JP2016015611A - Imaging device and driving method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device in which the characteristic variation of amplifiers provided for each column is suppressed, while suppressing reduction of frame rate, and to provide a driving method therefor.SOLUTION: An imaging device has first calculation means for calculating the signals from optical black pixels amplified by a plurality of amplification means, respectively, and acquiring correction values for correcting the signals outputted from the plurality of amplification means, respectively, second calculation means for calculating the signals from effective pixels amplified by the plurality of amplification means, respectively, by using the correction values acquired by the first calculation means, and third calculation means for obtaining the difference between a signal from an optical black pixel, corrected by the correction value, and amplified by the amplification means, and the calculation result from the second calculation means.

Description

  The present invention relates to an imaging apparatus and a driving method thereof.

  Patent Document 1 describes a CMOS image sensor having a pixel array section in which pixel circuits are arranged in a matrix. The pixel circuit outputs a signal (pixel signal) through a vertical signal line commonly connected to each column. The pixel signal of each column is input to the column amplifier via the switching selector circuit and amplified. The output terminals of the column amplifiers are commonly connected to the horizontal signal line via a column signal readout switch controlled by a horizontal scanning circuit. The pixel signals in the column selected by the horizontal scanning circuit are output to the horizontal signal line and output from the video output terminal via the output buffer amplifier.

  The amplifier characteristics such as the gain of the column amplifier of each column may vary. This characteristic variation may cause fixed pattern noise. For this reason, Patent Document 1 discloses a technique for measuring the characteristic variation of the column amplifier by switching the input of the column amplifier from the vertical signal line to the test voltage generation circuit by the switching selector circuit.

JP 2008-306565 A

  However, the read flow according to the configuration disclosed in Patent Document 1 requires time for measuring the test voltage for detecting the gain of the column amplifier. For this reason, a decrease in the frame rate can be a problem.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an imaging apparatus that suppresses variations in characteristics of amplifiers provided for each column and suppresses a decrease in frame rate, and a driving method thereof. That is.

  An imaging apparatus according to an embodiment of the present invention includes an effective pixel region in which a plurality of effective pixels including a photoelectric conversion unit that generates and accumulates charges according to an incident light amount are arranged in a matrix, and light-shielded photoelectric conversion. A plurality of optical black pixels each having a first optical black pixel region arranged corresponding to each column of the plurality of effective pixels, and each including an effective pixel in each column and an optical black pixel in each column A plurality of signal lines connected to each of the plurality of signal lines, and a plurality of amplification means respectively connected to each of the plurality of signal lines for amplifying signals output from the effective pixels and the optical black pixels, and each of the plurality of amplification means A first computing means for computing a signal from the optical black pixel amplified by step (a) and obtaining a correction value for correcting a signal output from each of the plurality of amplifying means; Using the correction value acquired by the calculation means, a second calculation means for calculating a signal from the effective pixel amplified by each of the plurality of amplification means, and the amplification means corrected by the correction value and amplified by the amplification means And a signal correction unit including a third calculation unit that obtains a difference between the signal from the optical black pixel and the calculation result of the second calculation unit.

  ADVANTAGE OF THE INVENTION According to this invention, the imaging device which suppressed the characteristic variation of the amplifier provided for every row | line | column and also suppressed the fall of the frame rate, and its drive method can be provided.

It is a block diagram which shows an example of the imaging device corresponding to the 1st Embodiment of this invention. It is a figure which shows an example of a structure of a pixel part. It is a figure which shows an example of a structure of the pixel circuit in an OB pixel area | region and an effective pixel area | region. It is a figure which shows an example of a structure of the pixel circuit in a reference | standard pixel area. It is a flowchart which shows operation | movement of 1st and 2nd embodiment. It is a block diagram which shows an example of the imaging device corresponding to the 2nd Embodiment of this invention. It is a block diagram which shows an example of the imaging device corresponding to the 3rd Embodiment of this invention. It is a flowchart which shows operation | movement of 3rd Embodiment. It is a figure which shows an example of the imaging system corresponding to the 4th Embodiment of this invention.

  Hereinafter, an example of an embodiment for implementing an imaging device according to the present invention will be specifically described with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram of an imaging apparatus according to the first embodiment of the present invention. The imaging apparatus includes a sensor unit 1, an analog gain control circuit 9, an AD converter 10, and a signal correction unit 50.

  The sensor unit 1 is a device that outputs a pixel signal corresponding to the amount of incident light and a correction signal used to correct the pixel signal. The sensor unit 100, a plurality of variable gain amplifiers (amplifying means) 5, a plurality of switches 6, and column control. A circuit 7 and a vertical scanning circuit 8 are provided. The pixel unit 100 includes an effective pixel area 2, a reference pixel area 3, and an optical black pixel area (OB pixel area) 4.

  The signal correction unit 50 includes a control circuit 11, multiplication circuits 14 and 18, a subtraction circuit 15, a column data averaging circuit 16, a column amplifier gain correction value calculation circuit 17, and a column address controller 19. The control circuit 11 includes a column data averaging circuit 12 and a subtraction circuit 13.

  FIG. 2 is a diagram showing a more detailed configuration of the pixel unit 100. The pixel unit 100 includes a plurality of pixel circuits 200 arranged in a matrix, a horizontal signal line 202 commonly connected to the pixel circuit 200 for each row, and a vertical signal line 201 commonly connected to the pixel circuit 200 for each column. . The vertical scanning circuit 8 transmits a control signal for selecting a row to the pixel circuit 200 via the horizontal signal line 202. The pixel circuits 200 included in the row selected by the vertical scanning circuit output a pixel signal that is an analog signal or a correction signal to the vertical signal line 201.

  The effective pixel area 2 includes effective pixels that convert the amount of incident light into an electrical signal and output it. FIG. 3 shows a circuit configuration of the pixel circuit 200 of the effective pixels included in the effective pixel region 2. The pixel circuit 200 includes transistors 203, 204, 206 and a photoelectric conversion unit 205. The transistors 203, 204, and 206 are configured with MOSFETs or the like. In the following description, each transistor is assumed to be an N-channel type MOSFET. The photoelectric conversion unit 205 generates and accumulates charges corresponding to incident light. The photoelectric conversion unit 205 is configured by a photoelectric conversion element such as a photodiode. The anode of the photoelectric conversion unit 205 is connected to the ground (GND), and the cathode is connected to the gate of the transistor 203 and the source of the transistor 206.

  The drain of the transistor 203 is connected to the power supply VCC, and the source of the transistor 203 is connected to the drain of the transistor 204. The gate of the transistor 204 is connected to the horizontal signal line 202, and the source is connected to the vertical signal line 201. The charge accumulated in the photoelectric conversion unit 205 is amplified by the transistor 203 and converted into a voltage signal. When the transistor 204 is turned on by a control signal from the vertical scanning circuit 8, this voltage signal is output to the vertical signal line 201. A reset voltage VRES is supplied to the drain of the transistor 206. When the transistor 206 is turned on by a control signal (not shown), the charge generated in the photoelectric conversion unit 205 is reset.

  The OB pixel area 4 has the same pixel circuit 200 as the effective pixel area 2. However, the photoelectric conversion unit 205 of the pixel circuit 200 in the OB pixel region 4 is provided with a light shielding film made of aluminum or the like at the light incident part. As a result, even if the pixel circuit 200 in the OB pixel region 4 is irradiated with light, no charge is generated by photoelectric conversion. Hereinafter, a pixel in which the photoelectric conversion unit 205 is shielded from light is referred to as an optical black pixel (OB pixel). The signal output from the OB pixel is used for correcting noise due to dark current or the like that can be generated in the photoelectric conversion unit 205 even when there is no incident light. The OB pixel region 4 includes a pixel row having at least one OB pixel. The OB pixel region 4 preferably has a plurality of pixel rows in order to reduce a noise component by processing such as averaging.

  The configuration of the pixel circuit 200 included in the reference pixel region 3 is shown in FIG. The reference pixel region 3 is different from the effective pixel region 2 and the OB pixel region 4 in that the photoelectric conversion unit 205 is not disposed. Hereinafter, a pixel in which the photoelectric conversion unit 205 is not arranged as described above is referred to as a reference pixel. Since other circuit configurations are the same, description thereof is omitted. The signal output from the reference pixel is used for removing the offset voltage of the variable gain amplifier 5 and the like. Similar to the OB pixel region 4, the reference pixel region 3 includes at least one pixel row. In order to reduce a noise component by processing such as averaging, it is preferable that the reference pixel region 3 also has a plurality of pixel rows.

  With reference to FIG. 1 again, processing of signals output from the pixel unit 100 will be described. The vertical scanning circuit 8 outputs a signal for selecting a pixel row included in the reference pixel region 3, the OB pixel region 4, and the effective pixel region 2. The vertical scanning circuit 8 performs scanning in the order of the reference pixel region 3, the OB pixel region 4, and the effective pixel region 2. Thereby, the electrical signals accumulated in the pixel circuit 200 are sequentially read out in units of rows. The electric signal output from the pixel circuit 200 is input to the variable gain amplifier 5. The gain (amplification factor) of the variable gain amplifier 5 is variable and is controlled by a control signal from the analog gain control circuit 9.

  A signal output from the variable gain amplifier 5 is input to one end of the switch 6. The switches 6 are sequentially selected by the column control circuit 7, and signals sequentially read from each column are input to the AD converter 10. The input signal is AD-converted from an analog signal to a digital signal by the AD converter 10, and is output to the control circuit 11.

  The digital signal input to the control circuit 11 is input to the column data averaging circuit 12 or the subtraction circuit 13. The column data averaging circuit 12 has a function of averaging the data of each row to calculate an average value for each column and holding it in a memory or the like. When a column is selected by a control signal from the column address controller 19, the column data averaging circuit 12 outputs the corresponding column data and outputs it to one end of the subtraction circuit 13. The subtraction circuit 13 subtracts the signal input from the column data averaging circuit 12 from the signal input from the AD converter 10, and outputs the calculation result. The output of the subtraction circuit 13 is input to the multiplication circuit 14.

  The multiplication circuit 14 receives the output of the subtraction circuit 13 and the output of the column amplifier gain correction value calculation circuit 17, and the operation result obtained by multiplying them is input to the subtraction circuit 15 and the column data averaging circuit 16. The column data averaging circuit 16 averages the data of each row, calculates an average value for each column, and holds it. When a column is selected by a control signal from the column address controller 19, the column data averaging circuit 16 outputs data of the corresponding column and outputs it to the column amplifier gain correction value calculation circuit 17 and the multiplication circuit 18.

  The column amplifier gain correction value calculation circuit 17 calculates the gain correction value of the variable gain amplifier 5 and outputs it to the multiplication circuit 14 and the multiplication circuit 18. The multiplication circuit 18 multiplies the data input from the column data averaging circuit 16 and the column amplifier gain correction value calculation circuit 17 and outputs the result to the subtraction circuit 15. The subtraction circuit 15 subtracts the data input from the multiplication circuit 14 and the multiplication circuit 18 and outputs the result to a subsequent video signal processing unit (not shown).

  FIG. 5 is a flowchart illustrating a signal correction operation performed in the above-described imaging apparatus. Steps S300 to S310 described in FIG. 5 represent operations performed within one frame period of the imaging apparatus.

  In step S300, the gain of the variable gain amplifier 5 is set based on the control signal from the analog gain control circuit 9.

  In step S301, a signal is read from the reference pixel region 3. A signal output from the pixel circuit 200 in the row selected by the vertical scanning circuit 8 to the vertical signal line 201 is amplified by the variable gain amplifier 5. The switch 6 at the subsequent stage of the variable gain amplifier 5 is sequentially selected by the column control circuit 7, and the output of the variable gain amplifier 5 is converted from an analog signal to a digital signal by the AD converter 10. The digital signal output from the AD converter 10 is input to the column data averaging circuit 12 in the control circuit 11. The column data averaging circuit 12 sequentially holds the data of each column in response to a control signal from the column address controller 19.

（ｎ：列番号、ｉ_１：基準画素領域３の行数、Ｄ_ｎ：入力データ） When the reference pixel region 3 includes a plurality of rows, the same operation is performed for each row. When reading the second and subsequent rows, the column data averaging circuit 12 averages the newly read data and the data held when the previous row is read, so that the signals of a plurality of rows are obtained. Averaged data can be acquired. Averaging may be performed by adding all rows and then dividing by the number of rows. Data D _{offset — n} held in the column data averaging circuit 12 by _averaging is expressed by the following equation. Note that the subscript n indicates the column number of the data, and this calculation process is performed for each column.

(N: column number, i ₁ : number of rows of reference pixel region 3, D _n : input data)

  In step S302, reading of the OB pixel area 4 is performed. The digital signal output from the AD converter 10 is input to the control circuit 11 in the same manner as the reading of the reference pixel region 3 in step S301.

  In step S <b> 303, the data read from the OB pixel region 4 is not subjected to data averaging processing by the column data averaging circuit 12 and is input to the subtraction circuit 13. In parallel with this, the averaged data of the reference pixel area 3 of the column designated by the control signal of the column address controller 19 is output from the column data averaging circuit 12 to the subtraction circuit 13. The subtraction circuit 13 subtracts the data of the column of the column data averaging circuit 12 from the data of the OB pixel region 4 of the column, and outputs the calculation result to the multiplication circuit 14. By this operation, the influence of the offset of the variable gain amplifier 5 is corrected from the data in the reference pixel region 3.

（ｎ：列番号、ｉ_２：ＯＢ画素領域４の行数、Ｄ_ｎ：入力データ） In step S <b> 304, the multiplication circuit 14 multiplies the output of the subtraction circuit 13 and the output of the column amplifier gain correction value calculation circuit 17. At this time, the value of data output from the column amplifier gain correction value calculation circuit 17 is 1. That is, the output value of the subtraction circuit 13 is output from the multiplication circuit 14 as it is and input to the column data averaging circuit 16. The column data averaging circuit 16 is controlled by the column address controller 19 and sequentially holds the data of each column. Data D _{ob — n} held in the column data averaging circuit 16 is expressed by the following equation.

(N: column number, i ₂ : number of rows in the OB pixel area 4, D _n : input data)

  When the OB pixel region 4 includes a plurality of rows, the same operation is performed for each row. When reading the second and subsequent rows, the column data averaging circuit 16 averages a plurality of rows by averaging the newly read data and the data held when the previous row is read. Obtained data can be acquired. Averaging may be performed by adding all rows and then dividing by the number of rows.

Usually, since the average value of the signal output from the reference pixel in the reference pixel region 3 and the signal output from the OB pixel in the OB pixel region 4 are different, the data D _{ob_n} does not become zero. However, there is a possibility that the voltages of the output signals of the reference pixel region 3 and the OB pixel region 4 coincide with each other and the data _{Dob_n} becomes 0 and is divided by 0 when calculating a correction value described later. In that case, the reset voltage VRES of the OB pixel may be different from the reset voltage VRES of the reference pixel so that the data _{Dob_n} does not become zero. This avoids the problem that the correction value cannot be calculated by division by 0, and the correction value can be calculated more reliably.

  In step S305, the effective pixel region 2 is read. Similarly to Step S301 and Step S302, the signal output from the pixel is converted into a digital signal and input to the control circuit 11.

In step S306, the signal input to the control circuit 11 is not subjected to the averaging process by the column data averaging circuit 12 as in the case of step 303, and is input to the subtraction circuit 13. The subtraction circuit 13 outputs data D _{pix1_n} obtained by subtracting the data D _{offset_n} held in the column data averaging circuit 12 from the read data D _{pix_n} of the effective pixel region 2 to the multiplication circuit 14. The subtraction performed in the subtraction circuit 13 is expressed by the following equation.

（Ａ_ｍ＿ｎ：補正値、ＲＥＦ：補正目標値、ｍ：ゲイン、ｎ：列番号） In step S307, the column data averaging circuit 16 outputs the data of the column based on the control signal designating the column from the column address controller 19. This data is input to the column amplifier gain correction value calculation circuit 17, and a correction value is output. The correction value is defined as follows.

(A _{m — n} : correction value, REF: correction target value, m: gain, n: column number)

Next, the multiplication circuit 18 multiplies the output of the column data averaging circuit 16 and the output of the column amplifier gain correction value calculation circuit 17, and outputs data REF × m to the subtraction circuit 15 based on the following equation.

  The correction target value REF can be determined in advance (for example, at the time of factory shipment) in consideration of the performance of the variable gain amplifier 5 and the like. For example, when the absolute value of the gain fluctuation of the variable gain amplifier 5 is constant, the average value of the gain fluctuations of all the variable gain amplifiers 5 may be set.

In step S308, the multiplication circuit 14 outputs the data _{D Pix2_n} corrected by multiplying a correction value _{A m_n} input from the data _{D Pix1_n} column amplifier gain correction value calculating circuit 17 which is inputted from the subtraction circuit 13, an amplifier Gain correction is performed. This correction is expressed by the following equation.

In step S 309, the data D _{pix2 — n} of the effective pixel region 2 after the amplifier gain correction and the data REF × m output from the multiplication circuit 18 are input to the subtraction circuit 15. Thereby, dark current correction of the pixel signal is performed. Data D _{pix_out_n} output from the subtraction circuit 15 is represented by the following equation.

  In step S310, it is determined whether reading from the effective pixel region 2 has been performed up to the last row. When the reading to the last row is completed, reading of the frame ends and reading of the next frame starts. If it is not the last line, the process returns to step S305 to read the next line.

In the data D _{pix_out_n} output by the above flow, pixel signals are corrected for each column, and the influence of variations in gain of the variable gain amplifier 5 in each column is suppressed. Further, even when the gain variation fluctuates due to the temperature change of the apparatus, the influence is also suppressed. In the present embodiment, since a signal output from an OB pixel in the OB pixel region 4 used for dark current correction or the like is used as a correction signal, there is no need to separately read a reference voltage for correcting gain variation. . Therefore, since the readout time per frame is shortened, the frame rate of the imaging apparatus can be improved.

In the above example, as shown in FIG. 4, the pixel circuit 200 in the reference pixel region 3 has a configuration that does not include the photoelectric conversion unit 205. However, the reference pixel region 3 may be configured by a light-shielded pixel like the OB pixel region 4, and the value of the reset voltage VRES of the reference pixel region 3 may be different from the value of the reset voltage VRES of the OB pixel region 4. . In this case, the value of VRES is set so that D _{ob — n} > D _{offset — n} and the reset voltage of the effective pixel region 2 is set to the same value as that of the reference pixel region 3. Also in this modification, the same effect as that of the above-described imaging apparatus can be obtained.

(Second Embodiment)
FIG. 6 is a block diagram showing an imaging apparatus according to the second embodiment of the present invention. A difference of the present embodiment from the first embodiment is a pixel readout circuit in the sensor unit 1. In the sensor unit 1 of the present embodiment, the variable gain amplifier 5 is not provided for each column. Instead of this, the signals from the pixels in each column are input to either of the two variable gain amplifiers (amplifying means) 5a or 5b. The output of the vertical signal line 201 is connected to one end of the switch 6 in each column. The other end of the switch 6 is connected to either the common signal line 62a or 62b. The common signal line 62a is connected to the variable gain amplifier 5a, and the common signal line 62b is connected to the variable gain amplifier 5b. More specifically, the switch 6 and the common signal lines 62a and 62b are arranged so that the vertical signal lines 201 of each column are alternately connected to the variable gain amplifier 5a or 5b every other column. For example, if the odd-numbered column switch 6 is connected to the variable gain amplifier 5a, the even-numbered column switch 6 is connected to the variable gain amplifier 5b. However, it is not essential to connect them alternately. It is only necessary that some of the plurality of switches 6 are connected to the common signal line 62a and the other part is connected to the common signal line 62b. Although the number of variable gain amplifiers and the number of columns in the pixel region can be changed as appropriate, in the following description, the number of variable gain amplifiers is two and the number of columns in the pixel region is n columns (however, n Is an even number).

  The outputs of the variable gain amplifiers 5a and 5b are connected to one ends of the switches 61a and 61b, respectively. The column control circuit 7 selects the switch 61a when the switch 6 connected to the variable gain amplifier 5a is selected, and selects the switch 61b when the switch 6 connected to the variable gain amplifier 5b is selected. Thus, the switches 61a and 61b are controlled. The other ends of the switches 61a and 61b are connected to the AD converter 10. Since other circuit configurations and connections are the same as those in the first embodiment, description thereof will be omitted.

  In the imaging apparatus of the second embodiment, the correction flow itself is the same as that of the first embodiment, but the processing and calculation formulas performed in each step are different from those of the first embodiment. Therefore, the operation of the imaging apparatus according to the second embodiment will be described with reference to the flowchart of FIG. 5 again.

  In step S300, the gains of the variable gain amplifiers 5a and 5b are determined based on the control signal from the analog gain control circuit 9.

（ａ：アンプナンバー、ｎ：列数、ｉ_１：基準画素領域３の行数、Ｄ_ｏｐ：入力データ、ｏｐ：ｎ／２の余りが１の場合ａ＝１、余りが０の場合ａ＝２） In step S301, a signal is read from the reference pixel region 3. The signal output from the pixel in the row selected by the vertical scanning circuit 8 is amplified by the variable gain amplifier 5a or 5b. The amplified signal is input to the AD converter 10 and converted from an analog signal to a digital signal. The digital signal output from the AD converter 10 is input to the column data averaging circuit 12 of the control circuit 11. The column data averaging circuit 12 is controlled by the column address controller 19 and sequentially holds the data of each column. At this time, the signal amplified by the variable gain amplifier 5a and the signal amplified by the variable gain amplifier 5b are held alternately and averaged individually for each amplifier. Data held in the column data averaging circuit 12 is represented by the following equation. The subscript amplifier number a indicates which variable gain amplifier the data after averaging is amplified. In this embodiment, since there are two variable gain amplifiers, a = 1. Or 2.

(A: amplifier number, n: number of columns, i ₁ : number of rows in the reference pixel region 3, D _op : input data, op: n = 1 when remainder is 1, a = 1, remainder is 0, a = 2)

  In step S302, reading of the OB pixel area 4 is performed. The digital signal output from the AD converter 10 is input to the control circuit 11 in the same manner as the reading of the reference pixel region 3 in step S301.

  In step S <b> 303, the data read from the OB pixel region 4 is not subjected to data averaging processing by the column data averaging circuit 12 and is input to the subtraction circuit 13. In parallel with this, averaged data of the variable amplifier 5 a or 5 b corresponding to the column designated by the control signal of the column address controller 19 is output from the column data averaging circuit 12 to the subtraction circuit 13. The subtraction circuit 13 subtracts the data of the corresponding variable amplifiers 5 a and 5 b of the column data averaging circuit 12 from the data of the OB pixel region 4 and outputs the calculation result to the multiplication circuit 14. By this operation, the influence of the offset of the variable gain amplifiers 5a and 5b is corrected from the data in the reference pixel region 3.

（ｉ_２：ＯＢ画素領域４の行数） In step S <b> 304, the multiplication circuit 14 multiplies the output of the subtraction circuit 13 and the output of the column amplifier gain correction value calculation circuit 17. At this time, the value of data output from the column amplifier gain correction value calculation circuit 17 is 1. That is, the output value of the subtraction circuit 13 is output from the multiplication circuit 14 as it is and input to the column data averaging circuit 16. The column data averaging circuit 16 is controlled by a column address controller 19 and sequentially holds input data corresponding to the variable gain amplifiers 5a and 5b. Data held in the column data averaging circuit 16 is expressed by the following equation.

(I ₂ : number of rows in the OB pixel area 4)

  When the OB pixel region 4 includes a plurality of rows, the same operation is performed for each row. When reading the second and subsequent rows, the column data averaging circuit 16 averages a plurality of rows by averaging the newly read data and the data held when the previous row is read. Obtained data can be acquired. Averaging may be performed by adding all rows and then dividing by the number of rows.

  In step S305, the effective pixel region 2 is read. Similarly to Step S301 and Step S302, the signal output from the pixel is converted into a digital signal and input to the control circuit 11.

In step S306, the signal input to the control circuit 11 is not subjected to data row averaging processing by the column data averaging circuit 12, and is input to the subtraction circuit 13. The subtracting circuit 13 outputs the data obtained by subtracting the data of the variable gain amplifier 5a or 5b of the column data averaging circuit 12 from the data D _{pix1_n} read out from the effective pixel region 2 to the multiplying circuit 14. The subtraction performed in the subtraction circuit 13 is expressed by the following equation.

（Ａ_ｍ＿ａ：補正値、ＲＥＦ：補正目標値、ｍ：ゲイン） In step S307, the column data averaging circuit 16 receives data related to the column (or the corresponding variable gain amplifier) based on the control signal designating the column (or the variable gain amplifier corresponding to the column) from the column address controller 19. Is output. This data is input to the column amplifier gain correction value calculation circuit 17, and a correction value is output. The correction value is defined as follows.

(A _{m — a} : correction value, REF: correction target value, m: gain)

Next, the multiplication circuit 18 multiplies the output of the column data averaging circuit 16 and the output of the column amplifier gain correction value calculation circuit 17 and outputs data REF × m to the subtraction circuit 15 based on the following equation.

In step S308, the multiplication circuit 14 multiplies the data D _{pix1_n} input from the subtraction circuit 13 by the correction value _{Am_a} input from the column amplifier gain correction value calculation circuit 17, and outputs corrected data D _{pix2_n.} Gain correction is performed. This correction is expressed by the following equation.

In step S 309, the data D _{pix2 — n} of the effective pixel region 2 after the amplifier gain correction and the data REF × m output from the multiplication circuit 18 are input to the subtraction circuit 15. Thereby, dark current correction of the pixel signal is performed. Data D _{pix_out_n} output from the subtraction circuit 15 is expressed by the following.

  In step S310, it is determined whether reading from the effective pixel region 2 has been performed up to the last row. When reading to the last row is completed, reading of the frame is completed and reading of the next frame starts. If it is not the last line, the process returns to step S305 to read the next line.

  With the above flow, in the circuit configuration of the present embodiment as well, the frame rate of the imaging apparatus can be improved while suppressing the influence of the gain variation of the variable gain amplifiers 5a and 5b as in the first embodiment.

(Third embodiment)
FIG. 7 is a block diagram showing an imaging apparatus according to the third embodiment of the present invention. Differences between the present embodiment and the first embodiment will be described. In the imaging apparatus according to the present embodiment, in addition to the configuration of the first embodiment, the signal correction unit 50 further includes a subtraction circuit 20, a multiplication circuit 21, a frame memory 22, and an address controller 23.

  Since the previous circuit of the subtraction circuit 15 is the same as that of the first embodiment, the description thereof is omitted. Output data from the subtraction circuit 15 is input to the subtraction circuit 20 and the frame memory 22. Output data from the column amplifier gain correction value calculation circuit 17 is input to the multiplication circuit 21. The data output from the frame memory 22 is further input to the multiplication circuit 21. The frame memory 22 is controlled by an address controller 23. Output data from the multiplication circuit 21 is input to the subtraction circuit 20.

The frame memory 22 holds in advance the output data of the subtraction circuit 15 when the gain of the variable gain amplifier 5 is 1 as the individual correction data D _{pixob_n, l} for all the pixels in the effective pixel region 2. The individual correction data can be acquired at a time point before the actual operation such as factory setting. When the gain at the time of factory setting is P, the individual correction data D _{pixob_n, l} corresponding to the case where the gain is 1 is acquired by holding the value obtained by multiplying the output value by 1 / P in the frame memory 22. Can do.

  FIG. 8 is a flowchart illustrating the operation of the imaging apparatus according to the third embodiment. Steps S300 to S309 are the same as those in the first embodiment, and a description thereof will be omitted.

（ｎ：列番号、ｌ：行番号） In step S309, the data of the effective pixel region 2 subjected to the amplifier gain correction is input to the subtraction circuit 15, and the first dark current correction (similar to the dark current correction in step S309 in the first embodiment) is performed. . Thereafter, second dark current correction is performed in step S311. At this time, the frame memory 22 outputs the individual correction data D _{pixob_n, l} of the effective pixel region 2 at the address (pixel row and column coordinates) designated by the address controller 23 to the multiplication circuit 21. The multiplication circuit 21 multiplies the output of the column amplifier gain correction value calculation circuit 17 and the individual correction data to obtain a second dark current correction value A _{mb_n, l} . The output of the multiplication circuit 21 is input to the subtraction circuit 20, and subtraction with the output of the subtraction circuit 15 is performed. The output data of the multiplier circuit 21 is expressed by the following formula.

(N: column number, l: row number)

The output data D _{pix_out2_n, l} of the subtraction circuit 20 is expressed by the following equation.

As described above, the output data D _{pix_out2_n, l subjected} to the second dark current correction can be obtained. Since the dark current correction in step S309 is performed for each column, the correction may not be sufficient for the variation in dark current for each pixel. Since the second dark current correction in step S311 of this embodiment is performed for each pixel, the dark current variation for each pixel can be corrected by adding the second dark current correction. it can. Therefore, in this embodiment, in addition to the effect of the first embodiment, the effect of improving accuracy by improving the variation in dark current can be obtained.

(Fourth embodiment)
FIG. 9 is a diagram showing a configuration of an imaging system 800 according to the fourth embodiment of the present invention. The imaging system 800 includes an optical unit 810, an imaging device 820, a video signal processing unit 830, a recording / communication unit 840, a timing control unit 850, a system control unit 860, and a playback / display unit 870. As the imaging device 820, the imaging devices of the first to third embodiments described above are used.

  An optical unit 810 that is an optical system such as a lens forms an image of a subject by imaging light from the subject on the pixel unit 100 of the imaging device 820. The imaging device 820 outputs a signal corresponding to the light imaged on the pixel unit 100 at a timing based on the signal from the timing control unit 850. The signal output from the imaging device 820 is input to the video signal processing unit 830, and the video signal processing unit 830 performs signal processing according to a method determined by a program or the like. The signal obtained by the processing in the video signal processing unit 830 is sent to the recording / communication unit 840 as image data. The recording / communication unit 840 sends a signal for forming an image to the reproduction / display unit 870 and causes the reproduction / display unit 870 to reproduce / display a moving image or a still image. The recording / communication unit 840 receives a signal from the video signal processing unit 830 and communicates with the system control unit 860, and also records an operation for recording a signal for forming an image on a recording medium (not shown). Do.

The system control unit 860 comprehensively controls the operation of the imaging system, and controls driving of the optical unit 810, the timing control unit 850, the recording / communication unit 840, and the reproduction / display unit 870. Further, the system control unit 860 includes a storage device (not shown) that is a recording medium, for example, and a program necessary for controlling the operation of the imaging system is recorded therein. Further, the system control unit 860 supplies a signal for switching the drive mode in accordance with, for example, a user operation in the imaging system. Specific examples include a change in a line to be read out and a line to be reset, a change in an angle of view associated with electronic zoom, and a shift in angle of view associated with electronic image stabilization. The timing control unit 850 controls the drive timing of the imaging device 820 and the video signal processing unit 830 based on control by the system control unit 860.
In the imaging devices of the first to third embodiments, the example in which the imaging device 820 includes the signal correction unit 50 has been described. As another example, the video signal processing unit 830 may include the signal correction unit 50.

  In the imaging devices of the first to third embodiments, variation in characteristics of variable gain amplifiers provided for each column is suppressed, and a decrease in frame rate is also suppressed. Therefore, according to the present embodiment, it is possible to provide an imaging system that realizes high-accuracy and high-speed imaging.

1: sensor unit, 2: effective pixel area, 3: reference pixel area, 4: OB pixel area, 5, 5a, 5b: variable gain amplifier, 6: switch, 7: column control circuit, 8: vertical scanning circuit, 9 : Analog gain control circuit, 10: AD converter, 11: control circuit, 12: column data averaging circuit, 13: subtraction circuit, 14: multiplication circuit, 15: subtraction circuit, 16: column data averaging circuit, 17: column Amplifier gain correction value calculation circuit, 18: multiplication circuit, 19: column address controller, 50: signal correction unit, 100: pixel unit

Claims (16)

An effective pixel region in which a plurality of effective pixels including a photoelectric conversion unit that generates and accumulates charge according to the amount of incident light is arranged in a matrix; and
A first optical black pixel region in which each of a plurality of optical black pixels having a light-shielded photoelectric conversion portion is arranged corresponding to each column of the plurality of effective pixels;
A plurality of signal lines each connected to the effective pixel in each column and the optical black pixel in each column;
A plurality of amplifying means connected to each of the plurality of signal lines for amplifying signals output from the effective pixels and the optical black pixels;
First computing means for computing a signal from the optical black pixel amplified by each of the plurality of amplifying means and obtaining a correction value for correcting a signal output from each of the plurality of amplifying means. When,
Second computing means for computing a signal from the effective pixel amplified by each of the plurality of amplifying means using the correction value acquired by the first computing means;
A signal correction unit having a third calculation unit that obtains a difference between the signal from the optical black pixel amplified by the amplification unit and corrected by the correction value, and a calculation result by the second calculation unit; An imaging apparatus comprising: The imaging apparatus further includes a reference pixel region in which each of a plurality of reference pixels not including the photoelectric conversion unit is disposed corresponding to each column of the plurality of effective pixels,
The calculation by the first calculation means further includes obtaining a difference between signals output from the plurality of amplification means and signals from the reference pixel region before obtaining the correction value. The imaging apparatus according to claim 1. The imaging apparatus further includes a second optical black pixel region in which each of the plurality of optical black pixels is arranged corresponding to each column of the plurality of effective pixels,
The calculation by the first calculation unit further includes obtaining a difference between the signal output from the amplification unit and the second optical black pixel region before obtaining the correction value. The imaging device according to claim 1.   The reset voltage supplied to the plurality of optical black pixels in the second optical black pixel region is lower than the reset voltage supplied to the plurality of optical black pixels in the first optical black pixel region. The imaging device according to claim 3. A plurality of effective pixel regions in which a plurality of effective pixels including a photoelectric conversion unit that generates and accumulates charge according to the amount of incident light is arranged in a matrix; and
A first optical black pixel region in which each of a plurality of optical black pixels having a light-shielded photoelectric conversion portion is arranged corresponding to each column of the plurality of effective pixels;
A plurality of signal lines each connected to the effective pixel in each column and the optical black pixel in each column;
A plurality of switches each having one end connected to each of the plurality of signal lines;
A first common signal line to which the other end of each of the plurality of switches is connected;
A second common signal line to which the other end of each of some other switches of the plurality of switches is connected;
A plurality of amplifying means connected to each of the first common signal line and the second common signal line for amplifying signals output from the effective pixels and the optical black pixels;
First computing means for computing a signal from the optical black pixel amplified by each of the plurality of amplifying means and obtaining a correction value for correcting a signal output from each of the plurality of amplifying means. When,
Second computing means for computing a signal from the effective pixel amplified by each of the plurality of amplifying means using the correction value acquired by the first computing means;
A signal correction unit having a third calculation unit that obtains a difference between the signal from the optical black pixel amplified by the amplification unit and corrected by the correction value, and a calculation result by the second calculation unit; An imaging apparatus comprising: The signal correction unit is
A frame memory that holds individual correction data of each effective pixel in the effective pixel region;
Fourth calculation means for calculating the correction value acquired by the first calculation means and the individual correction data output from the frame memory;
6. The apparatus according to claim 1, further comprising a fifth calculation unit that obtains a difference between the calculation result of the third calculation unit and the calculation result of the fourth calculation unit. Imaging device. An effective pixel region in which a plurality of effective pixels including a photoelectric conversion unit that generates and accumulates charge according to the amount of incident light is arranged in a matrix; and
A first optical black pixel region in which each of a plurality of optical black pixels having a light-shielded photoelectric conversion portion is arranged corresponding to each column of the plurality of effective pixels;
A plurality of signal lines each connected to the effective pixel in each column and the optical black pixel in each column;
A method for driving an imaging apparatus, comprising: a plurality of amplifying means each connected to each of the plurality of signal lines, for amplifying signals output from the effective pixels and the optical black pixels,
A first step of calculating a signal from the optical black pixel amplified by each of the plurality of amplifying means to obtain a correction value for correcting a signal output from each of the plurality of amplifying means; ,
A second step of calculating a signal from the effective pixel amplified by each of the plurality of amplifying means using the correction value;
And a third step of obtaining a difference between the signal from the optical black pixel amplified by the amplifying means and corrected by the correction value, and a calculation result of the second step. Driving method of imaging apparatus. The imaging apparatus further includes a vertical scanning circuit that performs scanning for reading signals from the effective pixel region and the first optical black pixel region;
8. The method of driving an image pickup apparatus according to claim 7, wherein the vertical scanning circuit scans the effective pixel area after scanning the first optical black pixel area.   9. The driving method of an imaging apparatus according to claim 8, wherein the scanning of the first optical black pixel area and the effective pixel area by the vertical scanning circuit is performed within one frame period.   An imaging system comprising: the imaging apparatus according to claim 1; and a video signal processing unit that generates image data using a signal output from the imaging apparatus. An effective pixel region in which a plurality of effective pixels including a photoelectric conversion unit that generates and accumulates charge according to the amount of incident light is arranged in a matrix; and
A first optical black pixel region in which each of a plurality of optical black pixels having a light-shielded photoelectric conversion portion is arranged corresponding to each column of the plurality of effective pixels;
A plurality of signal lines each connected to the effective pixel in each column and the optical black pixel in each column;
An imaging device having a plurality of amplifying means each connected to each of the plurality of signal lines for amplifying signals output from the effective pixels and the optical black pixels;
First computing means for computing a signal from the optical black pixel amplified by each of the plurality of amplifying means and obtaining a correction value for correcting a signal output from each of the plurality of amplifying means. When,
Second computing means for computing a signal from the effective pixel amplified by each of the plurality of amplifying means using the correction value acquired by the first computing means;
A signal correction unit having a third calculation unit that obtains a difference between the signal from the optical black pixel amplified by the amplification unit and corrected by the correction value, and a calculation result by the second calculation unit; An imaging system comprising: The imaging apparatus further includes a reference pixel region in which each of a plurality of reference pixels not including the photoelectric conversion unit is disposed corresponding to each column of the plurality of effective pixels,
The calculation by the first calculation means further includes obtaining a difference between signals output from the plurality of amplification means and signals from the reference pixel region before obtaining the correction value. The imaging system according to claim 11. The imaging apparatus further includes a second optical black pixel region in which each of the plurality of optical black pixels is arranged corresponding to each column of the plurality of effective pixels,
The calculation by the first calculation unit further includes obtaining a difference between the signal output from the amplification unit and the second optical black pixel region before obtaining the correction value. The imaging system according to claim 11.   The reset voltage supplied to the plurality of optical black pixels in the second optical black pixel region is lower than the reset voltage supplied to the plurality of optical black pixels in the first optical black pixel region. The imaging system according to claim 13. A plurality of effective pixel regions in which a plurality of effective pixels including a photoelectric conversion unit that generates and accumulates charge according to the amount of incident light is arranged in a matrix; and
A first optical black pixel region in which each of a plurality of optical black pixels having a light-shielded photoelectric conversion portion is arranged corresponding to each column of the plurality of effective pixels;
A plurality of signal lines each connected to the effective pixel in each column and the optical black pixel in each column;
A plurality of switches each having one end connected to each of the plurality of signal lines;
A first common signal line to which the other end of each of the plurality of switches is connected is connected to the other end of each of the other part of the plurality of switches. A second common signal line;
An imaging apparatus having a plurality of amplifying means connected to each of the first common signal line and the second common signal line, which amplifies signals output from the effective pixels and the optical black pixels; ,
First computing means for computing a signal from the optical black pixel amplified by each of the plurality of amplifying means and obtaining a correction value for correcting a signal output from each of the plurality of amplifying means. When,
Second computing means for computing a signal from the effective pixel amplified by each of the plurality of amplifying means using the correction value acquired by the first computing means;
A signal correction unit having a third calculation unit that obtains a difference between the signal from the optical black pixel amplified by the amplification unit and corrected by the correction value, and a calculation result by the second calculation unit; An imaging system comprising: The signal correction unit is
A frame memory that holds individual correction data of each effective pixel in the effective pixel region;
Fourth calculation means for calculating the correction value acquired by the first calculation means and the individual correction data output from the frame memory;
16. The apparatus according to claim 11, further comprising a fifth calculation unit that obtains a difference between the calculation result of the third calculation unit and the calculation result of the fourth calculation unit. Imaging system.

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