JPH058625B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an imaging device using a solid-state imaging device.

(Prior art) When a solid-state image sensor, such as a CCD (charge-coupled device), is used in a television camera, by converting the driving method of the solid-state image sensor, the field (or frame) time of the television signal can be It has been proposed in the past that the accumulation time can be shortened.

For example, in a solid-state image sensor called a frame transfer type, the charge in the light receiving part that performs photoelectric conversion and charge accumulation is removed by vertical transfer once in the middle of the vertical period, and then the remaining vertical period is effectively The driving method that operates as the accumulation time is
For example, this is proposed in Japanese Patent Application No. 55-61098.

According to the above method, for example, in an NTSC type review camera, the accumulation time can be set to 1/60 second, 1/500 second, etc., so even when a large amount of light is incident, the image of a high-speed moving object does not become blurred due to the small aperture. There are effects such as no. However, when performing the above-mentioned operation, when eliminating the charge accumulated up to the middle of the vertical period without extracting it as a signal as described above, especially when the actual accumulation time is shortened, the eliminated charge The amount becomes extremely large. For example, if the effective accumulation time (t ₁ ) is 1/500 seconds, the ratio of the accumulation time t ₂ of the charge to be removed is t ₂ /t ₁ = (1/60-1/500)/1500≒7.3 Approximately Assuming that the charge accumulated at t ₁ is 7.3 times the standard level, at t ₂ it will be at the standard level.
7.3 times more charge is accumulated. When such a large amount of charge is accumulated, it is very difficult to eliminate it all so that it does not affect the actual accumulation time. In particular, the amount of charge generated in so-called highlight areas on the screen is extremely large, and when vertical transfer is performed to discharge charge in the middle of the vertical period, a large amount of charge remains and is output on the screen. There will be a negative impact on.

In addition, this remaining charge becomes 4 to 10 times the signal level (approximately the saturation signal level of the image sensor) at the output of the image sensor, causing an abnormal response of the signal processing circuit, or causing gain control or aperture control. This may cause malfunction.

Furthermore, an imaging device has been proposed in which charges in both the light receiving section and the storage section are removed during the vertical period. In this case, no output signal is obtained in the period before the intermediate transfer, and aperture control, gain control, etc. become inaccurate.

(Objective) It is an object of the present invention to propose a solid-state imaging device that can eliminate the drawbacks of the conventional example described above and at the same time eliminate the adverse effects on the screen when the substantial storage time is varied.

(Example) Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a frame transfer type CCD solid-state imaging device that can be applied to the present invention. 1
is a frame transfer type CCD solid-state image sensor,
2 is a light receiving section that photoelectrically converts incident light from an imaging optical system (not shown) and accumulates charge; 3 is a storage section that transfers the charge of light receiving section 2 and further reads it out every horizontal period; 4 is a storage section 3 is a horizontal register that horizontally transfers the charge transferred every horizontal period by φT, 5 is a charge-voltage converter that converts the charge from the horizontal register 4 into a voltage and outputs it, and DG is provided along the register 4. gate or barrier, DR is the overflow drain.

Figure 2a shows the drive waveform of the frame transfer CCD image sensor 1 in the short time mode, and φI
indicates the driving waveforms of the light receiving section 2, φS of the storage section 3, φT of the horizontal shift register section 4, and φR of the charge-voltage conversion section 5, respectively.

IV is the vertical period of the television signal, and _T2 is the substantial accumulation period.

At the beginning of the vertical period, the charge in the light receiving section 2 is vertically transferred to the storage section 3 by the vertical transfer pulse shown in , and the charge is transferred to the horizontal register 4 one line per horizontal period by the subsequent pulse, and the charge is transferred to the horizontal register 4 one line per horizontal period. The signal is horizontally transferred to the charge-voltage converter 5 by the pulse , where it is converted into a voltage by the pulse and taken out as an output.

After photoelectric conversion and charge accumulation in the light receiving section 2 during the T ₁ period, only the light receiving section is vertically transferred by the pulse, and the charges accumulated during the T ₁ period are removed from the light receiving section. Thereafter, the charges received and accumulated during the _T2 period are vertically transferred to the accumulation section 3 by the pulse. The following operations are similar to those described above.
In addition, in the standard mode in which the accumulation period is about one field period as shown in FIG. 2b, the pulses in FIG. 2 are omitted. Here, only the light receiving part 2 performs vertical transfer due to the pulse in the short time mode, and when eliminating the charge accumulated during the T ₁ period, compared to T ₂ ,
Since the amount of charge accumulated in T ₁ is large, it cannot be completely eliminated and remains.

FIG. 3 shows the output waveform of the image thus obtained.

Vsat is the saturated output voltage of the image sensor, Vav is the standard average output voltage of the image sensor, and T _BLK is the vertical blanking interval. As described above, the remaining charge that could not be eliminated in the vertical transfer before the actual accumulation period _T2 is output, and an output at the Vsat level is generated in the initial period _T3 of the vertical period. If T ₃ is short, it will not appear on the screen, but since Vsat is extremely large, about 3 to 5 times as large as Vav, it has a large negative impact on signal processing, aperture control, gain control, etc.

FIG. 4 shows a first embodiment of the present invention. 101
1 is an imaging optical system including an imaging lens, an optical filter, etc.; 102 is an aperture; 103 is a sample hold circuit that converts the discrete output from the image sensor 1 into a continuous one;
04 is a signal processing circuit that processes the output of the 103 sample and hold circuit and synthesizes a television signal, 1
05 is a smoothing circuit that smoothes the luminance signal output from 104, and 106 is a reference level and smoothing circuit 105.
error amplifier circuit for comparing the outputs of , 107, 108
is a voltage divider that generates a reference level, 109 is 10
7, a switch as a correction means for switching the reference level created in 108; 110 a diaphragm drive circuit as a control means for controlling the amount of photoelectric charge formed in the image sensor by driving the diaphragm; 111 a switch for controlling the image sensor 1; A drive circuit 112 is a synchronization signal as an accumulation time control means for generating drive pulses for the image sensor 1, drive pulses for the sample and hold circuit 103, synchronization pulses for signal processing, television synchronization signals, etc. as shown in the second diagram. Generation circuit, 113
is a switch that changes the output mode of the synchronization signal generation circuit and changes the operation mode of the image sensor 1. Switch 109 and switch 113 are in an interlocking relationship. The image sensor 1 has two operating modes: a standard mode similar to a normal video camera in which the storage time is the vertical period of the television signal, and a short time mode in which only the light receiving section performs vertical transfer in the middle of the vertical period. , the operation mode is switched by switching the output of the synchronizing signal generating circuit 112 using the switch 113.

The subject image passes through the imaging optical system 101 and the aperture 102, is photoelectrically converted by the image sensor 1, is made continuous by the sample hold circuit 103 which outputs it in accordance with the synchronization signal, and is subjected to signal processing by the signal processing circuit 104. A television signal is combined with the synchronization signal from the synchronization signal generation circuit 112 and output to the television signal output terminal 114. On the other hand, a luminance signal for aperture control is output from the middle of the signal processing circuit 104, smoothed by a smoothing circuit 105, compared with a reference level by an error amplification circuit 106, and input to an aperture drive circuit 110 to control the aperture 102.

With this control, the output voltage of the smoothing circuit 105, that is, the average value of the output voltage of the image sensor 1 is adjusted to the voltage divider 1.
Feedback control is performed to maintain a constant voltage set at 07 or 108.

In this embodiment, the reference voltage of the error amplifier 106 is 2
As described above, the switch 109 is operated in an interlocking relationship with the switch 113. That is, the reference voltage is configured to be set depending on whether the image sensor is operated in a standard mode or a short time mode. In addition, 1,101 to 10
8, 110 to 114, etc. constitute an imaging means.

When performing the short-second mode with the operation shown in FIG. 2, the output of the voltage divider 108 in the short-second mode is approximately the third
Set the voltage to be higher by the product of _T3 period and Vsat in the figure. As a result, it was confirmed that in the television signal obtained as the output of the image sensor 1, the brightness of the object on the screen could be kept constant regardless of the operation mode of the image sensor 1.

Although the reference level is configured to be changed by the switch 109, the actual storage time is also configured to be varied continuously or stepwise, and the reference voltage is also changed continuously or stepwise in accordance with the variation. However, the present invention also includes such a method. The present invention is also effective in a device that uses a shutter to control the video signal level of the imaging means instead of using an aperture.

Furthermore, this shutter includes not only mechanical and physical shutters, but also electronic shutters, that is, those that control the storage time.

Of course, it is also effective for controlling the amount of photocharge formed by using a combination of two or three of aperture, shutter, and accumulation time control depending on the video signal level, and thereby controlling the video signal level. be.

In addition, the operation of the sample and hold circuit 103 is
The output of the image sensor during the T ₃ period in FIG. 3 is configured so that it does not enter the input side of the signal processing circuit 104 by shutting it off for the T ₃ period in FIG. 3 or inserting a gate circuit into the signal system to shut it off for the T ₃ period. It's okay. In that case as well, the present invention can be implemented in the same manner as described above. However, in this case, since the video signal is at the black level during the _T3 period, it is necessary to lower the reference level for short seconds.

In the above embodiment, in the short time mode of the image sensor, only the light receiving section performs vertical transfer in the middle of the vertical period, but the charges in both the light receiving section and the storage section are eliminated in the middle of the vertical period. The present invention can also be implemented in this manner. In this case, the reference voltage in the short time mode is set to a voltage lower than that in the standard mode.

FIG. 5 is a diagram showing a second embodiment of the present invention, and shows a modification of the short time mode. In this embodiment, high-speed vertical transfer in the storage section is performed in synchronization with high-speed vertical transfer in the light receiving section. Therefore, the charges in the light receiving section and the storage section are collected in the horizontal shift register 4 and overflow occurs. This overflow charge is transferred to the drain via the gate or barrier DG.
It flows into the DR and is discharged.

Therefore, the output of the charge-voltage converter 5 is missing at the portion . In this case, as described above, the reference voltage in the short time mode is corrected by a switch or the like using a correction means so that it has a value lower than that in the standard mode.

In addition, various types of image sensors such as interline CCDs, MOS image sensors, etc. that are capable of controlling the storage time are being considered, and the output characteristics of the image sensor in the short exposure mode are different from those in the standard mode. The present invention can also be applied to such cases.

Furthermore, although the above embodiment was applied to an aperture control system,
The present invention can also be implemented in a gain control system that operates to vary the gain by voltage and keep the output level constant.

That is, the present invention also includes controlling the video signal level in the output system of the image sensor.

FIG. 6 is a diagram showing a third embodiment of the present invention, in which the same numbers as in FIG. 4 indicate the same elements.

115 is an amplification circuit, 116 is a smoothing circuit that smoothes the output of the amplification circuit 115, 117 is an error amplification circuit that compares the smoothed output with a reference level and forms an error signal, and 118 is the output of this error amplification circuit. This is a transistor whose impedance changes, and this transistor changes the video input level to the amplifier 115, resulting in gain adjustment.

Reference numerals 120 and 121 each represent a voltage divider that outputs a reference level, one of which is input to the error amplification circuit 117 as the reference level. Further, the output level of 120 is higher than the output level of 121.

A switch 119 serves as a correction means for performing the switching, and is switched in conjunction with the switching of the switch 113 that switches the operation mode of the image pickup device.

That is, when the switch 113 is in the short speed mode, the output of the voltage divider 120 is input to the error amplification circuit 117, and when the switch 113 is in the standard mode, the output of the voltage divider 121 is input to the error amplification circuit 117. Set switch 9 to .

Other examples of the configuration in which the video signal level of the imaging device is controlled by gain adjustment as described above include a configuration in which the video signal level of the imaging device is controlled by adjusting the sensitivity of the imaging device itself.

These gain adjustment methods have the advantage of extremely good responsiveness compared to methods that use an aperture, shutter, or the like to change the video signal level.

(Effects) According to the present invention, even if the actual storage time of the image sensor is set short, the influence of unnecessary charges on the screen can be removed.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the frame transfer type CCD, Figure 2 a is an explanatory diagram of the short-time mode, and Figure 2 b
3 is an explanatory diagram of the standard mode, FIG. 3 is an explanatory diagram of unnecessary signals in the short-time mode, FIG. 4 is a diagram illustrating an example of the configuration of the imaging device of the present invention, and FIG. 5 is a tine diagram of the second embodiment of the present invention. FIG. 6 is a diagram showing a configuration example of the third embodiment of the present invention, 102...Aperture, 1...Image sensor, 109...
Switch, 107, 108... Voltage divider, 113...
...Switch, 112...Synchronization signal generator, 105
... Smoothing circuit, 106 ... Error amplification circuit, 115
... Width increase circuit.

Claims (1)

[Scope of Claims] 1. An imaging device that photoelectrically converts imaging light from a subject to obtain a charge, an imaging means for obtaining a video signal based on the charge, a driving means for driving the imaging device, and the above-mentioned an accumulation time switching means for continuously switching charge accumulation time in the imaging device; and controlling the amount of light incident on the imaging device based on a comparison output between the output level of the imaging device and a predetermined reference level. and an exposure amount control means capable of switching the electrical control characteristics by stepwise switching the reference level, and switching the electrical control characteristics in the exposure amount control means and changing the accumulation time in the accumulation time switching means. An imaging device characterized in that switching is linked to each other.