JP2009171027A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power consumption compared to the case of fixing the output current value of a constant current source during the read operation of an amplification part at a high current value at all times. <P>SOLUTION: An imaging apparatus includes a plurality of two-dimensionally disposed pixels 31. Each pixel 31 has a photodiode PD for generating and storing signal charges based on the light quantity of incidence light from an object, and an amplification transistor AMP to output pixel signals based on the signal charges to a signal line 34 by a read operation. The imaging apparatus further includes a constant current source 35 for forming a source follower circuit together with the amplification transistor AMP during the read operation of the amplification transistor AMP, and a current control part 36 for variably controlling the output current value of the constant current source 35 during the read operation of the amplification transistor AMP according to supplied control signals ϕA and ϕB. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging device that captures a subject image.

  In a video camera, an electronic still camera, and the like, a CCD type or amplification type solid-state imaging device is used. In such a solid-state imaging device, a plurality of pixels each having a photoelectric conversion unit are arranged in a matrix, and signal charges are generated by the photoelectric conversion unit of each pixel.

  In the amplification type solid-state imaging device, a signal corresponding to the signal charge generated and accumulated in the photoelectric conversion unit of the pixel is output from the pixel by the amplification unit provided in the pixel (Patent Documents 1 and 2 below). In the amplification type solid-state imaging device, a constant current source that forms a source follower circuit together with the amplification unit is provided during the readout operation of the amplification unit, and a pixel signal is output to the signal line by the source follower operation. (Patent Documents 1 and 2 below).

Conventionally, in such an amplification type solid-state imaging device, the output current value of the constant current source is always fixed to the same value during the reading operation of the amplification unit. Note that the amplification type solid-state imaging device disclosed in Patent Document 2 is provided with current limiting means for limiting the current flowing through the constant current source other than during the reading operation of the transistor constituting the amplification unit. Is merely limiting the current of the constant current source except during the read operation of the transistor, and Patent Document 2 discloses that the output current value of the constant current source is variable during the read operation of the amplifying unit. I did not suggest.
Japanese Patent Application Laid-Open No. 11-196331 JP-A-8-18866

  By the way, in the amplification type solid-state imaging device as described above, since a signal line to which a pixel signal is output has a parasitic capacitance or the like, even if the signal on the signal line is changed, it cannot be changed instantaneously. In addition, it changes slowly to some extent according to the time constant of the signal line, and it takes some time for the signal on the signal line to stabilize. Here, the time required for the signal on the signal line to stabilize is referred to as a settling time. The shorter the settling time, the faster the pixel signal can be read out. On the other hand, since the settling time is determined by the time during which the parasitic capacitance of the signal line is charged by the output current from the constant current source, the settling time can be shortened as the output current value of the constant current source is high. . Therefore, the pixel signal can be read at high speed by setting the output current value of the constant current source to a high value.

  However, in the conventional amplification type solid-state imaging device, since the output current value of the constant current source is always fixed to the same value during the reading operation of the amplifying unit, the reading operation of the amplifying unit to read out the pixel signal at high speed If the output current value of the constant current source at the time is set to a high value, the output current value of the constant current source at the time of the read operation of the amplifying unit is always a high current value, which increases the power consumption. End up.

  The present invention has been made in view of such circumstances, and reduces power consumption as compared with the case where the output current value of the constant current source is always fixed to a high current value during the read operation of the amplifying unit. An object of the present invention is to provide an imaging device capable of performing the above.

  In order to solve the above problems, an imaging apparatus according to a first aspect of the present invention generates a signal charge according to the amount of incident light from a subject and stores the signal charge according to the signal charge by a read operation. A constant current source that includes a plurality of pixels each having an amplification unit that outputs a pixel signal to a signal line, and in which the plurality of pixels are two-dimensionally arranged, and forms a source follower circuit together with the amplification unit; A current control unit that variably controls the output current value of the constant current source during the read operation of the amplification unit in accordance with a supplied control signal.

  An imaging apparatus according to a second aspect of the present invention includes, in the first aspect, a control unit that supplies the control signal to the current control unit, wherein the control unit is in a predetermined operation mode and other predetermined In the operation mode, the control signal is supplied to the current control unit so that the output current values of the constant current sources during the read operation of the amplification unit are different from each other.

  An imaging apparatus according to a third aspect of the present invention includes, in the first aspect, a control unit that supplies the control signal to the current control unit, and a photometry unit that performs photometry on the subject, and the control unit includes: Based on the photometric result of the photometry unit during a predetermined operation mode, when the light amount of the incident light is small, compared with the case where the light amount of the incident light is large, The control signal is supplied to the current control unit so that the output current value becomes small.

  An imaging device according to a fourth aspect of the present invention includes, in the first aspect, a control unit that supplies the control signal to the current control unit, and the control unit outputs the pixel signal in a predetermined operation mode. Based on the above, the current control unit is configured such that the output current value of the constant current source is smaller when the light amount of the incident light is smaller than when the light amount of the incident light is large. To supply the control signal.

  In the imaging device according to a fifth aspect of the present invention, in any one of the first to fourth aspects, each of the plurality of pixels receives the signal charge from the photoelectric conversion unit of the pixel and receives the signal. A charge-voltage conversion unit that converts charge into voltage, a charge transfer unit that transfers charge from the photoelectric conversion unit to the charge-voltage conversion unit, a reset unit that resets the potential of the charge-voltage conversion unit, and the pixel The amplifying unit outputs a signal corresponding to the potential of the charge-voltage conversion unit as the pixel signal.

  According to the present invention, it is possible to optimize the output current value of the constant current source during the read operation of the amplification unit according to the operation mode and the situation. Compared with the case where the output current value is always fixed to a high current value, the power consumption can be reduced.

  Hereinafter, an imaging device according to the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic block diagram showing an electronic camera 10 as an imaging apparatus according to an embodiment of the present invention.

  In FIG. 1, a photographing lens 12 is attached to the electronic camera 10. In the image space of the photographing lens 12, the imaging surface of the image sensor 11 is arranged. The imaging sequence of the image sensor 11 is timing-controlled by a control pulse group generated by the timing generator 14. These control pulse groups are supplied to the image sensor 11 via the drive circuit 100.

  Image data read from the image sensor 11 by this imaging sequence is temporarily stored in the memory 17 via the signal processing unit 15 (including the sensitivity setting unit) and the A / D conversion unit 16.

  This memory 17 is connected to a bus 18. A microprocessor 19, a recording unit 22, an image compression unit 24, a monitor display unit 30, an image processing unit 25 and the like are also connected to the bus 18. The microprocessor 19 is connected to a timing generator 14, an operation unit 19a such as a release button, a photometry unit 19b, and an imaging sensitivity input unit 19c. A recording medium 22a is detachably attached to the recording unit 22.

  Note that the microprocessor 19 can also generate a preview image (through image or the like) before actual photographing by controlling the timing generator 14 and the image sensor 11.

  FIG. 2 is a circuit diagram showing the image sensor 11 in FIG. The image sensor 11 is configured as a CMOS solid-state image sensor.

  As shown in FIG. 2, the image sensor 11 has a plurality of unit pixels 31 (in FIG. 2, only 2 × 2 pixels 31 are arranged), like a general CMOS solid-state image sensor. ), A vertical scanning circuit (vertical scanning unit) 32, a horizontal scanning circuit (horizontal scanning unit) 33, and an output signal of a pixel 31 in a corresponding column provided corresponding to each column of pixels 31 is supplied. Vertical signal lines 34 and constant current sources 35 connected to the vertical signal lines 34. Further, the image sensor 11 includes a current control unit 36 unlike a general CMOS solid-state imaging device, and the current control unit 36 variably controls the output current value of the constant current source 35. ing. This point will be described in detail later with reference to FIG. Needless to say, the number of pixels 31 is not limited.

  Each pixel 31 includes a photodiode PD as a photoelectric conversion unit that generates and accumulates signal charges according to incident light, and receives the signal charges and converts the signal charges into voltage as in a general CMOS solid-state imaging device. A floating diffusion FD serving as a charge-voltage conversion unit that converts to a voltage, an amplifying transistor AMP serving as an amplifying unit that outputs a signal corresponding to the potential of the floating diffusion FD by a read operation (and thus a signal corresponding to the signal charge), and a photo As a transfer transistor TX as a charge transfer unit for transferring charges from the diode PD to the floating diffusion FD, a reset transistor RES as a reset unit for resetting the potential of the floating diffusion FD, and a selection unit for selecting the pixel 31 And a selection transistor SEL, are connected as shown in FIG. In the present embodiment, the transistors AMP, TX, RES, and SEL of the pixel 31 are all nMOS transistors. In FIG. 2, Vdd is a power supply voltage.

  The gate of the transfer transistor TX is connected to a control line for supplying a control signal φTX for controlling the transfer transistor TX from the vertical scanning circuit 32 to the transfer transistor TX for each row. The gate of the reset transistor RES is connected to a control line that supplies the reset transistor RES with a control signal φRES for controlling the reset transistor RES from the vertical scanning circuit 32 for each row. The gate of the selection transistor SEL is connected to a control line for supplying a control signal φSEL for controlling the selection transistor SEL from the vertical scanning circuit 32 to the selection transistor SEL for each row.

  The photodiode PD generates a signal charge according to the amount of incident light (subject light). The transfer transistor TX is turned on during the high level period of the transfer pulse (control signal) φTX, and transfers the signal charge accumulated in the photodiode PD to the floating diffusion FD. The reset transistor RES is turned on during a high level period of the reset pulse (control signal) φRES to reset the floating diffusion FD.

  The amplification transistor AMP has its drain connected to the power supply voltage Vdd, its gate connected to the floating diffusion FD, its source connected to the drain of the selection transistor SEL, and the selection transistor SEL turned on during the read operation of the amplification transistor AMP. A source follower circuit having the constant current source 35 as a load is configured. One end of each constant current source 35 is connected to each vertical signal line 34, and the other end of each constant current source 35 is grounded. Accordingly, the constant current source 35 causes a current to flow through the vertical signal line 34 when the selection transistor SEL of the pixel 31 corresponding to the vertical signal line 34 is turned on. This current is a source follower bias current of the amplification transistor AMP of the pixel 31. The amplification transistor AMP outputs a read current to the vertical signal line 34 via the selection transistor SEL according to the voltage value of the floating diffusion FD. The selection transistor SEL is turned on during a high level period of the selection pulse (pixel control signal) φSEL, and connects the source of the amplification transistor AMP to the vertical signal line 34.

  The vertical scanning circuit 32 receives a control pulse (not shown) from the drive circuit 100 and outputs a selection pulse φSEL, a reset pulse φRES, and a transfer pulse φTX for each row of the pixels 31. The horizontal scanning circuit 33 receives a control pulse (not shown) from the drive circuit 100 and outputs a horizontal scanning signal φH for each column.

  The image sensor 11 samples and holds signals according to the signals of the vertical signal lines 34 according to the sampling control signals φTVN and φTVS, and also holds the held signals according to the horizontal scanning signal φH. A sample hold unit 37 for supplying to 38S is provided. In the present embodiment, the sample hold unit 37 includes optical signal storage capacitors CS and dark signal storage capacitors CN provided corresponding to the vertical signal lines 34, and optical information photoelectrically converted by the pixels 31. An optical signal sampling switch TVS for storing the optical signal in the optical signal storage capacitor CS in accordance with the optical signal sampling control signal φTVS, and a so-called dark signal as a differential signal including a noise component to be subtracted from the optical signal is a dark signal. A dark signal sampling switch TVN for storing in the dark signal storage capacitor CN in accordance with the sampling control signal φTVN, and an optical signal stored in the optical signal storage capacitor CS to the optical signal horizontal signal line 38S in accordance with the horizontal scanning signal φH. The dark signal stored in the horizontal transfer switch THS for the optical signal and the dark signal storage capacitor CN in accordance with the horizontal scanning signal φH. And a horizontal transfer switch THN for dark signal to be supplied to the dark signal horizontal signal line 38N. Actually, each transistor for resetting the horizontal signal lines 38N and 38S to a predetermined potential at a predetermined timing is provided, but the illustration of these transistors is omitted. Output amplifiers APN and APS are connected to the horizontal signal lines 38N and 38S, respectively. In this embodiment, the switches TVS, TVN, THS, and THN are all nMOS transistors.

  The gates of the optical signal sampling switches TVS are connected in common, and an optical signal sampling control signal φTVS is supplied from the drive circuit 100 to the gate. When the optical signal sampling switch TVS is turned on in response to the optical signal sampling control signal φTVS, the optical signal on the vertical signal line 34 is stored in the corresponding optical signal storage capacitor CS. The gates of the dark signal sampling switches TVN are connected in common, and a dark signal sampling control signal φTVN is supplied from the drive circuit 100 thereto. When the dark signal sampling switch TVN is turned on in response to the dark signal sampling control signal φTVN, the dark signal on the vertical signal line 34 is stored in the corresponding dark signal storage capacitor CN.

  The gates of the horizontal transfer switch for optical signal THS and the horizontal transfer switch for dark signal THN are connected in common to each column, and the horizontal scanning signal φH of the corresponding column is supplied from the horizontal scanning circuit 33 thereto. When the horizontal transfer switches THS and THN of each column are turned on in accordance with the horizontal scanning signal φH of each column, the optical signal stored in the optical signal storage capacitor CS and the dark signal storage capacitor CN of the corresponding column and The dark signals are respectively output to the optical signal horizontal signal line 38S and the dark signal horizontal signal line 38N, and are output to the signal processing unit 15 in FIG. 1 through the output amplifiers APS and APN, respectively.

  Although not shown in the drawing, the signal processing unit 15 obtains a difference between outputs of the output amplifiers APS and APN by a differential amplifier or the like. Thereby, correlated double sampling is realized, and an optical information signal from which fixed pattern noise and the like are removed is obtained as an image signal from the signal processing unit 15.

FIG. 3 is a circuit diagram showing a specific example of the constant current source 35 and the current control unit 36 in FIG. In this example, the constant current source 35 is configured by a MOSFET 41 and is connected to the vertical signal line 34 and the current control unit 36 as illustrated. The current control unit 36 is configured using a current mirror circuit, and includes a reference current source 51 and MOSFETs 52 to 58, which are connected as illustrated. Now, the value of the current generated by the reference current source 51 is I _0, and the value of the current flowing through the MOSFET 58 is I ₁ . When both the MOSFETs 54 and 56 are turned off by the control signals φA and φB supplied from the drive circuit 100 in FIG. 1, I ₁ = I ₀ ≡Imin, and the pixels connected to the related vertical signal line 34 In a state where the selection switch SEL of 31 is turned on and the amplification transistor AMP of the pixel 31 is connected to the vertical signal line 34, the value of the current flowing through the vertical signal line 34 (output current value of the constant current source 35) I is a Imin = _{I 0.}

When one of the MOSFETs 54 and 56 is turned on and the other is turned off by the control signals φA and φB, I ₁ = 2 × I ₀ ≡Imid, and the selection switch SEL of the pixel 31 connected to the related vertical signal line 34 is In the state where the amplification transistor AMP of the pixel 31 is connected to the vertical signal line 34, the value of the current flowing through the vertical signal line 34 (the output current value of the constant current source 35) I is Imid = 2 × I ₀ .

When both of the MOSFETs 54 and 56 are turned on by the control signals φA and φB, I ₁ = 3 × I ₀ ≡Imax, and the selection switch SEL of the pixel 31 connected to the related vertical signal line 34 is turned on, and In a state where the amplification transistor AMP of the pixel 31 is connected to the vertical signal line 34, the value of the current flowing through the vertical signal line 34 (the output current value of the constant current source 35) I is Imax = 3 × I _0. .

  As described above, in this example, the current control unit 36 determines the output current value of the constant current source 35 during the read operation of the amplification transistor AMP according to the control signals φA and φB supplied from the drive circuit 100. It is configured to be variably controlled in three stages of Imid and Imax. However, the number of variable steps of the output current value of the constant current source 35 is not limited to three, but may be two or more. In the present embodiment, the drive circuit 100 is a control unit that supplies the control signals φA and φB to the current control unit 36.

  4 to 6 are timing charts showing an example of a reading operation of the electronic camera 10 (particularly, the image sensor 11) according to the present embodiment. 4 shows a case where I = Imin, FIG. 5 shows a case where I = Imid, and FIG. 6 shows a case where I = Imax. 4 to FIG. 6 in which the output current value I of the constant current source 35 is different from each other, the change in potential of the vertical signal line 34 and the length of the horizontal blanking periods T2, T4,. Only the width T13 of the pulse φTVS, and the basic operation is the same in either case. Differences in each case will be described later with reference to FIG. 7. First, basic operations will be described with reference to FIGS.

  In the present embodiment, a mechanical shutter (not shown) is opened for a predetermined exposure period and charges are accumulated in the charge accumulation layer of the photodiode PD of each pixel 31, and then each row is selected one by one. The same operation is sequentially performed on the rows. 4 to 6 mainly show the operation when the pixel 31 in the nth row is selected and the pixel 31 in the (n + 1) th row is subsequently selected.

  The period T1 is a horizontal scanning period of the output of the pixel 31 in the (n−1) th row and corresponds to a period T3 described later. A period T2 after the period T1 is a horizontal blanking period of the output of the pixel 31 in the n-th row.

  In the period T2, the pixel 31 in the nth row is selected by the vertical scanning circuit 32, the reset pulse φRES (n) in the nth row changes to a low level, and the reset transistor RES in the nth row is turned off. Further, in the period T2, the selection pulse φSEL (n) in the nth row changes to a high level, and the selection transistor SEL in the nth row is turned on. When the selection transistor SEL in the n-th row is turned on, the source of the amplification transistor AMP in the n-th row is connected to the vertical signal line 34. The n-th amplification transistor AMP operates as a source follower circuit by the constant current source 35.

  In the period from the start of the period T2 to the start of the period T12, the n-th row selection transistor SEL is turned on, and at the same time, the n-th row reset transistor RES is turned off. The gate voltage of the amplification transistor AMP enters a floating state, and the reset level of the pixel 31 in the nth row appears on the vertical signal line 34. At this time, in the period T11 after the period T2 starts, the dark signal sampling pulse (control signal) φTVN changes to the high level, and the dark signal sampling switch TVN is turned on. As a result, the dark signal of the pixel 31 in the n-th row is accumulated in the dark signal storage capacitor CN. This operation is executed simultaneously in parallel for the pixels 31 in each column of the nth row.

  Next, in the period T12 in the period T2, the transfer pulse φTX (n) in the nth row changes to a high level, and the transfer transistor TX in the nth row is turned on. When the transfer transistor TX in the n-th row is turned on, the signal charge photoelectrically converted and accumulated by the photodiode PD of the pixel 31 in the n-th row is transferred to the corresponding floating diffusion FD. As a result, the voltage of the floating diffusion FD becomes a voltage corresponding to the transferred charge amount, and this voltage is applied to the gate electrode of the amplification transistor AMP. As a result, a level including the optical information of the pixels 31 in the nth row appears on the vertical signal line 34. At this time, in the period T13 after the period T12, the optical signal sampling pulse (control signal) φTVS changes to the high level, and the optical signal sampling switch TVS is turned on. As a result, the optical signal of the pixel 31 in the n-th row is stored in the optical signal storage capacitor CS. This operation is executed simultaneously in parallel for the pixels 31 in each column of the nth row.

  In this way, in the period T2, the output signal of the pixel 31 in the n-th row is sampled, and the dark signal of the pixel 31 in the n-th row is accumulated in the dark signal storage capacitor CN for each column. The optical signal storage capacitor CS stores the optical signal of the pixel 31 in the n-th row.

  A period T3 after the period T2 is a horizontal scanning period of the output of the pixel 31 in the n-th row. In the period T3, the horizontal transfer switch for dark signal THN and the horizontal transfer switch for optical signal THS are sequentially turned on and stored for each of the vertical signal lines 34 by horizontal scanning using the horizontal scanning signal φH from the horizontal scanning circuit 33. The dark signal and the optical signal respectively stored in the capacitors CN and CS are sequentially read out to the dark signal horizontal signal line 38N and the optical signal horizontal signal line 38S for each corresponding to each vertical signal line 34, and output. The signals are output to the signal processing unit 15 through the amplifiers APN and APS, respectively. The signal processing unit 15 obtains the difference between the outputs of the output amplifiers APS and APN using a differential amplifier or the like. Thereby, an optical information signal from which fixed pattern noise and the like are removed is obtained as an image signal from the signal processing unit 15.

  Next, in the periods T4 and T5, the same operation as that performed in the periods T2 and T3 for the nth row is performed for the (n + 1) th row, and the same operation is repeated thereafter.

  FIGS. 4 to 6 also show changes in the potential of the vertical signal line 34. To facilitate comparison, FIG. 7 shows the vertical signal lines 34 in the periods T1 and T2 in FIGS. The potential of the signal line 34 and the pulses φSEL (n), φRES (n), and φTX (n) are also shown. Although the length of the period T2 is different as shown in FIGS. 4 to 6, the period T2 is described as being in the case of FIG. 4 (in the case of I = Imin) in FIG. 4 to 7, the amounts of incident light are the same and relatively large (therefore, the difference between the signal level (light signal level) and the reset level (dark signal level) is the same and relatively large). As shown.

  Since there is a parasitic capacitance or the like in the vertical signal line 34 from which the pixel signal is output, even if the signal on the vertical signal line 34 is changed, it cannot be changed instantaneously, as shown in FIGS. As described above, the signal changes slowly to some extent according to the time constant of the vertical signal line 34, and a certain amount of stabilization time (stabilization time) is required until the signal of the vertical signal line 34 is stabilized from the reset level to the signal level. This stabilization time can be shortened as the output current value I of the constant current source 35 is higher. As shown in FIGS. 4 to 7, there is a case where the output current value I of the constant current source 35 is Imin. The case where the output current value I is Imid is the second longest, and the case where the output current value I is Imid is the shortest. Therefore, as the output current value I is larger, even when the width T13 of the sampling control signal φTVS is shortened and the horizontal blanking period T2 is shortened, the settled signal level can be appropriately sampled. Therefore, in the example shown in FIGS. 4 to 7, as the output current value I is larger, the width T13 of the sampling control signal φTVS is shortened to shorten the horizontal blanking period T2. In the present embodiment, when I = Imin is set by the control signals φA and φB supplied to the current control unit 36 by the timing generator 14 and the drive circuit 100, the width of φTVS and the period T1 are set as shown in FIG. When it is set relatively long and I = Imid, the width of φTVS and the period T1 are set to medium as shown in FIG. 5, and when I = Imax, the width of φTVS is set as shown in FIG. The period T1 is set to be relatively short. When the horizontal blanking period T2 is shortened, the reading of the pixel signal becomes faster. Therefore, the larger the output current value I, the faster the pixel signal can be read.

  Even if this embodiment is modified so that the current controller 36 is removed and the constant current source 35 always outputs the same value of current in a fixed manner as in the prior art, the constant current source 35 is fixed during the read operation of the amplification transistor AMP. As long as the output current value I of the current source 35 is always set to Imax, the pixel signal can be read at high speed as in the case of FIG. However, in this case, even when it is not necessary to read out the pixel signal at such a high speed, the output current value I of the constant current source 35 at the time of the reading operation of the amplification transistor AMP is always Imax. Resulting in.

  On the other hand, according to the present embodiment, the output current value I of the constant current source 35 during the read operation of the amplification transistor AMP is set to Imin, Imid and Id according to the control signals φA and φB supplied from the drive circuit 100. Since it can be variably controlled in three stages of Imax, the output current value I can be optimized according to the operation mode and the situation. Therefore, according to the present embodiment, the power consumption can be reduced as compared with the case where the output current value I is always fixed at a high Imax.

  In the present embodiment, for example, in the case of a high-speed moving image shooting mode that captures a very fast moving subject as a moving image, the operation shown in FIG. 6 is realized, and a low-speed moving image shooting mode that captures a subject that does not move so fast as a moving image. 5 may be realized, and in the still image shooting mode, the operation shown in FIG. 4 may be realized. This can be realized by controlling the timing generator 14 and the drive circuit 100 by the microprocessor 19 that has received the photographing mode setting operation by the operation unit 19a. In this case, high-speed moving image shooting by high-speed reading is realized, and power consumption is reduced in the low-speed moving image shooting mode and the still image shooting mode.

  In the present embodiment, for example, at least in a predetermined operation mode, the read operation of the amplification transistor AMP is smaller when the incident light amount is small than when the incident light amount is large, according to the incident light amount with respect to the image sensor 11. The control signals φA and φB may be supplied to the current control unit 36 by the timing generator 14 and the drive circuit 100 under the control of the microprocessor 19 so that the output current value I of the constant current source 35 at the time becomes small. Specifically, for example, when the incident light quantity with respect to the image sensor 11 is small by the operation of the timing generator 14 and the drive circuit 100 under the control of the microprocessor 19, the operation shown in FIG. 5 may be realized, and the operation shown in FIG. 6 may be realized when the amount of incident light is large. At this time, the microprocessor 19 may determine the magnitude of the amount of incident light of the image sensor 11 based on a photometric result obtained by the photometric unit 19 or based on an image signal obtained by imaging in advance. You may judge. Even if I = Imid and I = Imax, if high-speed reading is not required, the length of the horizontal blanking periods T2, T4,. You may make it the same as FIG. 4 in the case of Imin.

  Assuming that the output current value I of the constant current source 35 during the read operation of the amplification transistor AMP is the same, if the amount of incident light to the image sensor 11 (that is, incident light to the pixel 31) is small, the reset level and signal Since the difference from the level is small, the settling time is shortened. On the other hand, if the amount of the incident light is large, the difference between the reset level and the signal level is large, and the settling time is lengthened. Therefore, in order to appropriately sample the settled signal level, if the amount of the incident light is large, the output current value I of the constant current source 35 during the read operation of the amplification transistor AMP is increased to increase the stabilization time. Although it is necessary to shorten it, if the amount of the incident light is small, the settling time does not become so long without increasing the output current value I. Therefore, it is not necessary to increase the output current value I.

  Therefore, as described above, if I = Imin when the incident light quantity to the image sensor 11 is small, I = mid when the incident light quantity is medium, and I = Imax when the incident light quantity is large, The power consumption can be reduced compared to the case where I = Imax regardless of the amount of light incident on the image sensor 11.

  Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments.

It is a schematic block diagram which shows the electronic camera by one embodiment of this invention. It is a circuit diagram which shows the image sensor in FIG. FIG. 2 is a circuit diagram illustrating a specific example of a constant current source and a current control unit in FIG. 1. 2 is a timing chart showing an example of a reading operation of the electronic camera shown in FIG. 1 when the output current of the constant current source is small. 2 is a timing chart showing an example of a reading operation of the electronic camera shown in FIG. 1 when the output current of the constant current source is medium. 2 is a timing chart showing an example of a reading operation of the electronic camera shown in FIG. 1 when the output current of the constant current source is large. FIG. 7 is a diagram illustrating a potential of a vertical signal line and pulses φSEL (n), φRES (n), and φTX in periods T1 and T2 in FIGS.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electronic camera 11 Image sensor 31 Pixel 32 Vertical scanning circuit 33 Horizontal scanning circuit 34 Vertical signal line 35 Constant current source 36 Current control part AMP Amplifying transistor

Claims (5)

A plurality of pixels having a photoelectric conversion unit that generates and accumulates signal charges according to the amount of incident light from a subject and an amplification unit that outputs a pixel signal corresponding to the signal charges to a signal line by a read operation; An imaging device in which a plurality of pixels are arranged two-dimensionally,
A constant current source that forms a source follower circuit together with the amplifier;
A current control unit that variably controls an output current value of the constant current source during a read operation of the amplification unit according to a supplied control signal;
An imaging apparatus comprising: A controller for supplying the control signal to the current controller;
The control unit controls the current control unit so that an output current value of the constant current source is different between a predetermined operation mode and another predetermined operation mode during a read operation of the amplification unit. The imaging apparatus according to claim 1, wherein a signal is supplied. A control unit that supplies the control signal to the current control unit, and a photometric unit that performs photometry of the subject,
In the predetermined operation mode, the control unit is configured based on the photometry result of the photometry unit when the light amount of the incident light is small and when the light amount of the incident light is large, compared with the case where the light amount of the incident light is large. The imaging apparatus according to claim 1, wherein the control signal is supplied to the current control unit so that an output current value of the constant current source becomes small. A controller for supplying the control signal to the current controller;
In the predetermined operation mode, the control unit has the constant current during the read operation of the amplifying unit based on the pixel signal when the incident light amount is small compared to when the incident light amount is large. The imaging apparatus according to claim 1, wherein the control signal is supplied to the current control unit so that an output current value of the source becomes small.   Each of the plurality of pixels receives the signal charge from the photoelectric conversion unit of the pixel and converts the signal charge into a voltage, and transfers the charge from the photoelectric conversion unit to the charge voltage conversion unit. A charge transfer unit, a reset unit that resets the potential of the charge-voltage conversion unit, and a selection unit that selects the pixel. The amplification unit outputs a signal corresponding to the potential of the charge-voltage conversion unit to the pixel The imaging apparatus according to claim 1, wherein the imaging apparatus outputs the signal as a signal.

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