JPS6319977A - Accumulation time switching solid-state image pickup device - Google Patents

Abstract

PURPOSE:To remove the level change of an output signal generated from an image pickup device by controlling a gain control circuit or a diaphragm control circuit at the time of switching accumulation time. CONSTITUTION:An image pickup element 2 constituted of an interline CCD outputs an image pickup electrical signal to the gain control circuit 3 based on a pulse signal outputted from a driving circuit 7. An output of the control circuit 3 is converted into an objective signal type by a process circuit 4 and outputted as a signal output. At the time of changing the charge accumulation time by switching a field accumulation mode and a frame accumulation mode, a system control circuit 8 controls the diaphragm control circuit 6 and the gain control circuit 3 in accordance with a detecting signal level detected by a level detecting circuit 5. The level of the detecting signal is kept at a constant value by controlling the aperture of a diaphragm 1 and the gain. Consequently, level variation at the time of mode switching can be removed and dynamic resolution can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The storage time switching imaging device of the present invention is used in television cameras, particularly single-chip television cameras, and eliminates signal level fluctuations when switching storage time modes. It is suitable as a home camera that can be used automatically and can be easily used by anyone.

, Prior Art A solid-state imaging device used in a conventional imaging device is shown in FIG. FIG. 7 is a schematic diagram of an interline COD, 101 is a photodiode that converts into an electric signal, 102
is a CCD that performs vertical scanning (hereinafter referred to as V-CCD),
103 is a CCD (hereinafter referred to as H-C) that performs horizontal scanning;
CD), 104 is a floating differential amplifier (hereinafter referred to as FDA) that converts the photoelectrically converted charge into voltage.The photodiode marked with Ω is the odd field 0V.
-CCDK is read out, and the photodiode marked with Δ is read out to the even field V-COD and sequentially scanned in the vertical and horizontal directions. For example, the signal from the photodiode 101-a is transferred from the location 102a attached to the vl electrode of the V-CCD, and is transferred vertically for each horizontal scan. Assuming that the electrodes of the V-COD are v1 to v4, the voltage waveforms of v1 to v4 are shown in FIG. 8a. The signal charge is transferred to the electrode with the higher applied voltage, and is sequentially transferred to the electrodes from 1 to v4. H- to perform horizontal scanning
Similarly, in COD, voltages are sequentially applied to the electrodes from H1 to H4. The voltage waveform is shown in FIG. 8C. In this way 1
When scanning of a field is completed, the signal charge of the next field is outputted as V-CODIC,d.

When the scanned field is an odd field marked with a circle, the next field is an even field marked with a Δ, and the voltage shown in Figure 8 is applied to perform scanning. Therefore, the period in which signal charges are read out from the same photodiode is every two fields, and the accumulation time is 1730 seconds, assuming that one field is 1/60 seconds.

Problems to be Solved by the Invention The imaging device that performs scanning by driving the COD as described above can obtain images with less flickering when captured under flickering lighting such as fluorescent lights, but when moving objects such as cars There is a problem in that when an image is captured, the image obtained becomes blurred.

As a second conventional example, as shown in FIG. 9, there is a method in which the reading method from the photodiode is changed and the storage time is set to the time of one field. In the odd field, signal charges are simultaneously read out from the O-marked photodiodes 101a and 101b to the v3 electrode of the V-COD. The voltage waveform is shown in Figure 10a.

The scanning in the horizontal direction is the same as in the first conventional example, and the data is sequentially transferred to v1 to v4 for each horizontal scan. In this way, signals L'l are output from all photodiodes in the same field. In the next even field, photodiode 1 marked with Δ
01b and 101c also simultaneously transfer signal charges to V-COD v
Read out to the 3rd electrode. The voltage waveform is shown in FIG. By reading the signal from the photodiode in this way, the accumulation time is set to one field or 1760 seconds, and there is a device that improves the blurring of an image when a moving object is imaged.

However, in this case, there is a problem in that images captured under flickering lighting such as fluorescent lamps tend to flicker more often.

A third conventional example is disclosed in, for example, Japanese Unexamined Patent Publication No. 57-17840. In this example, the driving method of the image sensor is switched to switch between frame accumulation and field accumulation as shown in Figs. It is now possible to switch to a method that is less affected by flicker.

However, in this method, the way the pixels and signals are mixed is different before the pixel signal is obtained as an output signal from the image sensor. Therefore, there is a problem in that it cannot be used in a single-chip color camera in which a mosaic color filter is attached to an image sensor and color separation is performed using level differences in pixel signals.

In view of this point, the present EIA switches the storage time to frame period and field period in a single-chip color camera, and
Another object of the present invention is to provide a storage time switching solid-state imaging device that can realize a single-chip color camera that can eliminate signal level changes during switching.

Means for Solving the Problems The present invention includes an aperture control circuit for controlling the amount of light incident on the image sensor, a system control circuit and a gain control circuit for controlling the storage time of the image sensor, and a control circuit for controlling the signal when switching the storage time. This is an imaging device that eliminates level changes in the output signal of the imaging device by performing level changes by combining aperture control and gain control.

Function: With the above-described configuration, the present invention transfers charges at high speed in ■-bunking, reads out signals from the image sensor in the same way as in the frame accumulation mode, and only saves the signal charge accumulation time to one frame scanning period. By switching to one field scanning period, it is possible to switch the accumulation time in a single-chip color camera, and the change in signal level caused by switching the accumulation mode is eliminated by using a gain control and aperture control circuit. It is. In this way, the storage time of the image sensor is controlled, and the illuminance is used to determine whether, for example, flickering of the illumination light is a problem or blurring (dynamic resolution) due to subject movement is a problem. When flickering is a problem in low illumination, the accumulation time is lengthened (frame accumulation mode) When the illuminance is high and blurring of the captured image due to subject movement is a problem, the accumulation time is shortened (field accumulation mode) This makes it possible to automatically switch between images to solve the problem of flickering and blurring of captured images.

Embodiment FIG. 1 shows a block diagram of a storage time switching solid-state imaging device according to a first embodiment of the present invention. 1st
In the figure, 1 is an aperture that controls the amount of incident light, 2 is an image sensor that converts an optical image into an electrical signal, 3 is a gain control circuit that varies the signal level, and 4 is a process circuit that converts the image signal into the desired signal format. , 6 is a level detection circuit that detects the signal level of the image sensor, 6 is a throttle control circuit that controls opening and closing of the throttle according to the input signal, and 8 is a system control circuit that determines the operating conditions of the imaging device according to the imaging conditions. be.

The operation of the storage time switching solid-state imaging device constructed as described above and according to the nine embodiments will be described below.

The configuration of the image sensor 2 and the mosaic filter are shown in FIGS. 2a and 2b. Image sensor 2f'i is an interline COD that has been conventionally used; 11 is a photodiode, and 12 is a V-COD that performs scanning by transferring signal charges in the vertical direction.
, 13 is H for scanning by transferring signal charges in the horizontal direction.
-COD, f4 is a floating dephasing amplifier (FDA) that converts signal charge into voltage and outputs it,
Figure 2 shows a mosaic filter attached to the front of this image sensor. W is a color filter that transmits all color light, G is a color filter that transmits green light, Ye is a color filter that transmits yellow light, and ay is a color filter that transmits cyan light. A color filter 16& is placed on the photodiode 11a, and a color filter 16b is placed on the photodiode 11b. Similarly, each mosaic color filter corresponds to a photodiode of the image sensor.

FIG. 3 shows the driving pulses applied to the image sensor.

The upper part of the figure shows the pulse position relationship in the frame accumulation mode, and the lower part shows the pulse position relationship in the field accumulation mode. (2) Pulse 28.30 is for driving the V-CCD 12, and H-pulse 29.31 is for driving the H-CCD 3. The pulses other than the V high-speed transfer pulses 24-26 are the same as those shown in FIGS. 8a-C. In the frame storage mode, the signals of the photodiodes are read out alternately field by field by readout pulses 21. Photodiodes 11a and 11c marked with ○ in Fig. 2a
etc., in the odd field, and from the photodiodes 11b, 11d, etc. marked with △, in the even field. This is a conventionally used signal readout mode, and a single-chip color camera (imaging device) is constructed using a mosaic color filter that allows color separation in this mode.

In each field, W, G, Cy, and Ye pixel signals are read out, and the process circuit 4 performs color separation as shown in the following equation.

R=%((W-Cy)+(Ye-G))82%((W-
Ye) +(Cy-G)]Y”% (W+G+Cy+Y
e) R indicates a red signal, B indicates a green signal, and Y indicates a luminance signal.

The process circuit No. 4 performs processing such as white balance, gamma correction, and matrix on these signals, converts them into, for example, NTSC signals, and outputs the signals.

In field storage mode, in V thinking
Add high-speed transfer pulses 24 to 26.

When the read pulse 21 is an odd field, the read pulse 241'j: reads signals from the photodiodes of 1M fields. If the 21st read pulse is an even field, the 24th read pulse is read from an odd field. After reading, a pulse 25 for high-speed transfer is applied to the V-CCD 12. Normal V transfer is approximately 15.5klh once per 1H scanning period, but high-speed transfer pulse is 200klh.
) The frequency should be about 1Z to 1T, and vertical scanning should be completed within blanking. During high-speed transfer, horizontal scanning is not performed, all electrodes of the H-CCD 13 are set to a high potential, and charges transferred from the FDA section 14 are read out.

By reading out charges from the photodiodes in addition to signal reading in this manner, frame readout with only shortened storage time becomes possible. In other words, it is possible to realize field storage frame reading. By using this readout method, the readout relationship of pixel signals does not change even if the storage time is changed, so it is possible to switch the storage time of the image sensor in a single-chip color camera that performs color separation based on signal level differences between pixels. Become.

Next, signal level control when switching between field accumulation mode and frame accumulation mode will be explained.

FIG. 4 shows the amount of light, the opening/closing of the aperture, the image sensor signal level, the gain of the gain control circuit, and the output signal level of the imaging device. The horizontal axis is time. The amount of light increases before and after tl, and the control values for the light and the apertures are closed to the reference level 1. At this point, the system control circuit sVi drive circuit 7 is controlled to switch the storage mode of the image pickup device from the frame storage mode to the field storage mode. Therefore, at the time of switching, the signal level of the image sensor decreases by %. The system control circuit 8 controls the gain control circuit 3 to control the gain from 1 to 2 at t1o after switching the Vi mode for one field scanning period. After controlling the accumulation mode and the gain control circuit in this manner, it is gradually opened and the gain of the gain control circuit is gradually lowered from 2 to 1 (period 11 to t2). In this way, by keeping the signal level constant and lowering the gain/gain of the gain control circuit to 1, the switching from frame accumulation mode to field accumulation mode is completed. Next, switching from field accumulation mode to frame accumulation mode will be explained.

The amount of light decreases before and after time t3, and the aperture control is opened to reference level 2. At this point, the system control circuit 8 controls the gain control circuit to gradually close the throttle and increase the gain to 2. At this time, control is performed so that the signal level after gain control is constant. At time t4 when the gain of the gain control circuit becomes 2, the field accumulation mode is switched to the 7 frame accumulation mode, and after one field scanning time, at t2°, the gain of the gain control circuit is changed from 2 to 1V.
Return C. In this way, it is possible to switch the accumulation mode without changing the output signal level of the imaging device.

As described above, according to this embodiment, by simultaneously controlling the system control circuit, the drive mode of the image sensor, the gain control circuit, and the aperture control circuit, a single-chip color camera using one image sensor can be used. It becomes possible to switch between frame accumulation mode and field accumulation mode, and it also becomes possible to eliminate fluctuations in signal level when switching modes.

FIG. 5 is a block diagram of a storage time switching solid-state imaging device showing a second embodiment of the present invention. In the figure, 1 is a sensor that controls the amount of light incident on the image sensor, 2 is an image sensor that converts an optical image into an electrical signal, 3 is a gain control circuit that changes the gain of the circuit system, and 5 is a signal level detector. a level detection circuit; 7 is a drive circuit for operating the image sensor 2;
The above configuration is similar to the configuration shown in FIG. The difference from the configuration shown in FIG. 1 is that the aperture control circuit 3o operates independently and is not controlled by the system control circuit 31, and the system control circuit 31 controls the drive circuit 7 and the gain control circuit to switch the accumulation mode of the image sensor. This is to control the control circuit 3.

The operation of the accumulation time switching solid-state imaging device of the second embodiment configured as described above will be described below.

The drive mode of the image sensor 2 is the same as that of the first embodiment,
There are frame storage mode and field storage mode. In the field accumulation mode, the signal charges of one field are reset by high-speed transfer during ①-blanking, and the charges of the remaining fields are read out in the same manner as in normal frame accumulation.

Frame accumulation mode is a normal mode without high speed transfer within V blanking. FIG. 6 shows control when switching between these two modes.

The amount of light increases before and after time t1, and the element output decreases at time t1.
becomes standard level 1. At time t1, the frame storage mode is switched to the field storage mode. At this time, the output of the image sensor 1 is %, so the gain of the gain control circuit is doubled at t1o after one field scanning period. As the amount of light increases, the output of the image sensor increases, and the gain of the gain control circuit is lowered accordingly. Next, switching from field accumulation mode to frame accumulation mode will be explained. The light amount decreases before and after time t4, and the level of the image sensor output reaches reference level 2 at time t4. 1/1 at time t4) 'Switch from Ia mode to frame accumulation mode. At this time, the level of the image sensor output doubles, so
The gain of the gain control circuit is set to t2o after one field running period.
%, the signal output level of the imaging device is kept constant, and the accumulation mode is switched.

As described above, according to this embodiment, the mode switching of the image pickup device can be performed without any fluctuation in the output signal level without any control from the aperture circuit trap system control circuit.

Although this embodiment has been described using a single-chip color camera using one image sensor as an example, it goes without saying that it can be used for a multi-chip camera.

Furthermore, although the decision to switch the storage mode of the image pickup device is made based on the signal level or the aperture control level, it goes without saying that the decision to switch the mode may also be made based on other factors, such as a flicker detection device.

As described in detail, according to the present invention, it is possible to switch the storage time even in a single-chip color camera. In addition, since there is no change in signal level when switching, arbitrary switching is possible during imaging.For example, it is also possible to automatically switch the accumulation time using changes in light intensity, and it is possible to use frame accumulation mode with fluorescent lighting. This practical effect has enabled us to realize an imaging device that can reduce the influence of flicker and capture images with high dynamic resolution (less blur) by using field accumulation mode when outdoors in bright conditions. is big.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an accumulation time switching imaging device according to an embodiment of the present invention, FIG. 2a is a schematic diagram showing the structure of an image sensor, FIG. 3 is a schematic diagram showing the structure of a color filter, and FIG. 4 is a waveform diagram showing the operational relationship of each block. FIG. 5 is a block diagram of the storage time switching imaging device according to the second embodiment of the present invention. FIG. 7 and 9 are schematic diagrams showing the configuration and signal readout method of a conventional image sensor, and FIGS. 8 and 10 are waveform diagrams showing the operational relationship of each block in the second embodiment. FIG. 3 is a waveform diagram showing drive pulses for the image sensor. 1...Shibo υ, 2...Image sensor, 3.
...gain control circuit, 4...process circuit,
5...Level detection circuit, 6,3o...
Throttle control circuit, 7... Drive circuit, 8.31
...System control circuit, 11...Photodiode, 12...Vertical CCD, 13...
・Horizontal CCD, 14 ・・Floating degeneration amplifier, 16 ・・・Mosaic color filter, 20 ・・・Vertical transfer pulse, 2j, 24
...Read pulse, 22...Horizontal blanking, 23...Horizontal transfer pulse, 25...
...Vertical high-speed transfer node, 26...Horizontal COD waveform of vertical high-speed transfer section. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 (OL) (b> ζ ゝ 3 swords ~ ~ 4 Figure 1 + and ゛ t4 City μ pattern Aoi Daizu Figure 5 Figure 6 11 8hi "t47 Shimugi no Senni\ Village No. 7 Figure 8 ML/'tfji vw'ti v
ii'w (0L) Figure 9

Claims (3)

[Claims] (1) A solid-state image sensor that converts an optical image into an electrical signal, a drive circuit that switches one period of time (hereinafter referred to as accumulation time) during which the solid-state image sensor converts light into an electrical signal, and an aperture control circuit that controls the amount of light to be output, a gain control circuit that varies the signal level of the solid-state image sensor, and a control circuit that controls the increase or decrease in the output signal level of the image sensor when switching the accumulation time in the drive circuit; An accumulation time switching solid-state imaging device comprising a system control circuit that controls a gain control circuit and a throttle control circuit to maintain a constant signal level. (2) The system control circuit controls the accumulation time to one frame scanning period (hereinafter referred to as frame accumulation mode) or one field scanning period (hereinafter referred to as field accumulation mode), and when switching from frame mode to field mode, one frame scanning After the period, when the gain of the gain control circuit is doubled and switched from field mode to frame mode, 1
2. The storage time switching solid-state imaging device according to claim 1, wherein the gain of said gain control circuit is halved after a frame scanning period. (3) When switching from the frame accumulation mode to the field accumulation mode, the system control circuit controls the aperture control circuit to gradually open the aperture until the amount of light doubles; The gain of the gain control circuit is controlled to be gradually halved so that the signal level does not change at the output of the gain control circuit, and when the conditions for switching from the field accumulation mode to the frame accumulation mode are met, Controls the iris control circuit to gradually close the iris until the amount of light becomes 1/2,
At the same time, the gain of the gain control circuit is controlled to gradually double, and the signal level at the output of the gain control circuit is controlled without fluctuation, and then the field accumulation mode is switched to the frame accumulation mode. An accumulation time switching solid-state imaging device according to claim 2.