JP4802688B2 - Imaging device and imaging apparatus - Google Patents

Description

  The present invention relates to an imaging device and an imaging device including the imaging device, and more particularly to an imaging device having a wide imaging dynamic range and an imaging device including the imaging device.

  Due to the recent trend toward downsizing and increasing the number of pixels in the image sensor, the pixel size of the image sensor continues to be reduced, and along with this, the illuminance range (so-called dynamic range) that can be imaged by the image sensor becomes narrower, resulting in improved image quality. It has a big influence. Therefore, a wide dynamic range of the image sensor is desired.

  In order to solve this problem, screens with different exposure amounts are shot multiple times, and images with a wider dynamic range than individual screens are selected by combining the images by selecting screen portions of the appropriate level from the multiple screens. An image pickup apparatus to be combined (see, for example, Patent Document 1) and a charge-voltage converter that converts photoelectric conversion signal charges of the image sensor into signal voltages, and the charge-voltage converter includes a plurality of capacitors having different voltage dependencies. An image sensor (for example, see Patent Document 2) having a variable dynamic range has been proposed.

In addition, a plurality of capacitors for holding the signal charge of the photodiode are provided, and the signal charge obtained by one exposure is read a plurality of times by switching the capacitance value, and the dynamic range is expanded by adding the read signals. A method has been proposed (see, for example, Patent Document 3).
Japanese Patent Publication No. 7-97841 JP 2000-165755 A JP 2000-165754 A

  However, since the imaging apparatus proposed in Patent Document 1 requires a plurality of times of shooting, it takes a long time to shoot and combines images by image processing from images with different exposure amounts. Since the stitches in the composition are unnatural and very difficult to see, very complex image composition is essential and the processing time is long. To shorten the processing time, it is necessary to use an expensive processing chip, and the cost Becomes very high.

  In addition, the image pickup device proposed in Patent Document 2 has a complicated device structure and a high manufacturing cost, and it is difficult to control the voltage dependency of the capacitance, so that adjustment for each device is necessary and causes an increase in cost.

  In addition, although the method proposed in Patent Document 3 seems to have expanded the dynamic range at first glance, in reality, the charge exceeding the saturation charge of the photodiode cannot be taken out as a signal, that is, the dynamic range is limited by the photodiode. It just looks like the dynamic range has expanded.

  The present invention has been made in view of the above circumstances, and by using a charge equal to or higher than the saturation charge of the photoelectric conversion means constituting the pixel of the image sensor as a signal charge, the dynamic range is expanded in a true sense. An object of the present invention is to provide an imaging device that can contribute to image quality improvement and an imaging device including the imaging device.

  The object of the present invention can be achieved by the following constitution.

1. In an image sensor having a plurality of pixels,
The pixel is
Photoelectric conversion means for photoelectrically converting light from a subject and storing the converted photoelectric charge ;
Discharging means for discharging the overflowing photoelectric charge from the photoelectric conversion means;
Accumulating means for accumulating photoelectric charges overflowing from the photoelectric conversion means;
A first potential barrier provided between the photoelectric conversion means and the discharge means;
A second potential barrier provided between the photoelectric conversion means and the storage means ,
A part of the photoelectric charge overflowing from the photoelectric conversion means by photoelectrically converting light from the subject in a state where the potential of the first potential barrier is different from the potential of the second potential barrier. Is stored in the storage means, and the rest is discharged from the discharge means .

2. Imaging device according to the 1, characterized by variably controlling the potential of said second potential barrier.

3. Imaging device according to the 1, wherein the benzalkonium be variably controlling the potential of the potential and the second potential barrier of the first potential barrier.

4). The pixel includes a charge detection unit,
Imaging device according to any one of the items 1 to 3, characterized in that to have a potential structure capable of complete transfer to the charge detection means of the charge accumulated in the photoelectric conversion means and the storage means.

5. 5. The image pickup device according to any one of 1 to 4, wherein the photoelectric conversion unit and the storage unit have an embedded diode structure .

6). An image pickup apparatus comprising the image pickup device according to any one of 1 to 5 above .

  According to the present invention, a part of the charge equal to or higher than the saturation charge of the photoelectric conversion means constituting the pixel of the image sensor is stored in the storage means via the second potential barrier, and the rest is stored via the first potential barrier. By discharging to the discharge means, the charge above the saturation charge of the photoelectric conversion means can be used as a signal charge, the true dynamic range can be expanded without increasing the storage means, and reset It is possible to provide an imaging device that can contribute to high image quality because noise can be completely removed, and an imaging device including the imaging device.

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

  First, a digital camera which is an example of an imaging apparatus according to the present invention will be described with reference to FIGS.

  1A and 1B are schematic external views of a digital camera. FIG. 1A is a front view and FIG. 1B is a rear view.

  In FIG. 1A, an interchangeable lens 20 is attached to the front surface of the body 10 of the digital camera 1. A release button 101, which is an operation member for imaging, is installed on the upper surface of the body 10, and an AF that operates in the first stage of pressing the release button 101 inside the body 10 is below the release button 101. A switch 101a and a two-stage switch constituting the release switch 101b that operates in the second stage of pressing the release button are arranged. A flash 102 is built in the upper part of the body 10 and a mode setting dial 112 for setting the operation mode of the digital camera 1 is arranged.

  In FIG. 1 (b), on the back of the body 10, a power switch 111 for turning on / off the power of the digital camera 1, a change dial 113 for changing various setting conditions of the camera, up / down / left / right and center five switches A jog dial 115 for performing various settings in each operation mode of the digital camera 1, a finder eyepiece 121a, and an image display means 131 for displaying recorded images and various information are arranged.

  FIG. 2 is a block diagram showing an example of a circuit of the digital camera 1 shown in FIG. In the figure, the same parts as those in FIG.

  The camera control means 150 that controls the digital camera 1 includes a CPU (central processing unit) 151, a work memory 152, a storage unit 153, a data memory 154, and the like, and programs stored in the storage unit 153 are stored in the work memory 152. And each unit of the digital camera 1 is centrally controlled according to the program.

  The camera control means 150 receives inputs from the power switch 111, the mode setting dial 112, the change dial 113, the jog dial 115, the AF switch 101a, the release switch 101b, etc., and communicates with the photometry module 122 on the optical viewfinder 121. Thus, the photometry operation is controlled, the AF operation is controlled by communicating with the AF module 144, the reflex mirror 141 and the sub mirror 142 are driven via the mirror driving means 143, and the shutter 145 is moved via the shutter driving means 146. And controlling the flash 102 and controlling the imaging operation by communicating with the imaging control means 161, displaying the captured image and various information on the image display means 131, and displaying various information on the finder display means 132. indicate.

  The camera control means 150 also includes a personal computer or a portable information terminal provided outside the digital camera 1 via an external interface (I / F) 185, captured image data, control signals for the digital camera 1, and the like. Exchange.

  Further, the camera control means 150 communicates between the body 10 and the interchangeable lens 20 on the mount (body side) 171 and the mount (lens side) 271 provided on the mount (body side) 171. Through the BL communication means (lens side) 272 provided, via the lens interface 251 of the interchangeable lens 20, a lens control means 241 for controlling the focus and zoom of the lens 211, and an aperture control means 222 for controlling the diaphragm 221. The entire interchangeable lens 20 is controlled by communicating with the lens information storage means 231 storing the unique information of the interchangeable lens 20.

  An image formed on an imaging surface 162a of an imaging element 162 (to be described later with reference to FIG. 3) by the lens 211 of the interchangeable lens 20 is photoelectrically converted by the imaging element 162, amplified by an amplifier 163, and analog / digital (A / A) D) Converted into digital data by the converting means 164, converted into digital image data subjected to predetermined image processing by the image processing means 165, once recorded in the image memory 181 and finally recorded in the memory card 182 Is done. These operations are controlled by the imaging control unit 161 under the control of the camera control unit 150. The imaging control unit 161, the amplifier 163, the A / D converter 164, and the image processing unit 165 constitute an imaging circuit 160.

  Next, FIG. 3 shows an example of each component constituting the image sensor according to the present invention and its arrangement. FIG. 3 is a schematic diagram illustrating an example of an arrangement of each component constituting the image sensor. The same parts as those in FIGS. 1 and 2 are given the same numbers.

  The imaging element 162 has an imaging surface 162a on which an image is formed by the lens 211 of the interchangeable lens 20, and a plurality of pixels 162b arranged in the horizontal and vertical directions on the imaging surface 162a, and a vertical scanning circuit. 162c, a sample-and-hold circuit 162d, an output circuit 162e, a horizontal scanning circuit 162f, an output amplifier 162g, a timing generator 162h, and the like. The row-by-horizontal arrangement of the pixels 162b and the vertical scanning circuit 162c are the row selection lines 162i. The arrangement of the pixels 162b for each vertical column and the sample hold circuit 162d are connected by a vertical signal line 162j.

  The imaging operation of the imaging element 162 is controlled by the timing generator 162h in accordance with the imaging control signal 161a from the imaging control means 161. The detailed imaging operation will be described later with reference to FIG. 6 and the like. As a general rule, the imaging output VOUT of the pixel 162b of the imaging device 162 for one row selected by the row selection line 162i is derived to the vertical signal line 162j. It is input to and held in the sample hold circuit 162d, and is sequentially output as imaging data 162k via the output amplifier 162g by the output circuit 162e in accordance with the operation of the horizontal scanning circuit 162f. A similar operation is performed for all horizontal rows. The output imaging data 162k is input to the amplifier 163.

  Next, the first embodiment of the pixel 162b of the image sensor 162 according to the present invention and the imaging operation thereof will be described with reference to FIGS.

  4A and 4B are schematic views showing a first embodiment of a main part related to imaging of the pixel 162b. FIG. 4A is a state viewed from the imaging surface 162a side, and FIG. 4B is FIG. FIG. 4C is a potential diagram of the AA ′ cross section of FIG. 4A.

  In FIG. 4 (a), a first potential barrier PB1 (hereinafter referred to as PB1) and a second potential barrier are adjacent to a photodiode PD (hereinafter referred to as PD) functioning as a photoelectric conversion means in the present invention. PB2 (hereinafter referred to as PB2) is provided, and an overflow drain OFD (hereinafter referred to as OFD) that functions as a discharge means in the present invention is provided on the opposite side of PD across PB1, and is opposite to PD across PB2. Storage means CP (hereinafter referred to as CP) is provided on the side.

  In FIG. 4B, PD and CP are formed by, for example, thinly implanting (N−) ions of N-type impurities into a P-type substrate (Psub), and further deepening (P +) ions of P-type impurities on the upper part thereof. By implantation, a buried structure is formed. OFD is also formed by ion implantation of N-type impurities to a P-type substrate (Psub) at a high concentration (N +). PB1 and PB2 are formed by ion-implanting P-type impurities into a P-type substrate (Psub). Both are formed so that desired characteristics can be obtained by heat treatment after ion implantation. The surface of each part is covered with an insulating layer INL such as an oxide film or a nitride film. Further, each part other than the PD is covered with a light shielding layer SL.

  FIG. 4C is a schematic diagram showing the potential of each part immediately after the initial reset operation, which will be described later with reference to FIG. 7. PD and CP are depleted potentials, and OFD is a fixed potential (for example, power supply voltage VDD). It is connected. In this example, the potentials of PD and CP are illustrated as almost the same, but this is not an essential condition, and there may be a difference between the two.

  The potentials of PB1 and PB2 are set higher than the potentials of PD, CP, and OFD, and the potential of PB1 is set lower by ΔVpt than the potential of PB2. The potential difference can be set according to ion implantation conditions at the time of formation, the width of the barrier, and the like. For example, if the P-type impurity concentration in the PB2 portion is higher than the concentration in the PB1 portion, the potential can be set higher. PB1 and PB2 are in a weak inversion state.

FIG. 5 is a schematic potential diagram showing a state of photoelectric conversion and photoelectric charge accumulation when light is incident on the main part related to imaging of the pixel 162b shown in FIG. Assuming that the potential of PB1 is V _g1 and the potential of PB2 is V _g2 , in FIG. 5A, when light (hν) is incident, photoelectric conversion is performed in the PD and a photocharge Qpd corresponding to the amount of incident light is generated. , Accumulated in PD. As shown in FIG. 4B, portions other than the PD are shielded from light by the light shielding layer SL. In the following drawings, the illustration of the light shielding layer SL is omitted.

  In FIG. 5B, the generated photocharge Qpd is accumulated in the PD up to the PD accumulation limit amount Qpdmax. In FIG. 5C, when the generated photocharge Qpd exceeds the PD accumulation limit amount Qpdmax, the PD A part overflows to the outside, and a part is discharged to the OFD and a part is accumulated in the CP as a photocharge Qcp. At this time, a current flows through the potential barrier, but this current value I follows the following equation when the potential barrier is in a weak inversion state.

However, I ₀ and α are constants, V _g is a potential of a potential barrier, V _s is a potential of PD, q, k, and T are elementary charges of electrons, Boltzmann constant, and absolute temperature, respectively.

If the potential barrier as in the present embodiment there are two, the current the current flowing through the light current Ipd, PB1 through the I _1, PB2 When I _2,

It is. Here, Ipd = I ₁ + I ₂ .

Therefore, the ratio r of the currents flowing through PB1 and PB2 is expressed as follows: if the potential difference between PB1 and PB2 is ΔVpt (= V _g1 −V _g2 ),

Thus, it can be seen that the ratio r of the current flowing through PB1 and PB2 can be controlled by the potential difference ΔVpt of the potential barrier.

  For example, if r = 9, 1/10 of the photocurrent overflowing from the PD is accumulated in the CP through the PB2, and for example, the CP capacitance Ccp is the same as the PD capacitance Cpd. However, since it becomes possible to accumulate photocharges corresponding to 10 times the light input, the dynamic range can be expanded without increasing the CP capacitance (= CP surface area). The relationship between the potential difference ΔVpt and the ratio r of the currents flowing through PB1 and PB2 is r = 10 when ΔVpt = about 60 mV and r = 100 when ΔVpt = about 120 mV at room temperature (25 ° C.).

  Next, the imaging operation of the first embodiment of the main part related to imaging of the pixel 162b shown in FIG. 4 will be described with reference to FIGS. FIG. 6 is a circuit diagram of a pixel 162b in which an imaging output readout circuit is connected to a main part related to imaging of the pixel 162b shown in FIG.

  In FIG. 6, the main part of the pixel 162b is composed of the PD, OFD, CP, PB1, and PB2 shown in FIG. 4, and five N-channel MOSFETs (metal oxide semiconductor field effect transistors: hereinafter referred to as transistors). ing. VDD is a power supply voltage, RSB is a reset potential, and SX (162i), RX, SEL1, and SEL2 are control signals.

  The transistor Qs1 is a switch that is controlled by the output signal SEL1 connected to the gate and completely transfers the photoelectric charge Qpd photoelectrically converted and accumulated by the PD to the parasitic capacitance of the gate of the transistor Qb. The transistor Qs2 is also connected to the gate. This switch is controlled by the connected output signal SEL2 and completely transfers the photocharge Qcp accumulated in CP to the parasitic capacitance of the gate of the transistor Qb.

  The transistor Qb has a drain connected to the power supply voltage VDD and a source connected to the drain of the transistor Qsel, and constitutes a source follower amplifier circuit that lowers the output impedance by performing current amplification on the potential input to the gate.

  The transistor Qsel is a signal readout transistor, the gate is connected to the row selection line 162i, operates as a switch that is turned on / off in response to the readout signal SX applied by the vertical scanning circuit 162c, and the source is a vertical signal. When the transistor Qsel is connected to the line 162j and the transistor Qsel is turned on, the output of the PD or CP whose impedance is reduced by the transistor Qb connected to the drain is the imaging output VOUT (PD imaging outputs Vpd and CP described later in FIG. 7). The image output Vcp) is derived to the vertical signal line 162j.

  The transistor Qr1 is a reset transistor, which is controlled by a reset signal RX connected to the gate, and resets (initializes) the gate of the transistor Qb to the reset potential RSB.

  FIG. 7 is a timing chart showing the flow of the imaging operation of the pixel 162b shown in FIG. In the present invention, the exposure amount control of the image sensor 162 is performed by a shutter.

  In FIG. 7, at timing T1 (initial reset operation), the reset signal RX and the output signals SEL1 and SEL2 are set to a high potential (H) in a state in which the shutter for controlling exposure to the image sensor 162 is closed. Thus, the remaining charges of PD and CP are completely transferred to the parasitic capacitance of the gate of transistor Qb, PD and CP are reset, and the gate of transistor Qb is reset to reset potential RSB. At this time, the PD and CP are depleted due to the complete transfer of the remaining charge, so no reset noise occurs.

  At timing T <b> 2 (imaging operation), the shutter is opened and light is incident on the imaging element 162 to perform imaging. This operation is the same as the operation shown in FIG. At the end of timing T2, the shutter is closed, and the imaging operation is completed. At this time, the photocharge Qpd is accumulated in the PD, and the photocharge Qcp is accumulated in the CP when the photocharge overflowing from the PD as shown in FIG. 5C.

  At timing T3 (PD signal read operation), the read signal SX and the output signal SEL1 are set to a high potential (H), so that the photocharge Qpd accumulated in the PD is completely transferred to the parasitic capacitance of the gate of the transistor Qb. It is converted to the gate potential VG, impedance is converted by the transistor Qb, and the PD imaging output Vpd of the pixel 162b is derived to the vertical signal line 162j by the transistor Qsel.

  At timing T4 (Qb reset operation), the reset signal RX is set to a high potential (H), whereby the gate of the transistor Qb is reset to the reset potential RSB.

  At timing T5 (CP signal read operation), the read signal SX and the output signal SEL2 are set to a high potential (H), so that the photocharge Qcp accumulated in the CP is completely transferred to the parasitic capacitance of the gate of the transistor Qb. It is converted to the gate potential VG, impedance is converted by the transistor Qb, and the CP imaging output Vcp of the pixel 162b is derived to the vertical signal line 162j by the transistor Qsel.

  The PD imaging output Vpd and the CP imaging output Vcp are temporarily held in the sample hold circuit 162d and then added, and output as imaging data 162k through the output amplifier 162g by the output circuit in accordance with the operation of the horizontal scanning circuit 162f. This is shown in FIG. FIG. 8 is a schematic diagram of a graph showing the photoelectric conversion characteristics of the image sensor 162 shown in FIG. 6. The horizontal axis represents the amount of incident light on the image sensor 162, and the vertical axis represents the image data 162k.

  In FIG. 8, the linear characteristic on the side where the incident light quantity is small is a photoelectric conversion characteristic (hereinafter referred to as PD characteristic) due to the accumulation of photocharge by PD, and the linear characteristic on the side where the incident light quantity is large is photoelectric conversion due to the accumulation of photocharge by CP. In the characteristics (hereinafter referred to as CP characteristics), a PD characteristic having a large inclination until the saturation output of PD (inclination is assumed to be A), and a CP characteristic having a small inclination for a light amount higher than that (in FIG. In the case of the ratio r = 9 of the current flowing through PB2 (that is, the case of slope A / 10), there is a point (hereinafter referred to as an inflection point) where the PD characteristic is discontinuously switched to the CP characteristic.

  The photoelectric conversion characteristic of a general image sensor having no CP characteristic is a characteristic in which the PD characteristic extends to the maximum output of the imaging data 162k (characteristic indicated by a broken line in FIG. 8). In this case, the imaging dynamic range is the dynamic range. 1 On the other hand, in the imaging device of the present invention, the imaging dynamic range is the dynamic range 2, and it can be seen that a wide dynamic range can be achieved.

  With the configuration as described above, charges equal to or higher than the saturation charge of the PD can be accumulated in the CP and used as signal charges, so that the imaging dynamic range of the imaging element can be expanded.

  Although the five transistors described above have been described as N-channel MOSFETs, it is of course possible to configure a circuit with P-channel MOSFETs.

  Next, a second embodiment of the pixel 162b of the image sensor 162 according to the present invention and its imaging operation will be described with reference to FIGS.

  FIG. 9 is a schematic diagram illustrating a second embodiment of the pixel 162b of the image sensor 162 according to the present invention. FIG. 9A illustrates a main part related to imaging of the pixel 162b illustrated in FIG. , A charge detection means CD (hereinafter referred to as CD), a first transfer gate TG1 (hereinafter referred to as TG1) that completely transfers the photocharge Qpd accumulated in the PD to the CD, and a photocharge accumulated in the CP. FIG. 9B is a circuit diagram in which a second transfer gate TG2 (hereinafter referred to as TG2) for completely transferring Qcp to a CD is added, and an imaging output readout circuit is connected. FIG. FIG. The cross section A-A ′ of FIG. 9A is the same as FIG.

  In FIG. 9A, TG1 is provided adjacent to PD, TG2 is provided adjacent to CP, and CD is arranged on the opposite side of PD and CP across TG1 and TG2. TG1 is controlled by the transfer signal TX1, and TG2 is controlled by the transfer signal TX2. The gate of the transistor Qb is connected to CD. The other configurations and functions of the transistor Qb and the configurations and functions of the transistors Qsel and Qr1 are the same as those in FIG.

  In FIG. 9B, PD, CP and OFD are formed by the same method as in FIG. The CD is formed by ion implantation of N-type impurities to the P-type substrate (Psub) in the same manner as the OFD, and the TG1 and TG2 are also P-type in the P-type substrate (Psub) like the PB1 and PB2. An impurity concentration distribution is formed in the substrate by ion implantation of the impurity, and a gate electrode EL is formed by laminating a conductor such as polysilicon on the insulating layer INL.

  Both are formed so that desired characteristics can be obtained by heat treatment after ion implantation. The surface of each part is covered with an insulating layer INL such as an oxide film or a nitride film. Further, each part other than the PD is covered with a light shielding layer SL.

  FIG. 10 is a timing chart showing a driving method of the pixel circuit shown in FIG. 9A. FIG. 10A is a diagram in which the photocharge accumulated in the PD and the photocharge accumulated in the CP are mixed by the CD. FIG. 10B is a timing chart of a method for reading out the photoelectric charge accumulated in the PD and the photoelectric charge accumulated in the CP individually. With the method of FIG. 10A, the timing signal related to signal readout is simplified, so the readout time is shortened, and the circuit for removing reset noise can be simplified. With the method shown in FIG. 10B, the capacity of the CD can be further reduced, which can contribute to downsizing of the pixel.

  In FIG. 10A, at timing T1 (initial reset operation), the reset signal RX and the transfer signals TX1 and TX2 are set to a high potential (H) while the shutter for controlling exposure to the image sensor 162 is closed. Thus, the remaining charges of PD and CP are completely transferred to CD via TG1 and TG2, and the transistor Qr1 is turned on to reset the gate of the transistor Qb and CD to the reset potential RSB. At this time, PD and CP are depleted because the remaining charges are completely transferred, and thus no reset noise is generated. However, a charge Qn1 due to reset noise is generated in CD. FIG. 11 shows the potential state of each part immediately after the timing T1.

  At timing T <b> 2 (imaging operation), the shutter is opened and light is incident on the imaging element 162 to perform imaging. This operation is the same as the operation shown in the potential diagram of FIG. At the end of timing T2, the shutter is closed, and the imaging operation is completed. At this time, the photocharge Qpd is accumulated in the PD, and the photocharge Qcp is accumulated in the CP when the photocharge overflowing from the PD as shown in FIG. 5C.

  At timing T3 (noise readout operation), the readout signal SX is set to a high potential (H), so that the potential Vn1 of CD in a state where the charge Qn1 due to reset noise is accumulated is impedance-converted by the transistor Qb, and the transistor Qsel is derived to the vertical signal line 162j as the reset noise output Vn1 of the pixel 162b. FIG. 12 shows the potential state of each part in the A-A ′ section and the B-B ′ section at the timing T <b> 3.

  At timing T4 (mixed signal read operation), the transfer signals TX1 and TX2 are set to a high potential (H), so that the photocharge Qpd accumulated in the PD and the photocharge Qcp accumulated in the CP are completely transferred to the CD. And superimposed on the charge Qn1 due to reset noise. At the same time, when the read signal SX is set to a high potential (H), the potential Vmix of the CD in a state where the mixed photocharge Qmix (= Qpd + Qcp) and the charge Qn1 due to reset noise are accumulated is converted by the transistor Qb. Then, the mixed signal output Vmix of the pixel 162b is derived by the transistor Qsel to the vertical signal line 162j. FIG. 13 shows a potential state of each part in the B-B ′ cross section at the timing T <b> 4.

  The reset noise output Vn1 and the mixed signal output Vmix derived to the vertical signal line 162j are stored in the storage means provided in the sample hold circuit 162d and a difference is taken (so-called correlated double sampling operation), so that the reset noise is obtained. Is output as imaging data 162k (FIG. 3) from which the image is completely removed.

  In FIG. 10B, the operation from timing T1 to timing T3 is the same as the operation in FIG.

  At timing T5 (PD signal read operation), the transfer signal TX1 is set to a high potential (H), so that the photocharge Qpd accumulated in the PD is completely transferred to the CD and superimposed on the charge Qn1 due to reset noise. At the same time, the read signal SX is set to a high potential (H), whereby the potential Vs1 of the CD in a state where the photocharge Qpd and the charge Qn1 due to reset noise are superimposed is impedance-converted by the transistor Qb, and the pixel 162b The PD signal output Vs1 is derived to the vertical signal line 162j. FIG. 14 shows the potential state of each part in the B-B ′ cross section at the timing T <b> 5.

  The reset noise output Vn1 and the PD signal output Vs1 derived to the vertical signal line 162j are stored in the storage means provided in the sample hold circuit 162d and a difference is taken (so-called correlated double sampling operation), thereby reset noise output. Is output as PD image data Vpd from which is completely removed.

  At timing T6 (CD reset), the reset signal RX is set to a high potential (H), whereby the transistor Qr1 is turned on, and the gate of the transistor Qb and CD are reset to the reset potential RSB. At this time, charge Qn2 due to reset noise is generated in the CD.

  At timing T7 (noise read operation), the read signal SX is set to a high potential (H), so that the potential Vn2 of the CD in the state where the charge Qn2 due to the reset noise is accumulated is impedance-converted by the transistor Qb. Qsel is derived to the vertical signal line 162j as the reset noise output Vn2 of the pixel 162b. FIG. 15 shows the potential states of the respective parts in the B-B ′ cross section immediately after the timing T6 and at the timing T7.

  At timing T8 (CP signal read operation), the transfer signal TX2 is set to a high potential (H), so that the photocharge Qcp accumulated in the CP is completely transferred to the CD and superimposed on the charge Qn2 due to reset noise. At the same time, the read signal SX is set to a high potential (H), whereby the potential Vs2 of the CD in a state where the photocharge Qcp and the charge Qn2 due to the reset noise are superimposed is impedance-converted by the transistor Qb, and the pixel 162b Is output to the vertical signal line 162j as the CP signal output Vs2. FIG. 16 shows the potential state of each part in the B-B ′ cross section at the timing T <b> 8.

  The reset noise output Vn2 and the CP signal output Vs2 derived to the vertical signal line 162j are stored in the storage means provided in the sample hold circuit 162d and the difference is taken (so-called CDS (correlated double sampling) operation). The CP imaging data Vcp from which the reset noise is completely removed is output and added to the PD imaging data Vpd, thereby obtaining the imaging data 162k from which the reset noise is completely removed.

  FIG. 11 is a potential diagram immediately after the timing T1 (initial reset operation) in FIG. 10 in the second embodiment of the pixel 162b shown in FIG. 9, and FIG. 11 (a) is an A- FIG. 11B in the A ′ section is a potential diagram in the BB ′ section.

  FIG. 11A is basically the same as FIG. 4C, but illustrates a state in which the potential at the time of depletion of PD and CP is different by ΔVpt2.

  In FIG. 11B, the potentials of PD and CP are the same depletion potentials as in FIG. CD is set to the reset potential RSB at the timing T1, and the charge Qn1 due to reset noise resulting from the reset operation is accumulated. Since the transfer signals TX1 and TX2 are set to a low potential (L) at the end of the timing T1, TG1 and TG2 are at a high potential and the transfer gate is closed.

  The potential of the A-A ′ cross section at the timing T2 (imaging operation) is the same as that shown in FIG.

  FIG. 12 is a potential diagram at the timing T3 (noise readout operation) in FIG. 10A. FIG. 12A is a cross-sectional view taken along the line AA 'in FIG. 9A, and FIG. It is a potential figure of each part in a B 'section. FIG. 12A is basically the same as FIG. 5C, and photocharges are accumulated in PD and CP.

In FIG. 12B, photocharges are accumulated in PD and CP, and charge Qn1 due to reset noise is accumulated in CD. When the capacitance of the CD is Ccd, the potential Vn1 of the CD with the charge Qn1 due to the reset noise being accumulated is
Vn1 = Qn1 / Ccd
It is represented by

FIG. 13 is a potential diagram of each part in the BB ′ cross section at the timing T4 (mixed signal reading operation) in FIG. The transfer signals TX1 and TX2 are set to a high potential (H), TG1 and TG2 are opened, and the photocharges accumulated in the PD and CP are completely transferred to the CD and mixed (mixed charge Qmix = Qpd + Qcp) due to reset noise. It is superimposed on the charge Qn1. The CD potential Vmix at this time is
Vmix = (Qmix + Qn1) / Ccd
= (Qpd + Qcp + Qn1) / Ccd
It is represented by

Therefore, the imaging data 162k is
Imaging data 162k = Vmix−Vn1
= ((Qpd + Qcp + Qn1) / Ccd)-(Qn1 / Ccd)
= (Qpd + Qcp) / Ccd
Thus, the reset noise is completely removed, and imaging data consisting only of photocharges (Qpd and Qcp) is obtained. Furthermore, since the photocharge Qcp accumulated in the CP is a photocharge that is shunted from the photocharge overflowing from the PD using the potential difference of the potential barrier, the photocharge Qcp is not simply accumulated more than the saturation charge of the PD. By accumulating charges that are shunted and reduced, the imaging dynamic range can be greatly expanded.

FIG. 14 is a potential diagram of each part in the BB ′ cross section at the timing T5 (PD signal read operation) in FIG. The transfer signal TX1 is set to a high potential (H) to open TG1, and the photocharge accumulated in the PD is completely transferred to the CD and superimposed on the charge Qn1 due to reset noise. The potential Vs1 of the CD at this time is
Vs1 = (Qpd + Qn1) / Ccd
It is represented by

Therefore, the PD imaging data Vpd is
Vpd = Vs1-Vn1
= Qpd / Ccd
Thus, the reset noise is completely removed, and imaging data consisting only of the photocharge Qpd is obtained.

FIG. 15 is a potential diagram of each part in the BB ′ section immediately after the timing T6 (CD reset operation) and at the timing T7 (noise reading operation) in FIG. In the CD, charge Qn2 due to reset noise resulting from the reset operation at timing T6 is accumulated, and the potential Vn2 of CD in a state where charge Qn2 due to reset noise is accumulated is
Vn2 = Qn2 / Ccd
It is represented by

FIG. 16 is a potential diagram of each part in the BB ′ cross section at the timing T8 (CP signal read operation) in FIG. The transfer signal TX2 is set to a high potential (H) to open the TG2, and the photocharge accumulated in the CP is completely transferred to the CD and superimposed on the charge Qn2 due to reset noise. The potential Vs2 of the CD at this time is
Vs2 = (Qcp + Qn2) / Ccd
It is represented by

Therefore, the CP imaging data Vcp is
Vcp = Vs2-Vn2
= Qcp / Ccd
Thus, the reset noise is completely removed, and imaging data consisting only of the photocharge Qcp is obtained.

Therefore, the imaging data 162k is
Imaging data 162k = Vpd + Vcp
= (Qpd + Qcp) / Ccd
Thus, the imaging data 162k from which the reset noise is completely removed is obtained. Furthermore, since the photocharge Qcp accumulated in the CP is a photocharge that is shunted from the photocharge overflowing from the PD using the potential difference of the potential barrier, the photocharge Qcp is not simply accumulated more than the saturation charge of the PD. By accumulating charges that are shunted and reduced, the imaging dynamic range can be greatly expanded.

  Next, a third embodiment of the pixel 162b of the image sensor 162 according to the present invention will be described with reference to FIG.

  FIG. 17 is a schematic diagram showing a third embodiment of the pixel 162b of the image sensor 162 according to the present invention. TG1 and TG2 of FIG. 9A are integrated into a transfer gate TG, and transfer signals TX1 and TX2 are obtained. The transfer signal TX is integrated. The operation is the same as that shown in FIG. 10A. The photocharge Qpd accumulated in the PD and the photocharge Qcp accumulated in the CP are simultaneously completely transferred to the CD and mixed to be output as a mixed signal output Vmix. The According to the third embodiment, since the number of wirings to the pixel can be reduced, it is possible to contribute to the downsizing of the pixel, or it is possible to contribute to the improvement of the manufacturing yield by reducing the number of fine wirings.

  Next, a fourth embodiment of the pixel 162b of the image sensor 162 according to the present invention will be described with reference to FIGS.

  FIG. 18 is a schematic diagram showing a fourth embodiment of the pixel 162b of the image sensor 162 according to the present invention, in which an electrode EL2 is provided in the portion of the second potential barrier PB2 in FIG. 9A. FIG. 18A is a schematic circuit diagram, and FIG. 18B is a cross-sectional view taken along the line A-A ′ of FIG. 9 (a) and 4 (b), an electrode EL2 on PB2 is added, and the electrode EL2 is connected to the control potential Vpb2.

  FIG. 19A shows a potential diagram of the A-A ′ cross section of FIG. Although it is basically the same as the potential diagram shown in FIG. 4C, the potential of PB2 can be variably controlled by changing the control potential Vpb2, and the potential difference ΔVpt between PB1 and PB2 is variably controlled. It is possible. This makes it possible to variably control the ratio of the current flowing through PB1 to the current flowing through PB2 when the PD photocharge overflows, that is, the shunt ratio.

  FIG. 19B shows photoelectric conversion characteristics in the fourth embodiment. As described above, since the diversion ratio of PB1 and PB2 can be variably controlled, the slope of the CP characteristic of the photoelectric conversion characteristic can be variably controlled, and the imaging dynamic range can be variably controlled.

  Next, a fifth embodiment of the pixel 162b of the image sensor 162 according to the present invention will be described with reference to FIGS.

  FIG. 20 is a schematic diagram showing the fifth embodiment of the pixel 162b of the image sensor 162 according to the present invention, in which the electrode EL1 is also provided on the first potential barrier PB1 in FIG. . FIG. 20A shows a schematic circuit diagram, and FIG. 20B shows a cross-sectional view of the A-A ′ cross section of FIG. 18A and 18B, an electrode EL1 on PB1 is added, and the electrode EL1 is connected to the control potential Vpb1.

  FIG. 21A shows a potential diagram of the A-A ′ cross section of FIG. Although basically the same as the potential diagram shown in FIG. 19A, the potential of PB1 can be variably controlled by changing the control potential Vpb1. As a result, the PD accumulation limit Qpdmax, that is, the PD saturation output in the photoelectric conversion characteristics can be variably controlled. Therefore, the photoelectric conversion characteristics can be dynamically and variably controlled by variably controlling the potentials of PB1 and PB2 individually or in conjunction with each other.

  FIG. 21B shows the photoelectric conversion characteristics in the fifth embodiment. As described above, since the PD saturation output can be variably controlled, the inflection point can be set at an arbitrary position on the line of the PD characteristic by controlling the PD saturation output. The range, that is, the imaging characteristics can be set freely. In addition, since the inclination of the CP characteristic can be variably controlled, both the imaging characteristic and the imaging dynamic range can be variably controlled.

  Next, a sixth embodiment of the pixel 162b of the image sensor 162 according to the present invention will be described with reference to FIGS.

  FIG. 22 is a schematic circuit diagram showing a sixth embodiment of the pixel 162b of the image sensor 162 in the present invention. In the circuit schematic diagram shown in FIG. 20A, the first transfer gate TG1 is a potential barrier PB1. The charge detection means CD also serves as the overflow drain OFD. PB1 and TG1 are connected to the transfer signal TX1.

  FIG. 23 shows a driving method of the pixel circuit shown in FIG. FIG. 23 is a timing chart showing a driving method of the pixel circuit shown in FIG. 22, and FIG. 23A shows the photocharge accumulated in the PD and the light accumulated in the CP, as in FIG. FIG. 23B is a timing chart of a method for reading out charges by mixing them with a CD, and FIG. 23B individually reads out the photocharges accumulated in the PD and the photocharges accumulated in the CP, as in FIG. 10B. It is a timing chart of a method.

  FIGS. 23A and 23B are different from FIGS. 10A and 10B in that the reset signal RX is held at a high potential (H) from the beginning of the timing T1 until the shutter is closed at the timing T2. And the transfer signal TX1 is set to the intermediate potential (M) from the end of the timing T1 until the shutter is closed at the timing T2. The intermediate potential (M) of the transfer signal TX1 is a gate potential of TG1 that has a potential such that TG1 functions as the potential barrier PB1.

  By doing so, TG1 operates as a potential barrier PB1 while the shutter is opened at timing T2, and is set to a low potential (L) after the shutter is closed at the end of timing T2. , PB1 has the maximum potential and TG1 is closed. Next, when the transfer signal TX1 is set to a high potential (H) at the timing T4 or T5, the TG1 functions as a transfer gate, and the photocharge accumulated in the PD is completely transferred to the CD. Operations other than those described above are the same as those in FIG. According to the sixth embodiment, OFD, PB1, and wiring between these and each part of the circuit are not necessary, which can greatly contribute to downsizing of the pixel.

  As described above, according to the present invention, a part of the charge equal to or higher than the saturation charge of the photoelectric conversion means constituting the pixel of the image sensor is accumulated in the accumulation means through the second potential barrier, and the rest is stored in the first. By discharging to the discharging means through one potential barrier, the charge equal to or higher than the saturation charge of the photoelectric conversion means can be used as a signal charge, and the dynamic range is expanded in a true sense without increasing the storage means. In addition, it is possible to provide an imaging device that can contribute to high image quality because the reset noise can be completely removed, and an imaging device including the imaging device.

  Note that the detailed configuration and detailed operation of each component that configures the imaging device according to the present invention and an imaging device equipped with the imaging device can be changed as appropriate without departing from the spirit of the present invention.

1 is a schematic external view of a digital camera that is an example of an imaging apparatus according to the present invention. It is a block diagram which shows an example of the circuit of the digital camera shown in FIG. It is a mimetic diagram showing an example of arrangement of each component which constitutes an image sensor. It is a schematic diagram which shows 1st Embodiment of the principal part in connection with imaging of a pixel. FIG. 5 is a schematic potential diagram when light enters a main part related to imaging of the pixel shown in FIG. 4. It is a circuit schematic diagram showing a first embodiment of a pixel. 7 is a timing chart illustrating a flow of an imaging operation of the pixel illustrated in FIG. 6. It is a schematic diagram of the graph which shows the photoelectric conversion characteristic of the image pick-up element shown in FIG. It is a schematic diagram which shows 2nd Embodiment of a pixel. It is a timing chart which shows the drive method of 2nd Embodiment of a pixel. FIG. 11 is a potential diagram immediately after timing T1 in FIG. FIG. 11 is a potential diagram at time T3 in FIG. FIG. 11 is a potential diagram at timing T4 in FIG. FIG. 11 is a potential diagram at time T5 in FIG. 10. FIG. 11 is a potential diagram immediately after timing T6 and at timing T7 in FIG. FIG. 11 is a potential diagram at timing T8 in FIG. It is a schematic diagram which shows 3rd Embodiment of a pixel. It is a schematic diagram which shows 4th Embodiment of a pixel. It is the schematic diagram of the graph which shows the potential diagram and photoelectric conversion characteristic in 4th Embodiment of a pixel. It is a schematic diagram which shows 5th Embodiment of a pixel. It is the schematic diagram of the graph which shows the potential diagram and photoelectric conversion characteristic in 5th Embodiment of a pixel. It is a schematic diagram which shows 6th Embodiment of a pixel. It is a timing chart which shows the drive method of 6th Embodiment of a pixel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Digital camera 10 Body 101 Release button 101a AF switch 101b Release switch 111 Power switch 112 Mode setting dial 113 Change dial 115 Jog dial 121 Finder 122 Metering module 131 Image display means 144 AF module 145 Shutter 150 Camera control means 151 CPU (Central processing unit) )
152 Work Memory 153 Storage Unit 160 Imaging Circuit 161 Imaging Control Unit 162 Imaging Device 162b Pixel 162k Imaging Data 163 Amplifier 164 Analog / Digital (A / D) Conversion Unit 165 Image Processing Unit 181 Image Memory 182 Memory Card 20 Interchangeable Lens 211 Lens 221 Aperture PD Photodiode (photoelectric conversion means)
OFD overflow drain (discharge means)
CP storage means PB1 first potential barrier PB2 second potential barrier TG1 first transfer gate TG2 second transfer gate CD charge detection means

Claims (6)

In an image sensor having a plurality of pixels,
The pixel is
Photoelectric conversion means for photoelectrically converting light from a subject and storing the converted photoelectric charge ;
Discharging means for discharging the overflowing photoelectric charge from the photoelectric conversion means;
Accumulating means for accumulating photoelectric charges overflowing from the photoelectric conversion means;
A first potential barrier provided between the photoelectric conversion means and the discharge means;
A second potential barrier provided between the photoelectric conversion means and the storage means ,
A part of the photoelectric charge overflowing from the photoelectric conversion means by photoelectrically converting light from the subject in a state where the potential of the first potential barrier is different from the potential of the second potential barrier. Is stored in the storage means, and the rest is discharged from the discharge means . Imaging device according to claim 1, characterized in that for variably controlling the potential of said second potential barrier. Imaging device according to claim 1, wherein the benzalkonium be variably controlling the potential of the potential and the second potential barrier of the first potential barrier. The pixel includes a charge detection unit,
Imaging device according to any one of claims 1 to 3, characterized in that have a complete transfer is possible potential structure to the charge detecting means of said accumulated in the photoelectric conversion means and the storage means charges . 5. The image pickup device according to claim 1 , wherein the photoelectric conversion unit and the storage unit have an embedded diode structure . 6. Imaging apparatus characterized by comprising an imaging element according to any one of claims 1 to 5.