JPH06133186A - Image pickup device - Google Patents

Abstract

PURPOSE:To realize the image pickup device from which a picture element with more accurate pulse waveform in which locking of a clamp level is excellent, sag in the pulse waveform is prevented, and a digital value of an optical black (O.B.) section is made coincident with a preset reference value. CONSTITUTION:The image pickup device is featured to be provided with a pulse clamp means 3 clamping an output signal of a sensor 1 by using a CPOB signal as a clamp pulse, a means 4 selecting only a picture element signal including the O.B. section of the sensor output signal and converting the signal into a digital signal, a means 11 generating a digital reference section of the O.B. section, and means 10, 9, 8 feeding back a difference signal between digital data and reference data of the 0.B. section receiving the sensor output signal to the pulse clamp means and controlling the clamp level of the pulse clamp means 3 so that the digital value of the O.B. section is coincident with the reference data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to signal processing of an image pickup device, and more particularly to an image pickup device for performing analog-to-digital (A / D) conversion of an output signal of an area sensor after clamping processing.

[0002]

2. Description of the Related Art Heretofore, as an example of this type of image pickup apparatus, one having a structure as described in the first embodiment of Japanese Patent Publication No. 2-257778 has been known. FIG. 5 is an example of a circuit block diagram of such a conventional image pickup device, and FIG. 6 is a timing chart of waveforms of respective parts.

In the conventional image pickup apparatus shown in FIGS. 5 and 6, the optical black (OB) portion of the pixel signal read from the area sensor 21 is accurately corrected without being affected by reset noise or the like. In order to match the clamp potential, by using a CPOB pulse gated by a sample hold pulse as a clamp pulse, only the optical black (OB) portion is selected,
It is designed to be pulse clamped.

[0004]

However, in the above-mentioned conventional example, since a so-called toothless pulse in which CPOB is gated by a sample hold pulse is used as the clamp pulse (see e in FIG. 6), the clamp period is reduced. However, there are drawbacks such as shortening, slow pull-in to the clamp potential, and lower sag absorption capability of the pulse waveform.

(Object of the Invention) The object of the present invention is to draw the clamp potential well and prevent sag of the pulse waveform.
It is an object of the present invention to realize an image pickup device in which the digital value of the optical black portion is made to match a preset reference value and a more accurate pixel signal of a pulse waveform can be obtained.

[0006]

As a means for solving the above-mentioned problems, the present invention provides a CPOB signal in an image pickup device for analog-digital (A / D) conversion after the output signal of an image sensor is clamped. Pulse clamp means for clamping the sensor output signal as a clamp pulse, means for digitally converting only the pixel signal portion of the sensor output signal including the optical black portion, and digital reference data of the optical black portion. Means for generating a digital signal of the optical black portion of the sensor output signal, a difference signal between the reference data, means for feeding back to the pulse clamp means, the difference signal fed back, the optical black portion of the optical black portion. Digital value is the reference data As match, there is provided an imaging apparatus characterized by having a means for controlling the clamp voltage of the pulse clamping means.

[0007]

According to the present invention, the digital feedback type pulse clamp means is provided, and only the pixel signal portion including the optical black portion is selected and A / D converted in the output signal of the area sensor, and the digital signal of the optical black portion is digitally converted. Since the data and the reference digital data of the optical black portion generated from the reference data generating means are compared and the clamp signal of the pulse clamping means is controlled by the difference signal, the digital value of the optical black portion of the sensor output is controlled. Can be automatically matched with a preset reference value.

Further, by selecting only the pixel signal of the video signal, A
Since / D conversion is performed, CPOB can be used as a clamp pulse, it is not necessary to shorten the clamp period, and an accurate pulse waveform can be obtained without lowering the clamp capability.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 is a schematic block diagram of an image pickup apparatus as a first embodiment of the present invention.

In the figure, 1 is an area sensor, 2 is an inverting amplifier for inverting and amplifying the polarity of the sensor output from the area sensor 1, 3 is a pulse clamp circuit, 4 is for converting an analog signal into a digital signal. A / D converter 5 is a digital signal processing circuit for performing various processes on the digital signal from the A / D converter 4, 6 and 8
D / for converting a digital signal to an analog signal
A converter 7 is a display device such as a monitor. 9 is a switch circuit which is switched and controlled by a CPOB signal from the outside, 10 is a subtraction circuit for calculating a difference signal between two digital values, 11 is a reference value of an optical black portion,
Reference data generating circuit 12 for generating preset digital reference data, and 12 is a delay element.

FIG. 2 is a timing chart of waveforms at various parts of this embodiment.

The operation of each part of the image pickup apparatus of FIG. 1 will be described below with reference to the timing chart of FIG.

The video signal (sensor output signal a) read from the area sensor 1 is supplied to the inverting amplifier 2 while the reset signal portion and the pixel signal portion (including the OB portion, that is, the optical black portion) are mixed. Is entered.

Here, since the sensor output has a negative polarity as an example, it is inverted to match the polarity of the A / D converter 4 and is amplified to match the proper input level of the A / D converter (inversion). Amplifier output signal b).

The video signal that has been inverted and amplified by the inverting amplifier 2 is input to the pulse clamp circuit 3, and the CPOB signal c that is also input causes the O.D. B. period,
After undergoing pulse clamp processing, it is input to the A / D converter 4.

Here, the video signal is digitally converted, and at that time, a sample and hold pulse delayed by the delay element 12 as the clock signal of the A / D converter 4 (clock signal d for A / D conversion) is used. Use, Figure 2
The central portion of the pixel signal of the inverting amplifier output signal b of the video signal is selected and digitally converted according to the timing relationship between the inverting amplifier output signal b and the clock signal d shown in FIG.

As a result, the influence of noise such as the reset signal portion of the video signal is completely removed when digital conversion is performed, and the effect of O.S. B. Only the pixel signal portion including the portion can be selected.

The digital pixel signal thus digitally converted is subjected to various processes in the digital signal processing circuit 5 and then converted into an analog signal by the D / A converter 6 to be displayed on a display device such as a monitor 7. Is output.

The digital pixel signal digitally converted by the A / D converter 4 is also input to the subtraction circuit 10, where the O.D. signal output from the reference data generation circuit 11 is output. B. The difference signal from the digital reference data of the part is calculated.

Further, this difference signal is output by the switch circuit 9 which is switched and controlled by CPOB. B. Only the part of the difference signal is input to the D / A converter 8, where it is converted into an analog signal and fed back to the pulse clamp circuit 3.

That is, digital feedback type pulse clamping is performed by the feedback, and B.
Since the clamp potential of the pulse clamp circuit 3 is controlled by the difference signal between the partial digital pixel signal and the reference data, the digital pixel signal of the optical black portion operates so as to match the reference data.

However, in the pulse clamp circuit 3, the pulse clamp circuit 3 has an O.S. B. Although it is performed during the period, since the noise is removed during the A / D conversion and the digital conversion is performed as described above, the clamp operation is not affected by the noise.

[Second Embodiment] FIG. 3 is a block diagram showing the configuration of the second embodiment of the present invention, and FIG. 4 is a timing chart of waveforms at respective portions.

Since this embodiment is almost the same as the first embodiment described with reference to FIG. 1, only the differences will be described below.

The video signal read from the area sensor 1 is immediately subjected to the same pulse clamp as in the first embodiment described above (however, since the video signal is clamped in the negative polarity, the polarity of the subtractor 10 is changed. is there.).

The video signal subjected to the pulse clamp is input to the clip circuit 13 to remove an unnecessary reset signal,
Clip processing is performed (see clip output b in FIG. 4), which is further input to the inverting amplifier 2 and is inversely amplified to match the polarity of the A / D converter 4 and an appropriate input level (see FIG. 4, inverting amplifier output c). .

This embodiment is for removing the reset signal and expanding the dynamic range when the gain of the inverting amplifier 2 is high. Since the output from the inverting amplifier is the same as that in the first embodiment described above, the description is omitted.

[0028]

As described above, since the image pickup apparatus of the present invention selects only the pixel signal of the video signal and performs A / D conversion, CPOB can be used as the clamp pulse, and the clamp pulse can be used as in the conventional case. It became unnecessary to shorten the period, and it became possible to make the digital value of the optical black portion exactly match the reference value without lowering the clamping ability.

Therefore, it is possible to obtain a pixel signal having a more accurate pulse waveform as compared with the conventional image pickup apparatus.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a signal processing circuit of an image pickup apparatus according to a first embodiment of the present invention.

FIG. 2 is a timing chart of waveforms at various points in the first embodiment.

FIG. 3 is a block diagram showing a schematic configuration of a signal processing circuit of an image pickup apparatus according to a second embodiment of the present invention.

FIG. 4 is a timing chart of waveforms at various points in the second embodiment.

FIG. 5 is a block diagram showing a schematic configuration of a signal processing circuit of a conventional image pickup apparatus.

FIG. 6 is a timing chart of waveforms at various points in a conventional example.

[Explanation of symbols]

 1 area sensor 3 pulse clamp circuit 4 A / D converter 5 digital signal processing circuit 6, 8 D / A converter 10 subtraction circuit 11 reference data generation circuit 12 delay element 13 clip circuit

Claims (3)

[Claims] 1. An image pickup apparatus for analog-digital (A / D) converting after an output signal of an image sensor is clamped, a pulse clamp means for clamping the sensor output signal using a CPOB signal as a clamp pulse, and the sensor. Output signal, means for selecting only a pixel signal portion including an optical black portion to perform digital conversion, means for generating digital reference data for the optical black portion, digital data for the optical black portion of the sensor output signal, A means for feeding back a difference signal from the reference data to the pulse clamp means, and a clamp for the pulse clamp means so that the fed back difference signal causes the digital value of the optical black portion to match the reference data. Control the potential Imaging apparatus characterized by comprising a means. 2. An imaging device for performing analog-digital (A / D) conversion after an output signal of an image sensor is clamped, and an inverting amplifier for inverting and amplifying the sensor output signal, and a CPOB signal as a clamp pulse for the inversion. A pulse clamp circuit for clamping an amplifier output signal, an A / D converter for converting the pulse clamp circuit output signal into a digital value, a reference data generating circuit for generating digital reference data of an optical black portion, and the A / D A subtraction circuit that outputs a difference signal between the converter output signal and the reference data generation circuit output signal, and a D / A that converts the subtraction circuit output signal into an analog signal
A converter, switch means for outputting the subtraction circuit output signal to the D / A converter, which is controlled by the CPOB signal, and feedback input of the D / A converter output signal to the pulse clamp circuit. And a means for controlling the clamp potential of the pulse clamp circuit so that the digital data of the optical black portion of the sensor output signal and the reference data become equal to each other. 3. The image pickup apparatus according to claim 2, further comprising a clipping circuit for clipping the output signal of the pulse clamp circuit and inputting it to the inverting amplifier circuit.