JPH01161978A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To improve the shutter speed with simple circuit design by applying processing to sweep out an undesired charge of a pickup section and a storage section separately before and after the period to read the electric charge from a photodetector of the pickup section to its vertical transfer section. CONSTITUTION:The processing to sweep out the undesired charge of the pickup section 20 and the storage section 30 is applied before and after the period to read the electric charge from photodetectors 22, 23 to set an electric shutter. Thus, the electric charge required to be swept out after the electronic shutter is turned on is less than the charge by 2 fields. Thus, the shutter time is shorter than the required time to sweep out the electric charge by 2 fields. Especially, the charge over the charge by one field is swept out before the electronic shutter is set, then the shutter time is reduced to the time required to obtain the charge by one field.

Description

DETAILED DESCRIPTION OF THE INVENTION [Objective of the Invention (Industrial Application Field) This invention relates to a charge-coupled image sensor (hereinafter referred to as a CCD), for example.
The present invention relates to a solid-state imaging device using a solid-state imaging device such as an imaging device.

(Prior Art) A solid-state imaging device using a solid-state imaging device such as a CCD imaging device has means for switching the readout timing of accumulated signal charges, and the timing of reading out the accumulated signal charges is changed. Some devices allow exposure time to be shorter than the usual 1/60 second. This makes it possible to sharpen special playback images such as still playback images and slow playback images on a video tape recorder.

Figure 4 shows such a frame interline transfer type C
1 is a diagram showing a conventional configuration of a CD solid-state imaging device.

As shown in FIG. 4, the solid-state imaging device includes an imaging section 11, an accumulation section 12, a horizontal transfer section 13, an output section 14, a drain section 15, and a control circuit 16.

Here, the shutter operation of the apparatus shown in FIG. 4 will be explained with reference to the signal waveform diagram in FIG. 5.

First, the first field shift pulse FSI at the level VFS shown in FIG.
The data is read out to the CD vertical transfer section. As a result, time t2
From then on, the device is in a shutter-on state.

Next, within the period from time t3 to time t4, the CCD vertical transfer section of the imaging section 11 and the storage section 12 generates a high-speed sweep pulse P1.
driven by. As a result, unnecessary charges such as signal charges and smear components remaining in the CCD vertical transfer section are swept out to the drain section 15.

Next, a second field shift pulse F is applied to the imaging unit 11.
S2 is supplied, and the charge accumulated in the light receiving element is read out to the CCD vertical transfer section within the period from time t5 to t6. As a result, after time t6, the apparatus enters the shutter-off state and the exposure ends.

Finally, the charges read out to the CCD vertical transfer section of the imaging section 11 are field-transferred to the storage section 12 according to the high-speed transfer pulse P2 within the period from time t7 to t8. Thereafter, this charge is read out one line at a time to the horizontal transfer section 14 in synchronization with image scanning, horizontally transferred at high speed, and output from the output section 14.

Note that pulses for controlling the above operations are output from the control circuit 16.

By the way, in the shutter operation, the sweep pulse P1, the second field shift pulse FS2, and the transfer pulse P2 are output during the vertical blanking period. On the other hand, the generation timing of the first field shift pulse FSI is changed according to the shutter time. When performing a high-speed shutter operation, the timing of generation of this first field shift pulse FSI is also set to the vertical blanking period. Therefore, in this case, 20H(
There are four types of pulses in a vertical blanking period (IH is one horizontal scanning period).

The limit of the shutter time on the high speed side is determined by the time required to sweep out unnecessary charges, represented by t3 to t4. this is,
This is the time required to sweep out two fields worth of charge. In the case of the NTSC method, this sweep time is approximately 500
This is the time required to output three sweeping pulses P1. Therefore, this sweep time is equal to the sweep pulse P
It can be shortened by increasing the frequency of 1.

However, the imaging unit 11 and the storage unit 12 generally have 1000
It has a capacitive load of pF. On the other hand, the pulse amplitude (VFS VL) (for example, 8V) is fixed. Therefore, it is difficult to drive the device at high speed by increasing the sweep frequency, and it is not very practical.

Therefore, as a configuration for increasing the shutter speed, a configuration other than a configuration for increasing the sweep frequency is required.
There is a configuration in which the charges in the storage section 12 are swept out to the horizontal transfer section 13. That is, in this way, the sweep positions of the imaging section 11 and the storage section 12 are changed. According to this configuration, two fields' worth of charges can be swept out in the time required to sweep out one field's worth of charges, so high-speed shutter operation can be realized without increasing the sweep frequency.

However, in such a configuration, when the amount of swept charge is large, such as when the shutter speed is fast or the amount of incident light is large, the horizontal transfer section 13 overflows, causing horizontal stripes to appear at the top of the reproduced image. is newly generated. In addition, the signal of the optical black part, which is the black reference in the line where the overflow occurred, is destroyed, and if this optical black part is clamped during DC reproduction, the signal level at the top of the reproduced image will sink. The problem also arises.

(Problems to be Solved by the Invention) As described above, in conventional solid-state imaging devices, in order to increase the shutter speed, there are configurations that increase the frequency at which unnecessary charges are swept out and configurations that change the position from which unnecessary charges are swept out. It was considered. However, the former method has the problem of making circuit design difficult, and the latter method has the problem of generating horizontal stripes and lowering the signal level due to charge overflow.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a solid-state imaging device that can increase the shutter speed without causing unnecessary charge overflow and with a simple circuit design.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention performs a process for sweeping out unnecessary charges in the imaging section and the storage section. This is carried out separately before and after the period in which charges are read out from the light-receiving element of the section to the vertical transfer section.

(Function) According to the above configuration, before starting electronic exposure, part of the charge for two fields is swept out, so after starting electronic exposure, less charge than the charge for two fields is swept out. Just put it out. Thereby, the shutter time can be made shorter than the time required to sweep out two fields' worth of charges. In particular, if more than one field's worth of charges is swept out before starting electronic exposure, the shutter time can be shortened to the time required to sweep out one field's worth of charges.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention.

Note that FIG. 1 shows a frame interline type CCD.
An imaging device is shown as a representative.

In FIG. 1, reference numeral 20 has a light receiving element that accumulates charges according to the amount of incident light and a vertical transfer section that can transfer the charges accumulated in this light receiving element in the vertical direction of image scanning. This is an imaging unit that captures image information. Reference numeral 30 denotes a storage section that has a CCD vertical transfer section that can transfer the charges transferred from the CCD vertical transfer section of the imaging section 20 in the vertical direction, and is capable of accumulating charges for one field.

Reference numeral 40 denotes a horizontal transfer section that can transfer charges transferred line by line from the storage section 30 in the horizontal direction of image scanning. Reference numeral 50 denotes an output section that outputs the charges transferred from the horizontal transfer section.

Reference numeral 60 denotes a drain section that receives charges swept out from the CCD vertical transfer section of the imaging section 20 and storage section 30. 70 is a control circuit that outputs various control pulses for controlling shutter operation.

The CCD imaging device has, for example, 500 pixels in the vertical direction,
It has a light receiving element for 800 pixels in the horizontal direction. in this case,
In order to support interlaced scanning, the imaging unit 20
Two light receiving elements 2 for one CCD vertical transfer section 21
It has 2.23. The CCD vertical transfer section 21 is divided into four electrodes 24-27. Each electrode 24 to 27 is
~I4 is connected to each of the four terminals 28.

Each of the 11 to I4 terminals 28 receives a four-phase vertical transfer pulse φ! output from the control circuit 70. □ to φI4 are added one by one. In this case, 1. By applying a pulse of level VFS to the third electrode 24,26, the light receiving element 2
From 2.23 onwards, charges can be read out to the CCD vertical transfer section 21.

On the other hand, the storage section 30 is completely shielded from light.

Each COD vertical transfer section 31 is composed of four electrodes 32 to 35, similar to the CCD vertical transfer section 21 of the imaging section 20. Each electrode 32-35 has four terminals 3, S1-S4.
6, respectively.

Each 5L-S4 terminal 36 receives one four-phase vertical transfer pulse φS1 to φ54 output from the control circuit 70, respectively.
are supplied individually.

The horizontal transfer section 40 has two terminals 41, H1 and H2. Two-phase horizontal transfer pulses φold and φH2 are supplied to each H1 and H2 terminal 41.

FIG. 2 shows the vertical transfer pulses φ11 to φI4 and φ supplied to the 11 to I4 terminals 28 and the Sl to S4 terminals 36.
5. ~φs4 is shown. As shown, vertical transfer pulse φ1
1 to φ■4 and φs1 to φ54 include the sweep pulse pH transfer pulse P2. In addition, vertical transfer pulse φ11+
φ1. Further, the first. Second field shift pulse F
Includes SI and FS2. In addition, vertical transfer pulses φ51 to φ
54 further includes transfer pulses Pa and P4 that transfer the charges in the storage section 30 to the horizontal transfer section 40 line by line.

In addition to these pulses, FIG. 2 shows a horizontal blanking pulse HBLK and a vertical blanking pulse VBLK. The control circuit 70 controls these blanking pulses H
Vertical transfer pulse φ11 using BLK, VBLK, etc.
~ φI4 and φ51 ~ φs4, horizontal transfer pulse φ old, φ
Output H2.

Note that FIG. 2 shows the situation near the vertical blanking period of an odd field. As shown in the figure, in Figure 2,
A case is shown in which the first field shift pulse FSI is within the vertical blanking period and a high-speed shutter operation is performed. The transfer pulses PL and P2 are output during a horizontal blanking period other than the vertical blanking period.

FIG. 3 is a diagram showing the state of charge movement when the device shown in FIG. 1 is driven with the various pulses shown in FIG. 2.

Now, the operation in FIG. 1 will be explained with reference to FIGS. 2 and 3.

As shown in FIG. 2, the levels of the vertical transfer pulses φ11 to φI4 are all set to vH during periods other than the vertical blanking period. This means that when the amount of incident light is excessive,
This is to prevent excess charges in the imaging section 20 from flowing into the storage section 30. On the other hand, during this period, the vertical transfer pulse φ5□~
As φs4, transfer pulse P3. P4 is being output. As a result, the CCD vertical transfer section 31 of the storage section 30 is driven, and the charges accumulated in the CCD vertical transfer section 31 are transferred line by line to the horizontal transfer section 40.

The charges transferred to the horizontal transfer section 40 are transferred to the output section 50 by horizontal transfer pulses φMin and φH2 supplied to the H1 and H2 terminals 41 during periods other than the horizontal blanking period.
will be forwarded to. In this case, when the charges of the last line are transferred from the storage section 30 to the horizontal transfer section 40, the image pickup section 20
Only smear components remain in the CCD vertical transfer section 21 of the storage section 30 and the CCD vertical transfer section 31 of the storage section 30. This situation is shown in FIG. 3(a). In the same figure (a), the imaging unit 20
and the smear component of the storage section 30, respectively.
It is displayed as S.

From this state, when the vertical blanking period begins, first,
During the period tA in FIG. 2, the vertical transfer pulses φ11 to φ14
And the sweep pulse P1 is outputted as φs1 to φ54. In this case, the number of output pulses P1 is set to be smaller than the number required to sweep out one field's worth of charges, for example. As a result, both the smear components present in the CCD vertical transfer section 21 of the imaging section 20 and the CCD vertical transfer section 31 of the storage section 30 are transferred to the drain section 60 side. Figure 3 (
Shown in b). As shown in the figure, the smear component X of the imaging section 20
, is partially swept out to the drain section 60, and the smear component Xs of the storage section 30 is shifted to the imaging section 20 side by that amount.

When this sweeping process is completed, the vertical transfer pulse φth
The first field shift pulse FSl is output as φ13. As a result, the light receiving element 22.2 of the imaging section 20
The charges accumulated in CCD 3 are transferred to the CCD vertical transfer section 21, and the electronic shutter is turned on. As a result, the imaging section 2
0 and the charges in the storage section 30 are as shown in FIG. 3(C).

Here, YI is the charge read out by the first field shift pulse FSI.

After this read processing is completed, a vertical transfer pulse φ2. The sweep-out pulse P1 is output again as ~φ14 and φ5□~φ54. In this case, the number of output pulses PL is the smear component X shown in FIG. 3(C),
The drain section 60 sweeps out all the charges Y* read out by Xs and the first field shift pulse FSI.
The number is set so that it can be swept out. FIG. 3(d) shows the state after this sweeping process is completed.

In this way, the processing for sweeping out unnecessary charges in the imaging section 20 and the storage section 30 is set with a period in between to sweep out the charges from the light receiving elements 22 and 23 to the CCD vertical transfer section 21 when the electronic shutter is turned on. two periods tA + tB
It is executed separately.

When this sweeping process is completed, the vertical transfer pulse φI+
+φ1. as the second field shift pulse F
, S2 are output. As a result, the electronic shutter turns off, and the light receiving element 22.2 of the imaging section 20
The charges accumulated in the CCD 3 are read out to the CCD vertical transfer section 21. This situation is shown in FIG. 3(e). In the figure, Zl is the charge read out from the light receiving elements 22 and 23.

After this read processing is completed, during period tc, transfer pulses P are used as vertical transfer pulses φth to φ14 and φs1 to φ54.
2 is output. As a result, the CCD vertical transfer section 21 of the imaging section 20 and the CCD vertical transfer section 31 of the storage section 30 are driven, and the charge XI of the imaging section 20 is transferred to the storage section 30. The state in which this transfer is completed is shown in FIG. 3(f).

Charge Z transferred to storage unit 30! is sequentially transferred in the vertical direction according to the transfer pulses Pa and P4 during the horizontal blanking period other than the vertical blanking period, and when it reaches the final stage CCD vertical transfer section 31, the horizontal transfer section 4
Transferred to 0.

As described above, this charge is horizontally transferred at high speed according to the two-phase horizontal transfer pulses φold and φH2, and is output from the output section 50.

As described above, in this embodiment, the processing for sweeping out unnecessary charges from the imaging section 20 and the storage section 30 is divided into two periods before and after the period during which charges are read out from the light receiving elements 22 and 23 in order to turn on the electronic shutter. This is what I decided to do. As a result, the charge that needs to be swept out after turning on the electronic shutter is less than the charge for two fields, so the shutter time can be made shorter than the time required to sweep out the charge for two fields. especially,
By sweeping out more than one field's worth of charges before turning on the electronic shutter, the shutter time can be shortened to the time required to sweep out one field's worth of charges.

Therefore, according to this embodiment, the sweep pulse PL
Considering that the frequency is fixed, the shutter speed can be doubled compared to the conventional configuration in which the sweep frequency is changed. Conversely, if you consider that the shutter speed is fixed,
Since the sweep frequency can be lowered, the device can be driven at a reasonable sweep frequency based on the circuit configuration.

For example, if the sweep frequency is 1.2 MHz, the sweep pulse P1 necessary to sweep out two fields worth of charge is
Assuming that the number of
seconds. On the other hand, the high-speed shutter speed that can be set in this example is 1/4800 seconds,
This is twice the speed as before.

On the other hand, if the shutter speed is 1/2400 seconds,
The sweep frequency in this example is 2400 x 250
-600 x 103 [Hzl], which means that the frequency is half of the conventional frequency.

In addition, in this embodiment, unnecessary charges from both the imaging section 20 and the storage section 30 are swept out and are swept out to the drain section 50, so that the amount of swept charges is considerably large, such as during high-speed shutter operation or when there is a large amount of incident light. Even when there is a large amount of charge, the horizontal transfer section 40 will not overflow due to excess charge. Therefore, the problem of white-level horizontal stripes occurring at the top of the reproduced image is eliminated. Furthermore, the signal of the optical black part, which is the black reference in the line where the overflow occurred, is destroyed, and the later signal processing circuit clamps it and reproduces the DC current, causing the signal level at the top of the reproduced image to sink. There is no longer any problem of it getting stuck.

In addition, in the previous description, the case where the sweep-out period tA before turning on the electronic shutter was shorter than the sweep-out period tB after turning on the electronic shutter was explained, but the period tA.

If the total of tB is longer than the period necessary to sweep out two fields' worth of charge, and the period tB is longer than the period necessary to sweep out one field's worth of charge, what is the condition? It may be set to any value. In this case, the highest shutter speed can be obtained when the period t8 is set to the period necessary to sweep out one field's worth of charge, as described above. This is possible by setting the period tA to be longer than the period required to sweep out one field's worth of charges. Note that when performing this high-speed shutter operation, as shown in Figure 1,
All pulses output from the control circuit 70 must be output within the vertical blanking period.

In addition, in the previous embodiment, C of the imaging section 20 and the storage section 30 is
Although the CD vertical transfer sections 21 and 31 have been described as being driven in four phases and the horizontal transfer section 40 being driven in two phases, it is needless to say that the present invention is not limited to this.

Furthermore, with regard to the number of pixels, it goes without saying that the number β is not limited to the number described above.

It goes without saying that various other modifications can be made without departing from the spirit of the invention.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to achieve a high shutter speed at a reasonable sweep frequency in terms of the circuit configuration, and to prevent horizontal stripes at a white level from occurring at the top of the reproduced image. In addition, it is possible to provide a solid-state imaging device that can obtain a high-quality shutter image in which the signal of that portion is not degraded by the clamping of a subsequent signal processing circuit.

[Brief explanation of the drawing]

1 is a diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a timing chart for explaining the operation of FIG. 1, FIG. 3 is a diagram for explaining the operation of FIG. 1, and FIG. FIG. 4 is a diagram showing the configuration of a conventional solid-state imaging device, and FIG. 5 is a signal waveform diagram for explaining the operation of FIG. 1. 20... Imaging unit, 21.31... CCD vertical transfer unit, 22.23... Light receiving element, 24-27... Electrode,
28゜36.41...terminal, 40...horizontal transfer section,
50... Output section, 60... Sweeping drain section, 7
0...Control unit. Applicant's agent Patent attorney Takehiko Suzue HBLK VBLK (d) (e)
(f) 31st N1

Claims (1)

[Scope of Claims] A light-receiving element that accumulates charges according to the amount of incident light and a vertical transfer section that can transfer the charges accumulated in the light-receiving element in the vertical direction of image scanning, and that can store image information for one field. A storage device comprising: an imaging unit for capturing an image; and a vertical transfer unit capable of vertically transferring charges transferred from the vertical transfer unit of the imaging unit, and capable of accumulating charges for one field in the vertical transfer unit; a horizontal transfer section capable of transferring charges transferred in line units from the storage section in the horizontal direction of image scanning; and a sweep section that receives charges swept out from the vertical transfer section of the imaging section and storage section. a drain section, and a first drive section that drives a vertical transfer section of the imaging section and storage section at a predetermined timing of the vertical blanking period, and sweeps out at least a part of the charge existing in the vertical transfer section to the drain section. After the sweeping process of the sweeping means and the first sweeping means is completed,
a first charge readout means for reading out the charge accumulated in the light receiving element of the imaging section to its vertical transfer section; and after the readout process by the first charge readout section is completed, vertical transfer of the charge accumulated in the image pickup section and the storage section; drive the part,
A second charge sweeping means sweeps out all the charges existing in the vertical transfer section to the drain section, and after the sweeping process of the second charge sweeping means is completed, the charges accumulated in the light receiving element of the imaging section are removed. a second charge readout means for reading out charges to the vertical transfer section; and after the charge readout process by the second charge readout means is completed, driving the vertical transfer section of the imaging section and the storage section; charge transfer means for transferring the charges in the vertical transfer section of the storage section to the vertical transfer section of the storage section; and after the charge transfer process by the charge transfer means is completed, the charges are transferred line by line in synchronization with the image scanning; A solid state comprising: a line transfer means for transferring to a horizontal transfer section; and a horizontal transfer means for transferring charges transferred to the horizontal transfer section by the line transfer means in the horizontal direction in synchronization with image scanning. Imaging device.