JP2000184294A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cope with the fluctuation of an optical black(OB) level by relatively inexpensive and small-scale circuit constitution by providing a reference voltage correction means for correcting the reference voltage of an A/D converter for converting analog video signals into digital signals by correction signals or the like. SOLUTION: An OB level correction circuit 11-1 compares the OB level of video signals converted into the digital signals by the A/D converter 7 with a black level set beforehand and computes an offset amount for matching both. The arithmetic result is inputted to a D/A converter 18 capable of arbitrarily controlling an output voltage and the voltage control of the reference voltage of the A/D converter 7 is performed by the output of the D/A converter 18. By the constitution, to the fluctuation of the OB level by the temperature characteristics of a clamp circuit, a sufficient correction range is secured by the relatively inexpensive and small-scale circuit constitution and stable video signals are obtained without making the black level of the video signals fluctuate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus such as a video camera, and more particularly to an image pickup apparatus which digitizes a video signal obtained by an image pickup device and performs signal processing.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing a configuration of an image pickup apparatus using a general photoelectric conversion element. In FIG. 1, reference numeral 1 denotes an imaging lens, 2 denotes an iris that controls the amount of incident light of imaging light from a subject passing through the imaging lens 1, and 3 denotes a photoelectric conversion of the imaging light to an electric signal (video signal). , Such as a CCD, and a double-correlation sampling circuit (hereinafter referred to as S / H) for reducing accumulated charge noise contained in a video signal output from the image sensor 3.
Circuit). Reference numeral 5 denotes an auto gain control circuit (hereinafter referred to as A
A reference numeral 6 designates a video signal output from the AGC circuit 5, and a clamp pulse output from a clamp pulse generation circuit described later converts the video signal output from the DC voltage generation circuit described later into an optical black (OB) signal. A) A / D converter for converting the video signal clamped to a predetermined voltage value by the clamp circuit 6 into a digital signal, and 8 an output from the A / D converter 7. A digital signal processing circuit (DSP circuit) that performs various signal processing required to convert the converted digital signal into a video signal. Reference numeral 9 denotes a timing generator circuit (hereinafter referred to as a TG circuit) including the above-described clamp pulse generation circuit that generates various timing pulses such as the above-described clamp pulse. 10 denotes the above-described DC voltage generation circuit that generates a predetermined clamp voltage.
An OB level correction circuit 11-2 compares the OB level of the video signal converted into a digital signal by the A / D converter 7 with a preset black level, and calculates an offset amount such that the two coincide. Then, the calculation result is added to or subtracted from the OB level of the video signal. Reference numeral 12 denotes a system control circuit composed of a microcomputer for controlling the entire system including the digital signal processing circuit 8, and reference numeral 13 denotes a digital video signal output from the digital signal processing circuit 8, which is controlled by the system control circuit 12. An image memory device 14 for storing and outputting a signal is a D / A converter for converting a digital video signal output from the image memory device 13 into an analog signal.

FIG. 5 is a block diagram showing a detailed circuit configuration of the OB level correction circuit 11-2. In the figure, 15
Is an OB integrated value detection for integrating a digital video signal output from the digital signal processing circuit 8 with a signal component corresponding to an OB portion in a video signal output of the image sensor 3 at every one horizontal line or at a preset interval. Circuit.

A correction data calculation circuit 16 compares the detected OB integral value with a preset black level and calculates correction data such that the OB integral value matches the preset black level. An addition / subtraction circuit for adding or subtracting the correction data calculated by the correction data calculation circuit 16 to or from the OB level of the video signal input to the OB level correction circuit 11.

Next, a specific operation of the imaging apparatus having the above-described configuration will be described.

First, an optical image picked up by an image pickup device passes through an image pickup lens 1, the light amount is adjusted by an iris 2, and then converted into an electric signal by an image pickup device 3. The video signal output from the image sensor 3 is removed by the S / H circuit 4 from charge accumulation noise contained in the video signal output of the image sensor 3 and amplified by the AGC circuit 5 with a preset gain.

The video signal output from the AGC circuit 5 is AC-coupled by passing through a capacitor and input to the clamp circuit 6. The video signal input to the clamp circuit 6 is clamped to an arbitrary voltage output from the DC voltage generation circuit 10 at the timing of the clamp pulse output from the TG circuit 9.

FIG. 6 is a diagram showing the operation timing of the clamp circuit 6. As shown, a clamp pulse is output during the blanking period of the video signal, and the signal component of the OB portion is clamped at this timing.

[0009] The clamped video signal is input to an A / D converter 7, converted into a digital signal, and then input to a digital signal processing circuit 8. Then, a part of the signal passes through the circuit 8 and is input to the OB level correction circuit 11-2.

The digital video signal input to the OB level correction circuit 11-2 is divided into two directions, one of which is input to the addition / subtraction circuit 17, and the other is input to the OB integration value detection circuit 15.

The integration value detection circuit 15 integrates a signal component corresponding to the optical black portion of the image sensor 3 in the video signal at one horizontal line or at a predetermined interval,
OB integrated value is detected. The next correction data calculation circuit 16 compares the OB integration value detected by the OB integration value detection circuit 15 with a preset black level, and calculates correction data such that the OB integration value matches the black level. I do. Then, in the next addition / subtraction circuit 17, the correction data calculated by the correction data calculation circuit 16 is added to or subtracted from the OB level of the video signal input to the OB level correction circuit 11-2. Then, the OB level correction circuit 1
The video signal output from 1-2 is input to the digital signal processing circuit 8 again.

As a result, the OB level of the video signal input to the digital signal processing circuit 8 is kept constant.

[0013]

However, in the conventional imaging apparatus as described above, the correction cannot be performed unless the correction range of the addition / subtraction circuit is larger than the fluctuation range of the clamp circuit. If the circuit scale is large and the OB level greatly fluctuates due to the temperature characteristics of the clamp circuit and becomes lower than the BOTTOM reference voltage of the A / D converter (OLSB or less), the output signal of the A / D converter is clipped. In principle, correct correction cannot be performed. Therefore, it is necessary to suppress the temperature characteristics of the clamp circuit to a value sufficiently lower than the correction range, so that it is costly to compensate for the temperature characteristics and to select components.

The present invention has been made under such circumstances, and a sufficiently wide correction range can be obtained with a simple circuit configuration even with respect to fluctuations in the OB level due to the temperature characteristics of the clamp circuit. Without changing the black level of the signal,
It is an object of the present invention to provide an imaging device capable of obtaining a stable video signal.

[0015]

In order to achieve the above-mentioned object, according to the present invention, an image pickup apparatus is configured as described in the following (1) and (2).

(1) In an image pickup apparatus which has an image pickup device for converting image pickup light into a video signal and converts an analog video signal from the image pickup device into a digital signal to perform digital signal processing, an image output from the image pickup device is provided. Detecting means for detecting the level of a signal component corresponding to an optical black portion in the video signal, and comparing the detected level value detected by the detecting means with a preset black level value to match the two. A calculating means for calculating the correction data; and a reference voltage correcting means for correcting a reference voltage of an A / D converter for converting the analog video signal into a digital signal with a correction signal based on the correction data obtained by the calculating means. Imaging device provided.

(2) The image pickup apparatus according to (1), further comprising a clamp unit for clamping a signal component corresponding to an optical black portion in the video signal by an arbitrary DC voltage, and the detecting unit clamps. An imaging device that integrates a signal component at predetermined intervals and detects a level value thereof.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below in detail with reference to examples. FIG. 1 is a block diagram showing the overall system configuration of an “imaging device” according to an embodiment. The same reference numerals as in FIG. 4 denote the same components.

In FIG. 1, reference numeral 1 denotes an imaging lens, 2 denotes an iris for controlling the amount of incident light of imaging light from a subject passing through the imaging lens 1, and 3 denotes a photoelectric conversion of the imaging light to an electric video signal. An image sensor 4 such as a CCD for conversion is an S / H circuit for reducing accumulated charge noise contained in a video signal output from the image sensor 3.

Reference numeral 5 denotes an automatic gain control circuit (hereinafter referred to as an AGC circuit) for maintaining the level of the video signal at a constant level, and reference numeral 6 designates a video signal output from the AGC circuit 5 at a predetermined voltage value by a clamp pulse. A clamp circuit 7 for clamping an optical black portion (OB portion), 7 is an A / D converter for converting a video signal clamped to a predetermined voltage value by the clamp circuit 6 into a digital signal, and 8 is an A / D converter 7 Is a digital signal processing (DSP) circuit that performs various signal processing required to convert a digital signal output from a video signal into a video signal.

Reference numeral 9 denotes a TG circuit including the above-described clamp pulse generation circuit for generating various timing pulses such as the clamp pulse, and reference numeral 10 denotes the above-described DC voltage generation circuit for generating a predetermined clamp voltage.

An OB 11-1 compares the OB level of the video signal converted into a digital signal by the A / D converter 7 with a preset black label, and calculates an offset amount such that the two coincide. The result of the operation is input to a D / A converter 18 capable of arbitrarily controlling an output voltage described later by a level correction circuit, and the output of the D / A converter 18 is used as a reference for the A / D converter 7. Voltage control of the voltage (BOTTOM side) is performed.

Reference numeral 12 denotes a system control circuit constituted by a microcomputer for controlling the entire system including the digital signal processing circuit 8, and 13 denotes a digital video signal output from the digital signal processing circuit 8 to the system control circuit 12. Control signal from
An image memory device 14 for storing and outputting is a D / A converter for converting a digital video signal output from the image memory device 13 into an analog signal. Reference numeral 18 denotes a D / A converter that outputs an arbitrary voltage based on a control signal from the system control circuit 12.

As shown in FIG. 3, the configuration of the OB level correction circuit 11-1 is obtained by removing the addition / subtraction circuit 17 from the circuit of FIG. 5 shown in the conventional example.

Next, a specific operation will be described. still,
Here, the circuit operation will be described with emphasis on the difference between the above-described conventional example and this embodiment.

The gain setting of the AGC circuit 5 in this embodiment is controlled by the system control circuit 12 (note that the gain setting of the AGC circuit 5 may be controlled by the system control circuit 12; Voltage control may be performed via a D / A converter or the like, or control may be performed via a digital signal processing (DSP) circuit 8).

Further, in this embodiment, the D / A converter 18 for generating the reference voltage (BOTTOM side) of the A / D converter 7 is controlled via the system control circuit 12, but the digital signal processing circuit ( A configuration in which control is performed directly from the DSP 8 may be employed, or a D / A converter may not be used as long as a reference voltage can be directly generated by the system control circuit.

First, the amount of light incident from the imaging lens 1 is adjusted by the iris 2 as in the prior art, and
, Where it is photoelectrically converted into an electrical signal. This video signal has its accumulated charge noise component removed by the S / H circuit 4 and is amplified to an appropriate video signal level by the AGC circuit 5.

The video signal output from the AGC circuit is capacitively coupled by a capacitor and input to the clamp circuit 6. Then, the voltage is clamped to an arbitrary voltage by the clamp circuit 6, converted into a digital signal by the A / D converter 7, and converted into a video signal by the digital signal processing circuit 8.

For example, in the case of the present embodiment, the A / D converter 7 uses a 10-bit A / D converter, and data of 32 LSB is previously set as the OB level setting data in the correction data calculation circuit 16 of FIG. The set data is compared with the output value from the OB integrated value detection circuit 15, and the calculated value is calculated from the difference.

Here, the output data value of the OB integral value detection circuit 15 (O
If the B level changes to 42 LSB, the correction data calculation circuit 16 sets a preset OB level (32 level).
LSB) and generates correction data from the difference, and outputs the correction data to the system control circuit 12. The system control circuit 12 supplies voltage control data to the D / A converter 18 based on the correction data, and as a result, the difference (10 LSB) of the output data value
Is the reference voltage of the A / D converter 7 (BOTTOM side)
Is output from the D / A converter 18.

For example, in the case of this embodiment, the A / D converter 7 operates at the TOP-side reference voltage of 3.00 V and the BOTTOM-side reference voltage of 1.00 V, and when the OB integrated value data value changes by 1 LSB. The clamp voltage is 2m
Since the circuit is set so as to be compatible with the V correction, the output data of the OB integrated value detection circuit 15 is assumed to be 4
When the LSB becomes 2 LSB, the fluctuation of the OB integral value can be corrected by increasing the clamp voltage by 20 mV (to 1.02 V).

FIG. 2 shows the change in the OB level due to the temperature characteristics of the clamp circuit 6 and the correction data calculation circuit 1 of this embodiment.
6 shows the relationship between the correction voltage value of the reference voltage of the A / D converter 7 and the correction voltage value by the correction data calculation circuit 16, and the horizontal axis shows the fluctuation of the clamp voltage of the OB section. I have.

With the correction data, the D / A converter 18 changes the output voltage from an ordinary voltage of 1063 mV to an arbitrary voltage, thereby detecting the OB level fluctuation due to the fluctuation of the clamp voltage value of the clamp circuit 6 or the like. By controlling the reference voltage of the A / D converter 7 so as to cancel, it is possible to minimize the influence of fluctuations in the OB level and to always provide an appropriate black level.

As described above, according to this embodiment,
With respect to fluctuations in the OB level due to the temperature characteristics of the clamp circuit, it is possible to secure a sufficient correction range with a relatively inexpensive and small-scale circuit configuration as compared with the conventional one, and the black level of the video signal fluctuates. And a stable video signal can be obtained.

[0036]

As described above, according to the present invention,
A relatively inexpensive and small-scale circuit configuration can cope with fluctuations in the OB level.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment.

FIG. 2 is a diagram illustrating an example of correction voltage control of a reference voltage of an A / D converter due to a change in an OB level;

FIG. 3 is a block diagram illustrating a configuration of an OB level correction circuit according to the embodiment;

FIG. 4 is a block diagram showing a configuration of a conventional example.

FIG. 5 is a block diagram illustrating a configuration of an OB level correction circuit.

FIG. 6 is a timing chart showing the operation of the clamp circuit.

[Explanation of symbols]

 Reference Signs List 3 image sensor 7 A / D converter 11-1 OB level correction circuit 18 D / A converter

Claims (2)

[Claims] An image pickup device for converting an image pickup light into a video signal, converting an analog video signal from the image pickup device into a digital signal, and performing digital signal processing. Detecting means for detecting the level of a signal component corresponding to an optical black portion in a video signal; and correcting the detected level value detected by the detecting means with a preset black level value so as to match the two. A calculating means for calculating data; and a reference voltage correcting means for correcting a reference voltage of an A / D converter for converting the analog video signal into a digital signal by a correction signal based on the correction data obtained by the calculating means. An imaging device characterized in that: 2. The image pickup apparatus according to claim 1, further comprising: a clamp unit that clamps a signal component corresponding to an optical black portion in the video signal with an arbitrary DC voltage, wherein the detection unit detects the clamped signal component. Is integrated at predetermined intervals, and the level value is detected.