JP5518025B2 - Photoelectric conversion device and imaging device - Google Patents

Description

The present invention relates to a photoelectric conversion device and an imaging device, and more particularly to a photoelectric conversion device and an imaging device such as a digital camera and a digital still camera.

  Conventionally, a photometric sensor mounted on a digital camera or the like uses a photodiode to convert an optical signal into electric charge for a predetermined time, accumulates the converted electric charge, and determines the exposure based on the accumulated amount of electric charge. I was measuring.

  FIG. 8 is an explanatory diagram of the charge accumulation time of the conventional photometric sensor. In FIG. 8, reference numeral 502 denotes a pulse indicating the charge accumulation timing when the luminance is high, and charges are accumulated when the level is high. A pulse 503 indicates the charge accumulation timing at the time of low luminance, and charges are accumulated at the high level.

  As shown in FIG. 8, the conventional photometric sensor changes the accumulation time of the charge converted by the photodiode according to the luminance. Specifically, the charge accumulation time T2 at the time of low luminance is set to 10 mS, for example, and the charge accumulation time T1 at the time of high brightness is set to 10 μS, for example.

  The reason for changing the charge accumulation time in accordance with the luminance in this way is to prevent the measurement of the brightness from becoming impossible due to saturation of the charge of the photodiode when the charge is too bright and the charge is large.

  The charge accumulation times T1 and T2 described above are examples. Actually, the accumulation time T1 determines the charge accumulation time for the next photometry based on the luminance information obtained by the previous photometry. There are many. The accumulation time T2 is often set to 10 mS, which is the cycle of the light emission waveform of the fluorescent lamp.

  However, the conventional technique has the following problems.

  FIG. 9 is a diagram illustrating a pulse indicating the charge accumulation timing illustrated in FIG. 8 and a light amount waveform of the fluorescent lamp. In FIG. 9, reference numeral 501 denotes the light intensity waveform of the fluorescent lamp, 504 denotes the light intensity of the fluorescent lamp when photometry is performed at point B, 505 denotes the light intensity of the fluorescent lamp when photometry is performed at point A, and 506 denotes the light intensity of the fluorescent lamp. Is the average value.

  Here, since the charge accumulation time T1 in photometry at low brightness is often 10 mS, which is the same as the period of the light quantity waveform of the fluorescent lamp, the light quantity change of the fluorescent lamp can be changed at any timing. Does not change the photometric accuracy.

  On the other hand, since the charge accumulation time T2 in photometry at high brightness is, for example, 10 μS, the amount of light emitted from the fluorescent lamp is different between when the photometry is performed at the point A and when the photometry is performed at the timing at the point B. As a result, the photometric accuracy decreases due to the change in the light quantity of the fluorescent lamp.

  For this reason, in order not to lower the photometric accuracy, it is necessary to obtain an average value 506 by performing photometry a plurality of times at high luminance or to determine an optimal charge accumulation time in advance. .

  When performing photometry multiple times, calculation processing is required to average the amount of accumulated charge, and complicated calculation is necessary to determine the optimal charge accumulation time in advance. Even if is used, the photometry time increases.

  Furthermore, in the conventional technique, when the brightness state at the previous metering and the brightness state at the next metering change abruptly, from the brightness information at the previous metering, The optimum accumulation time cannot be determined, and a great deal of time is required until this determination. As a result, for example, when the brightness of the object scene changes abruptly, such as when the flash means emits light, accurate photometry cannot be performed.

  Therefore, an object of the present invention is to prevent a reduction in photometric accuracy without performing troublesome calculations. Another object of the present invention is to perform accurate photometry even when the luminance information of the scene changes suddenly.

One aspect of the present invention relates to a photoelectric conversion device having a plurality of pixels, and each of the plurality of pixels includes a photoelectric conversion element, and an amplification unit that outputs a signal based on a charge generated in the photoelectric conversion element; A transfer unit that includes a first transistor connected to the photoelectric conversion element, and transfers charges generated in the photoelectric conversion element to an input node of the amplification unit through the first transistor; and is connected to the photoelectric conversion element. A charge generated in the photoelectric conversion element including the second transistor is connected to the power supply from the photoelectric conversion element through the second transistor by connecting the photoelectric conversion element and the power supply by the second transistor. Discharge means for discharging the output to the input node, and reset means for resetting the voltage of the input node of the amplification means. Charge is discharged to the power source, and accumulation of charge in the photoelectric conversion element starts when the discharge ends, and the period in which charge is accumulated in the photoelectric conversion element is longer than that in the first luminance. is rather long, the transfer means towards the case of the lower second luminance than the luminance, the charge generated in the photoelectric conversion element to transfer a plurality of times to said input node, said input across said plurality of times by said transfer means The charge transferred to the node is added at the input node, and the charge is discharged from the photoelectric conversion element to the power source by the discharge means during the transfer of the charges in the plurality of times by the transfer means. The

  As described above, according to the present invention, it is possible to add the charges converted by the photoelectric conversion element and selectively extracted at a constant period, so that the photometric accuracy is not lowered without performing troublesome calculations. Can be.

It is explanatory drawing of the operation principle of the photometric sensor of Embodiment 1 of this invention. FIG. 2 is an equivalent circuit diagram of a photometric sensor that realizes the operation shown in FIG. 1. FIG. 3 is a diagram illustrating a state of a pulse signal applied to each gate of the reset switches 4 and 7, the selection switch 6, the transfer switches 2 and 3, and the switch 9 in FIG. It is a top view of the photometric sensor 310 of Embodiment 2 of this invention. It is an equivalent circuit schematic of the photometric sensor of Embodiment 3 of the present invention. FIG. 5 shows a state in which the pulse signals applied to the gates of the reset switches 4 and 7, the selection switch 6, the transfer switches 2 and 3, the switch 9, the read MOS transistors 15 and 16, and the reset MOS transistor 19 in FIG. FIG. It is a block diagram which shows the structural structure of the imaging device of Embodiment 4 of this invention. It is explanatory drawing of the accumulation | storage time of the charge of the conventional photometric sensor. It is a figure which shows the pulse which shows the accumulation | storage timing of an electric charge shown in FIG. 8, and the light emission waveform of a fluorescent lamp.

(Embodiment 1)
“Description of Principle”
FIG. 1 is an explanatory diagram of the operation principle of the photometric sensor according to Embodiment 1 of the present invention. In FIG. 1, 100 is a light quantity waveform of a fluorescent lamp.

  Reference numeral 101 denotes a pulse indicating the charge accumulation timing at the time of low luminance, and charges are accumulated at the high level. Here, the high-level period T2 is set to, for example, 10 mS which is the period of the fluorescent lamp so as not to be affected by flicker.

  Reference numeral 102 denotes a pulse indicating charge accumulation timing at high luminance, and charges are accumulated at high level. Here, the high-level periods t1, t2,..., T10 are set to 1 μS, for example, and high / low is switched 10 times within 10 mS, for example. Note that the high luminance means the time when the accumulated charge is saturated when the charge is accumulated at the timing of the low luminance.

  When the accumulation time is as described above, the ratio of the charge accumulation time between the high luminance and the low luminance is 1: 1000. Incidentally, the charge accumulated at the time of high luminance is subjected to arithmetic processing for photometry after addition.

  Incidentally, it is generally assumed that the photometric range required for the photometric device of the camera is EV0 to EV20, that is, about 20 EV in the dynamic range. However, most of the dynamic range of the image sensor is about 10 EV.

  Therefore, it is necessary to adjust the accumulation time to adjust the required photometric range to the optimum level including the main subject.

  Specifically, when the luminance value in the field is EV0 to EV20, the illuminance on the light receiving surface of the photoelectric conversion element when a standard photographing lens is attached is approximately 0.01 Lx to 10000 Lx. .

  Assuming that the sensitivity of the photoelectric conversion element is about 20 V / lx · S and the saturation output is about 2 V, when the charge accumulation time is 10 μS, the photometric range is about EV10 to EV20, and the charge accumulation time is 10 mS. Sometimes the photometric range is EV0 to EV10.

  That is, by adjusting the accumulation time of the photoelectric conversion element in the range of 10 μS to 10 mS, the dynamic range of EV0 to EV20 that is a photometric range required for the photometric device of the camera can be realized for the first time.

"Configuration Description"
FIG. 2 is an equivalent circuit diagram of a photometric sensor that realizes the operation shown in FIG. In FIG. 2, reference numeral 1 denotes a photodiode which is a photoelectric conversion element that converts light into electric charge and stores the converted electric charge, and reference numerals 2 and 3 denote transfer switches that selectively transfer electric charge accumulated in the photodiode 1. , 7 is a reset switch for resetting the transfer destination potential of the charges by the transfer switches 2 and 3 to a reference potential, 5 is a source follower for generating an amplified signal based on the charges transferred by the transfer switch 2, and 6 is an amplified signal. 10 is a load current source for reading the amplified signal together with the source follower 5, 9 is a switch for sending the read amplified signal to the output line 22, and 8 is the charge transferred by the transfer switch 3. 21 is a floating diffusion (hereinafter referred to as “FD”) in which charges are transferred by the transfer switch 2. It is referred to.).

  Note that the reset switch 7 does not necessarily have to be operated if the charge accumulated in the capacitor 8 does not affect the charge accumulated in the photodiode 1.

  The transfer switch 3 may be connected to a reference voltage such as VCC or GND instead of the capacitor 8.

"Description of operation"
FIG. 3 is a diagram showing a high-luminance state of the pulse signal applied to the gates of the reset switches 4 and 7, the selection switch 6, the transfer switches 2 and 3, and the switch 9 in FIG. 2. FIG. 3 also includes the accumulation times t1 to t10 shown in FIG. Hereinafter, the operation of the photometric sensor of FIG. 2 will be described with reference to FIG.

  First, the operation at high luminance will be described. The low level pulse signal φR1 applied to the gate of the reset switch 4 is temporarily switched to the high level, and the potential of the FD21 is reset. The potential of the FD21 becomes a dark level.

  Then, light enters the photodiode 1 and the incident light is converted into electric charges. The converted charge is accumulated in the photodiode 1.

  At the start of charge accumulation, the transfer switches 2 and 3 are turned off, and the photodiode 1 is not electrically connected to the FD 21 and the capacitor 7, so that the FD 21 and the capacitor 8 are converted by the photodiode 1. The charged charge is not transferred.

  Next, the low level pulse signal φSEL applied to the gate of the selection switch 6 is set to the high level, and the load current source 10 and the source follower 5 are operated.

  In this state, the pulse signals φTX1 and φTX2 applied to the gates of the transfer switches 2 and 3 are continuously switched to high / low alternately, and the charge accumulated in the photodiode 1 is transferred to the FD 21 or the capacitor 8. The

  At this time, each time the transfer switches 2 and 3 are turned on, the pulse signal φR2 applied to the reset switch 7 is switched from the low level to the high level, and the potential of the capacitor 8 is reset.

  Incidentally, in the photodiode 1, charge accumulation is started from the moment when the transfer switches 2 and 3 are switched to the low level, and transfer of the accumulated charge is started from the moment when the transfer switches 2 and 3 are switched to the high level. In other words, after the pulse signal φTX2 is switched to the low level, the time until the charge of the photodiode 1 is transferred to the FD 21 and the pulse signal TX1 is turned off is the accumulation time t1, t2,.

  Here, as shown in FIG. 3, when pulse signals φR2, φTX1, and φTX2 are applied to the switches 7, 2 and 3, charges are transferred to the FD 21 at a timing synchronized with the pulse 102 shown in FIG.

  When the transfer switch 2 is turned off, the voltage of the FD 21 is held and added by the transferred charge. Thereafter, when φT1 applied to the gate of the switch 9 is turned on, an amplified signal based on the electric charge added by the FD 21 is sent to the output line 22.

  Finally, the pulse signal φSEL applied to the gate of the selection switch 6 is returned to the low level, and the operation shown in FIG.

  Next, the operation at low luminance will be described. When the luminance is low, the pulse signal φTX2 applied to the gate of the transfer switch 3 is kept at the low level, and the high / low state of the pulse signal φTX1 applied to the gate of the transfer switch 2 in the state where the transfer switch 3 is turned off. And the transfer switch 2 is turned on by, for example, 10 mS. The other pulse signals φR1, φR2, φSEL, and φT1 are the same as those in FIG.

  Then, charges are transferred to the FD 21 at a timing synchronized with the pulse 101 shown in FIG. 1. Thereafter, when φT1 applied to the gate of the switch 9 is turned on, an amplified signal based on the charges transferred to the FD 21 is output to the output line. 22 is sent.

(Embodiment 2)
In Embodiment 2 of the present invention, for example, the photodiodes 1 and the like shown in an equivalent circuit in FIG. 2 are two-dimensionally arranged like a matrix, a delta, or a honeycomb, and charge accumulation for low luminance is performed in odd rows. The high-intensity charges are accumulated in even-numbered rows.

  FIG. 4 is a plan view of the photometric sensor 310 according to the second embodiment of the present invention. The rectangles in FIG. 4 indicate the photodiodes 1 and the like shown in the equivalent circuit diagram of FIG. 4 shows the charge accumulation time in each row 301 to 308. The accumulation time in the odd rows 301 and 303 corresponds to the pulse 101 in FIG. 1, and the accumulation time in the even rows 302 and 304. Corresponds to the pulse 102 in FIG.

  As shown in FIG. 4, when charge accumulation for low luminance and high luminance can be performed, a wide dynamic range can be secured, and even if the luminance state of the object scene suddenly changes. The photometric accuracy will not decrease.

  Here, an example has been described in which charge accumulation for low luminance and high luminance is performed in odd rows and even rows, respectively. For example, charges for medium luminance that are intermediate between these are accumulated. You may do it. Further, the charge accumulation time may be changed between the odd-numbered column and the even-numbered column, or the charge accumulation time may be changed in an oblique lattice shape.

(Embodiment 3)
A photometric sensor according to Embodiment 3 of the present invention is provided with noise removing means for removing noise generated during switching of the switches 2 to 5 and the like in the photometric sensor shown in FIG.

"Configuration Description"
FIG. 5 is an equivalent circuit diagram of a photometric sensor according to Embodiment 3 of the present invention. In FIG. 5, 12 is a MOS transistor for outputting a signal based on the amplified signal transmitted by the switch 9, 11 is a storage capacitor for storing a noise signal charge and an optical signal charge including the noise signal charge, and 14 is connected to a power supply voltage VDD. MOS transistor, 13 is a load power source for extracting a signal from the MOS transistor 12, 16 is a read MOS transistor for reading out a noise signal charge, 18 is a capacitor for reading out the noise signal charge, and 15 is an optical signal charge including a noise component. Is a read MOS transistor for reading the optical signal charge, 17 is a capacitor for reading the optical signal charge including the noise component, 19 is a reset MOS transistor for resetting the potential of the capacitors 17 and 18, and 20 is a difference between the noise signal charge and the optical signal charge. It is a differential amplifier.

  The MOS transistors 12 and 14, the load power supply 13, and the noise storage / storage capacitor 11 constitute noise component removing means. In FIG. 5, the same reference numerals are given to the same parts as those in FIG. 2.

"Description of operation"
FIG. 6 shows the reset switches 4 and 7, the selection switch 6, the transfer switches 2 and 3, the switch 9, the read MOS transistors 15 and 16, and the reset MOS transistor 19 shown in FIG. FIG. Hereinafter, the operation of the photometric sensor of FIG. 5 will be described with reference to FIG.

  First, the operation at high luminance will be described. The pulse signals φR1 and φCR applied to the reset switch 4 and the gate of the reset MOS transistor 19 are temporarily switched from a low level to a high level, and the potential of the FD 21 and the capacitors 17 and 18 are reset. The potential of the FD21 becomes a dark level.

  Then, light enters the photodiode 1 and the incident light is converted into electric charges. The converted charge is accumulated in the photodiode 1. As in the first embodiment, the transfer switches 2 and 3 are turned off at the start of charge accumulation.

  Next, the low level pulse signal applied to the gate of the selection switch 6 is switched to the high level, and the load current source 10 and the source follower 5 are activated.

  Next, the pulse signal φT1 applied to the gate of the switch 9 is set to the high level, and the noise component generated when the FD 21 is reset is stored in the storage capacitor 11.

  Then, the pulse signals φTX1 and φTX2 applied to the gates of the transfer switches 2 and 3 are alternately made high / low alternately, and the electric charge accumulated in the photodiode 1 is transferred to the FD 21 or the capacitor 8.

  At this time, each time the transfer switches 2 and 3 are turned on, the pulse signal φR2 applied to the reset switch 7 is switched from the low level to the high level, and the potential of the capacitor 8 is reset.

  Incidentally, in the photodiode 1, charge accumulation is started from the moment when the transfer switches 2 and 3 are turned off, and transfer of the accumulated charge is started from the moment when it is turned on.

  When the transfer switch 2 is turned off, the voltage of the FD 21 is held and added by the transferred charge.

  After the final charge accumulation is completed, the pulse signal φTN applied to the gate of the read MOS transistor 16 is switched from the low level to the high level, and the pulse signal applied to the gate of the MOS transistor 14 is switched to the low level. When switching from the level to the high level, the noise component accumulated in the storage capacitor 11 is transferred to the capacitor 18.

  Thereafter, when φT1 applied to the gate of the switch 9 is turned on, an amplified signal based on the electric charge added by the FD 21 is sent to the output line 22 and transferred to the storage capacitor 11.

  Then, when the pulse signal φTN applied to the gate of the read MOS transistor 17 is switched from the low level to the high level, the optical signal charge including the noise component stored in the storage capacitor 11 is transferred to the capacitor 17.

  Thereafter, the pulse signal applied to the gate of the MOS transistor 14 is returned to the low level, and the pulse signal applied to the gate of the MOS transistor provided between the capacitors 17 and 18 and the differential amplifier 20 is low. When the level is switched to the high level, the signal components respectively held in the capacitors 17 and 18 are sent to the differential amplifier 20 to perform noise removal.

  Finally, the pulse signal applied to the gate of the selection switch 6 is returned to the low level, and the operation shown in FIG. 6 ends.

  Next, the operation at low luminance will be described. When the luminance is low, the pulse signal φTX2 applied to the gate of the transfer switch 3 is kept at the low level, and the high / low state of the pulse signal φTX1 applied to the gate of the transfer switch 2 in the state where the transfer switch 3 is turned off. And the transfer switch 2 is turned on by, for example, 10 mS. The other pulse signals φR1, φR2, φT1, φTS, φTN, and φCR are the same as those in FIG.

  Then, charges are transferred to the FD 21 at a timing synchronized with the pulse 101 shown in FIG. 1, and an optical signal charge from which noise components are removed is output from the differential amplifier 20.

(Embodiment 4)
FIG. 7 is a block diagram showing a structural configuration of an imaging apparatus according to Embodiment 4 of the present invention. In FIG. 7, reference numeral 51 denotes a barrier that serves as a lens switch and a main switch, 52 denotes a lens that forms an optical image of a subject on the solid-state image sensor 54, 53 denotes an aperture for changing the amount of light passing through the lens 52, and 54 denotes A solid-state image sensor for capturing an object imaged by the lens 52 as an image signal, 55 is an image signal processing circuit for performing various corrections, clamps, and the like on the image signal output from the solid-state image sensor 54, and 56 is a solid-state image sensor. An A / D converter that performs analog-digital conversion of an image signal output from the image sensor 54, and a signal processing unit 57 that performs various corrections on the image data output from the A / D converter 56 and compresses the data. , 58 are used to output various timing signals to the solid-state imaging device 54, the imaging signal processing circuit 55, the A / D converter 56, the signal processing unit 57, and the photometric sensor 64. 59 is a general control / arithmetic unit for controlling various computations and the entire still video camera, 60 is a memory unit for temporarily storing image data, and 61 is a recording unit for recording or reading data on a recording medium. A medium control interface unit 62 is a removable recording medium such as a semiconductor memory for recording or reading image data, 63 is an external interface (I / F) unit for communicating with an external computer, and 64 is an embodiment. 1 is a photometric sensor described in 1-3.

  Next, the operation of the still video camera at the time of shooting in the above configuration will be described. When the barrier 51 is opened, the main power supply is turned on, the control system power supply is turned on, and the power supply of the imaging system circuit such as the A / D converter 56 is turned on.

  Then, in order to control the exposure amount, the overall control / calculation unit 59 opens the diaphragm 53 and light from the object scene enters the photometric sensor 64. The photometric sensor 64 is driven according to the procedure described in the first to third embodiments, and outputs a signal based on charges to the overall control / calculation unit 59.

  The overall control / calculation unit 59 determines the brightness of the object scene based on the output signal, and controls the diaphragm 53 according to the result.

  Next, imaging is performed. First, light from the object scene is input to the solid-state image sensor 54, and based on a signal based on the electric charge output from the solid-state image sensor 54, a high-frequency component is extracted to calculate the distance to the subject. 59.

  Thereafter, the lens 52 is driven to determine whether or not it is in focus. When it is determined that the lens is not in focus, the lens 52 is driven again to perform distance measurement. Then, after the in-focus state is confirmed, the main exposure starts.

  When the exposure is completed, the image signal output from the solid-state imaging device 54 is corrected in the imaging signal processing circuit 55, and further A / D converted by the A / D converter 56, and is controlled through the signal processing unit 57. Accumulated in the memory unit 60 by the calculation 59.

  Thereafter, the data stored in the memory unit 60 is recorded on a removable recording medium 62 such as a semiconductor memory through the recording medium control I / F unit under the control of the overall control / arithmetic unit 59. Further, the image may be processed by directly entering the computer or the like through the external I / F unit 63.

DESCRIPTION OF SYMBOLS 1 Photodiode 2,3 Transfer switch 4,7 Reset switch 5 Source follower 6 Selection switch 8 Capacity | capacitance 9 Switch 10 Load current source 12 MOS transistor 11 Storage capacity 14 MOS transistor 13 Load power supply 15,16 Read-out MOS transistor 17,18 Capacity 19 Reset MOS transistor 20 Differential amplifier 21 Floating diffusion (FD)
22 Output line

Claims (5)

A photoelectric conversion device having a plurality of pixels,
Each of the plurality of pixels is
A photoelectric conversion element;
Amplifying means for outputting a signal based on the charge generated in the photoelectric conversion element;
Transfer means including a first transistor connected to the photoelectric conversion element, and transferring the charge generated in the photoelectric conversion element to the input node of the amplification means through the first transistor;
A second transistor connected to the photoelectric conversion element, and the charge generated in the photoelectric conversion element is connected to the photoelectric conversion element and a power source by the second transistor , thereby passing through the second transistor. Discharging means for discharging from the photoelectric conversion element to the power source;
Resetting means for resetting the voltage at the input node of the amplifying means,
Charge is discharged to the power source by the discharge means, and accumulation of charge in the photoelectric conversion element starts when the discharge ends, and the period in which charge is stored in the photoelectric conversion element is compared with the case of the first luminance. Te, rather long better when the first second luminance lower than the luminance,
The transfer means transfers the charge generated in the photoelectric conversion element to the input node a plurality of times, and the charge transferred to the input node by the transfer means a plurality of times is added at the input node,
Charges are discharged from the photoelectric conversion element to the power source by the discharging unit between the transfer of the plurality of times of transferring the charge by the transfer unit.
A photoelectric conversion device characterized by that. One main node of the second transistor is connected to the photoelectric conversion element, and the other main node of the second transistor is connected to the power source.
The photoelectric conversion device according to claim 1. The reset means does not reset the potential of the input node during a plurality of times of charge transfer to the input node by the transfer means.
The photoelectric conversion device according to claim 1 . The plurality of pixels include a first pixel and a second pixel, and the charge accumulation time of the first pixel by the photoelectric conversion element is longer than the charge accumulation time of the second pixel by the photoelectric conversion element. The first pixel and the second pixel are controlled;
The photoelectric conversion device according to any one of claims 1 to 3, characterized in that. Imaging apparatus characterized by comprising a photoelectric conversion device according to any one of claims 1 to 4.

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