JP2008131331A - Driving method of solid-state imaging element, and imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state imaging element driving method which can achieve both high sensitivity and high S/N. <P>SOLUTION: The driving method of the solid-state imaging element 5 comprising photoelectric conversion elements 101 formed on the surface of a semiconductor substrate, vertical charge transfer paths 102 for transferring charges generated by the photoelectric conversion elements 101 vertically, and a charge read-out region 105 for reading out charges generated by the photoelectric conversion elements 101 into the vertical charge transfer paths 102 is provided. The driving method includes a step wherein a read-out pulse is supplied to the charge read-out region 105 several times and the charges are read out into charge accumulation packets formed in the vertical charge transfer paths 102 in several divided times. In this step, charges read out into the vertical charge transfer paths 102 by an arbitrary read-out pulse is transferred vertically by the time when a next read-out pulse is supplied after the arbitrary read-out pulse is supplied so that the charge accumulation packets may have been cleared out when the next read-out pulse is supplied. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention provides a plurality of photoelectric conversion elements formed on the surface of a semiconductor substrate, a plurality of vertical charge transfer paths for transferring charges generated in each of the plurality of photoelectric conversion elements in a vertical direction, and the plurality of photoelectric conversion elements. And a charge readout region for reading out the charge generated in each of the above to the vertical charge transfer path.

  As a method for realizing high sensitivity of the solid-state imaging device, a method of gain amplification of signals corresponding to charges generated by a plurality of photoelectric conversion elements, or impact ionization when reading charges from the photoelectric conversion elements to the vertical charge transfer path A method of generating a phenomenon and amplifying at a charge stage is known. In the former case, amplifier noise and the like are also amplified, so that the S / N deteriorates. On the other hand, since the latter is amplified at a stage before passing through the amplifier, the S / N can be improved and is a technique to be noted in realizing high sensitivity.

  For example, Patent Documents 1 to 3 are cited as documents that describe the impact ionization phenomenon.

JP-A-8-340099 Japanese Patent Laid-Open No. 7-153888 JP 2002-290836 A

  The present invention proposes a novel method that is different from the above-described conventional technology, and drives a solid-state imaging device capable of achieving both high sensitivity and high S / N by charge multiplication using an impact ionization phenomenon. It aims to provide a method.

  The solid-state imaging device driving method of the present invention includes a plurality of photoelectric conversion elements formed on the surface of a semiconductor substrate, and a plurality of vertical charge transfer paths for transferring charges generated in each of the plurality of photoelectric conversion elements in a vertical direction. A solid-state imaging device including a charge readout region for reading out the charges generated in each of the plurality of photoelectric conversion elements to the vertical charge transfer path, and supplying a readout pulse to the charge readout region A charge reading step of performing a plurality of times to drive the charge accumulation packet formed in the vertical charge transfer path to read the charges in a plurality of times, and supplying an arbitrary read pulse of the plurality of read pulses. The charge storage is performed when the next read pulse is supplied during the period from completion until the start of supply of the next read pulse of the arbitrary read pulse. As packets is empty, and a charge transfer step of performing driving for transferring the arbitrary charge read to the charge storage packet by reading pulse to the vertical direction.

  According to the solid-state imaging device driving method of the present invention, the supply period of the read pulse excluding the read pulse to be supplied last among the plurality of read pulses is shorter than the supply period of the read pulse to be supplied last.

  In the solid-state imaging device driving method according to the present invention, the number of times of supply of the readout pulse in the charge readout step is changed according to imaging conditions.

  In the solid-state imaging device driving method according to the present invention, the minimum number of the charge accumulation packets required to transfer the maximum amount of charge that can be accumulated in the photoelectric conversion element is A, and the charge in the charge reading step is A. When the number of stored packets is B, A> B.

  In the driving method of the solid-state imaging device of the present invention, the value B is changed according to the shooting conditions.

  In the solid-state imaging device driving method according to the present invention, the minimum number of the charge accumulation packets required to transfer the maximum amount of charge that can be accumulated in the photoelectric conversion element is A, and the charge in the charge reading step is A. Assuming that the number of stored packets is B, the value of B is changed according to the shooting conditions within a range that satisfies the condition of A ≧ B.

  In the solid-state imaging device driving method of the present invention, the plurality of photoelectric conversion elements include a plurality of types of photoelectric conversion elements that detect light in different wavelength ranges, and the number of times of supply of the readout pulse is determined by the plurality of types of photoelectric conversion elements. Control is performed independently for each conversion element.

  In the solid-state imaging device driving method according to the present invention, the plurality of photoelectric conversion elements each include a plurality of types of photoelectric conversion elements that detect light in different wavelength ranges, and the number of times of supplying the readout pulse and the value of B are calculated as follows: Control is performed independently for each of the plurality of types of photoelectric conversion elements.

  The solid-state imaging device driving method of the present invention includes a plurality of photoelectric conversion elements formed on the surface of a semiconductor substrate, and a plurality of vertical charge transfer paths for transferring charges generated in each of the plurality of photoelectric conversion elements in a vertical direction. A solid-state imaging device including a charge readout region for reading out the charges generated in each of the plurality of photoelectric conversion elements to the vertical charge transfer path, and supplying a readout pulse to the charge readout region And a charge read step for driving the charge storage packet formed in the vertical charge transfer path to read the charge, and at least necessary to transfer the maximum amount of charge that can be stored in the photoelectric conversion element. A> B, where A is the number of charge storage packets and B is the number of charge storage packets in the charge reading step.

  In the driving method of the solid-state imaging device of the present invention, the value B is changed according to the shooting conditions.

  In the solid-state imaging device driving method according to the present invention, the plurality of photoelectric conversion elements each include a plurality of types of photoelectric conversion elements that detect light in different wavelength ranges, and the value of B is set as the plurality of types of photoelectric conversion elements. Control each independently.

  The imaging device of the present invention includes a driving unit that performs driving based on a driving method of the solid-state imaging device, and the solid-state imaging device.

  ADVANTAGE OF THE INVENTION According to this invention, the drive method of the solid-state image sensor which can make high sensitivity and high S / N compatible by charge multiplication using an impact ionization phenomenon can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram illustrating a schematic configuration of a digital camera which is an example of an imaging apparatus according to the first embodiment of the present invention.
The imaging system of the digital camera shown in the figure includes a photographic lens 1, a CCD type solid-state imaging device 5, a diaphragm 2 provided therebetween, an infrared cut filter 3, and an optical low-pass filter 4.

  A system control unit 11 that performs overall control of the electrical control system of the digital camera controls the flash light emitting unit 12 and the light receiving unit 13 and controls the lens driving unit 8 to adjust the position of the photographing lens 1 to the focus position and zoom. The exposure amount is adjusted by adjusting the aperture amount of the aperture 2 via the aperture drive unit 9.

  Further, the system control unit 11 drives the solid-state imaging device 5 via the imaging device driving unit 10 and outputs a subject image captured through the photographing lens 1 as a color signal. An instruction signal from the user is input to the system control unit 11 through the operation unit 14.

  The electric control system of the digital camera further includes an analog signal processing unit 6 that performs analog signal processing such as correlated double sampling processing connected to the output of the solid-state imaging device 5, and RGB output from the analog signal processing unit 6. And an A / D conversion circuit 7 for converting the color signals into digital signals, which are controlled by the system control unit 11.

  Furthermore, the electric control system of this digital camera generates image data by performing main memory 16, memory control unit 15 connected to main memory 16, interpolation calculation, gamma correction calculation, RGB / YC conversion processing, and the like. A digital signal processing unit 17, a compression / decompression processing unit 18 that compresses image data generated by the digital signal processing unit 17 into a JPEG format or decompresses compressed image data, and a digital signal processing unit 17 that integrates photometric data. The integration unit 19 for obtaining the gain of white balance correction performed by the camera, the external memory control unit 20 to which the removable recording medium 21 is connected, and the display control unit 22 to which the liquid crystal display unit 23 mounted on the back of the camera is connected. These are connected to each other by a control bus 24 and a data bus 25, and are controlled by commands from the system control unit 11. That.

FIG. 2 is a schematic plan view of the solid-state image sensor 5.
The solid-state imaging device 5 has a large number of photoelectric conversion elements 101 arranged in a vertical direction on the surface of the semiconductor substrate and a horizontal direction orthogonal thereto, and a plurality of charges that transfer charges generated in each of the large number of photoelectric conversion elements 101 in the vertical direction. Vertical charge transfer paths 102 (only one is shown in FIG. 2), a line memory 105 for temporarily storing charges transferred through each of the plurality of vertical charge transfer paths 102, and output from the line memory 105 A horizontal charge transfer unit (HCCD) 103 that transfers the charged charges in the horizontal direction, and an output unit 104 that outputs a signal corresponding to the charges transferred from the HCCD 103.

  A large number of photoelectric conversion elements 101 are configured by arranging m (m is a natural number of 1 or more) photoelectric conversion element rows including n photoelectric conversion elements 101 arranged in the horizontal direction (n is a natural number of 2 or more) in the vertical direction. Alternatively, n photoelectric conversion element arrays composed of m photoelectric conversion elements 101 arranged in the vertical direction are arranged in the horizontal direction. The odd-numbered photoelectric conversion element rows are arranged so as to be shifted in the horizontal direction by about 1/2 of the photoelectric conversion element arrangement pitch of each photoelectric conversion element row with respect to the even-numbered photoelectric conversion element rows, so-called honeycomb arrangement It has become.

  The odd-numbered photoelectric conversion element rows are rows in which the photoelectric conversion elements 101 (hereinafter referred to as G photoelectric conversion elements 101. Symbol G in FIG. 2) that detects light in the green wavelength range are arranged in the horizontal direction. .

  The even-numbered photoelectric conversion element rows include a photoelectric conversion element 101 that detects light in the blue wavelength range (hereinafter referred to as B photoelectric conversion element 101; reference numeral B is shown in FIG. 2), and light in the red wavelength range. The photoelectric conversion elements 101 (hereinafter referred to as R photoelectric conversion elements 101; denoted by reference symbol R in FIG. 2) are arranged in a row of BR photoelectric conversion elements alternately arranged in the horizontal direction with the B photoelectric conversion elements 101 at the head. , RB photoelectric conversion element rows alternately arranged in the horizontal direction with the R photoelectric conversion element 101 at the head, and these two rows are arranged alternately in the vertical direction.

  One vertical charge transfer path 102 is provided corresponding to each photoelectric conversion element array. In each vertical charge transfer path 102, charges are read from the m photoelectric conversion elements 101 included in the corresponding photoelectric conversion element array. The vertical charge transfer path 102 is formed by meandering in the vertical direction so as to avoid the photoelectric conversion element 101 at the side of each photoelectric conversion element array.

  Between each photoelectric conversion element array and the corresponding vertical charge transfer path 102, a charge readout region 105 schematically shown by an arrow in the figure is formed, and exposure is performed via this charge readout region 105. Charge generated in the photoelectric conversion element 101 during the period is read out to the vertical charge transfer path 102.

  In the horizontal direction on the surface of the semiconductor substrate, vertical transfer electrodes V1, V2,..., V8 are laid to meander to avoid the photoelectric conversion elements 101. The vertical charge transfer path 102 is driven by applying a transfer pulse output from the image sensor driving unit 10 to vertical transfer electrodes V1 to V8 provided thereon and arranged in the vertical direction.

  The transfer pulse applied to the vertical transfer electrodes V1 to V8 can take three levels: a high (H) level, a middle (M) level, and a low (L) level. The H level transfer pulse serves as a read pulse for reading out charges from the photoelectric conversion element 101 to the vertical charge transfer path 102.

  The vertical transfer electrode V3 is disposed on the upper side of the BR photoelectric conversion element row corresponding to the BR photoelectric conversion element row.

  The vertical transfer electrode V4 is disposed on the lower side of the BR photoelectric conversion element row corresponding to the BR photoelectric conversion element row. The vertical transfer electrode V4 also overlaps with the charge readout region 105 between each photoelectric conversion element 101 in the BR photoelectric conversion element row and the corresponding vertical charge transfer path 102, and the vertical transfer electrode is transferred from the image sensor driving unit 10 to the vertical transfer electrode V4. By applying a read pulse to V4, the charge generated in each photoelectric conversion element 101 included in the BR photoelectric conversion element row can be read out to the vertical charge transfer path 102 corresponding to each photoelectric conversion element 101.

  The vertical transfer electrode V7 is disposed on the upper side of the RB photoelectric conversion element row corresponding to the RB photoelectric conversion element row.

  The vertical transfer electrode V8 is disposed on the lower side of the RB photoelectric conversion element row corresponding to the RB photoelectric conversion element row. The vertical transfer electrode V8 also overlaps with the charge readout region 105 between each photoelectric conversion element 101 in the RB photoelectric conversion element row and the corresponding vertical charge transfer path 102, and the vertical transfer electrode is transferred from the imaging element driving unit 10 to the vertical transfer electrode. By applying a read pulse to V8, the charge generated in each photoelectric conversion element 101 included in the RB photoelectric conversion element row can be read out to the vertical charge transfer path 102 corresponding to each photoelectric conversion element 101.

  The vertical transfer electrode V5 is arranged on the upper side of the photoelectric conversion element row corresponding to the photoelectric conversion element row arranged between the vertical transfer electrode V4 and the vertical transfer electrode V7 in the odd-numbered photoelectric conversion element rows. Has been.

  The vertical transfer electrode V6 corresponds to the photoelectric conversion element row disposed between the vertical transfer electrode V4 and the vertical transfer electrode V7 among the odd-numbered photoelectric conversion element rows, and is provided on the lower side of the photoelectric conversion element row. Has been placed. The vertical transfer electrode V6 also overlaps with the charge readout region 105 between each photoelectric conversion element 101 in this photoelectric conversion element row and the corresponding vertical charge transfer path 102, and the vertical transfer electrode is transferred from the image sensor driving unit 10 to the vertical transfer electrode V6. By applying a read pulse to V6, the charge generated in each photoelectric conversion element 101 included in this photoelectric conversion element row can be read out to the vertical charge transfer path 102 corresponding to each photoelectric conversion element 101.

  The vertical transfer electrode V1 is arranged on the upper side of the photoelectric conversion element row corresponding to the photoelectric conversion element row arranged between the vertical transfer electrode V3 and the vertical transfer electrode V8 in the odd-numbered photoelectric conversion element rows. Has been.

  The vertical transfer electrode V2 corresponds to the photoelectric conversion element row arranged between the vertical transfer electrode V3 and the vertical transfer electrode V8 among the odd-numbered photoelectric conversion element rows, and is arranged on the lower side of the photoelectric conversion element row. Has been placed. The vertical transfer electrode V2 also overlaps with the charge readout region 105 between each photoelectric conversion element 101 in the photoelectric conversion element row and the corresponding vertical charge transfer path 102, and the vertical transfer electrode is transferred from the image sensor driving unit 10 to the vertical transfer electrode V2. By applying a read pulse to V2, charges generated in each photoelectric conversion element 101 included in this photoelectric conversion element row can be read out to the vertical charge transfer path 102 corresponding to each photoelectric conversion element 101.

  The line memory 105 is composed of n charge storage regions corresponding to each VCCD 102 and drive electrodes provided thereabove, and the charges transferred from the corresponding VCCD 102 are temporarily stored in the charge storage regions. Accumulated in. The drive electrodes of the line memory 105 are supplied with a drive pulse φLM output from the image sensor driving unit 10, and the line memory 105 is driven by this drive pulse φLM.

  Although the terms “vertical” and “horizontal” have been used, this means “one direction” along the surface of the semiconductor substrate and “a direction substantially perpendicular to the one direction”.

  The image sensor drive unit 10 can drive the solid-state image sensor 5 in a charge multiplication drive mode in which charges generated in the photoelectric conversion element 101 are multiplied using an impact ionization phenomenon and read.

  In the charge multiplication drive mode, the image sensor driving unit 10 reads the charge generated in the photoelectric conversion element 101 to be read out to the vertical charge transfer path 102 corresponding to the photoelectric conversion element 101 to the charge reading region 105. The read pulse is supplied a plurality of times to drive the charge accumulation packet formed in the vertical charge transfer path 102 to be read out in a plurality of times. Hereinafter, the operation of the image sensor drive unit 10 in the charge multiplication drive mode will be described by taking as an example a case where charges are read from all the photoelectric conversion elements 101 in four fields at the time of still image shooting.

  FIG. 3 is a diagram for explaining the operation of the first field in the charge multiplication drive mode of the solid-state imaging device 5 of the first embodiment. In FIG. 3, T1 to T10 indicate times, and the diagram illustrated below each of T1 to T10 is a photoelectric in which the G photoelectric conversion elements 101 are arranged in the photoelectric conversion element array of the solid-state imaging element 5 illustrated in FIG. FIG. 5 is an enlarged view of a part of a conversion element array, and shows a state of a vertical charge transfer path 102 at each time. In FIG. 3, the same components as those in FIG. FIG. 4 is a diagram showing waveforms of the vertical transfer electrodes V1 to V8 at each time shown in FIG.

  It is assumed that an L level transfer pulse is applied to the vertical transfer electrodes V1 to V8 during the exposure period. After the exposure period, the image sensor driving unit 10 applies M-level transfer pulses to the vertical transfer electrodes V8, V1, V2, and V3 to form four charge accumulation packets in the charge transfer channel, and then performs vertical transfer. A read pulse is applied to the electrode V2 to read out charges from these four charge storage packets (time T1). Here, four charge storage packets are formed, but the number of charge storage packets formed here is the minimum in order to transfer the maximum amount of charge that can be stored in the photoelectric conversion element 101 to be read. What is necessary is just to make it a necessary number. That is, it is sufficient that the total capacity of the charge storage packet is the same as the maximum charge amount that can be stored in the photoelectric conversion element 101 to be read. It is to be noted that the application period of the read pulse that enables reading of all charges of the maximum charge amount that can be accumulated in the photoelectric conversion element 101 to be read to the vertical charge transfer path 102 by one read operation is “1”. Then, the read pulse application period at time T1 is set to a period shorter than “1”, for example, 1/3.

  Next, the image sensor driving unit 10 applies the L level transfer pulse to the vertical transfer electrode V8 and the M level transfer pulse to the vertical transfer electrodes V4 to V6 (time T2), and then the L level to the vertical transfer electrodes V1 to V4. A transfer pulse is applied to transfer the charges read at time T1 in the vertical direction (time T3).

  Next, the image sensor driving unit 10 applies M-level transfer pulses to the vertical transfer electrodes V8, V1, V2, and V3 to form four charge accumulation packets in the charge transfer channel (time T4). Thereafter, a read pulse is applied to the vertical transfer electrode V2 to read out charges from these four charge accumulation packets (time T5). The application time of the readout pulse at time T5 is longer than that at time T1 and shorter than “1”, for example, 1/2.

  Next, the image sensor drive unit 10 applies the L level transfer pulse to the vertical transfer electrode V8 and the M level transfer pulse to the vertical transfer electrode V4 (time T6), and then the L level transfer pulse to the vertical transfer electrodes V1 to V4. And the charge read at time T5 is transferred in the vertical direction (time T7).

  Next, the image sensor driving unit 10 applies M-level transfer pulses to the vertical transfer electrodes V8, V1, V2, and V3 to form four charge accumulation packets in the charge transfer channel (time T8). Thereafter, a read pulse is applied to the vertical transfer electrode V2 to read out charges from these four charge storage packets (time T9). The application time of the readout pulse at time T9 is set to a longer period than that at time T5, for example, 1.

  Next, the image sensor drive unit 10 applies the L level transfer pulse to the vertical transfer electrode V8 and the M level transfer pulse to the vertical transfer electrode V4, and the charges read at time T9 and the vertical transfer electrodes V5 and V6 are below. The charges read at times T1 and T5 are mixed (time T10). After that, by applying a transfer pulse of a predetermined pattern to the vertical transfer electrodes V1 to V8, the read charges are sequentially transferred in the vertical direction.

  As described above, the charge is read out from the photoelectric conversion element 101 in three times, and the charge accumulation packet formed in the vertical charge transfer path 102 is always empty at the time of the three times of charge reading. Thus, as compared with the case where the charges made up of a large number of electrons are read out at a time, the potential difference (the potential at the position where the electrons were first and the potential at the position after the movement) when each of the large number of electrons moves The average of the difference can be increased. As a result, an impact ionization phenomenon can be generated and the charge can be multiplied.

  In this driving method, since it is necessary to read out the charge in three steps, if the read pulse application time is set to “1” during the first charge read-out, the charge is accumulated in the photoelectric conversion element 101 at that time. All the charges that have been read out are read out, and the charges do not move during the second and third charge readings, and the charge multiplication effect may not be obtained. In the present embodiment, the application time of the read pulse in each of the three charge reads is shorter than “1” in the first and second times, and is set to “1” in the last read. The read pulse application time at the time of reading is made shorter than that at the time of the last reading. For this reason, it is possible to reliably prevent a situation in which no charge remains in the photoelectric conversion element 101 at the time of the next charge reading. In addition, since the readout pulse is applied for a time that allows all charges to be read at the time of the last readout, all the charges accumulated in the photoelectric conversion element 101 can be read out without fail.

  Further, in the method of amplifying the charge after converting it into a signal at the output unit 104, the noise component contained in the charge is also amplified, so that the S / N is deteriorated. Since charge multiplication is performed using the phenomenon, S / N deterioration can be prevented.

  Here, the charge is read out in three steps, but not limited to three times, the effect can be obtained as long as it is two or more times. Since the charge multiplication factor can be adjusted by changing the number of times of charge reading, it is also possible to change the photographing ISO sensitivity by using this fact. For example, information on the number of readings corresponding to each of a plurality of shooting ISO sensitivities is stored in the internal memory, and the image sensor driving unit 10 loads the solid-state imaging device 5 with the number of readings corresponding to the set shooting ISO sensitivity. What is necessary is just to drive.

  In addition, when driving in the above-described charge multiplication drive mode when photographing a high-luminance subject, sensitivity variations due to charge multiplication, that is, fixed pattern noise occurs. For this reason, it is not preferable to always drive the solid-state imaging device 5 in the charge multiplication drive mode. Therefore, in the present embodiment, when the imaging element driving unit 10 has a photographing ISO sensitivity lower than a predetermined value, the imaging element sensitivity is higher than the predetermined value by performing known driving for reading out charges from the photoelectric conversion element 101 once. In this case, it is possible to suppress the occurrence of fixed pattern noise by performing driving in the above-described charge multiplication driving mode in accordance with the set photographing ISO sensitivity.

(Second embodiment)
In the charge multiplication drive mode described in the first embodiment, since the charge is read out in a plurality of times, the capacity of the charge storage packet formed in the vertical charge transfer path 102 at the time of one charge read is set as the photoelectric to be read. There is no problem even if it is smaller than the maximum charge amount that can be stored in the conversion element 101. For example, assuming that the maximum charge amount read to the vertical charge transfer path 102 at each of the three charge reading times is the same as the total capacity of two charge storage packets, at times T1, T5, and T9 in FIG. There is no problem even if the transfer pulse applied to the vertical transfer electrodes V3 and V8 is set to the L level.

FIG. 5 is a diagram illustrating the potential of a certain photoelectric conversion element and a vertical charge transfer path from which charges are read.
It is known that the potential of the photoelectric conversion element 101 is pulled by the lower potential and the surface potential increases as the peripheral potential is lower. For example, at time T1, T5, T9 in FIG. 3, if a canceling pulse (L level transfer pulse) is applied to the vertical transfer electrodes V3, V8 to reduce the number of charge accumulation packets from four to two, the photoelectric conversion element 101 Since the portion where the potential decreases around the periphery increases, the surface potential of the potential of the photoelectric conversion element 101 increases as shown by the broken line in FIG. When a read pulse is applied to the vertical transfer electrode V2 in a state where a cancel pulse is applied, as shown in FIG. 5, compared to a case where no cancel pulse is applied, a potential difference at the time when charges accumulated in the photoelectric conversion element 101 move. Becomes larger. For this reason, the charge multiplication effect is obtained, and the multiplication factor can be increased as compared with the case where no cancellation pulse is applied. The multiplication factor resulting from the cancellation pulse increases as the number of electrodes to which the cancellation pulse is applied increases, that is, as the number of charge storage packets decreases.

  In the present embodiment, the image sensor driving unit 10 performs driving for increasing the multiplication factor of the charge by combining the method of reading the charge described in the first embodiment in a plurality of times and the method of applying the cancellation pulse. To do. Hereinafter, a driving method combining a method of reading out charges in multiple times and a method of applying a canceling pulse will be described. Hereinafter, the operation of the image sensor drive unit 10 in the charge multiplication drive mode will be described by taking as an example a case where charges are read from all the photoelectric conversion elements 101 in four fields at the time of still image shooting.

  FIG. 6 is a diagram for explaining the operation of the first field in the charge multiplication drive mode of the solid-state imaging device according to the second embodiment. In FIG. 6, T1 to T10 indicate times, and the diagram illustrated below each of T1 to T10 is a photoelectric in which the G photoelectric conversion elements 101 are arranged in the photoelectric conversion element array of the solid-state imaging element 5 illustrated in FIG. FIG. 5 is an enlarged view of a part of a conversion element array, and shows a state of a vertical charge transfer path 102 at each time. In FIG. 6, the same components as those in FIG. FIG. 7 is a diagram showing waveforms of the vertical transfer electrodes V1 to V8 at each time shown in FIG.

  6 differs from FIG. 3 in that, at time T1, T5, T9, before applying the readout pulse, a canceling pulse (L-level transfer pulse) is applied to the vertical transfer electrodes V3, V8, and is formed here. The number of charge accumulation packets to be reduced is reduced from four to two. Other operations are the same as those in the first embodiment.

  According to such a driving method, in addition to the charge multiplication effect obtained by reading out charges in multiple times, the charge multiplication effect obtained by applying the cancellation pulse can be obtained, so the first embodiment The charge multiplication factor can be increased as compared with the driving method. In addition, since the charge multiplication factor can be determined by a combination of the number of charge readouts (= 2 or more natural number) and the number of electrodes to which the cancellation pulse is applied (= 0 or more natural number), it is finer than the first embodiment. The charge multiplication factor can be set.

  According to the present driving method, the charge multiplication factor is determined by the combination of the number of times of charge reading and the number of charge storage packets formed at the time of charge reading. By changing this combination, the imaging ISO sensitivity is changed. It is possible. When the shooting ISO sensitivity is set, the image sensor driving unit 10 may change the number of charge readouts and the number of charge accumulation packets according to the set shooting ISO sensitivity.

  In the present embodiment, the image sensor driving unit 10 executes a combination of a driving method for reading out charges in multiple times and a driving method for applying a cancellation pulse in the charge multiplication driving mode. Of course, it is possible to obtain the charge multiplication effect even if only the driving method of applying the cancellation pulse is executed. In this case, the imaging element driving unit 10 performs a known driving for reading out charges from the photoelectric conversion element 101 at one time, and the number of charge accumulation packets formed at the time of driving is necessary for the set photographing ISO sensitivity. The solid-state imaging device 5 may be driven by setting the number so that a sufficient multiplication factor can be obtained.

  Even when only the driving method for applying the cancellation pulse is executed, if this driving method is executed when photographing a high-luminance object, fixed pattern noise is generated. Therefore, even in this case, when the imaging ISO sensitivity is lower than the predetermined value, the imaging element driving unit 10 performs known driving without applying the cancellation pulse, and when the imaging ISO sensitivity is higher than the predetermined value, the set imaging is performed. Generation of fixed pattern noise can be suppressed by performing driving in which the number of electrodes to which the cancellation pulse is applied is set according to the ISO sensitivity.

(Third embodiment)
In the first embodiment and the second embodiment, the example in which the arrangement of the photoelectric conversion elements 101 of the solid-state imaging element 5 is a honeycomb arrangement has been described. However, the present invention can be applied even when the arrangement of the photoelectric conversion elements 101 is a square arrangement. Of course, it is applicable. In the present embodiment, a case where the charge multiplication driving method of the present invention is applied to a solid-state imaging device 5 of a square array type will be described.

FIG. 8 is a schematic plan view of the solid-state imaging device of the third embodiment.
The solid-state imaging device shown in FIG. 8 includes a large number of photoelectric conversion elements 51 arranged in a vertical direction on the surface of the semiconductor substrate 50 and in a horizontal direction perpendicular thereto. A large number of photoelectric conversion elements 51 are configured by arranging m (m is a natural number of 1 or more) photoelectric conversion element rows composed of n photoelectric conversion elements 51 arranged in the horizontal direction (n is a natural number of 2 or more) in the vertical direction. Alternatively, n photoelectric conversion element arrays composed of m photoelectric conversion elements 51 arranged in the vertical direction are arranged in the horizontal direction.

  The odd-numbered photoelectric conversion element rows are formed by alternately arranging G photoelectric conversion elements 51 that detect light in the green wavelength range and B photoelectric conversion elements 51 that detect light in the blue wavelength range. . In the even-numbered photoelectric conversion element rows, the R photoelectric conversion elements 51 that detect light in the red wavelength region and the G photoelectric conversion elements 51 are alternately arranged.

  A vertical charge transfer path 52 is formed on the side of each photoelectric conversion element array corresponding to each photoelectric conversion element array. The vertical charge transfer path 52 transfers charges generated in the photoelectric conversion elements 51 of the corresponding photoelectric conversion element array in the vertical direction.

  Between the photoelectric conversion element 51 of each photoelectric conversion element array and the corresponding vertical charge transfer path 52, a charge read region 53 for reading out the charge generated in the photoelectric conversion element 51 to the corresponding vertical charge transfer path 52. Is provided.

  Vertical transfer electrodes V1, V2,..., V8 (not shown) are laid in the horizontal direction on the surface of the semiconductor substrate 50 so as to avoid the photoelectric conversion elements 51. The vertical charge transfer path 52 is driven by applying a transfer pulse output from the image sensor driving unit 10 to vertical transfer electrodes V1 to V8 provided thereon and arranged in the vertical direction. The vertical transfer electrodes V1 to V4 correspond to the photoelectric conversion elements 51 in the odd-numbered photoelectric conversion element rows, and the vertical transfer electrodes V5 to V8 correspond to the photoelectric conversion elements 51 in the even-numbered photoelectric conversion element rows.

  The vertical transfer electrode V1 also overlaps the charge readout region 53 between the photoelectric conversion element 51 in the odd-numbered photoelectric conversion element row and the corresponding vertical charge transfer path 52, and applies a read pulse to the vertical transfer electrode V1. Thus, the charges generated in the photoelectric conversion elements 51 in the odd-numbered photoelectric conversion element rows can be read out to the vertical charge transfer paths 52 corresponding to the photoelectric conversion elements 51.

  The vertical transfer electrode V5 also overlaps the charge readout region 53 between the photoelectric conversion element 51 of the even-numbered photoelectric conversion element row and the corresponding vertical charge transfer path 52, and applies a read pulse to the vertical transfer electrode V5. Thus, the charges generated in the photoelectric conversion elements 51 in the even-numbered photoelectric conversion element rows can be read out to the vertical charge transfer paths 52 corresponding to the photoelectric conversion elements 51.

  Next, the operation of the image sensor drive unit 10 in the charge multiplication drive mode will be described. Hereinafter, the operation of the image sensor drive unit 10 in the charge multiplication drive mode will be described by taking as an example a case where charges are read from all the photoelectric conversion elements 51 in two fields at the time of still image shooting.

  FIG. 9 is a diagram for explaining the operation in the first field of the solid-state imaging device of the third embodiment. In FIG. 9, T1 to T10 indicate times, and the diagram illustrated below each of T1 to T10 is the G photoelectric conversion element 51 and the R photoelectric conversion in the photoelectric conversion element array of the solid-state imaging element illustrated in FIG. FIG. 5 is an enlarged view of a part of a photoelectric conversion element array in which elements 51 are arranged, and shows a state of a vertical charge transfer path 52 at each time. 9, the same components as those in FIG. 8 are denoted by the same reference numerals. FIG. 10 is a diagram showing waveforms of the vertical transfer electrodes V1 to V8 at each time shown in FIG.

  It is assumed that an L level transfer pulse is applied to the vertical transfer electrodes V1 to V8 during the exposure period. After the exposure period, the image sensor driving unit 10 applies M-level transfer pulses to the vertical transfer electrodes V8, V1, V2, and V3 to form four charge accumulation packets in the charge transfer channel, and then performs vertical transfer. A read pulse is applied to the electrode V1 to read out charges from these four charge storage packets (time T1). Here, four charge storage packets are formed, but the number of charge storage packets formed here is the minimum in order to transfer the maximum charge amount that can be stored in the photoelectric conversion element 51 to be read. What is necessary is just to make it a necessary number. That is, it is sufficient that the total capacity of the charge storage packet is the same as the maximum charge amount that can be stored in the photoelectric conversion element 51 to be read. Note that the supply period of the read pulse that enables reading of all charges of the maximum charge amount that can be accumulated in the photoelectric conversion element 51 to be read to the vertical charge transfer path 52 by one read operation is “1”. Then, the read pulse application period at time T1 is set to a period shorter than “1”, for example, 1/3.

  Next, the image sensor driving unit 10 applies an M level transfer pulse to the vertical transfer electrodes V4 to V6 (time T2), and then applies an L level transfer pulse to the vertical transfer electrodes V1 to V4 and V8. The charges read at time T1 are transferred in the vertical direction (time T3).

  Next, the image sensor driving unit 10 applies M-level transfer pulses to the vertical transfer electrodes V8, V1, V2, and V3 to form four charge accumulation packets in the charge transfer channel (time T4). Thereafter, a read pulse is applied to the vertical transfer electrode V1 to read out charges from these four charge storage packets (time T5). The application time of the readout pulse at time T5 is longer than that at time T1 and shorter than “1”, for example, 1/2.

  Next, the image sensor driving unit 10 applies an M level transfer pulse to the vertical transfer electrode V4 (time T6), and then applies an L level transfer pulse to the vertical transfer electrodes V1 to V4 and V8. The charges read at T5 are transferred in the vertical direction (time T7).

  Next, the image sensor driving unit 10 applies M-level transfer pulses to the vertical transfer electrodes V8, V1, V2, and V3 to form four charge accumulation packets in the charge transfer channel (time T8). Thereafter, a read pulse is applied to the vertical transfer electrode V1 to read out charges from these four charge storage packets (time T9). The application time of the readout pulse at time T9 is longer than that at time T5, for example, “1”.

  Next, the image sensor drive unit 10 applies an M-level transfer pulse to the vertical transfer electrode V4, and charges read at time T9 and charges read at times T1 and T5 below the vertical transfer electrodes V5 and V6. Are mixed (time T10). After that, by applying a transfer pulse of a predetermined pattern to the vertical transfer electrodes V1 to V8, the read charges are sequentially transferred in the vertical direction.

  Thus, the present invention can be applied even if the solid-state imaging device is a square array type.

(Fourth embodiment)
In the fourth embodiment, a driving method in which a method of applying a cancellation pulse is combined with the driving method of the third embodiment will be described.

  FIG. 11 is a diagram for explaining the operation in the first field of the solid-state imaging device of the fourth embodiment. In FIG. 11, T1 to T10 indicate times, and the figure shown below each of T1 to T10 is a G photoelectric conversion element 51 and an R photoelectric conversion in the photoelectric conversion element array of the solid-state imaging element shown in FIG. FIG. 4 is an enlarged view of a part of a photoelectric conversion element array in which the elements 51 are arranged, and is a diagram illustrating a state of the vertical charge transfer path 52 at each time. 11, the same components as those in FIG. 8 are denoted by the same reference numerals. FIG. 12 is a diagram showing waveforms of the vertical transfer electrodes V1 to V8 at each time shown in FIG.

  11 differs from FIG. 9 in that, at time T1, T5, T9, before applying the readout pulse, a canceling pulse (L level transfer pulse) is applied to the vertical transfer electrodes V3, V8, and is formed here. The number of charge accumulation packets to be reduced is reduced from four to two. Other operations are the same as in the third embodiment. Thus, the present invention can be applied even if the solid-state imaging device is a square array type.

(Fifth embodiment)
In the present embodiment, in the first embodiment to the fourth embodiment, the solid-state imaging device is configured such that charges can be read independently for each photoelectric conversion element that detects light in different wavelength regions, and light in different wavelength regions is used. An example in which the charge multiplication factor can be independently controlled for each photoelectric conversion element that detects the above will be described.

FIG. 13 is a schematic plan view of the solid-state imaging device of the fifth embodiment. In FIG. 13, the same components as those in FIG.
In the solid-state imaging device shown in FIG. 13, a large number of photoelectric conversion elements 51 are arranged in an R photoelectric conversion element row in which the R photoelectric conversion elements 51 are arranged in the horizontal direction and a G photoelectric conversion element 51 in the horizontal direction. A pattern in which the G photoelectric conversion element rows and the B photoelectric conversion element rows in which the B photoelectric conversion elements 51 are arranged in the horizontal direction is arranged in this order in the vertical direction is repeatedly arranged in the vertical direction.

  The charge readout region 53 adjacent to the R photoelectric conversion element 51, the charge readout region 53 adjacent to the G photoelectric conversion element 51, and the charge readout region 53 adjacent to the B photoelectric conversion element 51 are independently read pulses. Is provided with a vertical transfer electrode.

  In the solid-state imaging device having such a configuration, in the charge multiplication drive mode, the imaging device driving unit 10 reads charges from the R photoelectric conversion element 51 in the first field, and charges from the G photoelectric conversion element 51 in the second field. In the third field, charges are read from the B photoelectric conversion elements 51, and the charges are read from all the photoelectric conversion elements 51. The driving method in each field employs the method described in the first embodiment or the second embodiment. Then, the charge multiplication factor (the number of charges read out or the combination of the number of charges read out and the number of electrodes to which a cancel pulse is applied) is controlled independently in each field. For example, when there are a photoelectric conversion element 51 with a reduced sensitivity and a photoelectric conversion element 51 with a higher sensitivity under a certain photographing condition, the charge multiplication factor at the time of reading a charge from the photoelectric conversion element 51 with a lower sensitivity is relatively set. The charge multiplication factor in the field for reading out charges from the photoelectric conversion element 51, which increases the sensitivity, is relatively lowered.

FIG. 14 is a flowchart for explaining a driving method of the solid-state imaging device according to the fifth embodiment.
The color temperature of the subject is calculated by the integrating unit 19 based on the image data set in the photographing mode and the image data obtained by the pre-imaging and the photometric data from the light receiving unit 13 (step S1). When the detected color temperature is lower than a first predetermined value (for example, 2500 K) (step S2: YES), the system control unit 11 determines that the sensitivity of the B photoelectric conversion element 51 is that of the R photoelectric conversion element 51. Since the sensitivity is lower than the sensitivity, the image sensor driving unit 10 drives the solid-state image sensor with the drive pattern 1 that makes the charge multiplication factor of the B photoelectric conversion element 51 larger than the charge multiplication factor of the R photoelectric conversion element 51. (Step S3).

  On the other hand, when the detected color temperature is higher than a first predetermined value (for example, 2500K) (step S2: NO), it is further determined whether or not the color temperature is higher than a second predetermined value (for example, 9000K). (Step S4). When the color temperature is higher than the second predetermined value (step S4: YES), in this case, the sensitivity of the R photoelectric conversion element 51 is lower than the sensitivity of the B photoelectric conversion element 51. The image sensor drive unit 10 is instructed to drive the solid-state image sensor with the drive pattern 2 that makes the charge multiplication factor of the image sensor larger than the charge multiplication factor of the B photoelectric conversion element 51 (step S5). When the color temperature is smaller than the second predetermined value (step S4: NO), the drive pattern 3 in which the R photoelectric conversion element 51, the G photoelectric conversion element 51, and the B photoelectric conversion element 51 have the same charge multiplication factor is used. An instruction is given to the image sensor drive unit 10 to drive the solid-state image sensor (step S6).

  When a shooting instruction is issued after steps S3, S5, and S6, the image sensor drive unit 10 drives the solid-state image sensor with the drive pattern instructed by the system control unit 11 (step S7).

  In this way, by controlling the charge multiplication factor independently for each photoelectric conversion element that detects light in different wavelength ranges, it is possible to reduce the sensitivity when the color temperature is extremely low or extremely high. It is not necessary to perform white balance adjustment by applying a high gain to the obtained signal, and S / N deterioration can be prevented.

The figure which shows schematic structure of the digital camera which is an example of the imaging device for demonstrating 1st embodiment of this invention. Plane schematic diagram of the solid-state imaging device of the first embodiment The figure for demonstrating operation | movement of the 1st field at the time of the charge multiplication drive mode of the solid-state image sensor of 1st embodiment. Timing chart of transfer pulse in first field in charge multiplication drive mode of solid-state imaging device of first embodiment Diagram for explaining charge multiplication effect by cancellation pulse The figure for demonstrating operation | movement of the 1st field at the time of the charge multiplication drive mode of the solid-state image sensor of 2nd embodiment. Transfer pulse timing chart in the first field in the charge multiplication drive mode of the solid-state imaging device of the second embodiment Planar schematic diagram of the solid-state imaging device of the third embodiment The figure for demonstrating the operation | movement in the 1st field of the solid-state image sensor of 3rd embodiment. Transfer pulse timing chart in the first field in the charge multiplication drive mode of the solid-state imaging device of the third embodiment The figure for demonstrating the operation | movement in the 1st field of the solid-state image sensor of 4th embodiment. Timing chart of transfer pulses in the first field in the charge multiplication drive mode of the solid-state imaging device of the fourth embodiment Planar schematic diagram of the solid-state imaging device of the fifth embodiment Flowchart for explaining the driving method of the solid-state image sensor of the fifth embodiment

Explanation of symbols

5 Solid-state imaging device 101 Photoelectric conversion device 102 Vertical charge transfer path 105 Charge readout region V1 to V8 Vertical transfer electrode

Claims (12)

A plurality of photoelectric conversion elements formed on the surface of the semiconductor substrate, a plurality of vertical charge transfer paths for transferring charges generated in each of the plurality of photoelectric conversion elements in a vertical direction, and generated in each of the plurality of photoelectric conversion elements A solid-state imaging device including a charge readout region for reading out the generated charge into the vertical charge transfer path,
A charge reading step of performing a drive for reading the charge in a plurality of times by supplying the read pulse to the charge reading region a plurality of times, and charging the charge accumulation packet formed in the vertical charge transfer path in a plurality of times;
When the next read pulse is supplied between the completion of the supply of an arbitrary read pulse of the plurality of read pulses and the start of the supply of the next read pulse after the arbitrary read pulse A solid-state image sensor driving method comprising: a charge transfer step of driving to transfer the charge read to the charge storage packet by the arbitrary read pulse in the vertical direction so that the charge storage packet is empty . A method for driving a solid-state imaging device according to claim 1,
A method for driving a solid-state imaging device, wherein a supply period of a read pulse excluding a read pulse supplied last among the plurality of read pulses is shorter than a supply period of a read pulse supplied last. A method for driving a solid-state imaging device according to claim 1 or 2,
A method for driving a solid-state imaging device, wherein the number of times of supply of the readout pulse in the charge readout step is changed according to imaging conditions. It is a drive method of the solid-state image sensing device according to any one of claims 1 to 3,
When the minimum number of the charge storage packets necessary for transferring the maximum amount of charge that can be stored in the photoelectric conversion element is A, and the number of the charge storage packets in the charge reading step is B, A A method for driving the solid-state imaging device, where> B. A method for driving a solid-state imaging device according to claim 4,
A method for driving a solid-state imaging device, wherein the value of B is changed according to imaging conditions. It is a drive method of the solid-state image sensing device according to any one of claims 1 to 3,
When the minimum number of the charge storage packets necessary for transferring the maximum amount of charge that can be stored in the photoelectric conversion element is A, and the number of the charge storage packets in the charge reading step is B, A A method for driving a solid-state imaging device, wherein the value of B is changed in accordance with imaging conditions within a range that satisfies a condition of ≧ B. It is a drive method of the solid-state image sensing device according to any one of claims 1 to 3,
The plurality of photoelectric conversion elements include a plurality of types of photoelectric conversion elements that detect light in different wavelength ranges,
A method for driving a solid-state imaging element, wherein the number of times of supplying the readout pulse is controlled independently for each of the plurality of types of photoelectric conversion elements. It is a drive method of the solid-state image sensing device according to any one of claims 4 to 6,
The plurality of photoelectric conversion elements include a plurality of types of photoelectric conversion elements that detect light in different wavelength ranges,
A method for driving a solid-state imaging device, wherein the number of read pulses supplied and the value B are independently controlled for each of the plurality of types of photoelectric conversion devices. A plurality of photoelectric conversion elements formed on the surface of the semiconductor substrate, a plurality of vertical charge transfer paths for transferring charges generated in each of the plurality of photoelectric conversion elements in a vertical direction, and generated in each of the plurality of photoelectric conversion elements A solid-state imaging device including a charge readout region for reading out the generated charge into the vertical charge transfer path,
A charge reading step of supplying a read pulse to the charge reading region to drive the charge storage packet formed in the vertical charge transfer path to read the charge;
When the minimum number of the charge storage packets necessary for transferring the maximum amount of charge that can be stored in the photoelectric conversion element is A, and the number of the charge storage packets in the charge reading step is B, A A method for driving the solid-state imaging device, where> B. A method for driving a solid-state imaging device according to claim 9,
A method for driving a solid-state imaging device, wherein the value of B is changed according to imaging conditions. It is a drive method of the solid-state image sensing device according to claim 9 or 10,
The plurality of photoelectric conversion elements include a plurality of types of photoelectric conversion elements that detect light in different wavelength ranges,
A method for driving a solid-state imaging element, wherein the value of B is controlled independently for each of the plurality of types of photoelectric conversion elements. Driving means for performing driving based on the driving method of the solid-state imaging device according to any one of claims 1 to 11,
An imaging apparatus comprising the solid-state imaging device.

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