JP2008227255A - Electronic device having charge detection amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To aim at gaining both of high charge detection sensitivity and a large amount of signal charge handling by a solid-state image pickup element, or the like. <P>SOLUTION: An electronic device having a charge detection amplifier outputting a signal corresponding to the amount of signal charge from an amplifier includes: a first charge detection amplifier 16 that outputs a signal corresponding to the amount of signal charge and transfers the signal charge after signal output to a poststage (FD section 12) completely; and a second charge detection amplifier 21 that has a difference in sensitivity to the first charge detection amplifier 16 and outputs a signal corresponding to the amount of signal charge completely transmitted to the poststage 12. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electronic device with a charge detection amplifier, and more particularly to an electronic device with a charge detection amplifier suitable for expanding the dynamic range of an output signal.

  In an electronic device such as a CCD image sensor or a CMOS image sensor, each pixel (photoelectric conversion element) detects a signal charge accumulated according to the amount of light received from a subject, and a signal detected by the charge detection unit An amplifier for converting the charge amount into a voltage value signal is provided.

  For example, in a normal CCD image sensor, a floating diffusion (FD) part is provided as a charge detection part at the output end of a horizontal charge transfer path (HCCD) as described in Non-Patent Document 1 below. In this FD section, a two-stage source follower amplifier is provided as an output amplifier, which is called a floating diffusion amplifier (FDA).

  In the case of a CMOS image sensor, a charge detection transistor and an output amplifier transistor connected to the output of this transistor are provided for each pixel, or these transistors are provided in the periphery of the light receiving area of the image sensor. To do.

  Although the floating diffusion amplifier has a simple structure, the signal charge converted into a voltage value signal is discarded in the drain and cannot be reused. That is, the feature is that the captured image signal is read destructively with respect to the signal charge. Further, since the input voltage amplitude that can be handled is limited by the drive amplitude of the reset gate, there is a problem that if the charge detection sensitivity is improved, the dynamic range for the input signal charge is reduced.

  On the other hand, Non-Patent Document 1 also introduces a floating gate amplifier (FGA) that can read a captured image signal without destroying signal charges. This floating gate amplifier is configured to detect a voltage value signal (captured image signal) corresponding to the signal charge without destroying the signal charge, and to completely transfer the detected signal charge to the subsequent stage.

  For this reason, in the prior art described in Patent Document 1 below, two charge detection units are provided in the charge transfer direction, and output imaging detected by the subsequent charge detection unit using a signal detected by the previous charge detection unit. The image signal is feedforward controlled to improve S / N.

  As other methods for nondestructively detecting the signal charge, there are a floating surface charge detector described in Non-Patent Document 2 and a detector described in Patent Document 2 which is an improved version thereof.

  Since this floating surface charge detector has an extremely high charge detection sensitivity (100 to 200 μV / electron), there is a problem that the maximum value of the input signal charge is reduced.

JP-A-5-75928 Japanese Patent No. 3375389 Book "Basics of CCD" Electronics Bunko, written by Tetsuo Tsukamoto, published by Ohmsha, pages 116-122 1988 “International Conference on Solid State Device and Materials (Extended Abstracts)” pp.355-358

  Non-destructive and complete transfer type "floating gate amplifier", "floating surface amplifier", and "improved floating surface amplifier" as output amplifiers that read voltage value signals according to the amount of signal charge However, the charge breakdown type “floating diffusion amplifier” has been explained. However, even if any output amplifier is used, there are advantages and disadvantages, and in recent solid-state image sensors with a finer pixel size, high charge detection sensitivity There is a problem that it is difficult to achieve both a high signal charge handling amount (dynamic range).

  An object of the present invention is to provide an electronic device with a charge detection amplifier that can achieve both high charge detection sensitivity and a high signal charge handling amount.

  The electronic device with a charge detection amplifier according to the present invention is an electronic device with a charge detection amplifier that outputs a signal according to the charge amount of the signal charge from the amplifier, and outputs a signal according to the charge amount of the signal charge and outputs the signal. The first charge detection amplifier that completely transfers the signal charge after output to the subsequent stage and the charge amount of the signal charge that has been completely transferred to the subsequent stage having a sensitivity difference between the first charge detection amplifier and the first charge detection amplifier And a second charge detection amplifier that outputs the received signal.

  The electronic device with a charge detection amplifier according to the present invention includes means for setting or selecting the sensitivity difference.

  The first charge detection amplifier of the electronic device with a charge detection amplifier according to the present invention is any one of a “floating gate amplifier”, a “floating surface amplifier”, and a “floating well amplifier”, and the second charge detection amplifier The amplifier is one of a “floating gate amplifier”, a “floating surface amplifier”, and a “floating diffusion amplifier”.

  The electronic device with a charge detection amplifier according to the present invention is a solid-state image sensor, and the signal charge is a signal charge accumulated by a photoelectric conversion element provided in the solid-state image sensor in accordance with the amount of received light.

  In the electronic device with an output amplifier according to the present invention, the solid-state imaging device has a plurality of signal charge output units, and the first charge detection amplifier and the second charge detection amplifier are provided for each signal charge output unit. It is characterized by.

  The digital camera of the present invention includes the solid-state imaging device described above, and a control unit that synthesizes captured image signals having different sensitivities output from the first charge detection amplifier and the second charge detection amplifier of the solid-state imaging device, respectively. It is characterized by providing.

  The control means of the digital camera of the present invention is characterized in that the captured image signal to be synthesized is signal-corrected based on the stored performance information of the first charge detection amplifier and the second charge detection amplifier.

  According to the present invention, since the first charge detection amplifier and the second charge detection amplifier having a difference in sensitivity obtain signals from the same signal charge, a signal having a wide dynamic range can be obtained by combining both signals. In addition, the signal charge detection sensitivity can be increased.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is an explanatory diagram of a CCD type solid-state imaging device according to an embodiment of the present invention. The CCD solid-state imaging device 1 includes a plurality of photodiodes (photoelectric conversion elements) 3 arranged in a square lattice on the surface portion of a semiconductor substrate 2 and a plurality of vertical charge transfer paths provided adjacent to each photodiode row. (VCCD) 4 and a horizontal charge transfer path 5 provided along the end of each vertical charge transfer path.

  Although FIG. 1 shows an interline transfer type CCD, other types of CCDs such as a full frame transfer type and a frame transfer type may be used. In addition, a CCD in which each photodiode 3 is arranged in a square lattice is shown, but a so-called honeycomb pixel array CCD in which even-numbered photodiodes are shifted by 1/2 pitch with respect to odd-numbered photodiodes is also shown. good.

  In the solid-state imaging device 1 of the present embodiment, a floating gate 11 as a first charge detection unit is provided on the output end side of the horizontal charge transfer path 5, and a floating diffusion as a second charge detection unit is provided at the subsequent stage. An (FD) portion 12 is provided, and a reset gate 13 is provided at the subsequent stage.

  A floating gate potential control terminal 15 is connected to the floating gate 11, and a well-known two-stage source follower amplifier 16 is connected. A captured image signal detected by the diode 3 is output.

  A well-known two-stage source follower amplifier 21 is connected to the floating diffusion (FD) unit 12, and a captured image signal detected by each photodiode 3 is output from an output terminal 22 of the two-stage source follower amplifier 21. Is output.

  FIG. 2 is a functional block diagram of a digital camera equipped with the CCD solid-state imaging device 1 shown in FIG. The digital camera 30 includes a system control unit 31 that performs overall control of the digital camera and performs image signal processing, a timing generator 32 that operates in response to an instruction from the system control unit 31, and a timing signal from the timing generator 32. And a CCD driver 33 for driving the CCD type solid-state imaging device 1 shown in FIG.

  The digital camera 30 also includes an interface unit 35 that performs an interface between the system control unit 31 and an external input / output terminal, an interface unit 36 that externally outputs moving image data captured by the CCD solid-state imaging device 1, and an external illustration. An interface unit 37 that performs control with a recording medium that is not to be recorded, a system memory 38 that is used by the system control unit 31, and a signal memory 39 that stores a captured image signal output from the CCD solid-state imaging device 1. Prepare.

  The digital camera 30 further includes a sample hold circuit 41 whose input end is connected to the output terminal 17 of the CCD type solid-state imaging device 1 described with reference to FIG. 1, and a gain control that takes the output of the sample hold circuit 41 and performs gain control. An amplifier 42, an analog / digital converter 43 that converts an analog signal output from the amplifier 42 into a digital signal and outputs the digital signal to the memory 39, and an input terminal is connected to the output terminal 22 of the CCD solid-state imaging device 1 described with reference to FIG. A sample-and-hold circuit 46, a gain control amplifier 47 that takes in the output of the sample-and-hold circuit 46 and performs gain control, and an analog-to-digital converter 48 that converts the output analog signal of the amplifier 47 into a digital signal and outputs it to the memory 39; Is provided.

  Next, operations of the above-described CCD type solid-state imaging device 1 and digital camera 30 will be described.

  When light from a subject enters the CCD solid-state imaging device 1, each photodiode 3 accumulates signal charges corresponding to the amount of received light. This signal charge is read to the vertical charge transfer path 4 and transferred to the horizontal charge transfer path 5, and then transferred to the output end side by the horizontal charge transfer path 5.

  The signal charge transferred to the output end side of the horizontal charge transfer path 5 first enters the floating gate 11, and a voltage value signal corresponding to the signal charge amount is a two-stage source follower amplifier 16 as a captured image signal. Are output from the output terminal 17.

  Since the floating gate amplifier composed of the two-stage source follower amplifier 16 and the floating gate 11 is a complete transfer type and non-destructive type, the signal charge that has entered the floating gate 11 is then transferred to the subsequent stage. The data is completely transferred to the floating diffusion (FD) unit 12.

  The floating diffusion amplifier including the FD unit 12 and the two-stage source follower amplifier 21 outputs a voltage value signal corresponding to the amount of signal charge flowing into the FD unit 12 from the output terminal 22 as a captured image signal. The signal charge from which the captured image signal has been read is discarded from the reset gate 13 to the substrate 2 side.

  In the example shown in FIG. 1, a floating gate amplifier is used as the first charge detection amplifier 16 and a floating diffusion amplifier is used as the second charge detection amplifier 21. Yes.

  If the first charge detection amplifier 16 and the second charge detection amplifier 21 have the same sensitivity, it is meaningless to extract two captured image signals from the same signal charge. However, in this embodiment, a difference is set in the sensitivity of both amplifiers 16 and 21, and the captured image signals of both amplifiers 16 and 21 are combined as will be described later, thereby achieving both high charge detection sensitivity and wide dynamic range shooting. I am letting.

  Since the floating gate amplifier provided in the previous stage is difficult to achieve high sensitivity, this amplifier is configured as a low sensitivity amplifier, and the floating diffusion amplifier provided in the subsequent stage is configured as a high sensitivity amplifier.

  Thereby, the output of each amplifier becomes as shown in FIG. That is, the output of the high-sensitivity amplifier is saturated with a small amount of incident light, but it is possible to obtain an output that changes greatly according to the change in the signal charge amount when the signal charge amount is small. On the other hand, the output of the low sensitivity amplifier does not immediately saturate even when the amount of incident light is large and the signal charge amount is large, and an output change corresponding to the signal charge amount can be obtained.

  Therefore, the digital camera 30 captures a high-sensitivity captured image signal from the sample hold circuit 46, captures a low-sensitivity captured image signal from the sample hold circuit 41, and stores it in the signal memory 39 with high sensitivity imaging converted into digital data. Save the image signal and the low-sensitivity captured image signal.

  Then, the system control unit 31 generates and outputs a captured image signal having a wide dynamic range by combining the high-sensitivity captured image signal and the low-sensitivity captured image signal as the characteristic line I or the characteristic line II illustrated in FIG. .

  When the high-sensitivity captured image signal and the low-sensitivity captured image signal are combined, the dynamic range of the combined captured image signal depends on the difference between the detection sensitivity of the high-sensitivity amplifier and the detection sensitivity of the low-sensitivity amplifier. Therefore, for example, even if the sensitivity difference between the two amplifiers is fixed to 2 times or more, 4 times or more, or 8 times or more, a configuration that can arbitrarily variably control or select the sensitivity difference is added. May be.

  In general, the maximum sensitivity ratio that humans feel comfortably is about 4 times, so if you combine the outputs of both amplifiers by making the difference in sensitivity between both amplifiers about 4 times, playback with a natural dynamic range Images can be combined.

  When performance information such as sensitivity and linearity of the individual output amplifiers 16 and 21 is stored in the system control unit 31 or the system memory 38 of the digital camera 30 and the system control unit 31 generates composite image data. By performing signal correction based on this performance information, it is possible to reduce the influence of variations in amplifier characteristics.

  FIG. 5 is an explanatory diagram of a CCD type solid-state imaging device 50 according to another embodiment of the present invention. In the solid-state imaging device 1 shown in FIG. 1, a low-sensitivity floating gate amplifier is used as the amplifier provided in the previous stage. However, in this embodiment, the amplifier 16 provided in the previous stage is described in Non-Patent Document 2 and Patent Document 2. The difference is that the high-sensitivity floating surface amplifier is adopted and the floating diffusion amplifier provided in the latter stage is a low-sensitivity amplifier. The sensitivity difference is about 4 times as described above.

  The floating surface amplifier employed in the present embodiment is an improved type described in Patent Document 2, and the signal charge provided and transferred at the output stage portion of the horizontal charge transfer path 5 is temporarily entered and the FD portion 12 at the next stage. A charge detection section (floating gate section) 51 that completely transfers to the gate, a MOS transistor 52 having the floating gate section 51 as a gate, and a two-stage source follower amplifier 18 having the MOS transistor 52 as a first stage transistor. The

  In the present embodiment, a high dynamic output of signal charges is obtained by the front-stage amplifier, a low-sensitivity output of signal charges is obtained by the back-stage amplifier, and a wide dynamic range is realized by combining the two.

  As described above, according to each of the above-described embodiments, two charge detection amplifiers having different sensitivity differences are provided in series at the signal charge output section, and the previous charge detection amplifier is a signal charge complete transfer type (non-destructive type). ) And combining the outputs of both charge detection amplifiers, it is possible to achieve both high charge detection sensitivity and a high signal charge handling amount.

  In the above-described embodiment, the output horizontal charge transfer path (HCCD) is described as an example of a solid-state imaging device. However, the HCCD is divided into a plurality of short divided HCCDs, and an output signal is read out from each of them. Although there are those in which the output part of the HCCD is branched into two or three and the output signal is read out from each of the branched HCCDs, the above-described embodiments can be applied to each of these charge output parts.

  In addition, the low-sensitivity amplifier and the high-sensitivity amplifier of the above-described embodiment may be provided in series in the portion for reading the signal charge of each pixel of the CMOS image sensor, and the pre-stage amplifier may be a complete transfer type.

Furthermore, in each of the above-described embodiments, the amplifier provided in the subsequent stage is a charge destructive amplifier, but it goes without saying that both the pre-stage and the subsequent stage may be non-destructive amplifiers.
Furthermore, the voltage breakdown type amplifier and the voltage non-destructive type amplifier are not limited to the above-described various amplifiers. For example, a floating well amplifier having higher sensitivity than the floating surface amplifier may be used in the preceding stage.

  Since the electronic device with a charge detection amplifier according to the present invention has a configuration in which two charge detection amplifiers have a sensitivity difference and synthesize the output signals of the output amplifiers, a combined signal with a wide dynamic range can be obtained, and solid-state imaging can be obtained. When applied to an element, a digital camera capable of capturing an image with a wide dynamic range can be configured.

It is explanatory drawing of the CCD type solid-state image sensor which concerns on one Embodiment of this invention. It is a functional block diagram of the digital camera carrying the CCD type solid-state image sensor shown in FIG. It is a figure which shows the example of an output of two amplifiers with which the sensitivity differs mounted in the CCD type solid-state image sensor shown in FIG. It is a graph which shows the example of a synthesis | combination of two outputs shown in FIG. It is explanatory drawing of the CCD type solid-state image sensor which concerns on another embodiment of this invention.

Explanation of symbols

1,50 CCD type solid-state imaging device 3 Photodiode 4 Vertical charge transfer path (VCCD)
5 Horizontal charge transfer path (HCCD)
DESCRIPTION OF SYMBOLS 11 Floating gate 12 Floating diffusion (FD) part 13 Reset gate 16 1st charge detection amplifier 17 Output terminal 21 of 1st charge detection amplifier 2nd charge detection amplifier 22 Output terminal 31 of 2nd charge detection amplifier 31 System control part

Claims (7)

  In an electronic device with a charge detection amplifier that outputs a signal corresponding to the amount of charge of a signal charge from an amplifier, the signal charge corresponding to the amount of charge of the signal charge is output and the signal charge after the output of the signal is completely transferred to the subsequent stage A first charge detection amplifier for transferring, and a second charge detection amplifier for outputting a signal corresponding to the charge amount of the signal charge which has a sensitivity difference between the first charge detection amplifier and has been completely transferred to the subsequent stage. An electronic device with a charge detection amplifier.   2. The electronic device with a charge detection amplifier according to claim 1, further comprising means for setting or selecting the sensitivity difference.   The first charge detection amplifier is one of a “floating gate amplifier”, a “floating surface amplifier”, and a “floating well amplifier”, and the second charge detection amplifier is a “floating gate amplifier”. 3. The electronic device with a charge detection amplifier according to claim 1, wherein the electronic device is a “floating surface amplifier” or a “floating diffusion amplifier”.   2. The electronic device with a charge detection amplifier is a solid-state image sensor, and the signal charge is a signal charge accumulated by a photoelectric conversion element provided in the solid-state image sensor in accordance with an amount of received light. The electronic device with an output amplifier according to claim 3.   The solid-state imaging device includes a plurality of signal charge output units, and the first charge detection amplifier and the second charge detection amplifier are provided for each signal charge output unit. Electronic device with charge detection amplifier.   6. A solid-state imaging device according to claim 4 or 5, and a control means for synthesizing captured image signals having different sensitivities output from the first charge detection amplifier and the second charge detection amplifier of the solid-state imaging device, respectively. A digital camera comprising:   7. The digital camera according to claim 6, wherein the control unit corrects the synthesized image signal based on the stored performance information of the first charge detection amplifier and the second charge detection amplifier. .

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