JP2007295109A - Video camera and imaging signal processing circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To take countermeasures against thermal noise when processing an image signal in a video camera. <P>SOLUTION: Provided are first and second sample-and-hold sections 20G<SB>1</SB>, 20G<SB>2</SB>for sampling and holding the image signal obtained by the output of an image pickup device 10G. The first and second sample-and-hold sections 20G<SB>1</SB>, 20G<SB>2</SB>perform sampling at the same timing, mix both the hold output for amplification by an amplifier 13G, and perform image processing. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a video camera and an imaging signal processing circuit included in the video camera.

  The video camera performs imaging using an imaging device configured as a CCD (Charge Coupled Devices) type imager, an imaging device configured as a MOS (Metal Oxide Semiconductor) type imager, or the like. The output of the image pickup device is supplied to the image pickup signal processing circuit, sampled in synchronization with the image pickup output of one pixel unit, the sampled signal is held and output, and the hold signal is a luminance value for each pixel. It is the structure taken out as a baseband signal.

  The image pickup signal output from the image pickup device has a very low signal level, and it is necessary to amplify the signal before sampling, amplify the held signal, and the like.

Patent Document 1 describes a configuration of a circuit system of an imaging signal of a conventional video camera.
JP-A-6-339080

  As described above, since the image signal output from the image sensor has a very low signal level, it needs to be amplified by an amplifier before and after sampling the image signal, but a circuit block including the amplifier is generated. There is a non-negligible amount of thermal noise relative to the thermal noise present at the output of the image sensor. Therefore, this is a cause of deteriorating the S / N ratio of the imaging signal.

  Patent Document 1 describes a process for reducing thermal noise of an image sensor when a CCD imager is used as the image sensor. However, in order to perform better imaging, it is necessary to take measures not only for the imaging element but also for the thermal noise of the imaging signal processing system such as an amplifier, but the thermal noise in the imaging signal processing system of the video camera is It was not enough.

  The present invention has been made in view of such a point, and an object thereof is to take measures against thermal noise when processing an imaging signal.

  The present invention is configured to include a first sample-and-hold unit and a second sample-and-hold unit as a sample-and-hold unit that samples and holds an imaging signal output from the imaging device. The first sample and hold unit and the second sample and hold unit sample at the same timing, and both hold outputs are mixed and amplified for video processing.

  By doing in this way, an imaging signal is sampled in parallel by two systems of circuits, the two sampled imaging signals are mixed and amplified, and video processing is performed as one system of imaging signals.

  According to the present invention, by mixing and amplifying imaging signals sampled in parallel by two circuits, the influence of thermal noise in the parallel processed circuit can be reduced and obtained by imaging with a video camera. It is possible to improve the image quality of the video signal. If the noise reduction amount is shifted in the direction of higher sensitivity, a wide dynamic range and higher sensitivity can be achieved with the same S / N.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a diagram showing a configuration example of an imaging signal processing system of the video camera of this example. The video camera of this example includes three CCD imagers 11R, 11G, and 11B for each of the primary color signals of red (R), green (G), and blue (B) as an image sensor, and each CCD imager 11R, 11G and 11B have a component configuration for processing each primary color signal individually.

Outputs of imaging signals from the CCD imagers 11R, 11G, and 11B of the respective colors are supplied to the first stage amplifiers 12R, 12G ₁ , 12G ₂ , and 12B, respectively, and are amplified. In this case, only the green image pickup signal is supplied to the _two first stage amplifiers 12G ₁ and 12G ₂ for amplification, and the other two color image pickup signals are supplied to the respective first stage amplifiers 12R and 12B. Amplify. The two first-stage amplifiers 12G ₁ and 12G ₂ that amplify the green imaging signal are amplifiers having the same characteristics.

The amplified outputs of the respective first stage amplifiers 12R, 12G ₁ , 12G ₂ , 12B are supplied to the respective CDS circuits 20R, 20G ₁ , 20G ₂ , 20B and sampled. The CDS circuit is a circuit referred to as a correlated double sampling circuit, and performs a process of sampling an imaging signal in units of one pixel to obtain a baseband imaging signal. The configuration of each CDS circuit 20R, 20G ₁ , 20G ₂ , 20B and the sampling principle will be described later.

Baseband imaging signals output by sampling in units of one pixel at each CDS circuit 20R, 20G ₁ , 20G ₂ , 20B are supplied to the video amplifiers 13R, 13G, 13B for each color and amplified. The green imaging signal is sampled and output by the _two CDS circuits 20G ₁ and 20G ₂ , but the two imaging signals are mixed and supplied to one video amplifier 13G. Subsequent signal processing systems are processed as one system signal for each color.

  The baseband imaging signals amplified by the video amplifiers 13R, 13G, and 13B for the respective colors are supplied to separate analog / digital converters 14R, 14G, and 14B, converted into digital data, and the converted digital signals for the respective colors. Data is supplied to the video processing circuit 15 to perform video processing to be a video signal of a predetermined format, and the processed video data is output from the output terminal 16.

  FIG. 2 is a diagram showing an arrangement example of the CCD imagers 11R, 11G, and 11B. The CCD imagers 11R, 11G, and 11B for the respective colors are disposed on different substrates 10R, 10G, and 10B, respectively. Imaging light incident on the video camera is decomposed into red light, green light, and blue light by a spectral mechanism such as a dichroic mirror (not shown), and the respective primary color lights are incident on the corresponding CCD imagers 11R, 11G, and 11B.

  A CDS circuit 20R and a first-stage amplifier 12R (not shown in FIG. 2) are disposed on a substrate 10R on which a CCD imager 11R that captures red light is mounted, and an imaging signal sampled by the CDS circuit 20R is received. , And supplied to the subsequent circuit board side connected by the connector 17R.

Two CDS circuits 20G ₁ and 20G ₂ and two first-stage amplifiers 12G ₁ and 12G ₂ (not shown in FIG. 2) are arranged on a substrate 10G on which a CCD imager 11G that captures green light is mounted. Yes, the imaging signals sampled by the _two CDS circuits 20G ₁ and 20G ₂ are mixed into one system of imaging signals and supplied to the subsequent circuit board side connected by the connector 17G.

  A CDS circuit 20B and a first-stage amplifier 12B (not shown in FIG. 2) are arranged on a substrate 10B on which a CCD imager 11B for imaging blue light is mounted, and an imaging signal sampled by the CDS circuit 20B is arranged. , And supplied to the subsequent circuit board side connected by the connector 17B.

3 and 4 are diagrams showing an example of sampling operation in each CDS circuit 20R, 20G ₁ , 20G ₂ , 20B. The imaging signal waveform output from the CCD imager is the signal waveform shown in FIG. That is, a signal waveform having a reset period, a 0 level period, and a signal period in one pixel period in which a signal of one pixel is read out. This one pixel period is set in synchronization with the pixel clock. FIG. 4 is a diagram showing a principle configuration of each CDS circuit 20R, 20G ₁ , 20G ₂ , 20B, and two switches 21 and 22 to be sampled and signals sampled and held by the two switches 21 and 22 It is comprised with the comparator 23 which compares a level. In FIG. 4, the circuit for holding the sampled signal level is omitted, but the sampled potential using a capacitor or the like is held until the next sampling period.

As the sampling timing of the two switches 21 and 22, sampling is performed by turning on one of the switches 21 in the 0-level period S / H1 shown in FIG. In the signal period S / H2, the other switch 22 is turned on to perform sampling. The comparator 23 detects a level difference between the zero level period and the signal period, and outputs a voltage signal of the level difference as a signal (imaging signal) of the luminance value of the corresponding pixel. Note that the sampling timing of the imaging signal in the CDS circuits 20R, 20G ₁ , 20G ₂ , 20B for each color signal shown in FIG. 1 is the same timing, and the two CDS circuits 20G ₁ , process for holding by sampling the image signal at the same timing even 20G ₂ is performed.

According to the video camera having the configuration described above, for the green image signal, amplified by two-stage amplifier 12G _1, 12G _2, and sampled in duplicate at two CDS circuits 20G _1, 20G _2, the double Since the sampled image signals are mixed and supplied to the video amplifier 13G, the influence of thermal noise generated in the circuit system from the first stage amplifiers 12G ₁ and 12G ₂ to the CDS circuits 20G ₁ and 20G ₂ is reduced. be able to. That is, by preparing the same circuit in two-circuit parallel connection, the thermal noise generated randomly in each circuit (first-stage amplifier and CDS circuit) can be reduced to a value represented by [1 / √2]. . The reduction of [1 / √2] corresponds to a reduction of −3 dB. This reduction of [1 / √2] is derived from the following equation. In general, when N random noises that are not correlated with each other are averaged by N circuits,
Total noise VNoise = √ (V ₁ ² + V ₂ ² + ... + V _n ² ) / N
It is expressed. In this example, N = 2 and [1 / √2] is derived.

Therefore, the influence of thermal noise generated in the first stage amplifier and the CDS circuit can be reduced accordingly. In the case of this example, in the video camera that performs component processing of the three primary color signals, the first stage amplifier and the CDS circuit are paralleled only by the processing system of the green imaging signal, so that thermal noise reduction is very effective. An effect is obtained. That is, in the case of an HD (High Definition) video camera, for example, the luminance signal Y is determined by the signal ratio of red (R), green (G), and blue (B) shown in the following equation.
Luminance signal Y = 0.701G + 0.212R + 0.087B

  As described above, since the luminance signal Y has a high green ratio, it is no exaggeration to say that the S / N of the luminance signal Y is largely determined by the green signal. Therefore, as shown in FIG. 1, by duplicating only the green signal processing system, a highly effective thermal noise reduction effect can be obtained with a minimum circuit configuration. In terms of power consumption, the minimum increase is sufficient.

  In the case of this example, since the circuit components from the image sensor to the duplicated CDS circuit are arranged on one circuit board as shown in FIG. 2, the signal path from the image sensor to the CDS circuit is minimized. This also contributes to noise reduction.

  In the configuration of FIG. 1, the first stage amplifier and the CDS circuit are paralleled for the green image pickup signal, but more thermal noise reduction effects can be obtained by parallelizing the three circuits or the four circuits. . However, increasing the number of circuits connected in parallel increases the complexity of the circuit configuration of the signal processing system of the video camera and increases the power consumption.

In the configuration of FIG. 1, both the first stage amplifier and the CDS circuit are duplexed. However, only the CDS circuit that is the sample and hold unit may be duplexed. That is, as shown in FIG. 5, the output of the imaging signal from the green CCD imager 11G is supplied to one first stage amplifier 12G and amplified. Then, the amplified output of this one first stage amplifier 12G is supplied to the _two CDS circuits 20G ₁ and 20G ₂ and sampled twice. The baseband imaging signal sampled and output in units of one pixel by each CDS circuit 20G ₁ and 20G ₂ is supplied to one video amplifier 13G for green and amplified. Other parts are configured in the same manner as the processing system shown in FIG.

  With the configuration shown in FIG. 5, the CDS circuit that performs sampling is duplicated, and the influence of thermal noise in the CDS circuit can be reduced by [1 / √2].

In a video camera that performs component processing for red, green, and blue, all primary color signal processing systems may be duplicated. That is, as shown in FIG. 6, the imaging output of the red CCD imager 11R is supplied to the _two first-stage amplifiers 12R ₁ and 12R ₂ and individually amplified, and the respective amplified outputs are individually supplied to the individual CDS circuits 20R ₁ , 20R ₁ , obtaining a baseband signal sampled at 20R _2. Then, the outputs of both CDS circuits 20R ₁ and 20R ₂ are mixed and supplied to one video amplifier 13R. Further, the imaging output of the blue CCD imager 11B is supplied to the _two first stage amplifiers 12B ₁ and 12B ₂ to be individually amplified, and the respective amplified outputs are sampled by the individual CDS circuits 20B ₁ and 20B ₂ to be used as a base. Get the band signal. Then, the outputs of both CDS circuits 20B ₁ and 20B ₂ are mixed and supplied to one video amplifier 13B. The processing system of the imaging output of the green CCD imager 11G is the same as that described in FIG.

  By adopting the configuration shown in FIG. 6, all the primary color signals are sampled and processed twice, and the effect of further reducing thermal noise is high.

  In the above description, an example of a video camera using a CCD imager as an image sensor has been described. However, the present invention can be applied to a configuration for processing the output of another image sensor. FIG. 7 shows an example of a video camera using a MOS imager as an image sensor. In the example of FIG. 7, the imaging signal output from the MOS imager 31 is supplied to the two first stage amplifiers 32a and 32b and amplified. The outputs of both first stage amplifiers 32a and 32b are supplied to sample and hold circuits 33a and 33b. The two sample and hold circuits 33a and 33b sample the image pickup signal in units of one pixel at the same timing in synchronization with the pixel clock that is a read clock from the imager 31. The signals sampled and held by the two sample and hold circuits 33a and 33b are mixed and supplied to one video amplifier 34 for amplification. The amplified output of the video amplifier 34 is supplied to an analog / digital converter 35 to be converted into digital data. The converted digital data is supplied to the video processing circuit 36 to perform necessary video processing and output the processed video data from the video data output terminal 37.

  As shown in FIG. 7, even when a MOS imager is used as an image sensor, the same circuit configuration can be obtained, and the same effect can be obtained. Further, in the configuration of FIG. 7, only one signal system is shown, but the processing of the present invention is a three-plate type component as shown in FIG. 1 regardless of which type of image sensor is used. The present invention can be applied to either a configuration that performs processing or a single-plate configuration that obtains color signals of each color from the imaging output of one imager.

  In the above-described embodiment, the present invention is applied to a configuration for taking out an imaging signal. However, the same double processing configuration is applied to other circuits connected to the imaging signal processing unit to reduce thermal noise. You may do it. For example, a circuit configuration is known in which an imaging signal is extracted from an imager and simultaneously separated into a luminance signal Y and a chroma signal (color signal) C. FIG. 8 shows a conventional circuit configuration example in that case.

  In the example of FIG. 8, the CCD imager 41 included in the video camera is configured by one imager, and the pixels of each primary color signal are alternately arranged by the one CCD imager 41. The imaging output of the CCD imager 41 is supplied to the first sample and hold circuit 42, and is sampled in units of pixels in synchronization with the sampling control signal obtained at the terminal 51, and the sampling signal is held. The subtracter 43 takes the difference between the signal held by the sample and hold circuit 42 and the signal not held at a predetermined timing. The operation of obtaining the difference by the subtracter 43 corresponds to the processing in the correlated double sampling circuit.

  The output of the subtracter 43 is supplied to second and third sample and hold circuits 44 and 45 as circuits for separating the luminance signal component and the chroma signal component. The sampling timing of the sample and hold circuits 44 and 45 is performed in synchronization with the sampling control signals obtained at the terminals 52 and 53, respectively, and control is performed so as to sample the pixel output of a specific color. The signals sampled and held by both sample and hold circuits 44 and 45 are supplied to the adder 46 and added to obtain the luminance signal Y at the output terminal 54. Further, the signals sampled and held by both sample and hold circuits 44 and 45 are supplied to a subtractor 47 to take a difference, and the output of the subtractor 47 is supplied to a low pass filter 48 to extract a low frequency component. Thus, the chroma signal C is obtained at the output terminal 55.

  Even in the case where the correlated double sampling circuit and the luminance / chroma separation circuit are integrated as shown in FIG. 8, the processing configuration of the present invention can be applied to obtain the configuration shown in FIG. .

  That is, as shown in FIG. 9, as a circuit system for supplying the imaging output of the CCD imager 41, a circuit from the first sample and hold circuit 42 and subtractor 43 to the adder 46 and subtractor 47 is further added. Prepare one. Newly prepared circuits include a first sample and hold circuit 42 ', a subtractor 43', second and third sample and hold circuits 44 'and 45', an adder 46 ', and a subtractor. 47 'and the circuit having the same configuration. Sampling control signals obtained at the respective terminals 51, 52 and 53 are also supplied to two identical sample and hold circuits (for example, circuits 42 and 42 ') and sampled at the same timing.

  Then, the outputs of the two adders 46 and 46 ′ are added and supplied to the luminance signal output terminal 54 to obtain the luminance signal Y. Further, the outputs of the two subtractors 47 and 47 ′ are added and supplied to the low-pass filter 48, and the filter output is supplied to the chroma signal output terminal 55 to obtain the chroma signal C. In the configuration shown in FIG. 9, by duplicating the correlated double sampling circuit and the luminance / chroma separation circuit, thermal noise can be reduced by that amount, and a good imaging signal (luminance signal and chroma signal) can be obtained. . Although the amplifier is omitted in the configuration of FIG. 9, even when an amplifier is necessary, the amplifier may be configured in a double manner as in the example of FIG. As already described, circuit configurations may be prepared in triplicate or more.

It is a block diagram which shows the structural example by one embodiment of this invention. It is a perspective view which shows the example of arrangement | positioning of the board | substrate by one embodiment of this invention. It is a wave form diagram which shows the example of the sampling timing by one embodiment of this invention. It is a block diagram which shows the example of control of the CDS circuit by one embodiment of this invention. It is a block diagram which shows the structure of the modification of one embodiment of this invention. It is a block diagram which shows the structure of another modification in one embodiment of this invention. It is a block diagram which shows the example which applied the structure by one embodiment of this invention to another image pick-up element. It is a block diagram which shows the example of a premise structure applied to other embodiment of this invention. It is a block diagram which shows the structural example (example performed to YC isolation | separation) by other embodiment of this invention.

Explanation of symbols

10R, 10G, 10B ... substrate, 11R, 11G, 11B ... CCD _{imager, 12R, 12R 1, 12R 2} , 12G 1, 12G 2, 12B, 12B 1, 12B 2 ... stage amplifier, 13R, 13G, 13B ... video amplifier , 14R, 14G, 14B ... analog / digital converter, 15 ... video processing circuit, 16 ... video data output terminal, 17R, 17G, 17B ... _{connector, 20R, 20R 1, 20R 2} , 20G 1, 20G 2, 20B, 20B ₁ , 20B ₂ ... CDS circuit, 21, 22 ... switch, 23 ... comparator, 31 ... MOS type imager, 32a, 32b ... first stage amplifier, 33a, 33b ... sample and hold circuit, 34 ... video amplifier, 35 ... analog / Digital converter, 36 ... Video processing circuit, 37 ... Video data output terminal, 41 ... CCD imager 42, 42 ', 44, 44', 45, 45 '... sample and hold circuit, 43, 43' ... subtractor, 46, 46 '... adder, 47, 47' ... subtractor, 48 ... low-pass filter

Claims (6)

An image sensor;
A first sample-and-hold unit that samples and holds an imaging signal output by the imaging device;
A second sample-and-hold unit that samples an imaging signal output by the image sensor at the same timing as the first sample-and-hold unit;
An amplification unit that mixes and amplifies the hold output of the first sample and hold unit and the hold output of the second sample and hold unit;
A video camera comprising: a video processing unit that processes an amplified output of the amplification unit as a video signal. The video camera according to claim 1.
Dividing the imaging signal into a first imaging signal and a second imaging signal at the output unit of the imaging element;
Sample and hold the first imaging signal in the first sample and hold unit,
A video camera, wherein the second imaging signal is sampled and held by the second sample and hold unit. The video camera according to claim 1.
The image sensor is composed of a plurality of image sensors by an image sensor for each primary color signal,
A video camera characterized in that an imaging signal output from at least one of the plurality of imaging elements is configured to be sampled and held by the first sample and hold unit and the second sample and hold unit. The video camera according to claim 1.
The image sensor is composed of an image sensor for green, an image sensor for blue, and an image sensor for red.
A video camera characterized in that an image signal output from the green image sensor is sampled and held by the first sample and hold unit and the second sample and hold unit. The video camera according to claim 4.
A video camera characterized in that each of the image signals output from the blue image sensor and the red image sensor is sampled and held by one sample and hold unit. A first sample-and-hold unit that samples and holds an imaging signal obtained by output from the imaging device;
A second sample and hold unit that samples the imaging signal at the same timing as the first sample and hold unit;
An amplification unit that mixes and amplifies the hold output of the first sample and hold unit and the hold output of the second sample and hold unit;
An imaging signal processing circuit comprising: a video processing unit that performs video signal processing on the amplified output of the amplification unit.

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