JP2016103701A - Imaging element and method of controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging element capable of obtaining a mixture signal of proper pixels by connecting a plurality of pixels to one vertical signal line without increasing power consumption.SOLUTION: An imaging element having: a floating diffusion (FD) holding electric charges generated by a photodiode; a reset switch resetting the potential of the FD to a reset potential; a plurality of pixels each having a signal output part outputting a signal corresponding to the potential of the FD and arranged in a matrix; a vertical scanning part selecting a plurality of pixels, row by row; and a vertical signal line to which a signal output part of a pixel selected by the vertical scanning part is connected properly controls an operation reference point so as to change the reset potential of the FD according to the number of signal output parts connected to one vertical signal line at the same time.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image sensor and a control method thereof.

  In recent years, CMOS image sensors used in digital cameras and the like have been increased in the number of pixels. On the other hand, for example, high frame rate shooting such as output of image data of 1920 × 1080 pixels at 30 fps or 60 fps like a full HD moving image. Needs are also increasing. In response to this need, a thinning readout method is known as a method for performing high frame rate imaging with a CMOS type image pickup device having a large number of pixels. In the thinning readout method, pixels are skipped at a specific cycle, and the data rate is lowered to increase the frame rate.

  However, in the thinning-out reading method, pixels are skipped at a specific cycle, so that there is a problem that moire, which is a kind of aliasing noise, is conspicuous as a feature of a captured moving image. As a technique for reducing this moire, a technique has been proposed in which a pixel signal read by the thinning readout method and a signal of an adjacent pixel that has been skipped are mixed and output. For example, in the pixel mixing method described in Patent Document 1, a row selection circuit outputs a mixed signal of a plurality of pixels on a vertical signal line by simultaneously selecting a plurality of rows.

Japanese Patent No. 5250474

  The pixel mixing method for outputting a mixed signal of a plurality of pixels on the vertical signal line by simultaneously selecting a plurality of rows as described above has the following problems. When a plurality of rows are simultaneously selected to output a mixed signal, the drive current per pixel of the MOS transistor in the signal output portion of the pixel is reduced. As a result, the potential of the source of the MOS transistor in the signal output portion of the pixel changes according to the number of selected rows, and the reset potential on the vertical signal line (hereinafter also referred to as an operation reference point) varies. At this time, there is a problem that the linearity of the signal deteriorates because the operation reference point deviates from an appropriate input range of a column amplifier provided for each column, a readout circuit such as a vertical signal line, an AD converter, or the like. It was. With respect to this problem, in Patent Document 1, the amount of current supplied to the vertical signal line is increased according to the number of selected rows. However, when the amount of current supplied increases, power consumption increases. In moving image shooting in which image signals are continuously read out at a predetermined frame rate, heat generation due to an increase in power consumption and image quality deterioration due to heat generation become a problem.

  An object of the present invention is to provide an imaging device capable of obtaining a mixed signal of appropriate pixels by connecting a plurality of pixels to one vertical signal line without increasing power consumption.

  An image pickup device according to the present invention includes a photoelectric conversion unit that converts incident light into charges, a charge holding unit that holds charges generated by the photoelectric conversion unit, a reset switch that resets the potential of the charge holding unit to a reset potential, And a plurality of pixels each having a signal output unit that outputs a signal corresponding to the potential of the charge holding unit and arranged in a matrix, a vertical scanning unit that selects the plurality of pixels in units of rows, and the plurality of the plurality of pixels A vertical signal line arranged for each column of pixels and connected to the signal output unit of the pixel selected by the vertical scanning unit; and the signal output unit connected to one vertical signal line at the same time. And a potential control unit that changes the reset potential according to the number.

  According to the present invention, since the reset potential of the pixel is changed according to the number of signal output units of the pixel connected to one vertical signal line at the same time, the power is not increased in one vertical signal line. A plurality of pixels can be connected to obtain an appropriate mixed pixel signal.

It is a figure which shows the structural example of the image pick-up element in 1st Embodiment. FIG. 3 is a schematic diagram illustrating a configuration example of a pixel and a circuit related to readout in the first embodiment. 3 is a timing chart illustrating an example of driving of the image sensor according to the first embodiment. It is a figure which shows the example of control of the electric potential SVDD in 1st Embodiment. It is a figure which shows the relationship between FD electric potential in this embodiment, and a vertical signal line electric potential. It is a schematic diagram which shows the structural example of the circuit which concerns on the pixel and readout in 2nd Embodiment. It is a figure which shows the example of control of the electric potential VRESL in 2nd Embodiment. It is a figure which shows the structural example of the imaging device in this embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
A first embodiment of the present invention will be described.
FIG. 8 is a block diagram illustrating a configuration example of an imaging apparatus according to an embodiment of the present invention. In FIG. 8, an optical system 801 includes a focus lens, and further includes a zoom lens and a diaphragm. The optical system 801 forms incident light (an optical image) on the image sensor 802. The image sensor 802 receives the optical image formed by the optical system 801, converts the received optical image into an electrical signal by photoelectric conversion, and outputs the electrical signal. The optical system drive unit 803 controls the focus lens position of the optical system 801 with a control signal in accordance with optical system drive information output from an AF (Auto Focus) control unit (not shown).

  An analog front end (AFE) 804 includes an analog / digital converter (AD converter), and adjusts a reference black level and performs analog / digital conversion on an image signal output from the image sensor 802. Perform processing. Note that in the case where the image sensor 802 includes an AD converter, the AFE 804 may not include the AD converter. A digital front end (DFE) 805 receives the digital output of each pixel output from the AFE 804 and performs digital processing such as pixel rearrangement.

  The digital signal processing unit 806 performs image processing (color conversion processing, white balance correction processing, gamma correction processing, etc.), resolution conversion processing, image compression processing, and the like on the image signal obtained from the DFE 805, and is not shown. The processed image signal is output to a recording device or a display device. The storage unit 807 is also used as a working memory for the digital signal processing unit 806 or as a buffer memory for continuous shooting or the like.

  FIG. 1 is a diagram illustrating a configuration example of an image sensor according to the first embodiment. As shown in FIG. 1, the image sensor according to the first embodiment includes a pixel unit 101, a vertical scanning unit 102, a reading unit 103, a horizontal scanning unit 104, a potential control unit 105, and a vertical signal line (column signal line) 107. Have.

  The pixel unit 101 includes a plurality of pixels 106 arranged in a matrix (two-dimensional), and receives an optical image formed by the optical system. Each pixel 106 includes a photoelectric conversion element that photoelectrically converts the received optical image into an electrical signal. In FIG. 1, for convenience of explanation, only pixels for six rows in the vertical direction and eight columns in the horizontal direction are shown, but in reality, the pixel portion 101 has more pixels 106 arranged therein. In FIG. 1, V0, V1, V2,... Indicate vertical addresses of pixels.

  The vertical scanning unit 102 selects the pixels 106 of the pixel unit 101 in units of rows. That is, the vertical scanning unit 102 sequentially selects one or a plurality of rows of the pixel unit 101. The pixel signals in the row selected by the vertical scanning unit 102 are supplied to the reading unit 103. The reading unit 103 includes a column amplifier, an AD converter, and the like, and samples signals of pixels in one or more rows selected by the vertical scanning unit 102. The horizontal scanning unit 104 sequentially selects the signal of each pixel sampled by the reading unit 103 in the horizontal direction and outputs it to a circuit such as an AFE in the subsequent stage.

  The potential control unit 105 supplies the reference potential SVDD to each pixel 106 of the pixel unit 101. In the first embodiment, the potential control unit 105 can control the reference potential SVDD to be supplied in accordance with the number of pixels connected to the vertical signal line 107 at the same time. The vertical signal line 107 is arranged for each column of the pixels 106 of the pixel unit 101, and can output a signal of each pixel of the pixel unit 101 to the reading unit 103. In the present embodiment, a mixed signal of one or more pixels connected to the vertical signal line 107 is output to the reading unit 103 via the vertical signal line 107.

  FIG. 2 is a schematic diagram illustrating a configuration example of a pixel and a circuit related to readout in the first embodiment. For the sake of explanation, FIG. 2 shows one pixel in the Vn-th row and a signal output path of the pixel.

  The pixel 106 includes one photodiode (PD) 201. A transfer switch 202 is connected to the photodiode 201, and a floating diffusion (FD) 203 is connected to the transfer switch 202. A reset switch 204 and a signal output unit (source follower amplifier) 205 are connected to the floating diffusion 203, and a selection switch 206 is connected to the signal output unit 205. The drain of the reset switch 204 and the signal output unit 205 are connected to a signal line to which the reference potential SVDD is supplied.

  The photodiode 201 functions as a photoelectric conversion unit, and generates and accumulates signal charges corresponding to the amount of received light (incident light amount). The transfer switch 202 is ON / OFF controlled by the pulse signal PTX output from the vertical scanning unit 102 and transfers the signal charge accumulated in the photodiode 201 to the floating diffusion 203. The floating diffusion 203 functions as a charge holding unit and holds the signal charge transferred from the photodiode 201. The floating diffusion 203 functions as a charge-potential conversion unit, and converts the held charge into a potential signal.

  The reset switch 204 is ON / OFF controlled by a pulse signal PRES output from the vertical scanning unit 102 and supplies a reference potential SVDD to the floating diffusion 203. As described above, in this embodiment, the reference potential SVDD can be controlled by the potential control unit 105 according to the number of pixels that are simultaneously connected to the vertical signal line 107, specifically, the number of signal output units 205. . The signal output unit 205 outputs a signal based on the potential of the floating diffusion 203 as a pixel signal. A source follower circuit is configured using the MOS transistor of the signal output unit 205 and the constant current source 207.

  The selection switch 206 is ON / OFF controlled by a pulse signal PSEL output from the vertical scanning unit 102, and connects the signal output unit 205 and the vertical signal line 107. The signal from the signal output unit 205 output to the vertical signal line 107 is sampled for each vertical signal line by the reading unit 103 and then output to a circuit such as an AFE in the subsequent stage. In the image sensor according to the present embodiment, when the vertical scanning unit 102 simultaneously turns on the selection switches 206 of a plurality of rows, a mixed signal of a plurality of pixels connected simultaneously appears on the vertical signal line 107.

Here, in FIG. 2, the pulse signals PTX, PRES, and PSEL input to the pixels 106 in the Vn row are represented as pulse signals PTX _Vn , PRES _Vn , and PSEL _Vn , respectively.

  Next, a driving method in the case where a mixed signal of two rows of pixels in the pixel portion 101 is output and read will be described. FIG. 3 is a timing chart illustrating an example of read driving of the image sensor according to the first embodiment. Here, driving of each pulse signal output from the vertical scanning unit 102 in the case where the signal of the pixel in the V1 row and the signal of the pixel in the V3 row are mixed and read will be described.

In FIG. 3, a horizontal synchronization signal HD is input at time t301. At a time t302 after a predetermined time has elapsed after the horizontal synchronization signal HD is input, the pulse signals PSEL _V1 and PSEL _V3 for selecting the pixels in the V1 row and the pixels in the V3 row are at a high level, and the V1 row is selected. The selection switch 206 for the pixel of the eye and the pixel of the V3th row is turned on. As a result, signals corresponding to the inputs of the signal output unit 205 (the potential of the floating diffusion 203) of the pixels in the V1 row and the pixels in the V3 row are mixed and supplied to the vertical signal line 107.

Further, at time t302, the pulse signals PRES _V1 and PRES _V3 supplied to the pixels in the V1 row and the V3 row become high level, and the reset switches 204 of the pixels in the V1 row and the pixels in the V3 row are turned on. Turn on. In the pixels in the V1 row and the pixels in the V3 row, the reference potential SVDD is supplied to the floating diffusion 203 when the reset switch 204 is turned on.

After that, at a time t303 after a predetermined time has elapsed, the pulse signals PRES _V1 and PRES _V3 are set to the low level, and the reset operation on the pixels in the V1 row and the pixels in the V3 row is cancelled. Through the above operation, signals corresponding to the reference potential SVDD from the pixels in the V1 row and the pixels in the V3 row are mixedly supplied to the vertical signal line 107. Then, during the period from time t303 to time t304, the mixed signal of the vertical signal line 107 after the reset is released is sampled as a noise component by the reading unit 103.

Next, at time t304, the pulse signals PTX _V1 and PTX _V3 are set to the high level to turn on the transfer switches 202 of the pixels in the V1 row and the pixels in the V3 row. Thereafter, at time t305 after a predetermined time has elapsed, the pulse signals PTX _V1 and PTX _V3 are set to the low level so as to turn off the transfer switches 202 of the pixels in the V1 row and the pixels in the V3 row.

  As a result, in the period from time t304 to time t305, the signal charges generated and accumulated by the photodiode 201 are transferred to the floating diffusion 203 in the pixels in the V1 row and the pixels in the V3 row. After time t 305, a mixed signal corresponding to the signal charges of the pixels in the V1 row and the V3 row is supplied to the vertical signal line 107 and sampled as a signal component in the reading unit 103.

  Up to this point, the mixed signals after the reset release of the pixels in the V1 row and the pixels in the V3 row are sampled by the reading unit 103 as noise components in each column, and the mixed signals corresponding to the signal charges are used as signal components in each column. Sampled by the reading unit 103. Subsequently, in the period from time t305 to t306, the reading unit 103 is scanned by the horizontal scanning unit 104, and sequentially outputs the difference between the noise component and the signal component for each column, so that the pixels in the V1 row and V3 Reading of the mixed signal of the pixels in the row is completed.

  The above is the description of the configuration of the image sensor and the reading drive method of the image sensor in the first embodiment. In FIG. 3, the driving method in the case where the mixed signal of the pixels in two rows is output and read out is shown. However, in the case where the signals of the pixels in a plurality of rows are mixed and read out, each pulse is similarly applied. If signals PRES, PRES, and PTX are driven simultaneously in a plurality of rows, a mixed signal can be obtained.

Here, the potential of the floating diffusion (FD) 203 of the pixel 106 is Vg, the potential of the vertical signal line 107 is Vs, and the current of the constant current source 207 is I. At this time, when one pixel is connected to the vertical signal line 107, the FD potential Vg and the vertical signal line potential Vs have the following relationship (Formula 1).
Vs = Vg−Vth−√ (2I / k) (Formula 1)
Vth is the threshold voltage of the MOS transistor of the signal output unit 205, and k is a constant determined from the MOS parameter.

Similarly, when two pixels are connected to the vertical signal line 107, the following relationship (Formula 2) is established.
Vs = Vg−Vth−√ (I / k) (Formula 2)

  From (Equation 1) and (Equation 2), it can be seen that the vertical signal line potential Vs increases as the number of pixels connected to the vertical signal line 107 increases from one to two. Thus, when the FD potential Vg and the constant current source current I are constant, there is a relationship that the vertical signal line potential Vs increases as the number of pixels connected to the vertical signal line 107 increases.

  That is, in the reading method in which a plurality of pixels are simultaneously connected to the vertical signal line 107 to obtain a mixed signal, the operation reference point (reset potential) varies depending on the number of pixels connected to the vertical signal line 107. It will be. Therefore, in the present embodiment, the operation reference point is within an appropriate input range of a readout circuit such as a column amplifier, a vertical signal line, or an AD converter according to the number of pixels connected to one vertical signal line 107 simultaneously. To control.

  Next, control of the reference potential SVDD by the potential control unit 105 in the first embodiment will be described with reference to FIGS. FIG. 4 is a diagram illustrating a control example of the reference potential SVDD in the first embodiment. As shown in FIG. 4, in this embodiment, the reference potential SVDD is controlled by the potential control unit 105 to a potential corresponding to the number of pixels connected to the vertical signal line 107 simultaneously.

In the example shown in FIG. 4, when the number of pixels connected to the vertical signal line 107 is one (vertical non-addition reading), the potential control unit 105 controls the reference potential SVDD to the potential V ₀ . Similarly, when two pixels are connected to the vertical signal line 107 at the same time (two-pixel connection), the potential control unit 105 controls the reference potential SVDD to the potential V ₁ . Also, when a pixel to be simultaneously connected to the vertical signal line 107 is 4 pixels (4 pixels connection), the potential control unit 105 controls the reference potential SVDD to the potential V _2. However, V ₂ <V ₁ <V ₀ .

In the first embodiment, by controlling the reference SVDD supplied to the pixel 106, the reset potential of the floating diffusion 203 is controlled to an appropriate potential according to the number of pixels connected to the vertical signal line 107 simultaneously. FIG. 4 shows that when the supplied reference potential SVDD is the potential V ₀ , the reset potential of the floating diffusion 203 becomes the potential Vg ₀ . Similarly, when the reference potential SVDD to be supplied is the potential V _1, the reset potential of the floating diffusion 203 becomes the potential Vg _1, when the reference potential SVDD is potential V _2, the reset potential of the floating diffusion 203 voltage Vg Become ₂ . However, it is _{Vg 2 <Vg 1 <Vg 0} .

  FIG. 5 is a diagram illustrating the relationship between the floating diffusion potential (FD potential) Vg and the vertical signal line potential Vs for each number of pixels that are simultaneously connected to the vertical signal line in the present embodiment. The relationship when two pixels are connected (two pixels connected simultaneously to the vertical signal line 107) and four pixels are connected (four pixels connected simultaneously to the vertical signal line 107) is the FD of the pixels connected simultaneously. In the following description, the potential Vg is equal.

  In FIG. 5, PA0, PA1, and PA2 indicate operation reference points when 1 pixel connection, 2 pixel connection, and 4 pixel connection are made to the vertical signal line in the present embodiment, respectively. In addition, PB0, PB1, and PB2 are connected to the vertical signal line by two pixels connected to the vertical signal line by the conventional control method, that is, regardless of the number of pixels that are simultaneously connected to the vertical signal line. The operation reference point when connected is shown.

As shown in FIG. 5, in the conventional control method, if the reference potential SVDD supplied to the pixel is fixed to the potential V ₀ , the reset potential of the floating diffusion 203 becomes the potential Vg ₀ . Therefore, whereas the operation reference point PB0 in the case of one pixel connected to the vertical signal line is the potential Vs _0, 2 pixels connected, 4 operating reference point PB1 in the case of pixels connected, PB2 the potentials Vs _1, Vs ₂ and higher than the potential Vs ₀ (Vs ₀ <Vs ₁ <Vs ₂ ).

When the operation reference point fluctuates in this manner, for example, the vertical signal line potential Vs deviates from the input range of the reading circuit in the reading unit 103, and the signal linearity is deteriorated. For example, as shown in FIG. 5, when the input range of the readout circuit is designed as potentials Vs _{a to} Vs _b , Vs _a <Vs ₀ <Vs _b and the potential Vs ₀ of the operation reference point PB0 is equal to the potential of the readout circuit. Within the input range. On the other hand, Vs _b <Vs ₁ and Vs _b <Vs ₂ , and the potentials Vs ₁ and Vs ₂ of the operation reference points PB1 and PB2 are outside the input range of the readout circuit. That is, in the conventional control method, when the reference signal SVDD supplied to the pixel is the potential V ₀ and the vertical signal line is connected to two pixels and four pixels, the vertical signal line potential Vs is the input range of the readout circuit. May come off.

In the image sensor according to the first embodiment, as shown in FIG. 4, the potential control unit 105 controls the reference potential SVDD according to the number of pixels connected to the vertical signal line, so the reset potential of the floating diffusion 203 is also a reference. The potential is controlled according to the potential SVDD. As shown in FIG. 5, when one pixel is connected to the vertical signal line, the reference potential SVDD supplied to the pixel is controlled to the potential V _0, and the reset potential of the floating diffusion 203 becomes the potential Vg ₀ .

When two pixels are connected to the vertical signal line, the reference potential SVDD supplied to the pixels is controlled to the potential V _1, and the reset potential of the floating diffusion 203 becomes the potential Vg ₁ . When four pixels are connected to the vertical signal line, the reference potential SVDD supplied to the pixels is controlled to the potential V _2, and the reset potential of the floating diffusion 203 becomes the potential Vg ₂ .

By controlling in this way, the operation reference points PA1 and PA2 when two pixels are connected to the vertical signal line and four pixels are connected are the same potential Vs ₀ as the operation reference point PA0 when both pixels are connected to the vertical signal line. Is controlled. Therefore, in this embodiment, even when the number of pixels simultaneously connected to the vertical signal line is 2 pixels and 4 pixels, the operation reference point is appropriately controlled so that the vertical signal line potential is within the input range of the readout circuit. And deterioration of signal linearity can be suppressed.

  According to the first embodiment, the potential control unit 105 controls the reference potential SVDD supplied to the pixel 106 according to the number of pixels connected to the vertical signal line at the same time, so that the floating diffusion 203 of the pixel 106 Change the reset potential. As a result, the mixed signal of the pixels can be read out by appropriately controlling the operation reference point according to the number of pixels connected to the vertical signal line so as not to deviate from the input range of the readout circuit or the like without increasing the power consumption. It becomes possible.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the second embodiment, the reset potential of the floating diffusion 203 of the pixel 106 is controlled according to the number of pixels simultaneously connected to the vertical signal line by a method different from that of the first embodiment. In the second embodiment, the reset potential of the floating diffusion 203 is controlled by controlling the potential supplied to the gate of the MOS transistor as the reset switch 204 of the pixel 106 without controlling the reference potential SVDD supplied to the pixel 106. To control.

  Here, the gate and source (floating diffusion 203) of the MOS transistor as the reset switch 204 of the pixel 106 have a coupling capacitance. With this coupling capacitance, it is possible to change the reset potential of the floating diffusion 203 in accordance with the voltage supplied to the gate of the reset switch 204. Specifically, the reset potential of the floating diffusion 203 can be lowered by lowering the low-level potential VRESL of the pulse signal PRES supplied to the gate of the reset switch 204. Hereinafter, differences from the first embodiment will be described.

  FIG. 6 is a schematic diagram illustrating a configuration example of a pixel and a circuit related to readout in the second embodiment. In FIG. 6, components having the same functions as those shown in FIG. 3 are given the same reference numerals, and redundant descriptions are omitted. In the second embodiment, the potential control unit 601 receives the pulse signal PRES output from the vertical scanning unit 102 and applies a low-level potential VRESL of the pulse signal PRES supplied to the pixel 106 to the vertical signal line 107. And control according to the number of pixels connected simultaneously.

  FIG. 7 is a diagram illustrating a control example of the potential VRESL by the potential control unit 601 according to the second embodiment. As shown in FIG. 7, in this embodiment, the low-level potential VRESL of the pulse signal PRES is controlled by the potential control unit 601 to a potential corresponding to the number of pixels connected to the vertical signal line 107 simultaneously.

In the example illustrated in FIG. 7, when the number of pixels connected to the vertical signal line 107 is one pixel (vertical non-addition reading), the potential control unit 601 controls the potential VRESL to the potential Vr ₀ . Similarly, when there are two pixels connected to the vertical signal line 107 (two-pixel connection), the potential control unit 601 controls the potential VRESL to the potential Vr ₁ . Also, when a pixel to be connected to the vertical signal line 107 is 4 pixels (4 pixels connection), the potential control unit 601 controls the potential VRESL to the potential Vr _2. However, Vr ₂ <Vr ₁ <Vr ₀ .

In the second embodiment, by controlling the low-level potential VRESL of the pulse signal PRES supplied to the pixel 106, the reset potential of the floating diffusion 203 is set to an appropriate potential according to the number of pixels connected to the vertical signal line 107. Control. FIG. 7 shows that when the potential VRESL is the potential Vr ₀ , the reset potential of the floating diffusion 203 becomes the potential Vg ₀ . Similarly, when the potential VRESL is potential Vr _1, the reset potential of the floating diffusion 203 becomes the potential Vg _1, when the potential VRESL is potential Vr _2, the reset potential of the floating diffusion 203 becomes Vg _2. However, it is _{Vg 2 <Vg 1 <Vg 0} .

Also in the second embodiment, as shown in FIG. 5, when one pixel is connected to the vertical signal line, the reset potential of the floating diffusion 203 becomes the potential Vg ₀ . When two pixels are connected to the vertical signal line, the reset potential of the floating diffusion 203 becomes the potential Vg ₁ . If four pixels connected to the vertical signal line, the reset potential of the floating diffusion 203 becomes the potential Vg _2.

At this time, as shown in FIG. 5, the operating reference point PA0 in the case of one pixel connected to the vertical signal line the potential Vs _0, 2 pixels connected to the vertical signal line, the four case where the pixel connection operation reference point PA1 , it is possible to control both to the potential Vs ₀ also PA2. Therefore, in this embodiment, even when the number of pixels simultaneously connected to the vertical signal line is 2 pixels and 4 pixels, the operation reference point is appropriately controlled so that the vertical signal line potential is within the input range of the readout circuit. And deterioration of signal linearity can be suppressed.

  In addition, the reset potential of the floating diffusion 203 of the pixel 106 can be changed to be low by reducing the high-level potential VRESH of the pulse signal PRES. For example, when the pulse signal PRES of the potential VRESH is input to the gate of the reset switch 204 of the pixel 106 at the time t302 in the driving example illustrated in FIG. 3, the floating diffusion 203 is supplied with the reference potential SVDD to the reset potential. Reset.

  The time required for this reset (the time to reach the reset potential) depends on the potential VRESH, and becomes longer as the potential VRESH is lower. Therefore, the potential control unit 601 controls the potential VRESH to be low during the period from time t302 to t303, so that the time required for reset becomes long. Thereby, the reset electric potential of the floating diffusion 203 after reset cancellation | release (time t303-t304) can be changed low. As described above, when the high-level potential VRESH of the pulse signal PRES is controlled, as in the method of controlling the low-level potential VRESL shown in FIG. 7, more pixels are simultaneously connected to the vertical signal line. Control may be performed so that the potential VRESH is lower.

  According to the second embodiment, the potential control unit 601 controls the low-level potential VRESL of the pulse signal PRES supplied to the pixel 106 according to the number of pixels connected to the vertical signal line at the same time, thereby floating. The reset potential of the diffusion 203 is changed. As a result, the mixed signal of the pixels can be read out by appropriately controlling the operation reference point according to the number of pixels connected to the vertical signal line so as not to deviate from the input range of the readout circuit or the like without increasing the power consumption. It becomes possible.

  In the first embodiment and the second embodiment described above, three modes in which one pixel is connected to the vertical signal line, two pixels are connected, and four pixels are connected are described as an example. These three modes are selectively used according to the shooting mode of the imaging apparatus, such as reading with one pixel connection during still image shooting and reading with two or four pixel connections during moving image shooting. Furthermore, according to the required number of read pixels and frame rate, it is also possible to read out by connecting 3 pixels, 5 pixels, or a larger number of pixels simultaneously. The present invention can be applied by controlling to a suitable reference potential SVDD or potential VRESL according to the number of pixels simultaneously connected to the vertical signal line. For example, the reference potential SVDD and the potential VRESL are controlled so that the reset potential of the floating diffusion 203 is lowered as the number of pixels simultaneously connected to the vertical signal line increases.

  In the embodiment of the present invention, since the reset potential of the floating diffusion 203 is changed according to the number of pixels connected to the vertical signal line, the dark output characteristics of the image sensor also change. Therefore, in the imaging apparatus to which the present invention is applied, the correction value for correcting the dark output characteristics of the image sensor is stored and used for correction according to the number of pixels connected to the vertical signal line. Appropriate correction of output characteristics is also possible. Further, in the embodiment of the present invention, the pixel portion of the image sensor has a configuration having one vertical signal line for each column, but may have a configuration having two or more vertical signal lines for each column. Good.

  The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

DESCRIPTION OF SYMBOLS 101: Pixel part 102: Vertical scanning part 103: Reading part 104: Horizontal scanning part 105: Potential control part 106: Pixel 107: Vertical signal line (column signal line) 201: Photodiode 202: Transfer switch 203: Floating diffusion 204: Reset transistor 205: Signal output unit 206: Selection transistor 207: Current source SVDD: Reference potential 601: Potential control unit 802: Image sensor

Claims (7)

A photoelectric conversion unit that converts incident light into charges, a charge holding unit that holds charges generated by the photoelectric conversion unit, a reset switch that resets the potential of the charge holding unit to a reset potential, and a potential of the charge holding unit A plurality of pixels each having a signal output section for outputting a corresponding signal and arranged in a matrix;
A vertical scanning unit that selects the plurality of pixels in units of rows;
A vertical signal line arranged for each column of the plurality of pixels and connected to the signal output unit of the pixel selected by the vertical scanning unit;
An image pickup device comprising: a potential control unit that changes the reset potential in accordance with the number of the signal output units connected simultaneously to one vertical signal line. The reset switch is provided between a signal line to which a first potential is supplied and the charge holding unit, and connects the signal line to which the first potential is supplied with the charge holding unit. Reset the potential of the charge holding unit to the reset potential,
The image sensor according to claim 1, wherein the potential control unit controls the first potential in accordance with the number of the signal output units connected simultaneously to one vertical signal line. The reset switch is on / off controlled by a control signal,
The said potential control part controls the electric potential of the said control signal which turns off the said reset switch according to the number of the said signal output parts connected simultaneously with respect to one said vertical signal line. The imaging device according to 1. The reset switch is on / off controlled by a control signal,
The said potential control part controls the electric potential of the said control signal which turns on the said reset switch according to the number of the said signal output parts connected simultaneously with respect to one said said vertical signal line, It is characterized by the above-mentioned. The imaging device according to 1. The reset switch is a MOS transistor having a source connected to the charge holding unit and a drain connected to a signal line to which a first potential is supplied;
The said potential control part controls the electric potential supplied to the gate of the said MOS transistor according to the number of the said signal output parts connected simultaneously with respect to one said vertical signal line. Image sensor.   The potential control unit is simultaneously connected to one vertical signal line from the reset potential when the number of the signal output units simultaneously connected to one vertical signal line is the first number. The imaging according to any one of claims 1 to 5, wherein the reset potential when the number of the signal output units to be performed is a second number larger than the first number is changed to be low. element. A photoelectric conversion unit that converts incident light into charges, a charge holding unit that holds charges generated by the photoelectric conversion unit, a reset switch that resets the potential of the charge holding unit to a reset potential, and a potential of the charge holding unit A plurality of pixels each having a signal output unit for outputting a corresponding signal, arranged in a matrix, a vertical scanning unit for selecting the plurality of pixels in units of rows, and arranged for each column of the plurality of pixels, A control method of an image sensor having a vertical signal line to which the signal output unit of the pixel selected by the vertical scanning unit is connected,
Selecting the pixels in one or more rows by the vertical scanning unit;
The method of controlling an image sensor, wherein the reset potential is changed according to the number of the signal output units simultaneously connected to one vertical signal line.

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