JPH02190087A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To ensure clamping of a black level and to obtain an excellent image pickup signal without decreasing the time constant of a clamp circuit by applying temperature control of a solid-state image pickup element based on an output of an optical black region. CONSTITUTION:The solid-state image pickup device is provided with a temperature control element 2 such as a Peltier element controlling the temperature of a solid-state image pickup element 1 and a sample-and-hold circuit 12 extracting an output signal at the optical black region of the solid-state image pickup element 1. Moreover, the device is provided with a control circuit 13 comparing an output voltage of the sample-and-hold circuit 12, a drive circuit 15 driving the temperature control element so as to make the output voltage of the sample-and-hold circuit 12 equal to the reference voltage based on the comparison output. Thus, the clamping of the black level is ensured without decreasing the time constant of the clamp circuit and an excellent image pickup signal is obtained.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention relates to a solid-state imaging device using a solid-state imaging element, and in particular to a solid-state imaging device that stabilizes a detection signal in an optical black region. Regarding equipment.

(Prior Art) Conventionally, in order to define the black level of a solid-state image sensor, a detection signal of an optical black region is clamped. In this case, since the dark current of the solid-state image sensor changes with temperature and the output voltage changes, it is even more necessary for the clamp circuit to clamp to the same voltage even if the input voltage changes.

Usually, clamping operations are performed during vertical and horizontal blanking periods, but clamping performed during horizontal blanking periods takes a short time, and the time constant required of the clamp circuit must also be shortened. In particular, in high-definition televisions and the like that have recently been attracting attention, the horizontal blanking period is extremely short, and the period of the optical black area is also extremely short, so that conventional clamp circuits may not be able to clamp them. moreover,
Even if there is an abnormality in the optical black area, it will be clamped as is, resulting in a problem that the output signal of the solid-state imaging device will be disturbed.

Further, due to the ambient temperature and the heat generated when driving the solid-state image sensor, changes in dark current due to the temperature of the solid-state image sensor directly appear as output signals in the optical black region. Conventionally, as shown in FIG. 4, the temperature of the solid-state image sensor 1 is detected by a temperature detection element 4 such as a thermal lightning pair, and the temperature is controlled by a Peltier element 2, a radiator 3, etc. so that the detected temperature is constant. The output fluctuations in the optical black area were reduced.

However, the detection by the temperature detection element 4 is only indirect, and there is a detection delay in the case of a sudden temperature change. Furthermore, it is necessary to provide the temperature detection element 4 and to provide wiring for guiding its detection output to the outside, which complicates the configuration near the solid-state image sensor.

(Problem to be Solved by the Invention) Conventionally, in order to clamp the black level in the optical black area, it is necessary to make the time constant of the clamp circuit sufficiently small, but there are limits to reducing this time constant. There is. In addition, since the optical black area is extremely short in devices used in high-definition televisions, etc.
There was a risk that it would not be able to be fully clamped. Furthermore, there is a problem in that an abnormality in the optical black area directly appears as an output abnormality of the solid-state imaging device.

Furthermore, since the output of the optical black area changes depending on the temperature of the solid-state image sensor, it is necessary to maintain the temperature of the solid-state image sensor constant. This method of using a temperature detection element as a temperature control means has a problem in that the configuration near the circumferential imaging element becomes complicated.

The present invention has been made in consideration of the above circumstances, and its purpose is to be able to reliably clamp the black level without reducing the time constant of the clamp circuit, and to provide a good imaging signal. An object of the present invention is to provide a solid-state imaging device that can be obtained.

Another object of the present invention is to be able to maintain a solid-state image sensor at a constant temperature without using a temperature detection element;
An object of the present invention is to provide a solid-state imaging device that can simplify the configuration near the solid-state imaging device.

[Object of the Invention] (Means for Solving the Problems) The gist of the present invention is to control the temperature of a solid-state image sensor based on the output of an optical black region. moreover,
The purpose of this method is to perform clamping during a blanking period excluding the optical black area so that the output of the optical black area matches a reference level.

That is, the present invention (claim 1) provides a solid-state imaging device using a solid-state imaging device having an optical black area,
A temperature control element such as a Bertier element that controls the temperature of the solid-state image sensor, a sample-and-hold circuit that extracts an output signal in an optical black region of the solid-state image sensor, and an output voltage of this sample-and-hold circuit and a reference voltage are compared. The temperature control device is provided with a comparison circuit and a drive circuit that drives the temperature control element so that the output voltage of the sample and hold circuit becomes equal to the reference voltage based on the comparison output of the comparison circuit.

Further, the present invention (claim 2) provides a solid-state imaging device that clamps a black level based on an output of an optical black region of a solid-state imaging device, in which a blanking period other than the optical black region of an output signal of the solid-state imaging device is used. A blanking noise removal circuit that removes noise, a sample hold circuit that takes out an output signal in the optical black area of the solid-state image sensor, a comparison circuit that compares the output voltage of this sample hold circuit with a reference voltage, and this comparison circuit. and means for clamping the signal level of the output signal of the solid-state image sensor through the noise removal circuit during the blanking period so that the output voltage of the sample and hold circuit becomes equal to the reference voltage based on the comparison output of the circuit. This is what I did.

Further, the present invention (claim 3) is such that a solid-state imaging device is constructed by combining the above-mentioned claims 1 and 2.

(Function) According to the present invention, the output in the optical black area is sampled and held, and based on this voltage, the output signal of the solid-state image sensor is clamped during the blanking period outside the optical black area. Here, the blanking period is much longer than the period corresponding to the optical black area and the other blanking periods.

Therefore, the black level can be reliably clamped without reducing the time constant of the clamp circuit. moreover,
By not performing clamping when the comparison output of the comparison circuit exceeds a predetermined level, it is also possible to prevent fluctuations in the black level due to abnormalities in the optical black area.

Furthermore, since the temperature of the solid-state image sensor is controlled based on the output of the optical black area, a temperature detection element, its wiring, etc. are not required, and the configuration near the solid-state image sensor can be simplified. Here, controlling the output of the optical black area to be constant is equivalent to keeping the temperature of the solid-state image sensor constant.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a block diagram showing a schematic configuration of a solid-state imaging device according to an embodiment of the present invention. In the figure, 1 is a CCD image sensor, and the temperature of this image sensor 1 is controlled by a Bertier element 2. The image signal output from the image sensor 1 is supplied to a blanking noise removal circuit 11 . This blanking noise removal circuit 11 removes noise during the blanking period except for the optical black area, and replaces it with a DC voltage. The signal passed through the noise removal circuit 11 is supplied to a first sample and hold circuit 12 for temperature control, and is also supplied to a second sample and hold circuit 22 for clamping and a signal processing circuit via a DC blocking capacitor 21. 26.

The first sample and hold circuit 12 samples and holds the DC level in the optical black area, and the first voltage comparison circuit 13 compares this sample and hold value with a reference level (dark current reference voltage). Here, 1
4 is a reference level generator for defining a reference level. The comparison output of the comparison circuit 13 is the Beltier element drive circuit 1.
5 and drives the Peltier element 2, which is a heat pump. The heat pumped by the Bertier element 2 is then radiated by the radiator 3.

On the other hand, the second sample and hold circuit 22 also samples and holds the signal in the optical black area, and this sample and hold value is supplied to the second voltage comparison circuit 23 and compared with the reference level of the reference level generator 24. . The comparison output of the comparison circuit 23 is supplied to the input terminal of the signal processing circuit 26 via the switch 25, and is also inputted to the gate circuit 27 as a gate signal.

The switch 25 is usually made of a semiconductor switch,
Only the blanking period is closed by the clamp pulse. Therefore, the voltage level during the blanking period becomes the same level as the output of the voltage comparator circuit 23, but the voltage level of the voltage comparator circuit 2
3 compares the optical black level with the black reference level. Therefore, the black level of the imaging signal is controlled to be the same level as the black reference level. In other words,
The circuit operates so that the difference between the input voltages of the voltage comparator circuit 23 is almost eliminated.

The gate circuit 27 gates the clamp pulse so as not to close the switch 25 if the input voltage difference of the voltage comparison circuit 23 is larger than a predetermined value. As a result, even if there is an abnormality in the optical black area, an imaging output with no fluctuation in black level can be obtained. Then, by processing this signal in the signal processing circuit 26, the output of the solid-state imaging device is obtained.

In addition, 28 in the figure is the timing for replacing the synchronization signal with the DC voltage of the blanking noise removal circuit 11, the timing for sampling the optical black area in the first sample hold circuit 12, and the timing for sampling the optical black area in the second sample hold circuit 22. This is a timing generation circuit that generates timing for sampling the black area and timing for clamping during the blanking period. Further, although not shown in the figure, a drive circuit for driving the solid-state image sensor 1, a power supply circuit, an imaging device, and the like are provided.

Figure 2 shows the waveforms of each part, where A is the blanking signal and B is the blanking signal.
denotes an image pickup signal, C denotes a blanking noise removal pulse, D denotes an image pickup signal in which noise during the blanking period is replaced with a DC voltage, and E denotes a sample pulse for temperature control.

Here, a method for controlling the temperature of the CCD image sensor 1 will be explained. The signal in the optical black area of the image sensor 1 consists only of dark current. It is well known that dark current increases as temperature rises. Therefore, a sample/hold pulse is used to sample and hold the signal in the optical black area during one horizontal scanning period (IH), and the sample and hold signal is compared with the voltage of the reference level generation circuit 14, and the Vertier element drive circuit 15 is operated. In this embodiment, the output voltage of the sample-and-hold circuit 12 increases as the dark current increases. Therefore, the comparison circuit 13
When the voltage increases, the Vertier element drive circuit 15 operates to cool the image sensor 1.

FIG. 3 is an enlarged view of an arbitrary horizontal scanning period in FIG. A to D are the same pulse signals as in FIG. F is a sample pulse for the clamp circuit, G is a sampled and held output, H is a state of a gate signal due to a defective optical black area, and ■ is a clamp pulse.

Here, the clamping operation will be explained.

A blanking noise removal circuit 11 replaces the blanking period of the image signal of the CCD image sensor 1 with a DC voltage by using a noise removal pulse to remove optical black. A signal in an optical black region of this image pickup signal during one horizontal scanning period is extracted using a sample/hold pulse and compared with a clamp level. The comparator circuit 23 is configured such that the output voltage is low if the input voltage to be compared is higher than the reference voltage, and higher if the input voltage is lower than the reference voltage.

This output is clamped as a clamp voltage during a blanking period from which noise has been removed. For example, set the reference voltage to O
When set to V, the clamp voltage becomes a voltage such that the optical black area (black level) becomes Ov.

Furthermore, if there is a defect in the optical black area, as shown in FIG. 3, the gate signal is closed only at the defective optical black area to prevent the clamp pulse from entering the clamp circuit. This prevents variations in the black level due to abnormalities in the optical black area. Although clamping is not performed at this time, it hardly causes any problem as long as the abnormality in the optical black area is one-off.

Thus, according to this embodiment, the sample and hold circuit 12
．． By the actions of the comparison circuit 13, drive circuit 15, etc., the signal in the optical black area is controlled to be constant. Therefore, the temperature of the CCD image sensor 1 is maintained constant. In this case, there is no need to use a temperature detection element or the like, and the configuration near the solid-state image sensor can be simplified.

Furthermore, since the black level is clamped during the blanking period excluding the optical black area, the black level can be reliably clamped without reducing the time constant of the clamp circuit. Therefore, a good imaging signal can be obtained. Furthermore, since the switch is forcibly turned off by the gate circuit when the comparative output differs greatly, it is possible to prevent fluctuations in the black level due to abnormalities in the optical black area.

Note that the present invention is not limited to the embodiments described above, and can be implemented with various modifications without departing from the gist thereof. For example, the Bertier element as the temperature control element may be controlled not only by DC drive but also by pulse drive.

Further, the temperature control element is not limited to a Bertier element, but may be any element that can absorb heat when energized.

[Effects of the Invention] As detailed above, according to the present invention, the temperature of the solid-state image sensor is controlled based on the output of the optical black area, so the temperature of the solid-state image sensor is controlled at a constant level without using a temperature detection element. The temperature can be maintained at a certain temperature, and the structure near the solid-state image sensor can be simplified. In addition, clamping is performed during the blanking period excluding the optical black area,
Since the output of the optical black area is made to match the reference level, the black level can be reliably clamped without reducing the time constant of the clamp circuit, making it possible to obtain a good imaging signal. becomes.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing a solid-state imaging device according to an embodiment of the present invention, Fig. 2 is a signal waveform diagram showing the timing of a sample pulse for temperature adjustment in the same device, and Fig. 3 is a clamp operation in the same device. FIG. 4 is a schematic configuration diagram showing a conventional solid-state imaging device equipped with a temperature control mechanism. 1... CCD image sensor, 2... Bertier element, 3...
...heatsink, 11...blanking noise removal circuit,
12.22...Sample hold circuit, 13.23.
...Voltage comparator circuit, 14.24...Reference voltage generator,
15...Bertier element drive circuit, 21...DC blocking capacitor, 25...switch, 26...signal processing circuit, 27...gate circuit, 28...timing generation circuit.

Claims (5)

[Claims] (1) A solid-state image sensor having an optical black area, a temperature control element that controls the temperature of the solid-state image sensor, a sample-and-hold circuit that extracts an output signal in the optical black area of the solid-state image sensor, and a sample-and-hold circuit that takes out an output signal in the optical black area of the solid-state image sensor A comparison circuit that compares the output voltage and a reference voltage, and a drive circuit that drives the temperature control element so that the output voltage of the sample and hold circuit becomes equal to the reference voltage based on the comparison output of the comparison circuit. A solid-state imaging device characterized by: (2) a solid-state imaging device having an optical black region; a blanking noise removal circuit for removing noise in a blanking period other than the optical black region of an output signal of the solid-state imaging device; a sample-and-hold circuit for extracting an output signal; a comparison circuit for comparing the output voltage of the sample-and-hold circuit with a reference voltage; and a comparison circuit for making the output voltage of the sample-and-hold circuit equal to the reference voltage based on the comparison output of the comparison circuit. , means for clamping a signal level during a blanking period of an output signal of the solid-state image sensor that has passed through the noise removal circuit. (3) a solid-state image sensor having an optical black area; a temperature control element that controls the temperature of the solid-state image sensor; a first sample and hold circuit that extracts an output signal in the optical black area of the solid-state image sensor; a first comparison circuit that compares the output voltage of the first sample and hold circuit with a reference voltage; and a first comparison circuit that makes the output voltage of the first sample and hold circuit equal to the reference voltage based on the comparison output of the first comparison circuit. a drive circuit that drives the temperature control element, a blanking noise removal circuit that removes noise in a blanking period other than the optical black region of the output signal of the solid-state image sensor, and an output signal of the solid-state image sensor in the optical black region. a second sample-and-hold circuit that takes out a signal; a second comparison circuit that compares the output voltage of this second sample-and-hold circuit with a reference voltage; It is characterized by comprising means for clamping the signal level during the blanking period of the output signal of the solid-state image sensor that has passed through the noise removal circuit so that the output voltage of the sample and hold circuit is equal to the reference voltage. Solid-state imaging device. (4) The solid-state imaging device according to claim 1 or 3, wherein the temperature control element is a Peltier element. (5) The clamp means includes a switch that is turned on during the blanking period to apply the comparison output of the comparison circuit to the output signal of the solid-state image sensor, and a switch that is turned on when the comparison output of the comparison circuit exceeds a predetermined level. 4. The solid-state imaging device according to claim 2, further comprising a gate circuit that forcibly turns off the solid-state imaging device.