JP2000350103A - Photoelectric conversion device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] In the case of still image capturing, all pixels are reset by reading out all pixels, and overflow of photoelectric charges can be prevented. It is an object of the present invention to prevent the influence of photoelectric charge overflow due to a pixel. A photoelectric conversion device includes a plurality of photoelectric conversion elements and a reset switch for resetting the photoelectric conversion elements, the pixels being arranged in a matrix, and a vertical scanning unit and a horizontal scanning unit for reading a signal of each pixel. Has a first pixel group that reads out the signal of the pixel and a second pixel group that does not read out the signal of the pixel, and at least a part of the signal charge accumulation period of the first pixel group The photoelectric conversion element included in the second pixel group is reset by the reset switch.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion device arranged in a matrix, and is applied to an imaging device such as a digital still camera or a video camcorder.

[0002]

2. Description of the Related Art FIG. 7 is a schematic explanatory view showing a conventional photoelectric conversion circuit. In FIG. 1, photoelectric conversion elements (photodiodes and the like) 1 accumulate electric charges according to the amount of incident light, and are arranged two-dimensionally in an example of 4 × 4. One end of the photoelectric conversion element 1 is connected to the gate of an amplification type source follower input MOS (Metal Oxide Silicon Transistor) 2, the drain of the source follower input MOS 2 is connected to the source of a vertical selection switch MOS3, and the source of the source follower input MOS 2 Is connected to a load current source 7 via a vertical output line 6, and the drain of the vertical selection switch MOS3 is connected to a power supply terminal 5 via a power supply line 4, and these constitute a source follower circuit as a whole. A reset switch 14 has a source connected to the gate of the source follower input MOS 2 and a drain connected to the power supply terminal 5 via the power supply line 4.

In this circuit, a signal voltage is generated at the gate of a source follower input MOS 2 according to the electric charge stored in the photoelectric conversion element 1 of each pixel, and the signal voltage is amplified by a source follower circuit and read out.

The gate of the vertical selection switch MOS 3 is connected to a vertical scanning circuit 9 by a vertical gate line 8. The gate of the reset switch 14 is connected to the vertical scanning circuit 9 by a reset gate line 15. The output signal of the source follower circuit is output to the outside through the vertical output line 6, the horizontal transfer MOS switch 10, the horizontal output line 11, and the output amplifier 12. The gates of the horizontal transfer MOS switches 10 are connected to the horizontal scanning circuit 13, respectively.

The operation of this circuit will be described with reference to the timing chart of FIG. Here, the pulses applied to the vertical gate lines of each pixel row are SEL1 to SEL4, and the pulses applied to the reset gate line 15 are RES1 to RES4. The pulses SEL1 to SEL4 and RES1 to RES4 are generated by the vertical scanning circuit 9. Also, H1
H4 is a horizontal scanning pulse generated by the horizontal scanning circuit 13, and is applied to the gate of the horizontal transfer MOS switch 10. PD1 and PD2 indicate changes in the potentials of the photoelectric conversion elements (photodiodes) in the first row and first column and the second row and first column, respectively.

First, at time t0, the pulse RES1 is set to a high level to turn on the reset switch 14, thereby resetting the photoelectric conversion element PD1. Next, the storage operation is started. A signal voltage is generated at the gate of the source follower input MOS 2 in accordance with the amount of accumulated signal charge. After the end of the accumulation time, at time t2, the pulses SEL1 and H generated by the vertical scanning circuit 9 and the horizontal scanning circuit 13 are output.
1 are applied to the corresponding switches 3 and 10, respectively, and the signal of the selected photoelectric conversion element PD1 is amplified by the source follower circuit and then output through the output amplifier 12.

Hereinafter, signals are output from the photoelectric conversion elements arranged in the first row by sequentially applying the H2 to H4 pulses. Similarly, the signals from the photoelectric conversion elements arranged in the second row are controlled and output by the pulses RES1, SEL1, and H1 to H4. For example, PD2 is at time t
It is reset to 1 and then enters the accumulation operation. After the end of the accumulation time, a signal from the photoelectric conversion element PD2 is output at time t3.

Another operation will be described with reference to an operation timing chart of FIG. In this timing, a signal for all pixels is not read out, but a part of the signal is read out. Referring to FIG.
2, SEL4, RES2, RES4, and SEL3, R
By generating the ES3 pulse, the signals in the second and fourth rows are skipped, and the signals in the first and third rows are read.

For example, when capturing a high-definition still image, signals of all pixels are read, and when outputting a moving image, signals are thinned out and high-speed signal reading is performed instead. A signal can be read, and the signal can be used to perform automatic focusing and automatic exposure.

[0010]

However, the photoelectric conversion element (for example, PD2 in FIGS. 7 and 9) which has been skipped in the present circuit configuration and operation timing is not reset, so that the electric charge accumulated in the photoelectric conversion element is small. After the light irradiation, the charge reaches the saturated charge amount, and the charge generated beyond the saturated charge amount flows into the adjacent photoelectric conversion element, causing a false signal to be generated in the adjacent pixel.

FIG. 10 is a schematic cross-sectional view of a photoelectric conversion element and a potential diagram thereof for explaining it in more detail. FIG. 10A is a schematic sectional view of the photoelectric conversion element. 7, the same numbers as those in FIG. 7 indicate the same members. FIG. 10 (a)
, 401 is a first conductivity type Si semiconductor substrate;
Reference numeral 2 denotes a second conductivity type well region opposite to the substrate 1, and reference numeral 403 denotes a first conductivity type diffusion region, which forms a PN photodiode with the well region 402. A reverse bias is applied to the PN photodiode, and photocharges generated according to the amount of light incident on the junction capacitance are accumulated. The voltage amplitude generated according to the number of photocharges is detected by a source follower amplifier and output to the outside as an electric signal.

Further, 403-a is replaced with PD1, 403 in FIG.
When −b is changed to PD2 in FIG. 7, FIGS. 10B to 10D show the potential states of the respective parts at times t4, t5, and t6 in FIG. 9, respectively.

As shown in FIG. 10B, since the photodiode PD2 of the skipped pixel is not reset, electric charge is accumulated, and as shown in FIG. Saturation is reached during the accumulation period. Therefore, the charge overflowing from the photodiode PD2 as shown in FIG. 10D flows into a neighboring pixel, for example, PD1, over a potential barrier and becomes a false signal.

According to the present invention, all pixels are reset by reading out all pixels in the case of capturing a still image, and overflow of photoelectric charges can be prevented. It is an object of the present invention to prevent the influence of the overflow of the photocharge due to the above.

[0015]

According to the present invention, as a means for solving the above-mentioned problems, pixels each including a plurality of photoelectric conversion elements and a reset switch for resetting the photoelectric conversion elements are arranged in a matrix, and In a photoelectric conversion device having a vertical scanning unit and a horizontal scanning unit for reading pixel signals, the first pixel group includes a first pixel group for reading signals and a second pixel group for not reading signals. The photoelectric conversion element included in the second pixel group is reset by the reset switch during at least a part of the signal charge accumulation period.

Further, the present invention provides a plurality of photoelectric conversion elements,
A matrix comprising: an amplifying unit that receives a signal charge generated in the photoelectric conversion element; a transfer switch unit that transfers the charge to the amplifying unit; and a reset switch that resets the photoelectric conversion element via the transfer switch unit. In a photoelectric conversion device having a vertical scanning unit and a horizontal scanning unit for reading out the signal of each pixel, a first pixel group that reads out the signal of the pixel and a second pixel that does not read out the signal of the pixel And at least a part of the signal charge accumulation period of the first pixel group during a period in which the photoelectric conversion elements included in the second pixel group are connected to the reset switch via the transfer switch means. To prevent accumulation of overcharge by the second pixel group that does not read out the signal of the pixel, and to store the adjacent pixel in the first pixel group. It is obtained so as to prevent the sound.

Also, the present invention provides a vertical scanning means and a horizontal scanning means for arranging pixels comprising a plurality of photoelectric conversion elements and a reset switch for resetting the photoelectric conversion elements in a matrix, and reading out signals of each pixel. In a photoelectric conversion device having a first pixel group that reads the signal of the pixel and a second pixel group that does not read the signal of the pixel, the photoelectric conversion element included in the second pixel group A means for constantly resetting by a reset switch is provided, and by constantly discharging a photocharge from a second pixel group that does not read out a pixel signal to a power supply line, a photocharge to an adjacent first pixel group is provided. This is to reduce adverse effects such as leakage.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described.
This will be described in detail with reference to the drawings.

[First Embodiment] The circuit configuration diagram of the photoelectric conversion device according to the first embodiment of the present invention is the same as that shown in FIG. FIG. 7 shows the configuration as described above. In other words, the photoelectric conversion element (such as a photodiode) 1 accumulates charges according to the amount of incident light. It is arranged at. Photoelectric conversion element 1
One end of the amplifier is an amplified source follower input MOS (Metal Oxid
e Silicon Transistor) 2, the other end is connected to the substrate of the semiconductor substrate, and the source follower input MOS2 drain is a vertical selection switch MOS
3 and the source follower input MOS2
Are connected to a load current source 7 via a vertical output line 6, and the drain of the vertical selection switch MOS3 is connected to a power supply terminal 5 via a power supply line 4, and these constitute a source follower circuit as a whole. I have. Reference numeral 14 denotes a reset switch whose source is connected to the cathode side of the photoelectric conversion element 1 and the gate of the source follower input MOS 2, whose drain is connected to the power supply terminal 5 via the power supply line 4, and whose gate is connected to the reset line RES 1. ing.

In this circuit, after resetting by the reset switch 14, a signal voltage is generated at the gate of the source follower input MOS 2 according to the electric charge accumulated in the photoelectric conversion element 1 of each pixel, and the signal voltage is amplified by the source follower circuit. And read it out.

FIG. 1 shows an operation timing chart of the first embodiment of the present invention. In the figure, selection switch pulses SEL2 and SEL are used for a thinning operation at the time of capturing a moving image.
4 is always at the low level, and the selection switch pulse SEL
After 1 is set to the high level, the reset switch pulse RES1 is set to the high level at time t0 to reset the PD1, then the selection switch pulse SEL1 is set to the high level, and the horizontal scanning pulse H1 is set to the high level at the time t9. Is read out via the output line 6.

Here, the reset switch pulse RES
2, RES4 is always at a high level, so the electric charge of the photoelectric conversion element PD2 passes through the reset switch 14,
It is connected to the power supply terminal 5 via the power supply line 4 and is discharged. The charge is prevented from flowing into the adjacent pixels and no false signal is generated. After the time t9, even if the horizontal scanning pulse H1 is set to the high level, no photocharge is output since no photocharge is accumulated in the PD2.

FIG. 2 shows a schematic cross-sectional view of a photoelectric conversion element and a potential diagram thereof for explaining it in more detail. FIG.
(A) is a schematic sectional view of a photoelectric conversion element. 7, the same reference numerals as those in FIGS. 7 and 10 denote the same members, and a duplicate description will be omitted. In FIG. 2A, when 403-a is PD1 in FIG. 7 and 403-b is PD2 in FIG. 7, FIGS. 2B to 2D respectively show times t0, t7,
The potential state of each part at t8 and t9 is shown.

As shown in FIG. 2B, since the photodiode PD2 of the skipped pixel has been reset, no electric charge is accumulated, and as a result, the photodiode PD2 of FIG.
As shown in (d), the charges generated by the photodiode PD2 do not generate a false signal without flowing into an adjacent pixel, for example, PD1, beyond the potential barrier.

By the above operation, generation of a false signal is prevented, and a high-quality image free from smear, blooming, and color mixture is obtained.

[Second Embodiment] FIG. 3 is a schematic circuit diagram of a vertical scanning circuit 9 for realizing the operation according to the second embodiment of the present invention.

In FIG. 3, reference numeral 501 denotes a shift pulse generating circuit, 502 denotes a first transfer switch, 503 denotes a second transfer switch, 504 denotes an OR gate, and 505 denotes a read mode switching signal input terminal for a moving image and a still image. It is.

Read mode switching signal input terminal 50
5, when the low level is input, the first transfer switch 502 is turned on and the second transfer switch 503 is turned off, so that RES1, SEL1 to RSE4, SEL
Four pulses are sequentially output, and signals of all pixels are read.

Next, when a high level is input to the read mode switching signal input terminal 505, the first transfer switch 502 is turned off and the second transfer switch 503 is turned on.
Are turned on, no shift pulse is transferred to the second and fourth shift pulse generation circuits 501. Therefore, a low level is always output as SEL2 and SEL4,
No signal is read from the pixel connected to the vertical gate line 8 to which this pulse is applied. At this time,
Since a high level is applied to one terminal of the OR gate 504 from the read mode switching signal input terminal 505, a high level is always output as RES2 and RES4, and the reset gate line 15 to which this pulse is applied is applied.
Since the reset switch 14 for resetting the photoelectric conversion element of the pixel connected to the pixel, that is, the skipped pixel, is always kept in a conductive state, the electric charge is immediately discharged to the power supply terminal 5 and a false signal is not generated.

The mode switching signal input terminal 505 has:
When a still image requires high density and high image quality, input a low level. When a high-speed frame conversion is required when shooting a moving image, set it to a high level and read out half of the photoelectric charge of the photoelectric conversion element. To do. Further, in the above-described embodiment, an example in which the odd-numbered vertical lines are not used to read out the even-numbered vertical lines has been described. However, this may be reversed, or one column may be read and n columns may not be read. For example, when setting the focus lens position for auto focus,
This can be applied to a case where the image quality is not important such as in the case of auto exposure.

As in the present circuit configuration, an OR gate is added at the subsequent stage of the shift pulse generating circuit, a read is performed at one of its inputs, and a mode switching signal is input, so that a new control pulse is not added. The desired operation is realized.

[Third Embodiment] FIG. 4 shows an example applied to another pixel configuration according to a third embodiment of the present invention. 7, the same reference numerals as those in FIG. 7 indicate the same members. The pixel of the present embodiment is of a type that directly reads out signal charges stored in the photodiode 1 without using a source follower amplifying unit. Also in the pixel having this configuration, the generation of the false signal can be suppressed by turning on the reset switch 14 of the pixel that is not read out and discharging the accumulated charge to the power supply line 4.

In FIG. 4, the photodiode 1 has an M
The source of the reset switch 14 of the OSFET is connected to the source of the transfer MOSFET 3, the gate of the reset switch 14 is connected to the reset pulse RES2, and the gate of the transfer MOSFET 3 is connected to the selection pulse SE.
L2 has its drain connected to output line 6. Each of the other photoelectric conversion devices is also connected to a similar peripheral circuit. In particular, when the photodiode 1 is the PD2, it is connected to the reset pulse RES2 that always sets the gate of the reset switch 14 to the high level.
Is always in a conductive state, is discharged without storing photocharges in PD2, and there is no overcharge. On the other hand, in the first and third columns of the normal operation, since the reset pulse and the selection pulse are applied as usual, they are reset for a predetermined scanning time, and are read out after the photodiode 1 has accumulated photocharges for a predetermined time. .

[Fourth Embodiment] FIG. 5 is an example of a circuit diagram of a pixel applied to still another pixel configuration according to a fourth embodiment of the present invention. Also in this figure, the same numbers as those in FIG. 7 indicate the same members. In the figure, reference numeral 901 denotes a photoelectric conversion element 1
Is a charge transfer switch for completely depleting transfer of the signal charge from the gate to the input gate of the source follower input MOS2. 902
Is a transfer gate line for controlling the transfer switch 901.
In general, in order to improve the sensitivity of the photoelectric conversion device, a method of increasing the size of the photoelectric conversion element 1 and increasing the amount of signal charges is adopted.
The parasitic capacitance of the gate of S2 also becomes large, and there is a problem that the sensitivity cannot be improved efficiently. However, with this structure, the capacitance of the input gate of the source follower input MOS2 is changed to the photoelectric conversion element 1 (photodiode or the like). The sensitivity can be improved by designing the capacitance value to be smaller than the value in (1) and performing the complete depletion transfer.

At the normal time when all pixels are read, the selection pulse 8
And the application of the reset pulse 15 are supplied according to the timing. After the application of the reset pulse 15, a pulse is applied to the transfer gate line 902 after a predetermined time and before the application of the selection pulse 8, and the charge transfer switch 901 is applied. Is conducted.
Then, the optical charge accumulated in the photodiode 1 is transferred to the gate of the source follower input MOS 2, and then the selection switch 3 is turned on by the application of the selection pulse 8, and the power is amplified to the output line 6 of the source of the source follower input MOS 2. And output.

When thinning out and reading out even-numbered pixels, the transfer gate line 902 is always set to the high level, the charge transfer switch 901 is turned on, and the reset pulse 15 is reset.
Is always at a high level, and the reset switch 14 is also turned on at the same time, so that the photocharge accumulated in the photodiode 1 is constantly discharged to the power supply line, eliminating the overcharge state,
The influence on the adjacent photodiode is eliminated.

Also in the present pixel configuration, generation of a false signal can be suppressed by discharging the accumulated electric charge that keeps the reset switch and the transfer switch of the pixel that is not read out.

[Fifth Embodiment] FIG. 6 is an operation timing chart showing a fifth embodiment of the present invention. The basic circuit configuration according to the present embodiment is the same as that in FIG. As shown in FIG. 6, the same effect can be obtained by setting the drive pulses RES2 and RES4 of the reset switch 14 of the skipped pixel to high level at least once in one video period. Unlike the timing of FIG. 8 described as a conventional example, PD1 and PD2 of the photodiode 1 are different.
Are simultaneously reset at times t0 and t10, and the selection pulse SEL2 is always at the low level.
The same photocharge is accumulated in D2, and at the same time, a reset pulse is applied, and the accumulated charge in PD1 is read out at time t2 after a predetermined time. Thus, neither PD1 nor PD2 accumulates overcharge, and the adjacent pixel PD1 by PD2 does not accumulate.
There is no effect on

In the above-described conventional example, the case of skipping one pixel row at a time of partial reading has been described as an example. However, the present invention is not limited to this, and the present invention is applicable to a case where arbitrary skipping is performed according to the application. Needless to say, it can be applied to

[0040]

As described above, by adopting the structure of the present invention, the generation of a false signal can be suppressed, and no blooming occurs, no smear occurs, no color mixing occurs, and a high-quality photoelectric conversion device can be obtained. Can be obtained.

[Brief description of the drawings]

FIG. 1 is an operation timing chart of a first embodiment according to the present invention.

FIG. 2 is a schematic sectional view and a potential diagram of a pixel according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a scanning circuit according to a second embodiment of the present invention.

FIG. 4 is a schematic diagram illustrating a pixel circuit according to a third embodiment of the present invention.

FIG. 5 is a schematic diagram illustrating a pixel circuit according to a fourth embodiment of the present invention.

FIG. 6 is an operation timing chart of a fifth embodiment according to the present invention.

FIG. 7 is a schematic explanatory view of a conventional photoelectric conversion device.

FIG. 8 is an operation timing chart at the time of reading all pixels of a conventional photoelectric conversion device.

FIG. 9 is an operation timing chart at the time of partial reading of the conventional photoelectric conversion device.

FIG. 10 is a schematic sectional view and a potential diagram of a conventional pixel.

[Explanation of symbols]

1 Photoelectric conversion element (photodiode, etc.) 2 Amplification type source follower input MOS (Metal Oxide Si
3 vertical select switch MOS 4 power supply line 5 power supply terminal 6 vertical output line 7 load current source 8 vertical gate line 9 vertical scanning circuit 10 horizontal transfer MOS switch 11 horizontal output line 12 output amplifier 13 horizontal scanning circuit 14 reset switch 15 Reset gate line 401 Semiconductor substrate 402 Well 403 Photodiode (PN coupling) 501 Scan pulse generator 502, 503 Transfer switch 504 OR circuit 505 Mode switching terminal 901 Transfer switch 902 Transfer switch pulse line

Claims (6)

[Claims] 1. A photoelectric conversion device comprising: a plurality of photoelectric conversion elements and pixels each including a reset switch for resetting the photoelectric conversion elements arranged in a matrix, and having a vertical scanning unit and a horizontal scanning unit for reading out a signal of each pixel. In the device, comprising a first pixel group that reads the signal of the pixel and a second pixel group that does not read the signal of the pixel, at least a part of the first pixel group during the signal charge accumulation period A photoelectric conversion device, wherein a photoelectric conversion element included in the second pixel group is reset by the reset switch during a period. A plurality of photoelectric conversion elements, amplification means for receiving signal charges generated in the photoelectric conversion elements, transfer switch means for transferring charges to the amplification means, and transfer transfer means for connecting the photoelectric conversion elements to each other. Pixels consisting of a reset switch that resets through a matrix are arranged in a matrix,
A photoelectric conversion device having a vertical scanning unit and a horizontal scanning unit for reading a signal of each pixel, comprising: a first pixel group for reading the signal of the pixel, and a second pixel group for not reading the signal of the pixel. Resetting the photoelectric conversion elements included in the second pixel group by the reset switch via the transfer switch means in at least a part of the signal charge accumulation period of the first pixel group. Characteristic photoelectric conversion device. 3. A photoelectric conversion device comprising a plurality of photoelectric conversion elements and pixels each including a reset switch for resetting the photoelectric conversion elements, arranged in a matrix, and having a vertical scanning unit and a horizontal scanning unit for reading a signal of each pixel. In the device, a first pixel group that reads the signal of the pixel and a second pixel group that does not read the signal of the pixel, the photoelectric conversion element included in the second pixel group is constantly controlled by the reset switch. A photoelectric conversion device comprising a reset unit. 4. The photoelectric conversion device according to claim 2, further comprising a selection unit that selects the first and second pixel groups, wherein the selection unit controls the constant reset unit at the same time. Photoelectric conversion device. 5. The photoelectric conversion device according to claim 1, wherein the first pixel group and the second pixel group read pixel signals from both pixel groups. A first mode in which a signal of a pixel in the first pixel group is read out and a signal of a pixel in the second pixel group is not read out, and
The photoelectric conversion device captures a still image in the second mode and captures a moving image in the second mode. 6. The photoelectric conversion device according to claim 5, wherein the switching between the first mode and the second mode includes a selection pulse for selecting reading of the pixel and a reset pulse for resetting the pixel. Wherein the reset pulse constantly discharges the unread pixels in the second mode.