JP2005217770A - Image pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deterioration in image quality due to the generation of carriers and recombination light emission by suppressing impact ionization. <P>SOLUTION: In an image pickup device; a photoelectric conversion region having a plurality of photoelectric conversion sections, a reading circuit for reading signals from the photoelectric conversion sections, and one part of a reference current generating circuit for driving the reading circuit are formed on the same semiconductor substrate. The device has a switch for interrupting a current flowing through the reference current generating circuit or suppressing a current flowing through the reference current generating circuit. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

In recent years, there has been a remarkable improvement in the image quality of photoelectric conversion devices used in digital still cameras and the like, and it has reached a level that can withstand long exposure photography such as astronomical photography. In long exposure photography, it is important to reduce heat generation in the photoelectric conversion device. This is because an increase in temperature of the photoelectric conversion device causes image quality deterioration due to an increase in dark current. As a conventional technique, there are several methods for reducing the temperature rise of the photoelectric conversion device (see, for example, Patent Document 1). In addition, in a configuration in which a constant current is supplied from the reference current generation circuit 121 to the output amplifier 118 by a current mirror circuit as shown in FIG. Thus, by restricting current supply during the non-signal readout period, power consumption in the output amplifier 118 can be reduced and temperature rise can be suppressed.
Special Registration No. 0579372

  As described above, the main purpose of the power consumption reduction measures according to the prior art is to suppress dark current mainly due to heat generation. However, for example, in long-time exposure photography exceeding 1 minute, a problem that is newly manifested is generation of carriers due to impact ionization. Impact ionization is particularly significant in an NMOS device operating in the pentode region, and the carrier mobility increases at low temperatures, so the effect becomes even more pronounced. Since not only carrier generation but also secondary recombination light emission accompanies, all analog circuit blocks having NMOS that operate on the same semiconductor chip and operate in the pentode region are all sources of carrier and light. sell. For example, in the reference current generating circuit 121 of the photoelectric conversion device according to the prior art shown in FIG. 5, the reference current source is always in operation, so that it is a carrier generation and light emission source. The dark output increased in the vicinity of the reference current generation circuit, which was a cause of image quality deterioration.

  In the imaging device of the present invention, at least a part of a photoelectric conversion region having a plurality of photoelectric conversion units, a read circuit for reading signals from the plurality of photoelectric conversion units, and a reference current generation circuit for driving the read circuit Are formed on the same semiconductor substrate, and have a switch that cuts off a current flowing through the reference current generation circuit or suppresses a current flowing through the reference current generation circuit.

  According to the imaging conversion device of the present invention, the impact ionization is suppressed in a period in which the reference current is not required by blocking or suppressing the current of the circuit portion causing the impact ionization in the reference current generating circuit by the switch. In addition, image quality deterioration due to carrier generation and recombination light emission can be prevented.

  Embodiments of the present invention will be described in detail below.

  The photoelectric conversion device according to the first embodiment of the present invention will be described in detail below. FIG. 1 is an equivalent circuit diagram showing a reference current generating circuit and an output amplifier section of the photoelectric conversion device of this embodiment. The reference current generation circuit 121 generates a reference current by converting the reference voltage VREF with a reference resistor 122, and the reference current is copied by a current mirror circuit and input to an output amplifier 118 that is an amplifier circuit. Yes. In the reference current generating circuit 121, a CMOS analog switch 124 is inserted in series with the reference resistor 122. When the control signal PSAVE becomes high level, the conduction of the negative power supply side terminal of the resistor to GND is cut off, and instead, VREF Connected to. At this time, since the voltage across the reference resistor 122 is 0, the reference current generated by the reference current generation circuit 121 is 0.

  Here, the current may be suppressed without completely interrupting the current of the reference current generating circuit.

  With such a configuration, in particular, the influence of impact ionization generated in the NMOS 125 can be reduced. The control signal PSAVE is preferably set to a high level during a period when the output amplifier 118 does not need to operate, that is, during an accumulation period or a horizontal blanking period.

  FIG. 2 is an equivalent circuit diagram showing the overall configuration of the photoelectric conversion device of this embodiment, which is formed on the same semiconductor substrate. In the photoelectric conversion device of the prior art, in the pixel region near the reference current generation circuit 121, carrier output due to impact ionization or dark output increase due to recombination light emission has been a problem, but in the photoelectric conversion device of this example, Even in long-time accumulation photography, carrier generation and light emission are suppressed, and a good image can be obtained.

  In FIG. 2, 101 is a photodiode which is a photoelectric conversion unit, 102 is a transfer MOS transistor for transferring a photodiode signal to the gate of the amplification MOS transistor, and 103 is a gate unit of the amplification MOS transistor 104. A reset MOS transistor 105 for supplying a reset voltage to the pixel 105 is a selection MOS transistor for outputting a signal of a selected pixel.

  106 is a vertical output line, 107 is a load MOS transistor that constitutes a source follower with the amplification MOS transistor 104, 108 is a clamp capacitor, 109 is a clamp MOS transistor for changing one terminal of the clamp capacitor to a fixed potential and a floating potential, 110 is a MOS transistor for transferring a signal to the capacitor 112, 114 is a MOS transistor for transferring a signal to the horizontal output line 116, 118 is an amplifier circuit for amplifying the signal of the horizontal output line, 119 is a horizontal scanning circuit , 121 is a reference current generating circuit, and 123 is a vertical scanning circuit.

  The control signal PSAVE can be given as shown in FIG. 3, for example. In FIG. 3, the control signal PSAVE is given so as to reduce the impact ionization in the horizontal blanking period and the accumulation period, and an arbitrary one line is shown for the horizontal blanking period and the horizontal scanning period. Note that the reference resistor 122 and the CMOS analog switch 124 of FIG. 1 may be on the same semiconductor substrate or externally, and it is clear that the effects of the present invention can be obtained in either case.

  As described above, the photoelectric conversion region including the plurality of photoelectric conversion units 101, the amplifier circuit 118 that is a read circuit that reads signals from the plurality of photoelectric conversion units, and the reference current generation circuit 121 that drives the read circuit. Is formed on the same semiconductor substrate, and a switch that cuts off a current flowing through the reference current generating circuit or suppresses a current flowing through the reference current generating circuit can prevent image quality deterioration.

  FIG. 4 is a configuration diagram of a system of an imaging apparatus using the photoelectric conversion apparatus of each embodiment described above as the imaging apparatus of the present invention. The image pickup apparatus forms an image with a barrier 1 that serves as a lens switch and a main switch, a lens 2 that forms an optical image of a subject on a solid-state image pickup device 4, a diaphragm 3 that changes the amount of light passing through the lens 2, and the lens 2. A solid-state imaging device 4 (corresponding to the photoelectric conversion device described in each of the above embodiments) for capturing the captured subject as an image signal, and various corrections, clamps, and the like on the image signal output from the solid-state imaging device 4 The image signal processing circuit 5 for performing image data, the A / D converter 6 for performing analog-digital conversion of the image signal output from the solid-state image sensor 4, and various corrections are performed on the image data output from the A / D converter 6. Timing generator for outputting various timing signals to the signal processor 7, the solid-state image sensor 4, the imaging signal processor 5, the A / D converter 6 and the signal processor 7 In constructed. Each circuit of 5 to 8 may be formed on the same chip as the solid-state imaging device 4. Also, an overall control / arithmetic unit 9 for controlling various computations and the entire still video camera, a memory unit 10 for temporarily storing image data, a recording medium control interface unit 11 for recording or reading on a recording medium, The solid-state imaging system includes a removable recording medium 12 such as a semiconductor memory for recording or reading image data, and an external interface (I / F) unit 13 for communicating with an external computer or the like.

  Next, the operation of FIG. 4 will be described. When the barrier 1 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 6 is turned on. Then, in order to control the exposure amount, the overall control / arithmetic unit 9 opens the aperture 3, and the signal output from the solid-state imaging device 4 passes through the imaging signal processing circuit 5 to the A / D converter 6. Is output. The A / D converter 6 performs A / D conversion on the signal and outputs it to the signal processing unit 7. The signal processing unit 7 performs an exposure calculation by the overall control / calculation unit 9 based on the data.

  The brightness is determined based on the result of the photometry, and the overall control / calculation unit 9 controls the aperture according to the result. Next, based on the signal output from the solid-state imaging device 4, the high-frequency component is extracted and the distance to the subject is calculated by the overall control / calculation unit 9. Thereafter, the lens 2 is driven to determine whether or not it is in focus. When it is determined that the lens is not in focus, the lens 2 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 4 is corrected in the imaging signal processing circuit 5, further A / D converted by the A / D converter 6, and totally controlled through the signal processing unit 7. Accumulated in the memory unit 10 by calculation 9 Thereafter, the data stored in the memory unit 10 is recorded on a removable recording medium 12 such as a semiconductor memory through the recording medium control I / F unit under the control of the overall control / arithmetic unit 9. Further, the image may be processed by directly entering the computer or the like through the external I / F unit 13.

FIG. 2 is an equivalent circuit diagram showing a reference current generating circuit and an output amplifier section in the photoelectric conversion device according to the first embodiment of the present invention. 1 is an equivalent circuit diagram illustrating an overall configuration of a photoelectric conversion apparatus according to a first embodiment of the present invention. It is a figure showing the drive timing in the photoelectric conversion apparatus of 1st Example of this invention. It is a conceptual diagram which shows the imaging system of 2nd Example of this invention. It is the equivalent circuit diagram which showed the reference current generation circuit and output amplifier part in the photoelectric conversion apparatus by a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Barrier 2 Lens 3 Diaphragm 4 Solid-state image sensor 5 Imaging signal processing circuit 6 A / D converter 7 Signal processing part 8 Timing generation part 9 Overall control and calculation part 10 Memory part 11 Recording medium control interface (I / F) part 12 Recording medium 13 External interface (I / F) section 121 Reference current generating circuit 122 Reference resistance 124 CMOS analog switch

Claims (4)

A photoelectric conversion region having a plurality of photoelectric conversion units, a read circuit for reading signals from the plurality of photoelectric conversion units, and at least a part of a reference current generation circuit for driving the read circuits are formed on the same semiconductor substrate. An imaging device formed,
An imaging apparatus comprising: a switch that cuts off a current flowing through the reference current generation circuit or suppresses a current flowing through the reference current generation circuit.   The reference current generation circuit includes at least one or more N-type MOSFETs operating in a pentode region, and the switch limits a drain current of at least one or more N-type MOSFETs. The imaging device according to claim 1.   An amplifier circuit for amplifying signals from the plurality of photoelectric conversion units is provided on the same semiconductor substrate, and the reference current generation circuit is a circuit for generating a reference current of the amplification circuit. Item 3. The imaging device according to Item 1 or 2. An analog / digital conversion circuit that converts signals from the plurality of photoelectric conversion units into digital signals, a signal processing circuit that processes signals from the analog / digital conversion circuit, and an image of light on the plurality of photoelectric conversion units The imaging device according to claim 1, further comprising: a lens that performs the operation.

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