JPH04207589A - Image pickup device - Google Patents

Abstract

PURPOSE:To substantially expand a dynamic range in a simple and economical processing circuit by providing a reset means which returns a photoelectric converting section and a charge holding means independently to an initial state. CONSTITUTION:The charges remaining at the base of a reading out transistor 60 are first cleared by conducting and resetting a rest MOS transistor 30 and a transfer MOS transistor 40 by driving pulses phiC and phiR2. An output line reset MOS transistor 90 is then conducted by a driving pulse phiVC and its emitter is set at a constant potential. The TR 60 is forward biased by impressing a positive driving pulse phiR2 to a capacitor 50. The charges remaining at the base are discharged and the reset operation ends. Then, from the reset operation of a photodiode 10 to the accumulation operation and from the transfer of the accumulated charges to reading out operation which are the basic operations of the image pickup element are executed by changing the timings of the driving pulses phiR1, phiR2, phiC, phiT, phiVC. The dynamic range is widened in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an imaging device, and particularly to a substantially dynamic imaging device.
The present invention relates to an imaging device with a wide range.

[Prior Art] Imaging devices are widely used as video camera units such as camera-integrated VTRs and still video cameras. Video cameras that use image pickup tubes or solid-state pseudoimaging elements have a narrower dynamic range than traditional silver-halide photographic systems, and as a result, when backlit, etc., whites and darks are crushed (parts with extremely high or low brightness levels). (common name) etc. occur.

With conventional video cameras, in such cases, the aperture is opened by about 2 stops either manually or by operating the retrograde correction button.
The amount of light was being adjusted.

However, even when such backlight compensation is performed appropriately,
Even if the main subject has the proper exposure, overexposure will occur in the background, leaving the screen with only a white background.

In other words, the narrow dynamic range of the imaging device cannot be solved by simply adjusting the light amount so that the exposure amount of the main subject is appropriate, as in conventional devices.

One way to solve this problem is to expand the dynamic range by performing two exposures, for example. This method uses a high-speed shutter operation (for example, 1/100
0 seconds). With this method, the exposure time differs by 16 times, so the dynamic range can be expanded by 16 times.

[Problems to be Solved by the Invention] However, the method of expanding the dynamic range by performing two exposures as described above has the following problems.

For example, in a movie camera that shoots moving images, a normal exposure signal and a high-speed shutter signal are read out for each field, so when two image signals are combined, the combined signal is 2.
The field is only an image signal for one image. Therefore, the same composite signal is output from the memory or the like during the two-field period, resulting in a problem that the dynamic resolution decreases.

Furthermore, since both of the two exposures are performed by scanning the image sensor in a predetermined sequence, the next scan cannot be performed until after all the signals have been output. In this case, the region where the image sensor is saturated is only a small part of the photographic screen.Signal replacement for improving the dynamic range of the above two image signals requires only a small amount of data. In other words, one image consists of a lot of unnecessary information, and it is uneconomical to output all two imaging signals and perform image processing as in the past.

In consideration of these problems, the present invention essentially aims to provide an imaging device that has a wide dynamic range, simple image processing, and can obtain normal moving images.

[Means for Solving the Problems] An imaging device of the present invention is an imaging device configured by arranging a plurality of photoelectric conversion elements, in which the photoelectric conversion element converts incident optical information into a charge signal. A charge holding means for temporarily holding charges generated in the photoelectric conversion section; and a reset means for independently returning the photoelectric conversion section and the charge holding means to their initial states. shall be.

[Function J] In the imaging device of the present invention, the photoelectric conversion element has a photoelectric conversion section, a charge holding means, and a reset means for independently and randomly returning these to the initial state, and the reset means , the desired area is reset and the exposure time is controlled to obtain areas with different exposure amounts within one image, so even if a bright subject that would otherwise saturate the imaging device is imaged, the imaging device will not become saturated.

[Example] Hereinafter, an example of the present invention will be described in detail using the drawings.

FIG. 1 is a block diagram showing a unit circuit of an embodiment of an image sensor according to the present invention.

FIG. 2 is a basic drive timing diagram of the unit circuit of FIG. 1.

In FIG. 1, 100 indicates a unit circuit section, which constitutes one photoelectric conversion element. 1o is a photodiode serving as a photoelectric conversion section, 2o is a transfer MOS transistor, and 30 is a reset MOS transistor. Note that the photodiode 1o is reset (as shown in Figure 2 (A)) by the transfer MO.
Sh transistor 20 and reset MOS transistor 3o
Drive pulse φ8. ．． This is done by controlling conduction with φC.

Further, 40 is a transfer MOS transistor, 5o is a capacitor, and 6
0 is a read transistor. The capacitor 50 can control the base potential of the read transistor 60 by driving pulse φ8□.

The accumulated charge photoelectrically converted by the photodiode 10 is transferred (as shown in FIG. 2 (B)) by the transfer MOS transistor 20.
and transfer MO5) run disk 4o with driving pulses φ□, φ
This is done by conducting conduction control using R2. The transferred charge is transferred to a readout transistor 6 which serves as a charge holding means.
It is temporarily accumulated in the parasitic base capacitance of o (not shown) and the capacitance 5o. When reading out this accumulated signal from the readout transistor 6o to the output signal line 65 (FIG. 2 (C)), a positive drive pulse φ is applied to the capacitor j150 to put the readout transistor 6o in a forward bias state. At this time,
When the transfer MOS transistor 70 connected to the output signal 1!65 is made conductive by the drive pulse φa, an emitter current flows from the read transistor 60 to the - storage capacitor 80, and an emitter voltage corresponding to the base potential appears.

To clear the charge remaining at the base of the readout transistor 60 (as shown in FIG. 2 (D)), first of all, the reset MO
S transistor 30 and transfer MOS l-transistor 4
0 is made conductive by driving pulses φ and φ8□ and reset (period T o). Next, the output line reset MoS transistor 90 is turned on by the drive pulse φvc, the emitter is set to a constant potential, and the read transistor 60 is put into a forward bias state by applying a positive drive pulse φ8□ to the capacitor 50, so that the charge remaining in the base is is discharged (transient refresh operation), and the reset operation ends (period T.2).

As mentioned above, drive pulse φ□1. φ8□.

φ. , φ1. By changing the timing of φvc, it is possible to perform the basic operations of the image sensor, from the photodiode reset operation to the accumulation operation, and from the transfer of accumulated charges to the readout operation.

FIG. 3 is a schematic diagram of an X'-Y type image sensor in which the above unit circuits are arranged.

Note that only four elements (2×2) are shown here for the sake of simplicity.

As shown in FIG.
, D>130, 140, a readout circuit 150, an output amplifier 160, and a photoelectric conversion element 100.

Each decoder 110, 120, 130, 140 outputs a desired selected driving pulse in response to a plurality of input pulses (φLゎ, φRn+φ.wa, φ..).

Any photodiode 10 can be reset by a combination of drive pulses for the row decoder 110 and column decoder 130.

Furthermore, by the combination of drive pulses from the row decoder 110 and the row decoder 120, the accumulated charge accumulated in the photodiode 0 is transferred to the readout transistor Go.

Furthermore, by the drive pulse of the row decoder 120, the accumulated charge is output from the readout transistor 60 of an arbitrary row as an output signal 1.
1i+65, and is amplified and transferred to the temporary storage capacity 80 (C,).

The base of any readout transistor 60 is reset by the combination of the drive pulses from the column decoder 130 and the row decoder 120, and the readout transistor 6 in any row is reset by the drive pulse from the row decoder 120 and the drive pulse φVC.
The read circuit 15 performs a transient refresh operation of 0.
The column decoder 140 transfers any signal temporarily stored at 0 to the horizontal output line, and outputs the signal to the outside via the output amplifier 160.

FIG. 4 is a block diagram showing an example of an imaging device using the above-mentioned imaging device.

In the figure, 310 is an imaging optical system, 320 is an aperture that controls the amount of light incident on the image sensor, and 200 is an X shown in FIG.
- It is a Y-type image sensor. The amount of light incident from the imaging optical system 310 is limited by the diaphragm 320, and the light beam enters the imaging device 200.
image is formed. The aperture 320 and the imaging optical system 310 (lens in the figure) are driven by a drive circuit 390 that is controlled by a control signal from the image processing section 360.

The signal processing circuit 330 is a well-known circuit that performs gamma correction and other video signal processing. This signal is sent to the A/D converter 340
is converted into a digital signal and recorded in the image memory 350.

The signal from image memory 350 is transferred to image processing section 360.

The image processing section 360 is composed of an address section, an arithmetic processing section, an arithmetic memory section, a control section, etc., and performs scan address determination for signal level determination, signal level conversion, and random control of the image sensor 200, which will be described later. It generates control signals for transfer, the imaging optical system 310 (lens (focal length)), and the aperture 320. The image processing unit 360 transfers the scan address to the random scan address circuit 370 based on the selection of the sensor scan method and the determination result of the sensor signal level. Random scan address circuit 370
randomly scans the image sensor 200 using the address signal via the scan interface 380. This random scan causes the row decoder (L, R
) 11.0° 120, column decoder (Ll, D) 130,
Manual data is sent to the photodiode 140, which transfers the accumulated charge of the photodiode 10 ((B) in FIG. 2), reads out the accumulated charge ((C) in FIG. 2), and resets the photodiode 10 ((FIG. 2)). (A)), resetting of the readout transistor 60 ((D) in FIG. 2), etc. are performed.

FIG. 5(a) is a control flowchart of the image sensor 200, and FIG. 5(b) is a flowchart regarding processing of pixel signals output from the image sensor 200.

In FIG. 5(a), when the operation of the imaging device is started (500), scanning of the imaging device 200 is first selected (502).As the scanning method, for example, (1) normal Pixel accumulation (T,
, = 1/60 seconds), and for pixels that are saturated with the accumulation time of TsH, the accumulation of pixels with a shorter accumulation time (T, = 1/1000 seconds) is performed. Accumulation method with different pixel accumulation times (2) - The first time, all the signals accumulated at T51 are read out, and the second time, only the pixels that were saturated in the first time are accumulated for the time T B2, and the pixels with different accumulation times (3) Method of reading out only the signals of pixels in a certain area (TI□
). Note that a detailed explanation of the scanning method will be given later.

When scanning is selected (502), the image processing unit 36
The scan pattern from 0 is transferred to the random scan address circuit 370 (504).

The address is transferred from the random scan address circuit 370 to the scan interface 380 (506), and is transferred to the image sensor 200 via this scan interface 380.
The operation of each pixel is controlled.

First, the image sensor 200 has selected pixels (x, y).
The accumulated charge in the photodiode 10 is transferred to the readout transistor ((B) in FIG. 2) (508).

Next, the signal of the pixel is read out from the image sensor 200 ((C) in FIG. 2), that is, the signal is output (5).
10). When this readout operation ((C) in FIG. 2) 510 is completed, the reset operation of the photodiode 10 ((A) in FIG. 2) and the reset operation of the readout transistor 60 ((D) in FIG. 2) are completed. is done (512). Each of these operations of the image sensor 200 is performed for each pixel or for each horizontal pixel column by a random scan address operation (504).

Other than the readout operation ((C) in FIG. 2) 510, it is possible to transfer accumulated charges in a plurality of horizontal pixel columns, reset the photodiode 10, and reset the readout transistor 60.

Also, after reading out the signal (C) in Figure 2 (510)
The read signal is loaded into the image memory 350 via the signal processing circuit 330 and the A/D converter 340 (514), and is subjected to arithmetic processing and the like in the image processing section 360 (516).

When the reset operation is completed, the same operation is repeated again.

Next, the flowchart shown in FIG. 5(b) will be explained.

The flowchart shown in FIG. 5(b) shows the above process 51.
6.

The image signal from the image memory 350 is first stored for an accumulation time T.
A determination is made as to whether the signal is an S2 signal (600). Here, if the signal is T12, it is transferred to the level converter (602), and the signal level is determined (602).
04). If the pixel signal is at the low level 71 or higher, the pixel address (X) is subsequently set to TB2 for the pixel accumulation time.

Y) is stored. Low level ■, if smaller,
The pixel accumulation time is set to Tgl (614).

T3□ In the level conversion section, -→tone calculation is performed at Tg (602), but since the dynamic range of the output device is generally narrow, coefficient processing of knee (KNEE) processing is further performed.

Further, if the pixel signal is not T3□ in the judgment 600, the signal is transferred as output data (6
10) Judgment of signal level, i.e. detection of saturation (■ o or more)
is performed (606). If the signal is saturated, the accumulation time for that pixel is T82, so the pixel address (X,
Y) is stored (608). If the signal is not saturated, the pixel accumulation time is set as T at (61
6).

This address is reflected from the image processing section 360 to the random scan address circuit 370, and the photodiode 10 is reset ((A) in FIG. 2).

After the output data is transferred (610), it is input to the D/A converter 400 and converted into analog data (612).

Exposure time control using random scanning will be explained below.

FIGS. 6(a) to (C) are explanatory diagrams of exposure time control by random scanning, FIG. 6(a) is a schematic diagram of an imaging screen, FIG. 6(b) is an explanatory diagram of vertical scanning, Figure 6(c)
is an explanatory diagram of horizontal scanning.

Points A and B shown in FIG. 6(a) indicate the start and end points of vertical scanning, and the area indicated by abcd on the screen has a much stronger amount of incident light than the surrounding area. It is assumed that at normal television (TV) rate (exposure time 1760 seconds) the pixels therein are saturated.

Here, the exposure time of the pixels in the area abcd is set to 1, for example.
An explanatory diagram of shortening the time to 7600 seconds is shown in FIG. 6(b).

During the field period fv(1), the pixels in each row sequentially transfer the accumulated charge ((B) in FIG. 2), read out the accumulated charge ((C) in FIG. 2), and reset the photodiode 10 ((B) in FIG. 2).
(A) in FIG. 2), and the read transistor 60 is reset ((D) in FIG. 2). Row scanning is area a
When approaching bcd, the photodiode 10 is reset prior to readout so that the exposure time of pixels in area abcd becomes 17,600 seconds.

FIG. 6(c) is an explanatory diagram of driving the image sensor during the -horizontal scanning period.

Transfer of accumulated charges during the horizontal blanking period HBLK (second
The process from (B) in the figure to resetting the readout transistor 60 ((D) in FIG. 2) is performed, and a signal is output from the image sensor 200 during the effective scanning period.

In addition, in FIG. 6(a) to FIG. 6(C), scanning was performed so as to shorten the exposure time of pixels that would be saturated with a normal exposure time, but the scanning method for expanding the dynamic range is similar to this embodiment. It is not limited to. For example, as described above, in another embodiment for expanding the dynamic range, first, an image signal obtained by 1760 seconds exposure is read out, a saturated pixel is detected from this image signal, and based on this detection signal, the pixel is Exposure is performed by shortening the exposure time of
Next, there is also a method of reading out only the signal of the pixel.

[Effects of the Invention] As explained above, according to the imaging device of the present invention, since the exposure time of any pixel can be changed, the dynamic range can be substantially widened ( Furthermore, since signals can be read out from any pixel, it can be applied to many image input devices.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a unit circuit of an embodiment of an image sensor according to the present invention. FIG. 2 is a basic drive timing diagram of the unit circuit of FIG. 1. FIG. 3 is a schematic diagram of an x-y type image sensor in which the above unit circuits are arranged. FIG. 4 is a block diagram showing an example of an imaging device using the above-mentioned imaging device. FIG. 5(a) is a control flowchart of the image sensor 200, and FIG. 5(b) is a flowchart regarding processing of pixel signals output from the image sensor 200. FIGS. 6(a) to 6(C) are explanatory diagrams of exposure time control by random scanning. ]O: Photodiode, 20: Transfer MOS transistor, 30: Reset MOS transistor, 40: Transfer M
OS transistor, 50: capacitor, 60: read transistor, 65: output signal line, 70: transfer MOS transistor, 80: storage capacitor, 90: output line reset MOS transistor, 1002 unit circuit section. Agent Patent Attorney Minoru Yamashita Handiwork Figure 1 Figure 2 Figure 3 Figure 5 ('Q) Figure 5 (b)

Claims (1)

[Claims] (1) In an imaging device configured by arranging a plurality of photoelectric conversion elements, the photoelectric conversion element includes a photoelectric conversion section that converts incident optical information into a charge signal, and a temporary converter that converts the charges generated in the photoelectric conversion section. An imaging device comprising: a charge holding means for holding the photoelectric conversion section and the charge holding means; and a reset means for independently returning the photoelectric conversion section and the charge holding means to an initial state.