JPS58220576A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To realize a long time exposure, by dividing one exposure time into plural small periods to compensate a dark current for each small period, and by accumulating an electric charge after the compensation. CONSTITUTION:A transfer element shown as a hatched portion of a photoelectric transfer part 16 is light-shielded to detect a dark current. One exposure time is divided into two small periods. When the 1st small period terminates, a controlling pulse is supplied to a controlling electrode 24, and the signal electric charge and the dark electric charge of a photoelectric transfer element 20 are supplied to a vertical transfer register 22. The electric charge in the transfer part 16 is successively transferred to an accumulation part 18 by a pulse for transferring. A differential amplifier 12 outputs only a signal electric charge which is inputted in a horizontal transfer register 36 through a coefficient multiplication circuit 14. When the correction electric charge of the component of the 4th line is inputted up to the 4th transfer stage of a register 36, the correction electric charge of the 4th line is supplied to the transfer stage of the 1st stage of a vertical transfer register 28. After that, the electric charges of the 3rd, the 2nd and the 1st lines are corrected. Then, the corrected electric charge is transferred to each accumulation cell 26 from the register 28. The accumulation cells 26 accumulate the corrected electric charge of the 1st small period and the electric charge of the 2nd small period in it. After that, a switch 44 is switched to read out the accumulated electric charge as a video signal.

Description

[Detailed description of the invention] The present invention relates to a solid-state imaging device.

In recent years, solid-state imaging devices using charge transfer devices such as charge-coupled devices (CCDs) have been widely used. This solid-state imaging device includes a large number of photoelectric conversion elements arranged in a matrix, and a storage section that temporarily stores the charges generated by these elements and outputs the charges for each element in time series. The photoelectric conversion element always receives incident light, and the storage section is shielded from light. All charges generated by the photoelectric conversion element are transferred to the storage section at every exposure time depending on the brightness of the subject.

That is, the photoelectric conversion element integrates the incident light during the exposure time. Here, the exposure time is set short when the subject is bright and long when the subject is dark so that the integral value always becomes a predetermined value. Incidentally, in general, a small amount of current called dark current flows through a photoelectric conversion element even when there is no incident light, so that in addition to signal charges corresponding to incident light, charges corresponding to this dark current are also generated. Therefore, during long-time exposure, the photoelectric conversion element may become saturated due to the influence of charges caused by this dark current. At present, even in the case of photodiodes used in facsimiles, etc., which are said to have a relatively small dark current, the dark current causes a tlloOms
It becomes saturated at about Of course, in reality, there is also a signal charge due to the incident light, so if the dark current is not removed, it will be several tens of m
Exposure times longer than 5 are not feasible. However, the cause of dark current is thermal excitation in the element or substrate, and it cannot be expected to be significantly suppressed because it is related to the material of the element and the manufacturing technology itself.

In addition, the intrinsic duttering method, in which a buried defect layer is provided inside the substrate and various defects generated during the device formation process are absorbed by this region layer and the surface layer of the device is kept defect-free, can also be used to suppress dark Na. Applied. However, although this method is useful for localized dark current peaks,
It is not very effective in reducing the overall value of dark current.

This invention was made to deal with the above-mentioned circumstances,
The object of the present invention is to provide a solid-state imaging device that compensates for the influence of dark current and enables long-time exposure.

Hereinafter, one embodiment of a solid-state imaging device according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the configuration of this embodiment. In this embodiment, the image sensor 10. Differential amplifier, device 12. It has a coefficient multiplication circuit 1 Z4. The image sensor 10 formed on one semiconductor substrate is roughly divided into a photoelectric conversion section 16 and a storage section 18.

The photoelectric conversion unit 16 includes 20 photoelectric conversion elements 20 arranged in a matrix of 4 rows and 5 columns, 5 columns of vertical transfer registers 22 provided for each column, and movement of 5 charges between them. It consists of one control electrode 24 that controls. Here, only the 4th row and 4th column of the 20 photoelectric conversion elements are open to light, and the shaded photoelectric conversion element in the 5th column on the far right is shielded from light for dark current detection. has been done. Other vertical transfer registers 22° control electrodes 24. The storage section 18 is also shielded from light.

The storage section I8 has 20 storage cells 26 arranged in a matrix of 4 rows and 5 columns corresponding to each photoelectric conversion element 20, and 5 columns of vertical transfer registers 28 are provided for each column. One end of the vertical transfer register 28 is connected to one horizontal transfer register 30. Two types of control electrodes 32 and 34 are provided between the storage cell 26 and the vertical transfer register 28. Control electrodes 32 are provided in the cells in the first, third, and third rows.
Control electrodes 34 are provided in the cells in the first and fourth rows of the second row. The charges in the vertical transfer register 22 of the photoelectric conversion unit 16 are transferred to one transfer stage of the horizontal transfer register 36 and to the control pole 38.
The data is configured to be transferred to the vertical transfer register 28 of the storage section 18 via the storage section 18. Additionally, the output stage of the horizontal transfer register 30 of the storage section 18 is connected to a dark current holding register 42 via a control electrode 40. Output of horizontal transfer register 30 and dark current holding register 42. The signals are respectively applied to the non-inverting and inverting inputs of the differential amplifier I2. The output signal of the differential amplifier 12 is selectively supplied via a switch 44 to an image signal output terminal 46 or a coefficient multiplication circuit I4. The output signal of the coefficient multiplication circuit 14 is supplied to the horizontal transfer register 36. Each register 22.2B, 30
．． Reference numeral 36 consists of a COD, and this transfer electrode is not shown in the drawings.To explain the operation of this embodiment, first, its principle will be explained. If the exposure time, that is, the integration time of incident light is short, the photoelectric conversion element will not be saturated, so even if a long exposure time is required, one exposure time is divided into multiple small periods Δt, and each The method is to read the charges every short period and accumulate them. Furthermore, the actual signal charge is obtained by subtracting the charge due to the dark current from the charge read out during each accumulation. FIG. 2 shows this situation as a graph. The solid line shows the total charge read out, and the broken line shows the charge due to dark current. QS is the saturation charge of the photoelectric conversion element 20, which is 2. The short period Δt is set to the time required for the charge due to the dark current to reach a value q that is sufficiently small compared to the saturation charge Qs. By doing this, even if the exposure time becomes long, the photoelectric conversion element 20 will not be saturated by dark current.

The operation of this embodiment will be described below with reference to the time charts shown in FIGS. 3(a) to 3(c) and the diagrams showing charge transfer shown in FIGS. 4(a) to 4(d). Here, it is assumed that each transfer register is operated by two-phase clock signals. Further, for convenience of explanation, it is assumed that one exposure time is divided into 2' small periods. When the first short period ends at time 11, the pulse shown in FIG. ) is supplied to the transfer stage of the vertical transfer register 22. At the same time, the vertical transfer register 22 has two-phase transfer signals as shown in (b) and (c) in the figure, and the vertical transfer register 28 has two-phase transfer signals as shown in (h). Transfer pulses are supplied. While this transfer i9 pulse is supplied, a high level signal is supplied to the control object, pole 38, as shown in FIG. Therefore, the charges in the photoelectric conversion section 16 are sequentially transferred to the storage section I8, and the transfer ends at time t2. The movement of charge from time t1 to t2 is expressed as the fourth
Shown in Figure (a). In FIG. 4, S represents the sum of the signal charge and dark charge, D represents the dark charge, and subscripts (1) and (2) represent the 1st, 2nd, and 3rd digits, respectively. means the charge during the second sub-period.

After time t2, data is further transferred to the vertical transfer register 28/
4' pulse is added, and the components of the fourth row are transferred to the horizontal transfer register 30. Then, on the control electrode 40 (see Fig. 3 ←)
A pulse as shown in is supplied, and the channel under the electrode becomes conductive. As a result, the component in the fourth row and fifth column, that is, the dark charge D4(1), is supplied to the register 42. Next, in the horizontal transfer register 30, (1) and (j
) A transfer pulse like this is supplied, and each charge 541(1) to 844
(1) are output sequentially. As a result, the differential amplifier 12
Only signal charges (SD) are output from the . The switch 44 is in the state shown in the figure, and the horizontal transfer register 36 is also in the state shown in the figure (
Since the transfer pulse is supplied as shown in d) and (e), the output signal of the differential amplifier z2 is sent to the coefficient calculating circuit z.
4 to the horizontal transfer register 36. S' indicates the charge after correction. When the correction charge of the component in the fourth row is input to the fourth transfer stage of the horizontal transfer register 36, the control electrode 38 becomes high level as shown in FIG. Same figure [with]).

Since a transfer pulse of only one period as shown in (h) is supplied, the correction charges S'41(1) to S'44(
1) is supplied to the first transfer stage of the vertical transfer register 28. Thereafter, the charges on the third, second, and first rows are corrected in the same manner. The state of charge movement at time t3 in the middle of this process is shown in FIG. 4 ω). When the correction charge in the first row is input to the vertical transfer register 28, the voltage in FIG. 3 (1), ←)
As shown in the control electrodes 32 , , ? 4 becomes conductive, and the correction charge S' is transferred from the vertical transfer register 28 to each storage cell 26 and held therein.

When the second short period ends, the charges in the photoelectric conversion element 20 are transferred to the vertical transfer register 28 of the accumulation section 18, similarly to after the first short period ends. The position of the load at the end of this transfer (h, time 14) is shown in FIG. 4(c). After this, as shown in FIG. 3(1) and (c), the control electrode 32.3
4 is supplied with a high level signal to the vertical transfer register 28.
Charges 5(2) and D(2) of the second sub-period are transferred into the storage cell 26. As a result, the first
The corrected charge S' (1) for the short period and the charge (uncorrected) for the second short period are accumulated. Thereafter, the state of the switch 44□ is changed, and the accumulated charge is read out as an image signal. Here, the output image signal is read every other line to match the format of the television signal. Instead, as shown in Fig. 3 (1), first, the control 11
Only pole 32 is set to a high level, and the same figure (b)
), a transfer pulse is supplied to the vertical transfer register 28 as shown in (h). As a result, first, the first. Third
The charges in the row are read out. And, as mentioned above,
Every time the horizontal transfer register soK charge is transferred from the vertical transfer register 28, the charge is transferred in the horizontal direction within the horizontal transfer register 30. At this time as well, the components in the fifth column are supplied to the register 42, and the dark charges in the fifth column are subtracted from the components in the first to fourth columns. The position of the charge at time t@ in the middle of this process is shown in FIG. 4(d). 1st. When the charges in the third row are read out, the control electrode 34 is set to a high level, as shown in FIG. The charges in the fourth row are read out. Incidentally, the coefficient multiplication circuit 14 multiplies the output signal of the differential amplifier 12 by an appropriate coefficient and supplies the resultant signal to the horizontal transfer register 36. Here, if this coefficient is changed for each short period, an effect similar to that of γ correction in photography can be obtained. In addition, the transfer efficiency of each transfer register is 100.
%, the charge will attenuate during multi-stage transfer, but this coefficient multiplier circuit I4 can also compensate for this. 'As explained above, according to this embodiment, 1
By dividing the exposure time into a plurality of small periods, compensating for dark current in each small period, and accumulating the charges after compensation, a solid-state imaging device capable of long-time exposure is realized.

Next, a second embodiment will be described with reference to FIG. 1st
In the second embodiment, the charge from the photoelectric conversion section is once accumulated in the storage section and then the correction is performed, but in the second embodiment, the charge from the photoelectric conversion section is accumulated after being corrected.

An output end of the interline transfer type photoelectric conversion section 50 is connected to a switch circuit 52 . 1::: Similar to the first embodiment, the photoelectric conversion elements in the rightmost row of the photoelectric conversion section 50 are shielded from light. The switch circuit 52 supplies only the signal from this light-shielded element to the sample/hold circuit 54 and the other signals to the non-inverting input terminal of the differential amplifier 56.

The output terminal of the sample/hold circuit 54 is a differential amplifier 56.
connected to the inverting input terminal of An output terminal of differential amplifier 56 is connected to a first input terminal of mixer 58 . The output signal of the mixer 58 is horizontally transferred to the storage section 60 for writing and is supplied to the nostar 62 . The storage section 6Q has storage cells corresponding to the photoelectric conversion elements of the photoelectric conversion section 50. The output end of the read coarse horizontal transfer register 66 of the storage section 60 is connected to a switch circuit 68 . Switch circuit 68 , like switch circuit 52 , supplies only the signals from the storage cells in the rightmost column to sample/hold circuit 70 , and supplies the others to the non-inverting input terminal of differential amplifier 72 .

The output terminal of the sample/hold circuit 70 is a differential amplifier 72.
connected to the inverting input terminal of The output terminal of the differential amplifier 72 is connected to the second input terminal of the mixer 58o'' via the first terminal of the switch 74. The second terminal of the switch 74 is connected to the image signal output terminal 76. The output of the mixer 58 The end is also connected to the child terminal of Kono Valley 1 Tough 8. Reference power supply V.

is connected to one terminal of the comparator 78, and the output signal of the comparator 78 is supplied to the control end of the switch 74.

On the other hand, power supply vcc is connected to clock pulse generator 82 via start switch 8Q. The first output signal of clock pulse generator 82 is transferred via switch 84 to
4' is supplied to the pulse generator 88 and the switch 8
6 is supplied to the transfer pulse generator 9Q. A second output signal of clock pulse generator 82 is provided to transfer pulse generator 90 via a second terminal of switch 86 . Con i'? The output signal of the regulator 78 is sent to the switch 8.
4. It is supplied to the control end of fJ6. Transfer pulse generator 8
The output signal of 8.90 is output from the photoelectric conversion unit 50. They are respectively supplied to the storage section 60.

To explain the operation of the second embodiment, each switch 74, 84
．． It is assumed that 86 is in the state shown in the figure.

In this embodiment as well, one exposure time is divided into a plurality of small periods, and the charge stored in the photoelectric conversion section 50 in each small period is corrected and supplied to the storage section 60 within the next small period. do. The charge from the photoelectric conversion element at the right end of the photoelectric conversion unit 60 is a dead charge, and the switch circuit 52 switches at the timing when this dark charge is read out, and samples only the dark charge.
The signal is supplied to the hold circuit 54. As a result, the output signal of the comparator 56 becomes a signal that is not affected by dark current. This signal is supplied to storage section 60 via mixer 58.

Since the signal from the accumulation section 60 is supplied to the other input terminal of the mixer 58, the mixer 58 accumulates the charges of each short period. Therefore, according to the present invention, since the cumulative charge is stored in the storage section 60, the saturation charge of this device is determined by the capacitance of the storage section 60, not that of the photoelectric conversion section 50.

Therefore, in order to prevent the storage section 60 from becoming saturated, the mixer 58
The output signal of is monitored by a comparator 78. When the output signal of the mixer 58 becomes larger than the signal from the reference power supply V, it is assumed that the accumulated charge in the accumulation section 60 approaches the saturated charge, and the subsequent accumulation is stopped.

That is, when the output signal of the comparator 78 becomes high level, the switches 74 and 86 are switched, and the switch 84 is switched.
will be released. As a result, the output signal of the comparator 72 is supplied to the image output terminal 76, and the output signal of the comparator 72 is supplied to the transfer noise generator 8.
8.90 is stopped, and the transfer pulse generator 90 is supplied with a second clock pulse suitable for reading out the image signal. This prevents the storage section 60 from becoming saturated. Note that the storage section 60 is an MO
This type of dark current compensation is also required for the storage section 60, although it is created using an S capacitor or the like. Therefore, in this embodiment, a zero level signal is written to the cells in the leftmost row of cells in the storage section 60 when a signal is written to the storage section 60. Then, when reading a signal from the storage section 60, the charge (corresponding to the dark charge) from the cell in the leftmost column is supplied to the sample/hold circuit 70, and dark current compensation is performed.

In this embodiment, an interline transfer type COD is used as the photoelectric conversion unit 5o, but the invention is not limited to this.
As shown in FIG. 6, the charges from the vertical transfer registers may be output in parallel without providing the horizontal transfer registers. That is, charges from the photoelectric conversion elements in each column of the photoelectric conversion unit 100 are supplied to the child terminals of each converter/lator 102 via the vertical transfer registers. The charge from the light-shielded photoelectric conversion element of the photoelectric conversion unit 100 is transferred to the comparator 1.
02 is supplied to one terminal.

The output terminal of each comparator 102 is connected to the first output terminal of each mixer 104.
Connected to the input end. The output signal of each mixer 104 is supplied to storage cells in each column of storage section 106. Accumulation section 106
has the same number of cells as the photoelectric conversion unit 100, and a ground level signal is supplied to the remaining storage cells in one row via the switch 108. The output signal of the storage cell in each column to which the output signal of the mixer 104 is supplied is transmitted to the comparator 1.
The output signal of the column which is supplied to the 10th terminal and which is supplied with the ground level signal is supplied to one terminal of the comparator llO. With this configuration, in which the output signal of the mixer 110 is supplied to the second input terminal of each mixer 104, the processing time for correction is shortened, and a switch circuit and a sample/hold circuit are not required. has advantages.

Note that in the embodiment shown in FIG. 6, a large number of comparators and mixers are required to process signals in parallel.
5 and 6 may be combined. In other words, in a normal interline type CCD, a plurality of horizontal transfer registers for reading may be provided to collectively process data outside the several columns in parallel.

As described above, according to the present invention, a solid-state imaging device capable of long-time exposure is provided.

Note that this invention is not limited to the embodiments described above, and various modifications can be made within the scope of this invention.

For example, the arrangement of the light shielding element for reading out signals from the photoelectric conversion unit and detecting dark current is not limited to the above example.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the solid-state imaging device according to the present invention, Fig. 2 is a diagram showing the principle of operation, and Figs. 3 (-) to f.
n) is a time chart showing this operation, and Fig. 4 C) to (
d) is a diagram showing charge transfer, FIG. FIG. 6 shows the second example of this invention. This is a diagram showing a third embodiment. z2... Differential amplifier, 20... Photoelectric conversion element, 26
...Storage cell, 30.36...Horizontal transfer register,
32, 34.3FJ, 40... control electrode, 42...
Dark current holding register. Applicant's agent Patent attorney Takehiko Suzue Submission of drawings (
No change in content) 1 Figure 2 Δt Δt △t Figure 4 (a) Figure 4 (b) Figure 4 (C) Figure 4 (d) Figure 6 Continuation of page 1 0 Invention Person: Terumasa Morita, 2-43-2 Hatagaya, Shibuya-ku, Tokyo, Inc., Lymphus Optical Industry Co., Ltd. Author: Hiroshi Matsui, Director of the In-house Patent Office, Kazuo Wakasugi, 1. Display of the case Patent application No. 104321/1989 3, Person making the amendment Relationship to the case Patent applicant (θ37) Olympus Optical Industry Co., Ltd. 4, Agent 5, Voluntary amendment

Claims (1)

[Claims] comprising a first photoelectric conversion section formed on a semiconductor substrate and formed of a large number of photoelectric conversion elements in a matrix that is not shielded from light, a second photoelectric conversion section that is shielded from light, and a storage section, -
A solid body that divides the exposure time into a plurality of small periods and uses the accumulation section to accumulate charges obtained by subtracting the charge of the second photoelectric conversion section from the charge of the first photoelectric conversion section for each small period. Imaging device.