JP2652152B2 - Imaging device - Google Patents

Description

Description: TECHNICAL FIELD [0001] The present invention relates to an imaging device using a solid-state imaging device, and more particularly to an imaging device that prevents image deterioration due to a rise in temperature of the solid-state imaging device. .

(Prior art)

For solid-state imaging devices used in imaging devices such as color television cameras, especially charge-coupled devices (CCDs),
The dark current increases as the temperature rises. As a result, the image quality of the television camera device deteriorates.

In a CCD, accumulated charge near the surface of a semiconductor substrate is used as an imaging signal, so that thermally excited charges generated on the surface leak into signal charges. CCD
Although the improvement can be achieved by the structure described above, the dark current generated in principle cannot be eliminated.

When the dark current of the solid-state imaging device increases, the difference in dark current between pixels increases, resulting in a decrease in the signal-to-noise ratio (S / N).
In particular, in order to compensate for the low sensitivity on the short wavelength side of the fixed imaging element, the gain of the output corresponding to the color filter on the short wavelength side is increased, and in a color television camera apparatus of a method of forming a luminance signal, N drops sharply.

 This will be described below.

FIG. 1 shows a solid-state imaging device of a frame transfer CCD. The imaging device 10 includes an exposure unit 11, a storage unit 13, a color stripe filter 15, a horizontal transfer CCD 17, and an FDA 19 that converts charges into a voltage. Here, the charge corresponding to the light image is formed in the exposure unit 11 and is stored in the accumulation unit 13 during the vertical blanking period.
Is transferred to the horizontal transfer CCD 17 every horizontal period to perform horizontal transfer. Thereafter, the voltage is converted into a voltage by the FDA 19 and output.

FIG. 2 shows an example of the color stripe filter 15. R filter 2 and G filter corresponding to the horizontal pixels of the exposure unit 11
23, a B filter 25 is formed. As a result, the output signal becomes an R, G, B point-sequential signal corresponding to each filter.

FIG. 3 shows a conventional color television camera device, and FIG.
FIG. 2 is a signal processing circuit of an output of the solid-state imaging device described in FIG. In the figure, since the output of the solid-state imaging device 10 is output in a dot sequence corresponding to the color filter 15 as described above, the corresponding sample-hold circuits 31, 33 corresponding to the pulse signals SH1, SH2, SH3 having three-phase timing, respectively. , 35 is sampled and held. As a result, the color signals are separated into three color signals of red (R), green (G) and blue (B). This output is
On the other hand, the variable gain amplifiers 37 and 39 use the R white balance (RWB) and B white balance signals (B
The gain is varied by WB). After a luminance signal 43 is formed by the switch circuit 41 and subjected to signal processing by the low-pass filter 45 and the luminance processing circuit 47, a luminance (Y) signal 48 is input to the encoder 49.

The three color signals are divided into three low-pass filters 51, 53,
After signal processing is performed by a series circuit of 55 and processing circuits 57, 59, 61, two color difference signals are generated by a color difference matrix circuit 63.
65RY and 65BY are formed. The encoder 67 receives an input luminance signal 48, two color difference signals 65RY and 65BY, and a synchronization signal 69.
To synthesize and output the television signal 71.

By the way, as shown in FIG. 4, the spectral sensitivity characteristics of the CCD are low on the short wavelength side and high on the long wavelength side. Therefore, the outputs of the sample and hold circuits 31 to 35 have a large R and a small B, depending on the color temperature of the subject. In particular, in the case of a subject having a low color temperature, the output of B becomes very small compared to the output of R.

In addition, the gains of the variable gain amplifiers 37 and 39 are Nyquist folded, so that the generation of a signal is minimized.
Is controlled so that R: G: B = 1: 1: 1. For this reason, the gain of the B signal increases in a subject having a low color temperature. In particular, when the temperature of the CCD becomes high and the dark current increases, the gain of the B signal is high, so the luminance S /
N decreases extremely.

[Object of the invention]

The present invention has been made in order to eliminate the above-mentioned disadvantages. In a normal use state, the generation of a signal is small, and in a high temperature use state, it is possible to prevent the deterioration of an image due to an increase in dark current. It is an object of the present invention to provide an imaging device that is enabled.

(Example of the invention)

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 5 shows an embodiment of the present invention. In the figure, the third
The same reference numerals as those in the drawings denote the same or corresponding parts, and a description thereof will be omitted. A temperature sensor 101 such as a thermistor for detecting the temperature of the solid-state imaging device 10 is arranged near the imaging device 10. A temperature signal 105 from a sensor amplifier 103 which is connected to the temperature sensor 101 and converts its output into a voltage is supplied to a non-inverting input terminal of a voltage comparator 107. The inverting input terminal of the comparator 107 has a reference voltage V _{R from the} voltage source 109.
Is supplied. The comparison output signal 1 of this voltage comparator 107
11 is supplied to the switching control terminal SC of the switching circuit 113, and outputs the B white balance signal (BWB) and the reference voltage Vr from the voltage source 115.
_By switching to ₁ , the gain control signal 117 is obtained.

If the temperature of the solid-state imaging device 10 from a constant temperature determined by the time that is a reference voltage Vr ₁ normal temperature used is low, since the B white balance signal (BWB) is the gain control signal 117, the operation of FIG. 5 is identical to Figure 3 It is.

However, when using a TV camera under high temperature,
When the temperature of the imaging device 10 becomes higher than the above-mentioned constant temperature, the output signal 111 of the voltage comparator 107 is inverted, and the switching circuit 11
3 is switched to the reference voltage source 115 side. Since the reference voltage Vr ₁ is a gain control signal 117, the gain of the variable gain amplifier 39 becomes a constant value. The gain at this time is substantially the same as the gain of the G signal (
₀ dB).

With the above configuration, when the temperature of the image sensor 10 becomes high, the gain of the B signal is switched (decreased) to a constant value, so that the image does not deteriorate.

FIG. 6 shows another embodiment of the present invention. In the figure, the fifth
The difference from the illustrated embodiment is that when the gain of the blue (B) signal is increased, the temperature at which the gain of the B signal switches (falls) to a constant value is changed.

In FIG. 6, the temperature signal 105 of the sensor amplifier 103 is compared with a reference voltage Vr ₂ by a voltage comparator 201. The gain-up switch 203 switches between the other voltage Vh supplied to the voltage application terminal (UP) and the ground potential connected to the ground terminal (NORM) to obtain the gain increase signal 205. Based on the gain increase signal 205 and the output signal 207 from the comparator 201, AND operation is performed by an AND gate 209. The OR gate 2 based on the output signal 211 and the output signal 111 of the comparator 107
A logical OR is performed at 13, and the output signal 215 is supplied to the switching control terminal SC of the switching circuit 113. Further, the gain increase signal 205 is also supplied to the luminance processing circuit 47, and the gain of the luminance (Y) signal is also controlled in conjunction therewith.

When the gain-up switch 203 is turned to the ground side (NORM), the output signal 211 of the AND gate 209 is “0”. Therefore, the gain control is performed by the switching circuit 113 in response to the output signal 111 of the comparator 107, and the operation in that case is the same as the operation described with reference to FIG.

Next, flip the gain up switch 203 to the UP side,
It is assumed that a command is issued to increase the gain of the B signal. In this case, the gain control of the B signal is performed by the output signal 207 of the comparator 201 or the output signal 111 of the comparator 107 by the AND gate 209.

Here, the reference voltage Vr ₂ is is set lower than the reference voltage V _R. The value of the voltage Vr ₂ is set in accordance with the temperature at which the S / N starts to decrease due to an increase in dark current caused by the solid-state imaging device 10 when the switch 203 is tilted to the UP side to increase the gain. is there.

In other words, the switching circuit 113 at a temperature determined by the reference voltage Vr ₂ is when the gain up is switched. Therefore, when the gain is increased, the S / N is sharply reduced. Therefore, the operation is performed so as to lower the gain of the B signal at a lower temperature, thereby preventing image deterioration from an early stage.

In the above-described embodiment, the detection of the increase in the dark current of the image sensor is detected by the temperature sensor. However, the dark current may be detected by sampling an optical black portion.

Also, the signal for controlling the gain is only the B signal,
Both the signal and the B signal may be used, and they may be selectively controlled.

Furthermore, although the gain is switched when the temperature of the image sensor becomes higher than a certain temperature, the gain may be continuously changed according to the amount of dark current. In the example of FIG. 6, the gain is manually increased, but in the case of a so-called AGC method in which the gain of the luminance signal is automatically controlled,
The control may be performed using the level of the luminance signal before controlling the gain or the AGC control signal.

〔The invention's effect〕

As described in detail above, according to the present invention, an imaging device that can reduce the number of signals in a normal use state and reduce the deterioration of an image due to an increase in dark current when used at a high temperature is realized. be able to.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a solid-state image sensor, FIG. 2 is a configuration diagram of a color stripe filter, FIG. 3 is a block diagram showing a configuration of a conventional color television camera device, and FIG. 4 shows a spectral sensitivity characteristic of a CCD. Each of the characteristic diagram, FIG. 5 and FIG. 6 is a block diagram showing the configuration of the imaging apparatus according to the embodiment of the present invention. 10 ...... solid-state imaging device 15 ...... color stripe filter 37, 39 ...... variable gain amplifier 41 ...... switching circuit 101 ...... temperature sensor 107,201 ...... voltage comparator 113 ...... switching circuit 203 ...... gain up switch V _R , Vr ₁ , Vr ₂ …… Reference voltage

Claims (1)

(57) [Claims] 1. An image pickup means, a variable gain control amplification means for changing a gain of a plurality of color signals formed by the image pickup means, and a gain of the variable gain control amplification means according to a color temperature of a subject. Gain control signal forming means for forming a gain control signal for adjusting a white balance by adjusting the level of the dark current in the imaging means with a predetermined reference value so that the level of the dark current is equal to the reference value. An imaging device comprising: a detection unit that forms a predetermined comparison output when the value is larger than a value; and a correction unit that corrects the gain control signal so as to reduce the gain of the blue signal in accordance with the predetermined comparison output of the detection unit. .