JP2003244561A - Imaging device and imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device and an imaging method for the imaging device not having the problem that black level depression occurs in an imaging signal following a black level with a markedly erroneous OB (optical black) output. <P>SOLUTION: In the imaging device provided with a feedback OB clamp circuit, including an amplifier 4 for amplifying an electric signal from an imaging element 1, the amplitude of a negative feedback signal in the OB clamp circuit is restrained to a value not greater than a prescribed value by diodes 5e, 5f connected in reverse in parallel, thereby avoiding the black sinking in the imaging signal. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

2. Description of the Related Art Normally, when displaying or recording a still image or a moving image captured by a solid-state image sensor such as a CCD, the optical black (optical Black, hereinafter referred to as OB) level is used. The OB refers to a pixel output that is shielded in the light receiving pixel portion of the image sensor and does not depend on the incident light.

FIG. 4 shows an example of the configuration of a feedback clamp system device which is a DC component reproducing (clamping) circuit using the OB level as a black reference of an image pickup signal and which is often used in a video camera. Is shown in FIG. 5, and its operation will be briefly described.

In FIG. 4, first, there is a solid-state image pickup device 101 such as a CCD, and an image pickup signal output from the image pickup device 101 is input to a circuit 102 called a CDS (correlation double sampling) circuit to reset noise. Is removed, the offset addition circuit 103 inputs the predetermined offset voltage, and the offset addition output is input to the variable amplifier 104.

Further, the CDS circuit 102 constitutes a CDS circuit which uses the predetermined reference voltage VREF input from the terminal 106 as a reference for the feedthrough portion of the image pickup signal. Similarly, the variable amplifier 104 has the reference voltage VREF. It forms a DC amplifier using VREF as a reference for DC amplification of an image pickup signal.

The variable amplifier 104 is a gain varying means for correcting the output sensitivity variation of the CCD 101 and switching the sensitivity setting of the image pickup device. Hereinafter, in order to simply and clearly explain the clamp operation of the image pickup device. , And the gain is assumed to be 1 time.

The amplified output signal from the variable amplifier 104 is
On the other hand, the OB clamp pulse, which is input to the image processing / recording / display circuit (not shown) and is input to the sample hold circuit 107 on the other hand and which is synchronized with the read timing of the OB pixel input from the terminal 109, The held OB level is the integration amplifier 105.
Entered in.

The integrating amplifier 105 includes a capacitor 105.
b and the resistor 105c form a predetermined integration time constant, and the sampled and held OB level and the terminal 1
The differential voltage (clamping error voltage) from the predetermined reference voltage VREF input from 06 is integrated by the integration time constant, and its output (deviation amount from the voltage VREF).
However, it has a negative feedback control configuration in which it is input to the offset addition circuit 103 and subtracted.

FIG. 5 shows the output signal 11 of the variable amplifier 104.
FIG. 7 shows how the OB level of C is clamped to the DC voltage level VREF and converges, and the operation waveform of each part at that time.

The signal waveform 11A is an output waveform of the CDS 102 and has an OB pixel output for a predetermined period for each horizontal line read from the image sensor 101.
The timing signal for sampling and holding a part of the pixel output period is the OB clamp pulse 11D.

The OB pixel output of the signal waveform 11A is the CDS
Although the DC voltage relatively close to the reference voltage VREF is maintained by the function of the (correlated double sampling) circuit 102, the difference component (CCD offset) between the feedthrough component and the signal component of the image sensor 101 is actually used. Further, a dark current component depending on the temperature of the image sensor is superimposed and has an offset error (usually several millimeters to several tens of millivolts).

This offset error varies from image sensor to image sensor and also varies depending on temperature. Then, this offset error is amplified by the variable amplifier 104 and finally output as the black level fluctuation VERR of the image pickup signal.

The black level fluctuation VERR is VRE by the sample hold circuit 107 and the integrating amplifier 105.
The difference between the F voltages is detected, integrated, and output as an integrated output signal 11B shown in FIG.
The amount of deviation from REF is the output signal 1 of the CDS circuit 102.
Subtracted from 1A.

By repeating this operation for each output of the OB clamp pulse 11D, the OB pixel output of the integrated output 11B and the output signal of the variable amplifier 104 converges to the reference voltage VREF like the signal waveform 11C.

By the way, in such a feedback type OB clamp circuit, the time constant of integration when the black level fluctuation VERR is integrated and negatively fed back is very important.

If the time constant is short, the response of the output OB level for each horizontal line to the VREF voltage becomes faster, but the amount of change (change frequency) for each clamp operation also increases accordingly.
Horizontal streak noise is likely to occur.

Therefore, the time constant must be set to a predetermined length so that the horizontal stripe noise does not cause a problem in image quality.

[0017]

In such a conventional feedback type OB clamp circuit, the CCD offset of the image sensor and the offset error due to the dark current component are assumed as the main factors of the OB fluctuation amount. The main design is to correct the offset error component of.

Originally, these offset error components are 10% of the full range (up to 1 volt) of the image pickup signal.
It is less than a fraction (several millimeters to tens of millivolts), which is not very large.

By the way, when a strong light such as direct sunlight is incident on a solid-state image pickup device such as a CCD, a phenomenon called so-called blooming occurs in which charges overflow in the photoelectric conversion portion. When blooming occurs, the light is originally blocked in the light-receiving pixel portion and does not depend on the incident light.
In some cases, the overflowed charges may flow into and accumulate in the B pixel portion.

Unlike the offset error component, the OB level in this case cannot be an accurate black reference, and in the case of intense blooming, the full range level (CCD saturation level VSAT) of the image pickup signal changes. Reach

FIG. 6 shows operation waveforms of respective parts for explaining the clamp operation when blooming occurs. The OB output of the CDS output 11A reaches the CCD saturation level VSAT rapidly with the occurrence of blooming. The OB output of the PGA output 11C is the integration amplifier 105.
With the response time according to the time constant set by, the erroneous OB level raised to the CCD saturation level VSAT is gradually lowered to the reference voltage VREF.

As described above, the conventional clamp circuit configuration has a problem in that when blooming occurs, it follows an erroneous black level that largely deviates from an appropriate OB level, resulting in black sinking of the entire image pickup signal. It was

Further, as a result of following an erroneous black level that greatly deviates from the proper OB level, it takes a very long time to return to the normal OB level even after the blooming of the image sensor is resolved, and during that time, There was a problem that the state of black sinking continued.

The present invention has been made under such a circumstance, and there is no problem that the OB output largely follows an erroneous black level to cause black sunkenness in an image pickup signal.
An object is to provide an imaging method of an imaging device.

[0025]

In order to achieve the above-mentioned object, in the present invention, an image pickup apparatus is configured as in the following (1) to (8), and an image pickup method of the image pickup apparatus is set to the following (9), (1
0).

(1) Image forming means for optically forming an image of a subject on an image pickup device, an image pickup device for converting an optical image of the subject into an electric signal, and an electric signal after photoelectric conversion by the image pickup device An offset adding means for adding the DC voltage, an amplifying means for amplifying with a predetermined gain or a variable gain, and an image pickup signal after the image pickup signal after the offset addition processing by the offset addition means and the amplification processing by the amplification means. Sampling and holding means for sampling and holding the included optical black level, and negative feedback for generating the DC voltage as a negative feedback signal based on a difference between a predetermined reference value and the optical black level held by the sampling and holding means. In an imaging device provided with a signal generating means, the negative feedback signal generating means is provided with feedback limiting means,
An imaging device for limiting the DC voltage added by the offset adding means.

(2) In the image pickup device according to (1), the negative feedback signal generating means has a predetermined integration time constant with respect to a change in the optical black level of the image pickup means.

(3) In the image pickup apparatus described in (1) above, the feedback limiting means limits the feedback of a negative feedback signal that deviates from the variation of the image pickup element or the temperature characteristic and the variation amount of the amplifying means. Imaging device.

(4) In the image pickup device described in (1) above, the feedback limiting means varies the feedback limit level for a negative feedback signal according to the gain of the amplifying means.

(5) Image forming means for optically forming an image of a subject on an image pickup device, an image pickup device for converting an optical image of the subject into an electric signal, and an electric signal after photoelectric conversion by the image pickup device. An offset adding means for adding a DC voltage, an amplifying means for amplifying with a predetermined gain or a variable gain, and an analog image pickup signal after the offset adding processing by the offset adding means and the amplification processing by the amplifying means is converted into a digital signal. AD conversion means and the AD
An optical black level extracting means for extracting an optical black level included in the digital signal obtained by the converting means, and a difference between a predetermined reference value and the optical black level extracted by the optical black level extracting means. Based on the above, in an imaging apparatus provided with a negative feedback signal generating means for generating the DC voltage as a negative feedback signal, the negative feedback signal generating means is provided with a feedback limiting means, and the direct current added in the offset adding means is added. An imaging device that limits the voltage.

(6) In the image pickup device according to (5), the negative feedback signal generating means has a predetermined integration time constant with respect to the fluctuation of the optical black level.

(7) In the image pickup apparatus described in (5) above, the feedback limiting means limits the feedback of a negative feedback signal that deviates from the variation of the image pickup element, the temperature characteristic, and the variation amount of the amplifying means. Imaging device.

(8) In the image pickup device according to (5), the feedback limiting means varies the feedback limiting level for a negative feedback signal according to the gain of the amplifying means.

(9) An image pickup method of an image pickup apparatus comprising an amplifying means for amplifying an electric signal from an image pickup device and a feedback type OB clamp circuit including the amplifying means, wherein a negative feedback in the OB clamp circuit is provided. An image pickup method for an image pickup apparatus, which limits the amplitude of a signal to a predetermined value or less.

(10) In the image pickup method of the image pickup apparatus according to (9), when the gain of the amplification means is variably set, the predetermined value is changed according to the set gain.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to examples of an image pickup apparatus. The present invention is not limited to the form of the apparatus, but can be implemented in the form of a method supported by the description of the embodiments.

[0037]

(Embodiment 1) FIG. 1 is a block diagram showing a configuration of a feedback type OB clamp circuit, which is a main part of an "imaging device" according to a first embodiment.

First, the configuration of FIG. 1 will be described.

Reference numeral 1 denotes a CCD (CCD image sensor) for converting an optical image of a subject into an electric signal.
The image pickup signal output from is input to a circuit 2 called a CDS (correlation double sampling) circuit to remove reset noise, and then input to an offset adding circuit 3 to add a predetermined offset voltage, The offset addition output is input to the variable amplifier 4.

Further, the CDS circuit 2 constitutes a CDS circuit in which a predetermined reference voltage VREF inputted from the terminal 6 is used as a reference of the feedthrough portion of the image pickup signal, and similarly, the variable amplifier 4 has the reference voltage VREF. It forms a DC amplifier using VREF as a reference for DC amplification of an image pickup signal.

The variable amplifier 4 is a gain changing means for correcting the output sensitivity variation of the CCD 1 and switching the sensitivity setting of the image pickup device. In the following, in the present embodiment, the clamp operation of the image pickup device will be simplified. For the sake of clear explanation, it will be simply treated as a gain of 1.

The amplified output signal from the variable amplifier 4 is input to an image processing / recording / display circuit (not shown) on the one hand, and to the sample hold circuit 7 on the other hand,
The OB level sampled and held by the OB clamp pulse synchronized with the read timing of the OB pixel input from the terminal 9 is input to the integrating amplifier 5 (corresponding to the negative feedback signal generating means in the claims).

The integrating amplifier 5 includes a capacitor 5b and a resistor 5
c forms a predetermined integration time constant, and a differential voltage (clamp error voltage) between the sampled and held OB level and a predetermined reference voltage VREF input from the terminal 6 is the integration time constant. In addition to being integrated, the output (deviation amount from the voltage VREF) is input to the offset addition circuit 3 as a subtraction value and subtracted by the feedback addition circuit 3.

Further, in the integrating amplifier 5, the amplitude limiting diodes 5e and 5f are connected in parallel with the capacitor 5b with the polarities of the anode and the cathode reversed, so that the clamp error voltage input to the integrating amplifier 5 can be adjusted. On the other hand, it functions to limit the output of the integrating amplifier 5 with a constant voltage amplitude (the forward voltages of the diodes 5e and 5f are opposite in direction).

The manner in which the OB level of the output signal 1C of the variable amplifier 4 is clamped to the DC voltage level VREF and converges is exactly the same as that of the conventional example shown in FIG. 5, and is not shown here. .

The OB pixel output of the CCD output 1A is the CDS
Although the DC voltage relatively close to the reference voltage VREF is maintained by the function of the (correlation double sampling) circuit 2, the difference component (CCD offset) between the feedthrough component and the signal component of the CCD 1 and the imaging A dark current component depending on the temperature of the element is superimposed and has an offset error (usually several millimeters to several tens of millivolts).

This offset error varies from image sensor to image sensor and also changes depending on the temperature. Then, this offset error is amplified by the variable amplifier 4 and finally output as the black level fluctuation VERR of the image pickup signal.

The black level fluctuation VERR is detected by the sample-hold circuit 7 and the integrating amplifier 5 as a difference in VREF voltage, integrated, and output as an integrated output signal 1B. The deviation amount of the output 1B from the voltage VREF is CDS. It is subtracted from the output signal 1A of the circuit 2.

At this time, it is assumed that the diode elements 5e and 5f having a forward voltage larger than this are selected so as not to limit the voltage to the integrated output due to the offset error.

As a result, this operation is repeated for each output of the OB clamp pulse 1D, whereby the OB pixel output of the integrated output 1B and the output signal of the variable amplifier 4 converges to the reference voltage VREF.

Next, a clamp operation when blooming occurs in this embodiment will be described.

FIG. 2 shows operation waveforms of the respective parts for explaining the clamp operation when blooming occurs in this embodiment.

The OB output of the CDS output 1A rises rapidly with the occurrence of blooming, and the CCD saturation level VS
Reach AT. The OB output of PGA output 1C is initially C
As the OB output of DS output 1A rises, it starts to rise,
It is input to the integrating amplifier 5 through the sample-hold circuit 7 and acts so as to gently reduce to the reference voltage VREF with respect to the increased OB level of the CDS output 1A with a response time according to the time constant set by the integrating amplifier 5.

However, the CCD saturation level VSAT is rapidly increased.
The OB fluctuation VSAT input to the integrating amplifier 5 is not integrated as it is with respect to the OB output that has risen up to the OB output.
The amount of subtraction to is limited.

Therefore, the OB pixel output of the integrated output 1B and the output signal of the variable amplifier 4 does not converge to the reference voltage VREF as in the normal clamp operation, but to the amplitude limit voltage VCLIP.

At this time, the OB output of the variable amplifier 4 is approximately VCLIP with respect to the original correct OB output level.
Since it is clamped to the reference voltage VREF when it rises by the voltage, the image pickup signal is the voltage VC.
Only the rise due to LIP will result in black sinking. Therefore, by appropriately setting the VCLIP voltage, it is possible to suppress the blackening of the image pickup signal after clamping.

After the blooming of the CCD is resolved,
This time, the OB output of the variable amplifier 4 is higher than the original correct OB output level by the VCL increased by blooming.
It is raised to the reference voltage VREF by the variation of the IP voltage. Therefore, by appropriately setting the VCLIP voltage, the time required for the image pickup signal after clamping to return to the correct OB output level can be shortened.

For example, the CCD saturation level VSAT is 1
If the VCLIP voltage is set to 0.2 V at V, the amount of black sunken and the recovery time during blooming will be approximately 5
It can be reduced to one-third.

Further, in order to briefly explain the basic operation of the clamp, in the present embodiment, the gain of the variable amplifier 4 is treated as one time, but the gain of the variable amplifier 4 is set in the offset addition circuit 3. It is needless to say that an appropriate VCLIP voltage is determined in consideration of the gain setting value, considering that the offset correction amount is multiplied by the gain.

(Embodiment 2) By the way, element characteristics of the diode shown in Embodiment 1 (forward voltage of the diode)
In the feedback limiting means utilizing the above, the voltage level (VCLIP voltage) to be limited depends on the element characteristics, and therefore cannot be adjusted with high accuracy.

Further, the VCLIP voltage suitable for limiting the OB fluctuation due to blooming depends on the set gain of the variable amplifier.

Therefore, by switching the VCLIP voltage in accordance with the set gain of the variable amplifier, the same effect can be obtained in all ranges from low gain to high gain, which is the sensitivity variable width of the image pickup apparatus. The second embodiment to be described below is one in which the operation is devised.

FIG. 3 is a block diagram showing the structure of the main part of the "imaging device" according to the second embodiment.

The configuration of FIG. 3 will be described.

Reference numeral 31 is a CCD (CCD image sensor) for converting an optical image of a subject into an electric signal.
The image pickup signal output from 32 is input to a circuit 32 called a CDS (correlation double sampling) circuit to remove reset noise, and then input to an offset addition circuit 35 to add a predetermined offset voltage, The offset addition output is input to the variable amplifier 38.

Further, the CDS circuit 32 constitutes a CDS circuit which uses the predetermined reference voltage VREF input from the terminal 33 as a reference of the feedthrough portion of the image pickup signal. Similarly, the variable amplifier 38 has the reference voltage VREF. It forms a DC amplifier using VREF as a reference for DC amplification of an image pickup signal.

The variable amplifier 38 is a gain varying means for correcting the output sensitivity variation of the CCD 1 and switching the sensitivity setting of the image pickup device.

The amplified output signal from the variable amplifier 38 is A
It is input to the / D converter 39 and converted into a digital signal. The image pickup signal converted into a digital signal is input to an image processing / recording / display circuit (not shown) on the one hand, and on the other hand, is input to the digital arithmetic circuit 42 and the OB level contained in the digital signal is Current DA extracted
It is converted to an analog current value via C40 (D / A converter) and output.

Digital arithmetic circuit 42 and current DAC 4
An OB clamp pulse synchronized with the read timing of the OB pixel is input to the terminal 0 from 0, whereby the OB level is extracted and the current DAC 40 is driven.

The output of the current DAC 40 is connected to the capacitor 37 whose one end is grounded. By charging and discharging the output current to the capacitor 37, the extracted OB is extracted.
The level is integrated with a predetermined time constant composed of the current value and the capacitor 37, and the output is offset via the buffer circuit 36 as a subtraction value
It has a configuration of feedback control in which it is input to 5 and subtracted.

Further, a voltage limiting circuit 34 is connected to the output of the current DAC 40. The voltage limiting circuit 34 is an NPN.
Comprising a transistor 34b, a PNP transistor 34d, and a resistor 34c, the transistor 3 having complementary characteristics
An emitter follower buffer formed by 4b and 34d is connected in a subordinate manner, and its output is connected to the output of the current DAC 40.

Limiting voltage VCL applied from terminal 34a
The IP is transmitted to the output of the DAC 40 so that the voltage temperature drift due to the transistor is canceled.

Output current of current DAC 40 and capacitor 3
When the voltage integrated and output by 7 is smaller than the limit voltage VCLIP, the transistor 34d is cut off, and almost no current flows through the emitter of the transistor 34d. Therefore, the voltage limit circuit 34 is electrically connected to the current DAC 40.
Is cut off from the output of the
When it is larger than P, a current is drawn from the capacitor 37 through the emitter of the transistor 34d, and the output of the current DAC 40 is limited by the limit voltage VCLIP.

The situation when the OB level of the output signal of the variable amplifier 38 is clamped to the DC voltage level VREF and converges is exactly the same as that of the conventional example shown in FIG. do not do.

The OB pixel output of the CCD output maintains a DC voltage relatively close to the reference voltage VREF by the function of the CDS (correlation double sampling) circuit 32, but in reality, the feedthrough component of the CCD 1 and the signal. A difference component (CCD offset) from the component and a dark current component depending on the temperature of the image sensor are superposed to have an offset error (usually several millimeters to tens of millivolts).

This offset error varies from image sensor to image sensor and also varies depending on temperature. Then, this offset error is amplified by the variable amplifier 38 and finally output as the black level fluctuation VERR of the image pickup signal.

The black level fluctuation VERR is detected by the digital operation circuit 42 and the current DAC 40, integrated, and passed through the buffer circuit 36 as a CD output as an integrated output signal.
It is subtracted from the output signal of the S circuit 32.

By repeating this operation for each output of the OB clamp pulse, the black level fluctuation VERR approaches zero, and the OB output of the CDS circuit 32 becomes the reference voltage VR.
As it approaches EF, the OB level after A / D conversion also converges to a predetermined target value correspondingly.

Here, the limiting voltage VCLIP given from the terminal 34a is a control voltage supplied by a DA converter for system voltage control (not shown), and can be variably set according to the gain setting value of the amplifier 38. To do.

That is, the limiting amount of the amplitude variation with respect to the reference voltage VREF when the gain setting value is 1 is A, and the limiting amount A of the amplitude variation with respect to the reference voltage VREF when the gain setting value is 1 is It is assumed that the offset error of the image sensor is not exceeded, that is, the variation amount due to the offset error is not limited.

At this time, the limit voltage VCLIP when the gain setting value is 1 is V
REF + A The limit voltage VCLIP when the gain setting value is double is V
REF + A / 2 Limit voltage VCLIP when the gain setting value is 4 times is V
For example, REF + A / 4, the limiting amount of the amplitude variation is set by being inversely proportional to the gain setting value and is given by switching.

By setting the limit voltage VCLIP in such a manner, the gain setting value of the variable amplifier 38 becomes 1
In any case of double, double, and quadruple, the limiting voltage corresponding to the output side of the variable amplifier 38 can be maintained at the constant voltage A.

Next, a clamp operation when blooming occurs in this embodiment will be described.

The operation waveforms of the respective parts for explaining the clamp operation at the time of blooming are almost the same as those of FIG. 2 used in the description of the first embodiment, and therefore FIG. (Including) will be described below.

The OB output of 1A, which is the output of the CDS 31, rises rapidly with the occurrence of blooming, and the CCD
The saturation level VSAT is reached. The OB output of 1C, which is the output of the PGA 38, starts to rise in accordance with the rise of the OB output of the CDS output 1A, and is input as a current value to the capacitor 37 through the AD converter 39 and the digital arithmetic circuit 42 and the current DAC 40. Is the response time according to the time constant set by the current DAC 40 and the capacitor 37,
As the integrated output 1B, it works so as to gently reduce to the reference voltage VREF with respect to the increased OB level of the CDS output 1A.

However, the CCD saturation level VSAT is rapidly increased.
The current value input to the capacitor 37 is integrated as it is with respect to the OB output that has risen to OB fluctuation VSAT.
The voltage limiting circuit 34 limits the amount of subtraction to the offset adder 35 by the predetermined voltage VCLIP.

Therefore, the OB of the output signal of the integrated output 1B and the variable amplifier 38 is the same as in the normal clamp operation.
The pixel output does not converge to the reference voltage VREF, but
It converges to the amplitude limit voltage VCLIP.

At this time, the OB output of the variable amplifier 38 is approximately VCLI with respect to the original correct OB output level.
Since the voltage is clamped to the reference voltage VREF when it rises by the amount of P voltage, the voltage V
Only the increase due to CLIP results in a decrease in black sinking. Therefore, by appropriately setting the VCLIP voltage, it is possible to suppress the blackening of the image pickup signal after clamping.

After the blooming of the CCD is resolved,
This time, the OB output of the variable amplifier 38 is the original correct OB.
VC increased by blooming against output level
The fluctuation of the LIP voltage is raised to the reference voltage VREF. Therefore, by appropriately setting the VCLIP voltage, the time required for the image pickup signal after clamping to return to the correct OB output level can be shortened.

For example, the CCD saturation level VSAT is 1
When V, (VCLIP-VREF) voltage, 0.2V
By setting with, it is possible to suppress the amount of black sunken amount and the recovery time to about 1/5 during blooming.

Then, as described above, (V
Since the CLIP-VREF) voltage is set to a constant amplitude limiting amount A irrespective of the gain of the variable amplifier 38, the black sunken amount and the recovery time also have a constant effect irrespective of the gain of the variable amplifier 38. realizable.

In the first and second embodiments, the image pickup device, the CDS circuit, the offset adder,
Although an example in which the configuration of the signal processing is configured in the order of the variable gain amplifier is described, the offset addition to the offset adder of the present invention is limited, that is, the element variation of the image pickup means and the variation due to the temperature characteristic and the amplifying means. The order of signal processing is not necessarily limited to the above-described configuration, based on the principle of limiting the feedback of the negative feedback signal that deviates from the amount.

[0093]

As described above, according to the present invention,
Even if OB level fluctuations that greatly deviate from the proper level occur in the CCD output due to the occurrence of CCD blooming, the amount of offset addition is limited by providing an appropriate feedback limiting means for the feedback signal of the feedback clamp circuit. , OB output can be obtained by following an erroneous black level and causing no problem of black sunkenness in the image pickup signal.

Further, even after the blooming of the CCD is resolved, the normal OB level can be quickly restored.
An image pickup signal with excellent responsiveness can be obtained.

Further, according to the present invention, the feedback limit level for the negative feedback signal is varied according to the gain of the variable amplifying means. In the entire range from low gain to high gain, which is the sensitivity variable width of the image pickup apparatus, it is possible to obtain an image pickup signal with a stable effect regardless of the sensitivity.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main configuration of a first embodiment.

FIG. 2 is an explanatory diagram of a clamp operation when blooming occurs.

FIG. 3 is a block diagram showing the main configuration of the second embodiment.

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

FIG. 5 is an explanatory diagram of a clamp operation.

FIG. 6 is an explanatory diagram of a clamp operation when blooming occurs in a conventional example.

[Explanation of symbols]

1 CCD 2 CDS circuit 3 Offset addition circuit 4 variable amplifier 5 integrating amplifier 5e, 5f Amplitude limiter 6 Reference voltage VREF 7 Sample and hold circuit

Claims (10)

[Claims] 1. An image forming means for optically forming an image of a subject on an image pickup device, an image pickup device for converting an optical image of the subject into an electric signal, and an electric signal after photoelectric conversion by the image pickup device. Offset adding means for adding a DC voltage,
Amplification means for amplifying with a predetermined gain or a variable gain,
Sample hold means for sample-holding the optical black level included in the image pickup signal after the image pickup signal after the offset addition processing by the offset addition means and the amplification processing by the amplification means, a predetermined reference value and the sample hold means In the image pickup apparatus having a negative feedback signal generating means for generating the DC voltage as a negative feedback signal based on the difference in the optical black level held by, the negative feedback signal generating means is provided with feedback limiting means. An imaging apparatus, wherein the DC voltage added by the offset adding means is limited. 2. The image pickup apparatus according to claim 1, wherein the negative feedback signal generating means has a predetermined integration time constant with respect to a change in the optical black level of the image pickup means. . 3. The image pickup apparatus according to claim 1, wherein the feedback limiting unit limits feedback of a negative feedback signal that deviates from variations in the image pickup element, temperature characteristics, and fluctuation amounts of the amplifying unit. A characteristic imaging device. 4. The image pickup apparatus according to claim 1, wherein the feedback limiting unit varies a feedback limiting level for a negative feedback signal according to a gain of the amplifying unit. 5. An image forming means for optically forming an image of a subject on an image pickup device, an image pickup device for converting an optical image of the subject into an electric signal, and an electric signal after photoelectric conversion by the image pickup device. Offset adding means for adding a DC voltage,
Amplification means for amplifying with a predetermined gain or a variable gain,
AD conversion means for converting the analog image pickup signal after the offset addition processing by the offset addition means and the amplification processing by the amplification means into a digital signal, and the optical black level included in the digital signal obtained by the AD conversion means is extracted. And a negative feedback signal generating means for generating the DC voltage as a negative feedback signal based on a difference between a predetermined reference value and the optical black level extracted by the optical black level extracting means. And a feedback limiting unit provided in the negative feedback signal generating unit to limit the DC voltage added by the offset adding unit. 6. The image pickup device according to claim 5, wherein the negative feedback signal generation means has a predetermined integration time constant with respect to the fluctuation of the optical black level. 7. The image pickup apparatus according to claim 5, wherein the feedback limiting unit limits feedback of a negative feedback signal that deviates from variations in the image pickup element, temperature characteristics, and fluctuation amounts of the amplifying unit. A characteristic imaging device. 8. The image pickup device according to claim 5, wherein the feedback limiting unit is responsive to a gain of the amplifying unit.
An image pickup device characterized by varying a feedback limit level for a negative feedback signal. 9. An amplifying means for amplifying an electric signal from a photographing element, and a feedback type OB including the amplifying means.
An image pickup method for an image pickup apparatus comprising a clamp circuit, wherein the amplitude of the negative feedback signal in the OB clamp circuit is limited to a predetermined value or less. 10. The imaging method according to claim 9, wherein when the gain of the amplifying unit is variably set, the predetermined value is changed according to the gain to be set. Method.