding circuit S/H6 which samples the CCD signal and a differential amplifier DA1 which amplifies and outputs the difference between the output signal of the sample holding circuit S/H6 and the CCD signal is installed in front of the Y/C signal separating circuit 2. Consequently, the constitution can be simplified and the initial stage for signal processing which is easily affected by noise is simplified to reduce thermal noise, 1/f noise, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit for a color CCD image pickup device, and more particularly to a signal processing circuit having a simple structure and capable of improving characteristics.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram of an example of a conventional signal processing circuit for a color CCD image pickup device. The circuit of FIG. 3 is roughly divided into correlated double sampling (Correlated Doubl
e Sampling (hereinafter referred to as CDS) circuit 1 and Y / C (luminance / color difference signal) separation circuit 2. And CDS
The circuit 1 includes sample and hold circuits S / H1 and S / H3 for sampling the CCD signal according to each sampling pulse, and a sample and hold circuit S for sampling the output signal of the sample and hold circuit S / H1 according to the sampling pulse. / H2 and the differential amplifier DA1 that outputs the signals obtained by amplifying the signal difference between the sample-hold circuits S / H2 and S / H3 as two input signals. In addition, the Y / C separation circuit 2
Sample-and-hold circuits S / H4 and S / H5 for sampling the output signal of the differential amplifier DA1 of the CDS circuit 1 according to each sampling pulse, and the output signal of the sample-and-hold circuit S / H4 and the sample-and-hold circuit S. / H5 output signal is added to output a luminance signal Y, and the sample hold circuit S
/ H4 and S / H5 output signals are two input signals, and a differential amplifier DA2 that outputs a signal obtained by amplifying the signal difference
And a low-pass filter LPF that outputs the color difference signal C by passing the output signal of the differential amplifier DA2 in the low-pass range.

The operation of the conventional signal processing circuit for the color CCD image pickup device having such a configuration will be described with reference to the timing chart shown in FIG. It should be noted that A to I in FIG. 4 show signal waveforms at the same reference numerals in FIG. In FIG.
A is a signal from the CCD image pickup device. This signal A is
As shown in the figure, after the reset, the reference voltage of T1 changes arbitrarily due to the reset noise. Therefore, in the CDS circuit 1, the three sample hold circuits S / H1 to
After double sampling the CCD signal using S / H3, the differential amplifier DA1 finds the voltage difference between T1 and T2 of the sampled CCD signal,
It is configured to output a signal from which reset noise has been removed.

The details will be described below. First, the CCD signal shown in A of FIG. 4 has sample / hold circuits S / H1 and S /
H3 and H3 respectively. Sample hold circuit S / H
3 samples the CCD signal by using the signal shown in C of FIG. 4 as a sampling pulse, and outputs the sampled signal as shown in F of FIG. On the other hand, the sample hold circuit S / H1 samples the CCD signal using the signal shown in B of FIG.
The sampled signal as shown in is output. The output signal D is sampled again by the sample hold circuit S / H2 using the signal shown in C of FIG. 4 as a sampling pulse, and is output as a sampled signal as shown in E of FIG. The output signals of the sample and hold circuits S / H2 and S / H3 are differential amplifiers DA.
1 is applied to each of the inverting input terminal and the non-inverting input terminal. The differential amplifier DA1 amplifies the difference between the output signals of the sample and hold circuits S / H2 and S / H3, and outputs a signal as indicated by G in FIG. C performing the above operation
As shown in FIG. 5, the output signal G of the DS circuit 1 indicates a color difference signal corresponding to the filter of the color CCD image pickup device.

Next, the operation of the Y / C separation circuit 2 which receives the output signal of the CDS circuit 1 and separates the luminance signal Y and the color difference signal C is described with reference to the filter of the color CCD image pickup device shown in FIG. And explain. As shown in FIG. 5, when the CCD signal is scanned by using the field integration mode in the (n + 1) th line of the even field, the output signal of the CDS circuit 1 is (G + Cy) _n-1 , (Mg + Ye). ) _n , (G + Cy) _{n + 1} ,
(Mg + Ye) _{n + 2} .... Here, Cy indicates cyan (blue green: complementary color of red), G indicates green (green), Mg indicates magenta (red purple: complementary color of green), and Ye indicates yellow (yellow). The output of the differential amplifier DA1 of the CDS circuit 1 is the sample / hold circuit S / in the Y / C separation circuit 2.
They are applied to H4 and S / H5, respectively, and are alternately sampled by the sampling pulses shown by H and I in FIG. The output signals of the sample hold circuits S / H4 and S / H5 sampled in this way are added by the adder AD.
Applied to D. Then, the adder ADD adds the two input signals and adds (G + Cy) _n-1 + (Mg + Ye) _n , (Mg +
Ye) _n + (G + Cy) _{n + 1} ... The luminance signal Y is (1/2) (G + Cy + Mg + Ye)
Therefore, the output of the adder ADD eventually becomes the luminance signal Y. Similarly, sample hold circuits S / H4 and S / H
The output signal of 5 is also applied to the inverting input terminal (− terminal) and the non-inverting input terminal (+ terminal) of the differential amplifier DA2. Therefore, the output of the differential amplifier DA2 is-(G + C
y) _n-1 + (Mg + Ye) _n , (Mg + Ye) _n- (G + Cy) _{n + 1} ,
The order is − (G + Cy) _{n + 1} + (Mg + Ye) _{n + 2} . At this time, since there is a relation of RY = (Mg + Ye) _n- (G + Cy), the output of the differential amplifier DA2 is RY, R-.
The order is Y, RY, and this signal is passed through the low-pass filter L.
The signal passed through the PF becomes the color difference signal. In addition, R shows red here. The next horizontal scan line, n
When scanning the CCD signal as the + 2nd line, as shown in FIG. 5, the adder AD of the Y / C separation circuit 2 is used.
The output of D becomes (Mg + Cy) + (G + Ye), and the output of the differential amplifier DA2 becomes-(Mg + Cy) + (G + Ye). Therefore, 2Y is obtained as the luminance signal Y, and-(RY) is obtained as the color difference signal C.

[0006]

However, such a conventional signal processing circuit for a color CCD image pickup device has the following problems.
The CDS circuit 1 is composed of three sample and hold circuits, and these use two kinds of sampling pulses with different timings, which makes the structure complicated and is susceptible to noise. Also, since the two sample and hold circuits are used again in the Y / C signal separation,
If the output signal of the CDS circuit 1 and the sampling pulse are slightly out of phase, there is a problem that the video signal becomes bad.

The present invention has been made in order to solve the above problems of the prior art, and provides a signal processing circuit for a color CCD image pickup device, which has a simple structure and can improve the characteristics. The purpose is to provide.

[0008]

In order to achieve the above object, the present invention is constructed as described in the claims. That is, the present invention provides a signal processing circuit for a color CCD image pickup device, which includes a Y / C signal separation circuit 2 for separating a luminance signal Y and a color difference signal C from a CCD signal by using a plurality of sample hold circuits. A sample hold circuit S / H6 for sampling a signal,
The output signal of the sample and hold circuit S / H6 and the C
A single sampling circuit 3 including a differential amplifier DA1 that amplifies and outputs a difference between CD signals is installed in the preceding stage of the Y / C signal separation circuit 2.

[0009]

The sample-hold circuit S / H6 samples the reference voltage (voltage at reset) of the CCD signal.
Then, the difference between the sampled value and the input CCD signal is obtained by the differential amplifier DA1. Therefore, even if the reference voltage fluctuates according to the reset noise, the influence of the fluctuation can be removed. As described above, in the present invention, instead of the conventional complicated CDS circuit 1, it is sufficient to use the single sampling circuit 3 including one sample and hold circuit S / H6 and one differential amplifier DA1, and therefore the configuration is It can be greatly simplified. Also, 1
Since the CCD signal can be sampled by using one sample hold circuit S / H6 and one sampling pulse, the system can be greatly simplified, and the first stage of signal processing where noise easily flows is simplified and thermal noise (Therma
l noise) and 1 / f noise etc. can be reduced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram of an embodiment of a signal processing circuit for a color CCD image pickup device according to the present invention. The same parts as those in FIG. 3 are designated by the same reference numerals. As shown in FIG. 1, the signal processing circuit of the present invention is
A single sampling circuit 3 is used instead of the conventional CDS circuit 1, and a portion of a Y / C separation circuit 2 that separates a luminance signal Y and a color difference signal C using an output signal of the single sampling circuit 3 is It is the same as the conventional one. The single sampling circuit 3 includes a sample hold circuit S / H6 for sampling a CCD signal,
Output signal of the sample and hold circuit S / H6 and CCD
And a differential amplifier DA1 that outputs a signal obtained by amplifying the difference between the signals and the non-inverted input signal and the inverted input signal. Further, the Y / C separation circuit 2 includes sample hold circuits S / H4 and S / H5 for sampling the output signal of the single sampling circuit 3 according to different sampling pulses as in the conventional case, and the sample hold circuit. An adder ADD that adds the output signals of S / H4 and S / H5 and outputs a luminance signal Y, an output signal of the sample hold circuit S / H4, and an output signal of the sample hold circuit S / H5 are inverted and non-inverted. A differential amplifier DA2 that outputs a signal obtained by amplifying the difference as an inverting input signal, and a low-pass filter LP that low-passes the output signal of the differential amplifier DA2 and outputs a color difference signal C
It is composed of F and.

The operation of the signal processing circuit shown in FIG. 1 will be described below with reference to the timing chart of FIG. In addition, A of FIG.
1 to F show signal waveforms at the same reference numerals in FIG. As shown in FIG. 1, the CCD signal is a differential amplifier DA.
It is applied to the inverting input terminal (-terminal) of No. 1 and to the sample hold circuit S / H6. The output of the sample hold circuit S / H6 is applied to the non-inverting input terminal (+ terminal) of the differential amplifier DA1. The sample-hold circuit S / H6 is at the T1 position of the CCD signal, and when a sampling pulse as shown in B of FIG. 2 is applied, C of FIG.
Clamp the reference voltage as shown in. The clamped value C changes according to the fluctuation of the reference voltage in A of FIG. This value C is applied to the non-inverting input terminal of the differential amplifier DA1, and this value and C applied to the inverting input terminal.
The difference signal (D in FIG. 2) from the CD signal is the differential amplifier DA1.
Is output from. This signal, as shown at D in FIG.
The CCD signal is obtained by removing the reset noise. The output signal of the differential amplifier DA1 of the single sampling circuit 3 is the sample / hold circuit S of the Y / C signal separation circuit 2.
/ H4 and S / H5. Then, the sample hold circuits S / H4 and S / H5 alternately sample the video signal portion of the CCD signal in accordance with the respective sampling pulses shown in E and F of FIG. The signals sampled through the respective sample hold circuits S / H4 and S / H5 are added by the adder A of the Y / C separation circuit 2.
The signals are added via DD, output as a luminance signal Y, and applied to the inverting terminal and the non-inverting terminal of the differential amplifier DA2 to output a signal amplified by the difference between the two signals. This signal is low-passed through the low-pass filter LPF and output as a color difference signal C. Note that Y /
The detailed description of the operation of separating the luminance signal Y and the color signal C through the C separation circuit 2 is the same as that of FIG.

[0012]

As described above, according to the present invention, the circuit connected to the preceding stage of the Y / C separation circuit 2 is
Since one sample hold circuit and one sampling pulse are used to sample the CCD signal, the configuration can be greatly simplified and the first stage of signal processing where noise easily flows is simplified. The effect is that thermal noise and 1 / f noise can be reduced. Further, since the number of sampling pulses is small as described above, when the present invention is applied to a CCD image pickup device for a high image quality TV camera that samples at a higher frequency than existing CCD image pickup devices, there are many types of sampling pulses. It is possible to obtain an effect that it is possible to prevent an interference phenomenon and a phase shift due to the above.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a signal processing circuit for a color CCD image sensor according to the present invention.

FIG. 2 is a timing chart for explaining the operation of the signal processing circuit shown in FIG.

FIG. 3 is a block diagram of an example of a conventional signal processing circuit for a color CCD image pickup device.

FIG. 4 is a timing chart for explaining the operation of the signal processing circuit shown in FIG.

FIG. 5 is a diagram showing a configuration of a filter of a color CCD image pickup device.

[Explanation of symbols]

 1 ... Correlated double sampling (CDS) circuit 2 ... Luminance / color difference signal (Y / C) separation circuit 3 ... Single sampling circuit S / H1 to S / H6 ... Sample and hold circuit DA1 to DA2 ... Differential amplifier ADD ... Adder LPF ... Low pass filter

Claims (1)

[Claims] 1. A CC using a plurality of sample and hold circuits.
Y / C for separating the luminance signal Y and the color difference signal C from the D signal
In a signal processing circuit for a color CCD image pickup device having a signal separation circuit 2, a sample hold circuit S for sampling a CCD signal
/ H6, and a single sampling circuit 3 including a differential amplifier DA1 that amplifies and outputs the difference between the output signal of the sample and hold circuit S / H6 and the CCD signal, in the preceding stage of the Y / C signal separation circuit 2. A signal processing circuit for a color CCD image pickup device, which is installed.