JP2017055320A - Imaging apparatus, imaging system and control method for imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable moving-picture photographing of satisfactory image quality even in a case where exposure time is changed for each frame, in an imaging apparatus having the function of a global electronic shutter.SOLUTION: In a first frame period among a plurality of frame periods for which a plurality of images composing a moving picture are acquired, electric charges generated in a first exposure period are accumulated. In a second frame period following the first frame period, electric charges generated in a second exposure period different in length from the first exposure period are accumulated. The interval between the time gravity center of the first exposure period and the time gravity center of the second exposure period, and the interval between the time gravity center of the first frame period and the time gravity center of the second frame period are equal.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an imaging apparatus, an imaging system, and a driving method of the imaging apparatus.

  In recent years, CMOS image sensors having a global electronic shutter function have been proposed. Patent Documents 1 and 2 describe an imaging apparatus having a global electronic shutter function. Such an image pickup apparatus has an advantage that the subject image is not easily distorted even when shooting a fast-moving subject.

JP 2004-111590 A JP 2006-246450 A

  In moving image shooting using an image pickup apparatus having a global electronic shutter function, there is a case where a function of shooting with changing an exposure period for each frame is required in order to cope with a change in luminance of a shooting scene. In such a case, since the interval between the centers of the exposure periods of the frames is not constant, image quality deterioration called jerkiness in which the motion of a moving subject becomes unnatural may occur.

  The present invention has been made in view of the above-described problems, and enables an image pickup apparatus having a global electronic shutter function to shoot a moving image with good image quality even when the exposure time is changed for each frame. For the purpose.

  According to an aspect of the present invention, a photoelectric conversion unit that generates charge according to incident light, a holding unit that holds the charge, an amplification transistor that outputs a signal based on the charge, and the photoelectric conversion unit A plurality of pixels each having a first transfer transistor that transfers the charge to the holding unit and a second transfer transistor that transfers the charge from the holding unit to the amplification transistor constitute a moving image In a first frame period of a plurality of frame periods for acquiring a plurality of images, charges generated in a first exposure period are accumulated, and in a second frame period subsequent to the first frame period, Charges generated in a second exposure period that is different in length from the first exposure period are accumulated, and an interval between the time centroid of the first exposure period and the time centroid of the second exposure period; Said Time center of the frame period and the time center interval of the second frame period the imaging device is provided, wherein the same.

  According to another aspect of the present invention, a photoelectric conversion unit that generates charge according to incident light, a holding unit that holds the charge, an amplification transistor that outputs a signal based on the charge, and the photoelectric conversion unit A plurality of pixels each having a first transfer transistor that transfers the charge to the holding unit and a second transfer transistor that transfers the charge from the holding unit to the amplification transistor constitute a moving image In the first frame period of the plurality of frame periods for acquiring a plurality of images, the charge generated in the first exposure period is accumulated, and a plurality of accumulation operations for accumulating the charges generated in a predetermined period are performed. And the plurality of accumulation operations include at least a first accumulation operation and a second accumulation operation that are different from each other in the predetermined period, and the plurality of accumulation operations are performed during the predetermined period. Imaging apparatus is provided which center of gravity is characterized by a constant distance.

  According to another aspect of the present invention, a photoelectric conversion unit that accumulates electric charge according to incident light, a holding unit that holds the electric charge, an amplification transistor that outputs a signal based on the electric charge, and the photoelectric conversion unit A driving method of an imaging device having a plurality of pixels, each of which includes a first transfer transistor that transfers the charge to the holding unit and a second transfer transistor that transfers the charge from the holding unit to the amplification transistor. In the first frame period of the plurality of frame periods for acquiring the plurality of images constituting the moving image, the charge generated in the first exposure period is accumulated, and the next frame period after the first frame period is stored. In the second frame period, charges generated in a second exposure period that is different in length from the first exposure period are accumulated, and the time centroid of the first exposure period and the second exposure period are accumulated. of The spacing and between the center of gravity, the driving method of the imaging apparatus, characterized in that equal to the spacing of the time center of the first time center and a second frame period of the frame period is provided.

  According to the present invention, in an imaging device having a global electronic shutter function, it is possible to shoot a moving image with good image quality even when the exposure time is changed for each frame.

1 is a block diagram illustrating a schematic configuration of an imaging apparatus according to a first embodiment. It is a figure showing the equivalent circuit of the pixel contained in the imaging device concerning a 1st embodiment. It is a timing diagram which shows the operation timing of the imaging device which concerns on 1st Embodiment. It is a schematic diagram which shows the read-out operation | movement in each flame | frame concerning 1st Embodiment. It is a timing diagram which shows the operation timing of the imaging device which concerns on 2nd Embodiment. It is a schematic diagram which shows the read-out operation | movement in each flame | frame concerning 2nd Embodiment. It is a timing diagram which shows the operation timing of the imaging device which concerns on the modification of 2nd Embodiment. It is a schematic diagram which shows the read-out operation | movement in each flame | frame which concerns on the modification of 2nd Embodiment. It is a timing diagram which shows the operation timing of the imaging device which concerns on 3rd Embodiment. It is a schematic diagram which shows the read-out operation | movement in each flame | frame concerning 3rd Embodiment. It is a timing diagram which shows the operation timing of the imaging device which concerns on 4th Embodiment. It is a schematic diagram which shows the read-out operation | movement in each flame | frame concerning 4th Embodiment. It is a timing diagram which shows the operation timing of the imaging device which concerns on 5th Embodiment. It is a schematic diagram which shows the read-out operation | movement in each flame | frame concerning 5th Embodiment. It is a timing diagram which shows the operation timing of the imaging device which concerns on 6th Embodiment. It is a schematic diagram which shows the read-out operation | movement in each flame | frame concerning 6th Embodiment. It is a timing diagram which shows the operation timing of the imaging device which concerns on the modification of 6th Embodiment. It is a schematic diagram which shows the read-out operation | movement in each flame | frame which concerns on the modification of 6th Embodiment. It is a block diagram of the imaging system concerning a 7th embodiment.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram illustrating a schematic configuration of the imaging apparatus according to the present embodiment. The imaging apparatus includes a pixel array 100, a vertical scanning circuit 101, a column amplification circuit 102, a horizontal scanning circuit 103, an output circuit 104, and a control circuit 105. The pixel array 100 includes a plurality of pixels 20 arranged in an XY matrix. The vertical scanning circuit 101 supplies a control signal for controlling the transistor of the pixel 20 to be on (conductive state) or off (non-conductive state). For the vertical scanning circuit 101, a logic circuit such as a shift register or an address decoder can be used. A column signal line 8 is provided in each column of the pixels 20, and a signal from the pixel 20 is read out to the column signal line 8 for each column. The column amplifier circuit 102 amplifies the pixel signal output to the column signal line 8 and performs correlated double sampling processing based on the signal at reset and the signal at photoelectric conversion. The horizontal scanning circuit 103 supplies a switch connected to the amplifier of the column amplifier circuit 102 and a control signal for controlling the switch on or off. The output circuit 104 includes a buffer amplifier, a differential amplifier, and the like, and outputs a pixel signal from the column amplifier circuit 102 to a signal processing unit outside the imaging apparatus. Note that an AD conversion unit may be provided in the imaging apparatus to output a digital image signal.

  FIG. 2 shows an equivalent circuit of the pixel 20 in the imaging apparatus according to the present embodiment. FIG. 2 shows nine pixels 20 of 3 rows × 3 columns among the plurality of pixels 20 two-dimensionally arranged in the row direction and the column direction. However, the imaging device has more pixels 20. doing.

  Each of the plurality of pixels 20 includes a photoelectric conversion unit 1, a holding unit 2, a first transfer transistor 4, a second transfer transistor 5, an overflow transistor 6, a selection transistor 7, a reset transistor 9, and an amplification transistor 10.

  The photoelectric conversion unit 1 photoelectrically converts incident light and accumulates photoelectrically converted charges. When the first transfer transistor 4 is turned on, the charge of the photoelectric conversion unit 1 is transferred to the holding unit 2. The holding unit 2 holds the charge transferred from the photoelectric conversion unit 1. The holding unit 2 is expressed as a capacitor having one node connected to the ground terminal 11 on the circuit diagram.

  When the second transfer transistor 5 is turned on, the charge of the holding unit 2 is transferred to the floating diffusion 3 that is an input node (gate node) of the amplification transistor 10. The amplification transistor 10 forms a source follower, and outputs a signal based on the voltage of the floating diffusion 3 to the column signal line 8 via the selection transistor 7. A constant current source 16 is connected to the column signal line 8. The reset transistor 9 is turned on to reset the voltage of the floating diffusion 3 with the voltage of the power supply terminal 12. A voltage output to the column signal line 8 of the p-th column is assumed to be Vout (p). The overflow transistor 6 discharges the electric charge generated in the photoelectric conversion unit 1 when turned on to a node (overflow drain) having the voltage of the power supply terminal 12.

  A common control signal is supplied from the vertical scanning circuit 101 to the pixels 20 in the same row. In other words, the control signals pTX1 (m), pTX2 (m), pSEL (m), and the control signals pTX1 (m), pTX2 (m), pSEL (m), Each pRES (m) is supplied. The overflow transistor 6 is supplied with a control signal pOFG (m). These transistors are turned on when the control signal is at a high level and turned off when the control signal is at a low level. Further, these transistors can be constituted by, for example, MOS transistors.

  With such a configuration, it is possible to perform an imaging operation, that is, a global electronic shutter operation, in which the periods of photoelectric conversion between the plurality of pixels 20 coincide. In addition, since the overflow transistor 6 is connected to the photoelectric conversion unit 1, charges generated in the photoelectric conversion unit 1 while the holding unit 2 holds charges can be accumulated in the photoelectric conversion unit 1. . Alternatively, the charges generated in the photoelectric conversion unit 1 can be discharged through the overflow transistor 6 without accumulating in the photoelectric conversion unit 1. Thereby, the exposure time can be controlled.

  The imaging device of this embodiment can be used for moving image shooting. When performing moving image shooting, the imaging apparatus acquires a plurality of images constituting the moving image every predetermined period (frame period).

  Note that exposure means that charges generated in the photoelectric conversion unit 1 by photoelectric conversion are accumulated or held as signals. The exposure period means a period from the start to the end of exposure in each frame period. The exposure time means the length of the exposure period.

  Next, a method for driving the imaging apparatus according to the first embodiment will be described with reference to FIGS. FIG. 3 is a timing diagram illustrating operation timings of the imaging apparatus according to the first embodiment. FIG. 4 is a schematic diagram showing a read operation in each frame according to the first embodiment. 3 and 4 illustrate the imaging operation from the nth frame to the (n + 2) th frame with different exposure times in a period (frame period) in which each of a plurality of still images constituting a moving image is captured. .

  As shown in FIG. 4, the exposure time of the (n + 1) th frame is shorter than the exposure time of the nth frame, and the exposure time of the (n + 2) th frame is shorter than the exposure time of the (n + 1) th frame. FIG. 3 shows control signals pTX1, pTX2, and pOFG supplied from the vertical scanning circuit 101 for the pixels in the m to m + 2th rows.

  In a period before time T1, the control signal pTX2 of each row sequentially becomes high level. As a result, the charges accumulated in the period of the frame before the n-th frame (the (n−1) th frame not shown) are sequentially transferred from the holding unit 2 to the floating diffusion 3 and the signal is read out. Time T1 is the time when this reading is completed. In FIGS. 3 and 4, the operation of the frame before the nth frame is indicated by a broken line.

  The exposure of the nth frame in the present embodiment is performed during a part or all of the period between time T1 and time T2. At the start time of the exposure period (time T1 in the nth frame), the control signal pTX1 is at a low level, and the first transfer transistor 4 is kept off. At the same time, the control signal pOFG changes from the high level to the low level at the same time in all rows, and the overflow transistors 6 are simultaneously turned on from off in all the pixels. When the overflow transistor 6 is turned off, charge accumulation in the photoelectric conversion unit 1 starts.

  In the present specification, “simultaneous” is not limited to the case where the time is strictly the same, but includes the case where the operation of the imaging apparatus is substantially the same. For example, when the operation time difference occurs due to the delay time of the control signal, etc., the case where a slight operation time difference is given within a range that does not substantially cause an operation for design reasons, etc. can be included in “simultaneous”. . Further, even in the case where a plurality of signals are shown to change at the same time in a timing diagram or the like, it is not limited to the case where the signals are strictly at the same time as described above. It is not intended to exclude cases where there is a time difference.

  Thereafter, the control signal pTX1 is changed from the low level to the high level at the same time in all rows, and the first transfer transistor 4 is simultaneously turned on from off in all the pixels. Thereby, the electric charge accumulated in the photoelectric conversion unit 1 is transferred to the holding unit 2. Thereafter, the control signal pTX1 becomes the low level simultaneously for all the rows. This time is the end time of the exposure period (time T2 in the nth frame).

  After the time when the control signal pTX1 becomes the low level at the same time for all the rows, the control signal pOFG changes from the low level to the high level at the same time for all the rows, and the overflow transistors 6 are simultaneously turned on from all the pixels off. Thereafter, the charge generated in the photoelectric conversion unit 1 is discharged to the overflow drain via the overflow transistor 6. In addition, from time T2, the control signal pTX2 of each row sequentially becomes a high level. As a result, the charges accumulated during the exposure period of the nth frame are sequentially transferred from the holding unit 2 to the floating diffusion 3 and the signal is read out.

  In a period from time T2 to time T3 when the first period elapses, the first transfer transistor 4 is kept off. In the present embodiment, the first transfer transistors 4 of all the pixels 20 are kept off. However, in at least one pixel, the first transfer transistor 4 only needs to be kept off from time T2 to time T3.

  Further, during a period from time T2 to time T3 when the first period elapses (first period in the (n + 1) th frame), the control signal pOFG is at a high level, and the overflow transistor 6 is kept on. In the present embodiment, it is assumed that the overflow transistors 6 of all the pixels 20 are kept on in the first period. However, in at least one pixel, the overflow transistor 6 only needs to be kept on from time T2 to time T3. The electric charge generated in the first period is discharged to the overflow drain through the overflow transistor 6.

  On the other hand, in the first period in the (n + 1) th frame, the holding unit 2 holds charges generated in the nth frame. During this period, the charges held in the holding unit 2 are sequentially transferred to the floating diffusion 3. The voltage of the floating diffusion 3 changes according to the capacity of the floating diffusion 3 and the amount of charge transferred. The amplification transistor 10 sequentially outputs a signal based on the voltage of the floating diffusion 3 to the column signal line 8. This readout operation is performed in each of the pixels from the first row to the last row. Time T3 is a time corresponding to time T1 of the previous frame, and is a time at which the operation of sequentially reading out the charges transferred to the holding unit 2 in the nth frame to the floating diffusion 3 is completed.

As described above, the exposure period of the nth frame is a period from time T1 to time T2. The time centroid T (n) in the exposure period of the nth frame is given by the following equation (1).
T (n) = (T1 + T2) / 2 (1)

  Next, the (n + 1) th frame whose exposure period is shorter than the nth frame will be described. At time (T3 + A) after time T3 by time A, the control signal pOFG becomes low level, and the overflow transistors 6 are simultaneously turned on from all pixels. As a result, charge accumulation in the photoelectric conversion unit 1 starts. That is, time (T3 + A) is the exposure start time of the (n + 1) th frame.

  Thereafter, the control signal pTX1 becomes a high level, and the first transfer transistor 4 is turned on at the same time for all the pixels, whereby transfer of charges from the photoelectric conversion unit 1 to the holding unit 2 is started. Thereafter, at a time (T4-A) that is a time A before time T4, the control signal pTX1 goes to a low level, and the first transfer transistor 4 is simultaneously turned on from all pixels. This time (T4-A) is the exposure end time of the (n + 1) th frame. Following this, the control signal pOFG becomes the high level at the same time for all the pixels, and the overflow transistor 6 is turned on from all the pixels at the same time.

As described above, the exposure period of the (n + 1) th frame is a period from time (T3 + A) to time (T4-A). The time centroid T (n + 1) in the exposure period of the (n + 1) th frame is given by the following equation (2).
T (n + 1) = {(T3 + A) + (T4-A)} / 2 = (T3 + T4) / 2 (2)

  Here, time T3 is the time after the lapse of one frame period at time T1, and time T4 is the time after the lapse of one frame period at time T2. Therefore, the time interval between the time centroid T (n + 1) in the exposure period of the (n + 1) th frame and the time centroid T (n) in the exposure period of the nth frame corresponds to the length of one frame period. Therefore, the positions of the time centroids of the exposure period in the nth frame and the (n + 1) th frame are aligned with respect to the frame period to which each time centroid belongs. The length of one frame period can be defined as, for example, the interval between the time centroid of the nth frame and the time centroid of the (n + 1) th frame. Alternatively, the length of the frame period can be defined as the length of the period from the start time T2 to the end time T4 of the (n + 1) th frame.

  In other words, it can be explained as follows. The exposure period of the first frame period is the first exposure period, and the exposure period of the second frame is the second exposure period. Here, it is assumed that the first frame period corresponds to the nth frame of the present embodiment, and the second frame period corresponds to the (n + 1) th frame of the present embodiment. At this time, the interval between the time centroid of the first exposure period and the time centroid of the second exposure period is the length of one frame period (for example, the time centroid of the first frame period and the time of the second frame period). Equivalent to the center of gravity). In addition, the same relationship is obtained when the first frame period is read as corresponding to the (n + 1) th frame of the present embodiment, and the second frame period corresponds to the (n + 2) th frame of the present embodiment. . When the above relationship is sequentially applied to an arbitrary n in this way, the intervals between the time centroids of the exposure periods between adjacent frames all correspond to the length of one frame period and become a constant value. From another viewpoint, an accumulation operation for accumulating charges generated in a predetermined exposure period is performed a plurality of times. The multiple accumulation operations include accumulation operations having different exposure periods, for example, the exposure period of the nth frame and the exposure period of the (n + 1) th frame in FIG. In these multiple accumulation operations, the time centroid of the exposure period is a constant interval. This constant interval is typically equal to the length of the frame period. For example, when shooting a moving image of 60 fps, the certain interval is 1/60 second.

  Next, the effect of this embodiment will be described with reference to FIG.

  FIG. 4 shows an exposure period in each frame, a period during which the photoelectric conversion unit 1 accumulates charges (accumulation period of the photoelectric conversion unit), and a period during which the holding unit 2 holds charges (holding of the holding unit). Period). In the section “Photoelectric Conversion Unit Accumulation Period”, “PD (n)” or the like is displayed during a period in which charge generation and accumulation are performed in each photoelectric conversion unit 1. Further, “OFD” is displayed during the period in which charge is discharged from the photoelectric conversion unit 1 to the overflow drain via the overflow transistor 6, and the frame is hatched. In the term “holding period of the holding unit”, the charge is transferred from the photoelectric conversion unit 1 to the holding unit 2, and “MEM (n)” or the like is displayed during the period in which the holding unit 2 holds the charge. Yes. As shown in FIG. 4, in the first period, a plurality of pixels are read out sequentially. Note that the read operation is an operation including transfer of charges from the holding unit 2 to the floating diffusion 3 by the second transfer transistor 5 and output of a signal from the amplification transistor 10.

  In the present embodiment, the exposure periods are different from each other in the three frame periods from the nth frame to the n + 2th frame. However, by operating the imaging apparatus at the operation timing as shown in FIG. 3, the position of the time centroid of the exposure period in each frame can be aligned with the frame period. In other words, the interval of the time centroid of the exposure period between adjacent frames is constant. As a result, in moving image shooting, image quality deterioration called jerkiness in which the motion of a moving subject becomes unnatural is less likely to occur. Therefore, in an imaging device having a global electronic shutter function, it is possible to shoot a moving image with good image quality even when the exposure time is changed for each frame.

[Second Embodiment]
The second embodiment will be described with reference to FIGS. This embodiment is different from the first embodiment in the driving method of the first transfer transistor 4. Since the circuit configuration of the image pickup apparatus and the operation of other transistors are the same as those in the first embodiment, description of common parts is omitted or simplified.

  A method for driving the imaging apparatus according to the second embodiment will be described with reference to FIGS. 5 and 6. FIG. 5 is a timing diagram illustrating operation timings of the imaging apparatus according to the second embodiment. FIG. 6 is a schematic diagram showing a read operation in each frame according to the second embodiment.

  In the present embodiment, at a time near the middle of the exposure period between time T1 and time T2, the control signal pTX1 once temporarily temporarily goes to the high level at the same time, and the plurality of first transfer transistors 4 are temporarily turned on simultaneously. Turned on. As a result, all the charges accumulated in the photoelectric conversion unit 1 during the period from the time T1 to the time when the control signal pTX1 becomes high level are transferred to the holding unit 2. Thereafter, the control signal pTX1 again becomes a low level, the plurality of first transfer transistors 4 are simultaneously turned off, and charges are accumulated in the photoelectric conversion unit 1 again. That is, in the present embodiment, in the first exposure period, the charge of the photoelectric conversion unit 1 is transferred to the holding unit 2 twice in the vicinity of the middle of the exposure period and the exposure end time. Different from form.

  Then, the effect of this embodiment is demonstrated. In the driving method of the present embodiment, the number of times charges are transferred from the photoelectric conversion unit 1 to the holding unit 2 within the exposure period of each frame is different from that of the first embodiment. That is, in this embodiment, the electric charge generated in the photoelectric conversion unit 1 in one exposure period is divided into two times and transferred to the holding unit 2. Therefore, the amount of charge that can be accumulated in one exposure period can be made twice the amount of saturation charge of the photoelectric conversion unit 1, and the amount of saturation charge of the pixel 20 can be substantially increased. As a result, an effect of improving the dynamic range can be obtained.

  Next, a modification of this embodiment will be described. FIG. 7 is a timing diagram illustrating the operation timing of the imaging apparatus according to the modification of the second embodiment. FIG. 8 is a schematic diagram showing a read operation in each frame according to a modification of the second embodiment. In this modification, the electric charge of the photoelectric conversion unit 1 generated in one exposure period is transferred in four times. In this case, the amount of charge that can be accumulated in one exposure period can be four times the saturation charge amount of the photoelectric conversion unit 1, and the saturation charge amount of the pixel 20 can be substantially increased. In other words, the number of transfers is not limited to twice, but can be any number of times, that is, two or more times. As described above, in this embodiment, the operation in which the plurality of first transfer transistors 4 are simultaneously turned on from off and then turned off again is repeated a plurality of times. When the number of transfers is a plurality of times, the time at which the first transfer transistor 4 is turned off at the end of the plurality of operations is the end time of the exposure period.

  In the present embodiment, in addition to the effects described in the first embodiment, the charge generated in the photoelectric conversion unit 1 during one exposure period is transferred to the holding unit 2 in a plurality of times, thereby increasing the dynamic range in moving image shooting. Can be improved.

  The timing at which the control signal pTX1 becomes high level and the first transfer transistor 4 is turned on, or the timing at which the control signal pTX1 becomes low level and the first transfer transistor 4 is turned off is at a constant interval. More preferably. This is because the saturation charge amount of the photoelectric conversion unit 1 can be utilized to the maximum, and the dynamic range is further improved.

[Third Embodiment]
A third embodiment will be described with reference to FIGS. 9 and 10. This embodiment is different from the first embodiment in the driving method of the first transfer transistor 4. Since the circuit configuration of the image pickup apparatus and the operation of other transistors are the same as those in the first embodiment, description of common parts is omitted or simplified. FIG. 9 is a timing diagram illustrating operation timings of the imaging apparatus according to the third embodiment. FIG. 10 is a schematic diagram showing a read operation in each frame according to the third embodiment.

  This embodiment is different from the first embodiment in that the control signal pTX1 becomes high level and the first transfer transistor 4 is turned on at the exposure start time (time when the control signal pOFG becomes low level). Yes. Thereafter, the first transfer transistor 4 is kept on until the first transfer transistor 4 is turned off to complete the exposure. This operation is performed simultaneously for all pixels. Thereby, the charge generated by the photoelectric conversion unit 1 immediately after the start of the exposure period is transferred to the holding unit 2 immediately after generation.

  Then, the effect of this embodiment is demonstrated. In the driving method of the present embodiment, the period during which the holding unit 2 holds electric charges in each frame is different from that in the first embodiment. In the present embodiment, the charge generated in the photoelectric conversion unit 1 immediately after the start of the exposure period is transferred to the holding unit 2 immediately after generation. Thereby, it can be considered that the saturation charge amount of the photoelectric conversion unit 1 is substantially sufficiently large, and an effect of improving the dynamic range is obtained.

  In the present embodiment, in addition to the effects described in the first embodiment, the charge generated in the photoelectric conversion unit 1 is immediately transferred to the holding unit 2 immediately after the start of the exposure period. Range can be improved.

[Fourth Embodiment]
A fourth embodiment will be described with reference to FIGS. 11 and 12. This embodiment is different from the first embodiment in the driving method of the first transfer transistor 4 and the overflow transistor 6. Since the circuit configuration of the image pickup apparatus and the operation of other transistors are the same as those in the first embodiment, description of common parts is omitted or simplified. FIG. 11 is a timing diagram illustrating operation timings of the imaging apparatus according to the fourth embodiment. FIG. 12 is a schematic diagram showing a read operation in each frame according to the fourth embodiment.

  First, description will be made with reference to the exposure period of the nth frame. In the present embodiment, the same operation from the exposure start operation to the exposure end operation similar to that in the first embodiment is intermittently repeated four times during the exposure period between time T1 and time T2. In other words, one exposure period is divided into a plurality. This embodiment is different from the first embodiment in this point. That is, in the exposure period from time T1 to time T2, only the charge generated during the time between the exposure start operation and the exposure end operation is transferred to the holding unit 2, and the charge in the other period overflows via the overflow transistor 6. It is discharged to the drain. This transfer and discharge are repeated intermittently. As described above, in this embodiment, since exposure is intermittently performed a plurality of times, a part of the exposure period contributes to the output signal among the charges generated by the photoelectric conversion in the photoelectric conversion unit 1. It only occurs in time (referred to as photoelectric conversion time).

  In the present embodiment, the exposure start time is the time at which the control signal pOFG first becomes low level in a certain frame period, and the overflow transistors 6 are simultaneously turned on from all pixels. The exposure end time is the time when the control signal pTX1 finally becomes low level and the first transfer transistor 4 is simultaneously turned on from all pixels.

  Next, a method for shortening the photoelectric conversion time will be described with reference to the exposure period of the (n + 1) th frame. In the (n + 1) th frame, the low level period of the control signal pOFG is short and the high level period is long with respect to the exposure of the nth frame. As a result, the time for discharging the charges is lengthened and the photoelectric conversion time is shortened. Even in this case, the position of the time centroid T (n + 1) with respect to the frame period is aligned with the time centroid T (n). Therefore, as in the first embodiment, the intervals between the time centers of the exposure periods between adjacent frames all correspond to the length of one frame period and are constant values.

  Next, another method for shortening the photoelectric conversion time will be described with reference to the exposure period of the (n + 2) th frame. In the (n + 2) th frame, both the period during which the control signal pOFG is at a low level and the period during which the control signal pOFG is at a low level are shorter than the exposure at the nth frame. This shortens the exposure period. Also in this case, the position of the time centroid T (n + 2) with respect to the frame period is aligned with the time centroid T (n).

  Then, the effect of this embodiment is demonstrated. When shooting a moving image including a subject with high brightness and flickering phenomenon (flicker), image quality degradation due to loss of signal charge may occur in some frames. Examples of such a subject include a display using a cathode ray tube, a fluorescent lamp, and the like. The same deterioration can occur in a subject that emits light with high brightness in a very short time such as flash light. If the exposure period is shortened, the deterioration of image quality due to the loss of signal charge can become more remarkable. In the driving method of this embodiment, accumulation and transfer of charges contributing to the output signal are performed intermittently. Therefore, the occurrence of signal charge loss within one frame can be reduced.

  In the present embodiment, in addition to the effects described in the first embodiment, the accumulation and transfer of charges contributing to the output signal are intermittently performed, thereby reducing the image quality due to the loss of signal charges in moving image shooting. Can be reduced.

[Fifth Embodiment]
The fifth embodiment will be described with reference to FIGS. 13 and 14. This embodiment is different from the first embodiment in the driving method of the first transfer transistor 4 and the overflow transistor 6. Since the circuit configuration of the image pickup apparatus and the operation of other transistors are the same as those in the first embodiment, description of common parts is omitted or simplified. FIG. 13 is a timing diagram illustrating operation timings of the imaging apparatus according to the fifth embodiment. FIG. 14 is a schematic diagram showing a read operation in each frame according to the fifth embodiment.

  In the driving method of the first embodiment, the first period in which the charge held in the holding unit 2 in the previous frame is transferred to the floating diffusion 3 and read out is not included in the exposure period. However, in the driving method of the present embodiment, the exposure period of the frame starts before time T1 when the operation of sequentially reading out the charges held in the holding unit 2 in the previous frame is completed.

  In the first period from time T0 to time T1 of the nth frame, the control signal pTX2 of each row is sequentially set to the high level. As a result, the charges accumulated in the frame before the nth frame (the (n−1) th frame not shown) are sequentially transferred from the holding unit 2 to the floating diffusion 3 and the signal is read out. In parallel with this, at time T0, the control signal pOFG of each row becomes low level, and the overflow transistor 6 is turned off. By this operation, the exposure period of the nth frame is started. With this driving method, one exposure period can be extended to a maximum of one frame period.

  For the (n + 1) th frame whose exposure period is shorter than that of the nth frame, the position of the center of gravity of the exposure period with respect to the frame period is set to be the same as in the first embodiment. That is, the time centroid T (n + 1) in the exposure period of the (n + 1) th frame is set to be the time after the lapse of one frame period from the time centroid T (n) in the exposure period of the nth frame. Thereby, the same effect as the first embodiment can be obtained.

  In the present embodiment, in addition to the effects described in the first embodiment, the exposure period of the frame starts before the time when the operation of sequentially reading the charges held in the holding unit 2 in the previous frame is completed. By doing so, the exposure period can be made longer.

[Sixth Embodiment]
The sixth embodiment will be described with reference to FIGS. 15 to 18. This embodiment is different from the first embodiment in the driving method of the first transfer transistor 4 and the overflow transistor 6. Since the circuit configuration of the image pickup apparatus and the operation of other transistors are the same as those in the first embodiment, description of common parts is omitted or simplified.

  A driving method of the imaging apparatus according to the sixth embodiment will be described with reference to FIGS. 15 and 16. FIG. 15 is a timing diagram illustrating operation timings of the imaging apparatus according to the sixth embodiment. FIG. 16 is a schematic diagram showing a read operation in each frame according to the sixth embodiment.

  In the present embodiment, at a time near the middle of the exposure period between time T0 and time T2, the control signal pTX1 temporarily becomes a high level once, and the first transfer transistor 4 is temporarily turned on from off. . As a result, all the charges accumulated in the photoelectric conversion unit 1 are transferred to the holding unit 2 during the period from the time T0 to the time when the control signal pTX1 becomes high level. Thereafter, the control signal pTX1 becomes low level again, the first transfer transistor 4 is turned off, and charges are accumulated in the photoelectric conversion unit 1 again. That is, in the present embodiment, as in the second embodiment, in one exposure period, the charge of the photoelectric conversion unit 1 is transferred to the holding unit 2 over the middle of the exposure period and twice at the exposure end time. Transferred. Further, in this embodiment, the transfer from the photoelectric conversion unit 1 to the holding unit 2 at a time near the middle of the exposure period is after time T1 when the sequential reading of the charges held in the holding unit 2 in the previous frame is completed. To be implemented.

  Then, the effect of this embodiment is demonstrated. In the present embodiment, as in the second embodiment, charges generated in the photoelectric conversion unit 1 in one exposure period are transferred to the holding unit 2 in two portions. Therefore, the amount of charge that can be accumulated in one exposure period can be made twice the amount of saturation charge of the photoelectric conversion unit 1, and the amount of saturation charge of the pixel 20 can be substantially increased. As a result, an effect of improving the dynamic range can be obtained. Further, as in the fifth embodiment, the exposure period of the frame starts before the time when the operation of sequentially reading the charges held in the holding unit 2 in the previous frame is completed. Can be made longer.

  Next, a modification of this embodiment will be described. FIG. 17 is a timing diagram illustrating operation timings of the imaging apparatus according to the modified example of the sixth embodiment. FIG. 18 is a schematic diagram showing a read operation in each frame according to the modification of the sixth embodiment. In this modification, the electric charge of the photoelectric conversion unit 1 generated in one exposure period is transferred in four times. In this case, the amount of charge that can be accumulated in one exposure period can be four times the saturation charge amount of the photoelectric conversion unit 1, and the saturation charge amount of the pixel 20 can be substantially increased. Thus, in the present embodiment, the number of transfers is not limited to two, and can be any number of times equal to or greater than two. Further, in the present modification, the first one of the four transfers is configured such that the exposure of the frame is performed in parallel with the reading of the charge of the previous frame, as in the fifth embodiment. It has become. Therefore, the exposure period can be made longer.

  In the present embodiment, in addition to the effects described in the first embodiment, the charge generated in the photoelectric conversion unit 1 during one exposure period is transferred to the holding unit 2 in a plurality of times, thereby increasing the dynamic range in moving image shooting. Can be improved. Furthermore, in this embodiment, since the exposure period of the frame starts before the time when the operation of sequentially reading the charges held in the holding unit 2 in the previous frame is completed, the exposure period is made longer. can do.

[Seventh Embodiment]
An imaging system according to the seventh embodiment will be described. The imaging devices of the above-described embodiments can be applied to various imaging systems. Examples of the imaging system include a digital still camera, a digital camcorder, a copying machine, a fax machine, a mobile phone, an in-vehicle camera, and an observation satellite. A camera module including an optical system such as a lens and an imaging device is also included in the imaging system. FIG. 19 shows a block diagram of a digital still camera as an example of an imaging system.

  The imaging system includes a barrier 1001 for protecting the lens 1002, a lens 1002 for forming an optical image of a subject on the imaging device 1004, a diaphragm 1003 for changing the amount of light passing through the lens 1002, and any of the above-described embodiments. The imaging device 1004 is included. In addition, the imaging system includes a signal processing unit 1007 that processes an output signal output from the imaging device 1004. The signal processing unit 1007 generates an image based on a signal output from the imaging device 1004. Specifically, the signal processing unit 1007 performs various corrections, data compression, and the like on the signal output from the imaging device 1004 and outputs image data.

  The imaging system further includes a timing generation unit 1008 that outputs various timing signals to the imaging apparatus 1004 and the signal processing unit 1007, and a control unit 1009 that controls the entire imaging system. The imaging system further includes a memory unit 1010 for temporarily storing image data, a recording medium 1012 such as a semiconductor memory for holding image data, and a recording medium interface (I / F) part 1011 is included. The recording medium 1012 may be built in the imaging system or may be detachable. Further, the imaging system includes an external interface (I / F) unit 1013 for communicating with an external computer or the like.

  Here, the timing signal or the like may be input from the outside of the imaging system, and the imaging system only needs to include at least the imaging device 1004 and the signal processing unit 1007 that processes the imaging signal output from the imaging device 1004.

  As described above, the imaging system of the present embodiment can perform an imaging operation by applying the imaging device 1004 of any of the above-described embodiments.

  Embodiments to which the present invention can be applied are not limited to the above-described embodiments. For example, an embodiment in which a part of the configuration of any of the embodiments is added to another embodiment, or an embodiment in which a part of the configuration of another embodiment is replaced is also an embodiment to which the present invention can be applied. Should be understood.

  The imaging system shown in the seventh embodiment shows an example of an imaging system to which the imaging apparatus of the present invention can be applied. The imaging system to which the imaging apparatus of the present invention can be applied is shown in FIG. The configuration is not limited.

DESCRIPTION OF SYMBOLS 1 Photoelectric conversion part 2 Holding | maintenance part 4 1st transfer transistor 5 2nd transfer transistor 6 Overflow transistor 10 Amplification transistor 20 Pixel

Claims (16)

A photoelectric conversion unit that generates a charge in response to incident light; a holding unit that holds the charge; an amplification transistor that outputs a signal based on the charge; and a first unit that transfers the charge from the photoelectric conversion unit to the holding unit. A plurality of pixels each having one transfer transistor and a second transfer transistor that transfers the charge from the holding unit to the amplification transistor;
In the first frame period of the plurality of frame periods for acquiring a plurality of images constituting the moving image, the charge generated in the first exposure period is accumulated,
In the second frame period subsequent to the first frame period, charges generated in a second exposure period having a different period length from the first exposure period are accumulated,
The time centroid of the first exposure period and the time centroid of the second exposure period are equal to the time centroid of the first frame period and the time centroid of the second frame period. An imaging device. In the first frame period, the first transfer transistor simultaneously transfers the charges generated in the first exposure period from the photoelectric conversion unit to the holding unit in the plurality of pixels.
In the second frame period, the second transfer transistor sequentially transfers the charge generated in the first exposure period from the holding unit to the amplification transistor in the plurality of pixels.
2. The imaging according to claim 1, wherein, in the second frame period, the amplification transistor outputs a signal based on the charge accumulated in the first exposure period in order in the plurality of pixels. apparatus. Each of the plurality of pixels further includes an overflow transistor that discharges the charge from the photoelectric conversion unit,
3. The imaging apparatus according to claim 1, wherein the first exposure period or the second exposure period starts when the overflow transistors of the plurality of pixels are simultaneously turned from on to off.   4. The first exposure period or the second exposure period ends when the first transfer transistors of the plurality of pixels are simultaneously turned on and off. The imaging apparatus according to item 1. In each of the plurality of pixels, the operation in which the first transfer transistor is turned on from off and then turned off again is repeated a plurality of times, and thus occurs in the first exposure period or the second exposure period. The charge is transferred from the photoelectric conversion unit to the holding unit a plurality of times,
The first exposure period or the second exposure period is ended by an operation that is turned off at the end of the plurality of operations of the first transfer transistor. Item 4. The imaging device according to any one of Items 1 to 3.   6. The operation according to claim 5, wherein, in a plurality of operations in which the first transfer transistor is turned on from off and then turned off again, the timing at which the first transfer transistor is turned off is a constant interval. The imaging device described. After the first exposure period or the second exposure period starts, the first transfer transistors of the plurality of pixels are turned on simultaneously from off,
Thereafter, the first transfer transistor of the plurality of pixels is turned from on to off, so that the first exposure period or the second exposure period ends. The imaging apparatus according to claim 3, wherein the transfer transistor is kept on. Each of the plurality of pixels further includes an overflow transistor that discharges the charge from the photoelectric conversion unit,
The operation in which the overflow transistors of the plurality of pixels are simultaneously turned on and off and then turned on again is repeated a plurality of times, whereby one exposure period is divided into a plurality of times,
3. The imaging according to claim 1, wherein the first exposure period or the second exposure period is started by an operation of turning off first of the plurality of operations of the overflow transistor. apparatus. In a part of the first exposure period, in parallel with the operation in which the photoelectric conversion units of the plurality of pixels accumulate the charges generated by incident light,
In order in the plurality of pixels, the second transfer transistor transfers the charge held by the holding unit to the amplification transistor,
The imaging device according to any one of claims 1 to 8, wherein the amplification transistor outputs a signal based on the charge in order in the plurality of pixels. A photoelectric conversion unit that generates a charge in response to incident light; a holding unit that holds the charge; an amplification transistor that outputs a signal based on the charge; and a first unit that transfers the charge from the photoelectric conversion unit to the holding unit. A plurality of pixels each having one transfer transistor and a second transfer transistor that transfers the charge from the holding unit to the amplification transistor;
In the first frame period of the plurality of frame periods for acquiring a plurality of images constituting the moving image, the charge generated in the first exposure period is accumulated,
A plurality of accumulation operations for accumulating charges generated in a predetermined period are performed,
The plurality of accumulation operations include at least a first accumulation operation and a second accumulation operation that are different from each other in the predetermined period,
In the plurality of accumulation operations, the time center of gravity of the predetermined period is a constant interval. The imaging apparatus according to claim 10, wherein the time centroid in each of the plurality of accumulation operations is an intermediate time between a start time of the predetermined period and an end time of the predetermined period. The imaging apparatus according to claim 11, wherein the first transfer transistors of the plurality of pixels are simultaneously turned from on to off at the start time. Each of the plurality of pixels further includes an overflow transistor that discharges the charge from the photoelectric conversion unit,
The imaging apparatus according to claim 11, wherein the overflow transistors of the plurality of pixels are simultaneously turned from on to off at the start time. The imaging device according to any one of claims 11 to 13, wherein the first transfer transistors of the plurality of pixels are simultaneously turned from on to off at the end time. The imaging device according to any one of claims 1 to 14,
An imaging system comprising: a signal processing unit that processes a signal output from the imaging device. A photoelectric conversion unit that generates a charge in response to incident light; a holding unit that holds the charge; an amplification transistor that outputs a signal based on the charge; and a first unit that transfers the charge from the photoelectric conversion unit to the holding unit. 1. A method for driving an imaging device having a plurality of pixels, each having one transfer transistor and a second transfer transistor that transfers the charge from the holding unit to the amplification transistor,
In the first frame period of the plurality of frame periods for acquiring a plurality of images constituting the moving image, the charge generated in the first exposure period is accumulated,
In a second frame period subsequent to the first frame period, charges generated in a second exposure period having a different period length from the first exposure period are accumulated,
The time centroid of the first exposure period and the time centroid of the second exposure period are equal to the time centroid of the first frame period and the time centroid of the second frame period. A driving method of the imaging apparatus.

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