JP2007181088A - Solid-state imaging apparatus and camera system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an MOS solid-state imaging apparatus and camera system for simultaneously achieving noise reduction, sensitivity improvement and dynamic range expansion in imaging under low illuminance. <P>SOLUTION: A solid-state imaging apparatus 500a comprises a plurality of column signal amplifying means 505 provided for each column of unit pixels 501. In accordance with a signal inputted to a gain switching terminal 510, the solid-state imaging apparatus 500a is capable of switching a gain of the column signal amplifying means 505. By increasing the gain of the column signal amplifying means 505 in imaging under low illuminance, the level of noise caused by a noise elimination circuit 506a is not amplified by an output amplifier 508, thereby simultaneously achieving sensitivity improvement and noise reduction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device and a camera system, and more specifically, a MOS type solid-state imaging device used for home video camera digital, a still camera, a mobile phone camera, an in-vehicle camera, and the like, and the solid-state imaging device The present invention relates to a camera system using.

  In recent years, in image input devices such as a digital still camera and a digital video camera, the number of pixels of a sensor has been increased in order to improve the quality of a captured image. In order to increase the number of pixels, it is required to reduce the pixel size, increase the readout time, and reduce the noise. In response to these requirements, a method of reading out a pixel signal by dividing it into a plurality of readout channels has been developed (see, for example, Patent Document 1).

  Hereinafter, a solid-state imaging device using a conventional noise reduction technique will be described.

  FIG. 8 is a schematic diagram of a conventional MOS solid-state imaging device described in Patent Document 1. In FIG.

  The solid-state imaging device 100 shown in FIG. 8 reads signals from a plurality of unit pixels 101 arranged two-dimensionally, a plurality of vertical signal lines 102 connected to each of the unit pixels 101 aligned in the same column, and the like. A row selecting unit 103 for selecting a row, a column selecting unit 104 for selecting a column from which a signal is read, a plurality of column signal amplifying units 105, a plurality of noise removing circuits 106, a horizontal signal line 107, and an output amplifier 108; Is provided.

  The unit pixel 101 accumulates charges obtained by photoelectrically converting incident light. In response to the selection of the row by the row selection means 103, each of the unit pixels 101 aligned with the selected row outputs an electrical signal corresponding to the accumulated charge to each of the vertical signal lines 102.

  Next, the column signal amplification means 105 amplifies the signal on the vertical signal line 102, and the noise removal circuit 106 removes noise included in the amplified signal by a process such as CDS (Correlated Double Sampling). The signal after noise removal is sequentially output to the horizontal signal line 107 in accordance with the column selection by the column selection means 104.

The signal output to the horizontal signal line 107 is amplified again by the output amplifier 108 and then output from the signal output terminal 109 to an external circuit or the like.
JP 2001-245221 A

  In recent years, solid-state imaging devices are required to achieve both high sensitivity and low noise as well as higher operating speed. However, the conventional solid-state imaging device as described above has a problem that it is difficult to achieve both high sensitivity and low noise.

  The details of the problem will be described below with reference to FIG.

  FIG. 9 is a diagram showing the relationship between the amount of incident light and output characteristics (photoelectric conversion characteristics) in a conventional MOS type solid-state imaging device. In FIG. 9, the broken line indicates the output characteristics when the gain of the amplifier circuit is set to a standard predetermined value, and the solid line indicates the case where the gain of the amplifier circuit is set to three times the predetermined value. Output characteristics are shown.

  The sensitivity of the solid-state imaging device can be improved by increasing the gain of the amplifier circuit. However, when setting the gain of the amplifier circuit, it is necessary to consider the saturation point of the subsequent circuit that processes the output signal from the solid-state imaging device.

  First, when imaging under standard illuminance, the gain is set so as to show the output characteristic as shown by the broken line in FIG. 9 with respect to the “saturation point of the subsequent circuit that receives the output signal” shown in FIG. Is set. In this case, the solid-state imaging device can output an image signal in the range of the incident light amount in which the output voltage is equal to or lower than the saturation point of the subsequent circuit.

  Next, when imaging under low illuminance is assumed, the output from the solid-state imaging device is designed so that the gain is, for example, three times the standard gain, as shown by the solid line in FIG. A method of amplifying the signal is generally adopted.

  However, when the solid-state imaging device is designed by simply fixing the gain to three times the standard gain, the amount of incident light reaching the “saturation point of the subsequent circuit that receives the output signal” is lower than that indicated by the broken line. Therefore, there arises a problem that the unit pixel cannot be used until its saturation output is reached.

  Furthermore, with respect to the problem that the unit pixel cannot be used until the saturation output, it is considered to provide a function such as AGC (automatic gain control) or digital gain variable by an AD converter inside the solid-state imaging device. Yes. However, these are functions that make the gain of the final output amplifier variable by the final output amplifier, the pipeline ADC, and the like, and it is impossible to achieve low noise.

  Therefore, the present invention provides a MOS type solid-state imaging device capable of realizing low noise even when gain is increased at low illuminance and making use of pixel saturation output even during standard imaging, and a camera system using the same The purpose is to provide.

  The first aspect of the present invention is directed to a solid-state imaging device. The solid-state imaging device includes a plurality of unit pixels that are two-dimensionally arranged including a light receiving element, a column amplification unit that is provided for each column of unit pixels, and that amplifies a signal output from the unit pixel, and column amplification Gain switching means for switching the gain of the means.

  The column amplifying means includes two or more amplifier circuits each having a different gain and connected in parallel, and the gain switching means includes at least one gain switching terminal. One of the amplifier circuits may be selected in accordance with the input signal.

  The solid-state imaging device is electrically connected to each of a plurality of unit pixels aligned in the same column, a plurality of vertical signal lines electrically connected to the column amplification means, and each of the vertical signal lines. A noise removing circuit for removing noise contained in a signal output from the column amplification means, a horizontal signal line electrically connected to each of the noise removing circuits, and an output amplifier electrically connected to the horizontal signal line And may further be provided.

  The solid-state imaging device includes a storage unit that holds a signal output from the column amplification unit, a noise removal circuit that removes noise included in the signal output from the column amplification unit, and a capacity of the storage unit And storage capacity switching means for switching between.

  In this case, the storage means includes two or more first storage parts each having a different capacity and connected in parallel, and a second storage part, and the storage capacity switching means switches the storage capacity switching. One of the first storage units may be selected in accordance with a signal input to the storage capacitor switching terminal.

  Furthermore, the gain switching means and the storage capacity switching means may be controlled independently.

  Alternatively, the gain switching means and the storage capacity switching means may be controlled simultaneously.

  Further, the solid-state imaging device may be a MOS type solid-state imaging device.

  The second aspect is directed to a camera system including the solid-state imaging device according to the first aspect. The camera system includes a solid-state imaging device and sensitivity setting means for outputting a control signal for designating sensitivity, and the gain switching means is based on the control signal output from the sensitivity setting means. The gain is switched.

  In this case, the sensitivity setting unit may detect illuminance and output a control signal based on the detected illuminance.

  Further, the camera system may be mounted on a vehicle having a light, and the sensitivity setting means may output a control signal according to switching between lighting and extinguishing of the light.

  The third aspect is directed to a solid-state imaging device. The solid-state imaging device includes a light receiving element, includes a plurality of unit pixels arranged two-dimensionally, and storage means for holding a signal output from the unit pixel, and is included in a signal output from the unit pixel. A noise removal circuit for removing the generated noise, and storage capacity switching means for switching the capacity of the storage means.

  In this case, the storage means includes two or more first storage parts each having a different capacity and connected in parallel, and a second storage part, and the storage capacity switching means switches the storage capacity switching. One of the first storage units may be selected in accordance with a signal input to the storage capacitor switching terminal.

  The fourth aspect is directed to a camera system including the solid-state imaging device according to the third aspect. The camera system includes a solid-state imaging device and sensitivity setting means for outputting a control signal for designating sensitivity, and the storage capacity switching means is based on the control signal output from the sensitivity setting means. The capacity is switched.

  In this case, the sensitivity setting unit may detect illuminance and output a control signal based on the detected illuminance.

  Further, the camera system may be mounted on a vehicle having a light, and the sensitivity setting means may output a control signal according to switching between turning on and off the light.

  According to the present invention, by adjusting the gain of the column amplifying means from the outside, it is possible to realize low-noise imaging when the gain is increased, and during normal gain, the unit pixel is effectively used until reaching the saturated output, and a high dynamic range is achieved. Therefore, both high sensitivity and low noise can be achieved.

  Further, by combining a configuration in which the storage capacity of the capacitor used in the noise removal circuit (CDS) can be freely selected, noise can be further reduced, and the degree of freedom in selecting an imaging state can be improved.

  In the MOS type solid-state imaging device according to the present invention, the circuit format of each pixel is not particularly limited. The pixel may be provided with a circuit that can perform photoelectric conversion and output the signal component and the signal component after reset. The MOS type solid-state imaging device may be an active type solid-state imaging device that converts a signal charge into a voltage by a floating diffusion capacitor and outputs the voltage using an amplifier circuit including an amplifier. It may be a passive solid-state imaging device that is not provided. Furthermore, the conductivity type of each element is not particularly limited.

(First embodiment)
FIG. 1 is a diagram showing a schematic configuration of a solid-state imaging apparatus according to the first embodiment of the present invention.

  The solid-state imaging device 500a includes a plurality of unit pixels 501, a plurality of vertical signal lines 502, a row selection unit 503 that selects a row in which the unit pixels 501 are aligned, and a column selection unit 504 that selects a column in which the unit pixels are aligned. A plurality of column signal amplifying means 505, a plurality of noise removing circuits 506a, a horizontal signal line 507, and an output amplifier 508.

  Each of the unit pixels 501 includes a light receiving element that accumulates charges obtained by photoelectrically returning incident light, such as a photodiode, and is two-dimensionally arranged in the row direction and the column direction. Each unit pixel 501 accumulates electric charge obtained by photoelectrically returning incident light, and outputs a signal to each vertical signal line 502 in accordance with row selection by the row selection means 503. Each of the vertical signal lines 502 is electrically connected to each of the plurality of unit pixels 501 aligned in the same column and each of the column signal amplifying means 505.

  Next, each of the column signal amplifying means 505 is provided for each column of the unit pixels 501 and amplifies the electric signal output from the unit pixel 501 to the vertical signal line 502 by a predetermined gain. Further details of the column signal amplification means 505 will be described later.

  Next, each of the noise removal circuits 506 a is provided for each column of the unit pixels 501 and is electrically connected to the column signal amplification unit 505. The noise removal circuit 506a removes noise included in the signal output from the column signal amplification unit 505 by performing processing such as CDS (Correlated Double Sampling), for example.

  The signals from which the noise has been removed are sequentially output to the horizontal signal line 507 in accordance with the column selection by the column selection means 504. The output amplifier 508 amplifies the signal output to the horizontal signal line 507 again and outputs the signal from the signal output terminal 509 to a subsequent circuit or the like.

  Furthermore, the solid-state imaging device 500a according to the present embodiment includes a gain switching terminal 510. The gain switching terminal 510 is electrically connected to each of the column signal amplification means 505.

  FIG. 2 is a diagram showing details of a portion A shown in FIG.

  The solid-state imaging device according to the present embodiment is characterized in that the gain of the column signal amplifying unit 505 can be switched according to the level (High or Low) of the signal input to the gain switching terminal 510. Hereinafter, this feature will be described in detail.

  First, as shown in FIG. 2, the column signal amplification means 505 includes amplification circuits 520a and 520b connected in parallel. In the example of FIG. 2, the amplifier circuit 520b is configured by connecting two amplifier circuits identical to the amplifier circuit 520a in series. For example, when the gain of the amplifier circuit a is A times, the gain of the amplifier circuit 520b is (A × A) times.

  Furthermore, the solid-state imaging device according to the present embodiment includes inversion means 600 that inverts the level of the signal input to the gain switching terminal 510, and switches 521a and 521b. The switch 521a is interposed between the amplifier circuit 520a and the vertical signal line 502, and the switch 521b is interposed between the amplifier circuit 520b and the vertical signal line 502. The gain switching terminal 510 is connected to the switch 521a and is connected to the other switch 521b via the inverting means 600. For example, the switches 521a and 521b are turned on when the level of the input signal is High, and are turned off when the level of the input signal is Low. In the present embodiment, the gain switching terminal 510, the inverting means 600, and the switches 521a and 521b correspond to the gain switching means.

  Here, the gain switching of the column signal amplification means 505 will be described.

  First, when a low level signal is input to the gain switching terminal 510 (hereinafter sometimes referred to as “standard mode”), the gain A of the amplifier circuit 520a is selected as the gain of the column signal amplifier 505.

  More specifically, when a low level signal is input to the gain switching terminal 510, the inversion means 600 outputs a high level signal, so that the switch 521a is turned on and the switch 521 is turned off. Therefore, only the amplifier circuit 520 a is connected to the vertical signal line 502, and the other amplifier circuit 520 b is disconnected from the vertical signal line 502. That is, the signal path having a gain of A times is conducted, and the signal path having a gain of (A × A) times is disconnected.

  On the other hand, when a high level signal is input to the gain switching terminal 510 (hereinafter sometimes referred to as “high gain mode”), the gain of the amplification circuit 520b is multiplied by the gain (A × A) as the gain of the column signal amplification means 505. Is selected.

  More specifically, when a high level signal is input to the gain switching terminal 510, the inversion means 600 outputs a low level signal, so that the switch 521a is turned off and the switch 521b is turned on. Therefore, the amplifier circuit 520a is disconnected from the vertical signal line 502, and only the other amplifier circuit 520b is connected to the vertical signal line 502. That is, the signal path having a gain of A times is disconnected, and the signal path having a gain of (A × A) times is conducted.

  As described above, the solid-state imaging device according to the present embodiment is characterized in that the gain of the column signal amplification unit 505 (hereinafter sometimes referred to as “column amplifier gain”) can be changed.

  Next, with reference to FIGS. 3A to 3C, the technical basis that noise reduction can be realized simultaneously with increasing the column amplifier gain will be described.

  FIG. 3A is a diagram schematically illustrating one signal path in the solid-state imaging device. FIG. 3B is a diagram illustrating a signal and noise level when the output amplifier gain is increased, and FIG. 3C is a diagram illustrating a signal and noise level when the column amplifier gain is increased. In FIGS. 3B and 3C, it is assumed that the pixel signals output from the solid-state imaging device are set to have the same amplitude.

  FIG. 3A shows a path from the signal output from the unit pixel 501 to the output from the output amplifier 508 through the vertical signal line 502, the column signal amplification means 505, the noise removal circuit 506a, and the horizontal signal line 507 in order. Indicates. Here, a point at which a signal is output from the unit pixel 501 to the vertical signal line 502 is defined as α point, a point at which a signal is output from the noise removal circuit 506a to the horizontal signal line is defined as β point, and the signal is output from the output amplifier 508. Let the point to be the θ point.

  First, a case where the pixel signal is amplified by increasing only the output amplifier gain will be described. As shown in FIG. 3B, pixel portion noise Npix is added to the signal at the point α. Further, the CDS noise Ncds is added to the signal at the point β by the noise removal circuit 506a. Thereafter, the signal at the point β is multiplied by Gout by the output amplifier 508, but not only the amplitude of the pixel signal but also the levels of the pixel noise Npix and the CDS unit noise Ncds are each amplified by Gout times.

  On the other hand, a case where the pixel signal is amplified by increasing only the column amplifier gain will be described. As shown in FIG. 3C, when increasing the gain of the column signal amplification means 505, the signal output from the unit pixel 501 is amplified to the output level before reaching the β point. In this case, the level of the pixel noise Npix is also amplified by Gcolumn times by the column signal amplifying unit 505, but the level of noise caused by the pixel portion at the β point is the same as the level at the θ point in FIG. 3B. Thereafter, the CDS noise Ncds is added to the pixel signal in the noise removal circuit. However, since the signal has already reached the required output level (signal amplitude), the output amplifier 508 receives the input signal and noise. There is no need to amplify.

  Therefore, by increasing the gain of the column signal amplifying unit 505, the level of noise caused by the noise removal circuit 506a can be reduced to an inverse number (1 / Gout times) of the output amplifier gain Gout.

  As described above, according to the solid-state imaging device according to the present embodiment, when a high-level signal is input to the gain switching terminal 510 (high gain mode), the gain of the column signal amplification unit 505 is (A × A ) Is set to double. Therefore, by increasing the gain, it is possible to improve the sensitivity of the solid-state imaging device and reduce noise caused by the noise removal circuit 506a.

  In the present embodiment, the solid-state imaging device that switches the gain in two stages by inputting a binary signal to one gain switching terminal has been described. However, the number of gain switching terminals and the input to the gain switching terminal are described. The type of signal to be performed and the number of gain switching stages are not limited to the above example.

  In the present embodiment, the circuit configuration is specified for convenience of explanation, but the circuit configuration of each unit is not particularly limited. In particular, instead of providing a column signal amplification unit including a plurality of amplification circuits as in the present embodiment, a column signal amplification unit including a single amplification circuit capable of gain switching is used to input to the gain switching terminal. Control may be made so that the gain is switched in accordance with the signal.

  Furthermore, in the present embodiment, the gain switching means is configured by using the gain switching terminal, the switch, and the inverting means. However, the gain switching means performs the column signal amplification according to the signal input to the gain switching terminal. What is necessary is just to be comprised so that the gain of a means can be switched.

(Second Embodiment)
FIG. 4 is a diagram showing a schematic configuration of a solid-state imaging apparatus according to the second embodiment of the present invention. Since the basic configuration of the solid-state imaging device 500b shown in FIG. 4 is the same as that according to the first embodiment, the following description will focus on the differences between the present embodiment and the first embodiment. explain.

  The solid-state imaging device 500b according to the present embodiment is characterized in that a signal is input from the storage capacitor switching terminal 511 to the noise removal circuit 506b in addition to the signal amplified by the column signal amplification unit 505. The solid-state imaging device 500b can switch the storage capacitor in the noise removal circuit 506b in accordance with the signal input from the storage capacitor switching terminal 511. The effect of switching the storage capacity will be described later.

  FIG. 5 is a diagram showing details of a portion B shown in FIG. As shown in FIG. 5, the configuration of the column signal amplifying unit 505 is the same as the configuration according to the first embodiment (FIG. 2), and the description thereof will be omitted.

  The noise removal circuit 506b includes clamp capacitors 610a and 610b, a sampling capacitor 612, and a clamp switch 613. The clamp capacitors 610a and 610b have different capacitances and are connected in parallel. As an example, the capacitance of the clamp capacitor may be set to (Ccp × 2) with respect to the capacitance Ccp of the clamp capacitor 610a. The clamp capacitors 610a and 610b are connected to the column signal amplifying means 505 via switches 621a and 621b, respectively. The sampling capacitor 612 is connected to a clamp power source 611 via a clamp switch 613. In the present embodiment, the clamp capacitors 610a and 610b correspond to the first storage unit, and the sampling capacitor 612 corresponds to the second storage unit.

  Further, the noise removal circuit 506b includes an inverting means 601 for inverting the level of the signal input to the storage capacitor switching terminal 511, and switches 621a and 621b. The switch 621a is interposed between the clamp capacitor 610a and the column signal amplification means 505, and the switch 621b is interposed between the clamp capacitor 610b and the column signal amplification means 505. The storage capacitor switching terminal 511 is connected to the switch 621 a and is connected to the other switch 621 b through the inverting means 601. The switches 621a and 621b are turned on or off in the same manner as the switches 521a and 521b depending on the level of the input signal. In the present embodiment, the storage capacitor switching terminal 511, the inverting means 601, and the switches 621a and 621b correspond to storage capacity switching means.

  A signal for switching the clamp capacitor of the noise removal circuit 506b is input to the storage capacitor switching terminal 511. For example, the clamp capacitor of the noise removal circuit 506b is switched in two steps corresponding to each of the binary signals (High or Low) input to the storage capacitor switching terminal 511.

  First, when a low level signal is input to the storage capacitor switching terminal 511 (standard state), the inversion means 601 outputs a high level signal, so the clamp capacitor 610a is electrically connected to the column signal amplification means 505. The other clamp capacitor 610b is disconnected from the column signal amplification means 505.

  On the other hand, when a high level signal is input to the storage capacitor switching terminal 511 (high gain mode), the inverting means 601 outputs a low level signal, so that the clamp capacitor 610a is connected to the column signal amplifying means 505. The other clamp capacitor 610b is electrically connected to the column signal amplification means 505.

  As described above, the solid-state imaging device 500b according to the present embodiment is characterized in that the gain is changed by changing the capacitance ratio between the clamp capacitor and the sampling capacitor included in the noise removal circuit 506b.

  Next, the operation principle of the noise removal circuit 506b and the effect of switching the storage capacitor will be described with reference to FIGS. 6A and 6B.

  FIG. 6A is a diagram illustrating a schematic configuration of the noise removal circuit, and FIG. 6B is a diagram illustrating timing of signals supplied to the noise removal circuit.

  A noise removal circuit 506b shown in FIG. 6A includes a clamp capacitor 610 for clamping a signal output from the column signal amplification unit 505, a clamp power source 611 for setting the terminal voltage of the clamp capacitor 610 to a reference potential, A clamp switch 613 and a sampling capacitor 612 for holding a differential voltage with respect to the reference potential are included.

  First, a dark signal (noise component) from a pixel is input to the noise removal circuit 506b via the column signal amplification unit 505. By turning on the clamp switch 613 simultaneously with the input of the dark signal, the sampling capacitor 612 holds the clamp voltage applied from the clamp power supply 611 as a reference voltage.

  Next, simultaneously with turning off the clamp switch 113, a signal obtained by amplifying a signal output from the unit pixel at the time of incident light is input from the column signal amplifying unit 505 to the clamp capacitor 610.

  As a result, the sampling capacitor 612 holds the voltage that has changed from the clamp voltage (noise component) by the amount of the signal at the time of light incidence, and thus outputs a differential signal (signal at point A) from which noise has been removed.

数１から明らかなように、クランプキャパシタ６１０のクランプ容量Ｃｃｐが増加するにつれて、Ｖｏｕｔの減衰量が小さくなる。 Here, assuming that the voltage of the signal output from the column signal amplifying unit 505 is Vin and the amplitude at the point A shown in FIG. 6A is Vout, in the noise removing circuit 506b operating as described above, Vout is capacity distribution. Is expressed as the following equation (1).

As apparent from Equation 1, as the clamp capacitance Ccp of the clamp capacitor 610 increases, the attenuation amount of Vout decreases.

よって、クランプ容量Ｃｃｐを大きくすることによって、ｋＴＣノイズを低減することができる。 Further, kTC noise generated when the column signal amplifying unit 505 charges the clamp capacitor 610 is expressed by the following equation (2).

Therefore, kTC noise can be reduced by increasing the clamp capacitance Ccp.

  However, when the clamp capacitor Ccp increases, the charging time required for the column signal amplifier 505 to charge the clamp capacitor 610 increases. Therefore, the noise removal circuit 506b in which the clamp capacitance is simply increased may not be suitable for high-speed imaging depending on the current supply capability of the column signal amplification unit 505. Therefore, it is particularly important that the clamp capacity can be switched according to the purpose of imaging as in the solid-state imaging device according to the present embodiment.

  Here, details will be described for a case where the noise removal circuit in which the clamp capacitance is simply increased is not suitable for high-speed imaging depending on the current supply capability of the column signal amplification means 505.

  For example, it is assumed that the clamp capacitance Ccp is 9 pF and 3 pF. Further, it is assumed that the sampling capacitor Csp of the sampling capacitor 612 is 2 pF.

First, when the clamp capacitance Ccp is 9 pF, by substituting the values of Ccp and Csp into the above equation 1, Vout is expressed as the following equation 3.

Next, when the clamp capacitance Ccp is 3 pF, by substituting the values of Ccp and Csp into the above equation 1, Vout is expressed as the following equation 4.

  If the resistance value R of the vertical signal line is 100Ω, the time constant T when the clamp capacitance Ccp is 9 pF is 0.9 ns. On the other hand, the time constant T when the clamp capacitance Ccp is 3 pF is 0.3 ns.

  The time constant T affects the row signal transfer period in the horizontal blanking period. Therefore, when this time constant T is large, the horizontal blanking period becomes long, so that the time required to construct an image of one frame becomes long. Therefore, an increase in clamp capacity has an effect on speeding up.

  As described above, the noise removal circuit in which the clamp capacitance is simply increased may not be suitable for high-speed imaging depending on the current supply capability of the column signal amplification means. However, since the solid-state imaging device according to the present embodiment can switch the clamp capacitance according to the imaging purpose, the gain can be made variable regardless of whether or not the column signal amplification means is employed. It has characteristics.

  In the present embodiment, the solid-state imaging device that switches the storage capacity in two stages by inputting a binary signal to one storage capacity switching terminal has been described. However, the number of storage capacity switching terminals, the storage capacity, The type of signal input to the switching terminal and the number of storage capacitor switching stages are not limited to the above example.

Hereinafter, an advantage of switching the gain of the column signal amplifying unit 505 and the clamp capacitor of the noise removing circuit 506b together will be described. By using the gain switching function of the column signal amplifying means 505 and the clamp capacity switching function of the noise removal circuit 506b in combination, the solid-state imaging device according to the present embodiment can cope with any imaging purpose.

Table 1 shows the correspondence between the combination of the gain and clamp capacity of the column signal amplification means and the imaging purpose. As shown in Table 1, it is preferable that the gain of the column signal amplification means and the clamp capacity can be switched independently according to the imaging purpose. However, when the number of control signals that can be input from the outside of the solid-state imaging device is limited, as shown in the following Table 2, there are two types of combinations of the gain of the column signal amplification means and the clamp capacitance. You may limit to. In this case, the gain of the column signal amplification means and the clamp capacity may be controlled simultaneously. One terminal may be shared as a gain switching terminal and a storage capacitor switching terminal.

  Further, common points and differences between the function of switching the gain of the column signal amplification means and the function of switching the clamp capacitance will be described. The point of adjusting the gain when a column signal (base signal) is amplified is common to both functions. However, the function of switching the gain of the column signal amplifying means is mainly intended to positively increase the gain, whereas the function of switching the clamp capacity is mainly intended to adjust the gain attenuation. . Therefore, in general, it can be said that the noise reduction effect by gain switching is greater than that by clamp capacitance switching.

  Furthermore, considering the fact that the readout time is increased by increasing the clamp capacity, in general, the switching of the gain of the column signal amplification means is superior from the viewpoint of high-speed imaging operation than the switching of the clamping capacity. I can say that. However, the function of switching the clamp capacitor has an advantage in that the gain can be adjusted regardless of whether or not the column signal amplification means is employed.

  Furthermore, in the present embodiment, the storage capacitor switching means is constituted by the storage capacitor switching terminal, the switch, and the inverting means, but the storage capacitor switching means is configured according to the signal input to the storage capacitor switching terminal. What is necessary is just to be comprised so that storage capacity can be switched.

  Furthermore, instead of the solid-state imaging device according to the present embodiment, a solid-state imaging device having only a storage capacity switching function may be configured. That is, the solid-state imaging device includes a plurality of unit pixels arranged in a two-dimensional manner and storage means that is electrically connected to each of the unit pixels aligned in the same column and holds a signal output from the unit pixel. In addition, a noise removal circuit that removes noise included in the signal output from the unit pixel and a storage capacitor switching unit that switches the capacity of the storage unit may be provided. According to such a configuration, the gain attenuation can be adjusted as described above regardless of the presence or absence of the column signal amplification means.

(Third embodiment)
FIG. 7 is a diagram showing a schematic configuration of a camera system according to the third embodiment of the present invention. More specifically, it is a diagram showing a schematic configuration of a camera system capable of controlling the column amplifier gain. The camera system is meant to include cameras for various uses, image input devices, and devices including these.

  The camera system 699 includes a solid-state imaging device 500b according to the second embodiment formed on a chip, an ISO sensitivity setting mechanism 700, an illuminance sensor 701, a headlight switch 702, a CDS / AD conversion unit 703, A DSP (signal processing unit) 704.

  A control signal is input manually or automatically from the ISO sensitivity setting mechanism 700, the illuminance sensor 701, and the headlight switch 702 to the gain switching terminal 510 and the storage capacitor switching terminal 511 of the solid-state imaging device 500b. As described in the second embodiment, the solid-state imaging device 500b can switch at least one of the column amplifier gain and the clamp capacitor in accordance with the input control signal.

  The CDS / AD conversion unit 703 converts the image information output from the signal output terminal 509 of the solid-state imaging device 500b into digital information.

  The DSP 704 performs predetermined signal processing on the digital information output from the CDS / AD conversion unit 703, and outputs the information subjected to the signal processing as an image.

  The ISO sensitivity setting mechanism 700 outputs a control signal corresponding to the sensitivity setting. Therefore, by using the ISO sensitivity setting mechanism 700, it is possible to switch between imaging a subject under low illuminance with low noise and imaging a subject under high illuminance giving priority to the dynamic range.

  The illuminance sensor 701 detects illuminance and outputs a control signal corresponding to the detected illuminance. Therefore, by using the illuminance sensor 701, it is possible to set a gain and a clamp capacity according to the illuminance.

  Alternatively, when the camera system 699 is used for in-vehicle use, the headlight switch 702 may be used both for controlling the headlight 800 and for switching the imaging state of the solid-state imaging device 500b.

  The camera system 699 according to the present embodiment is configured such that all of the ISO sensitivity setting mechanism 700, the illuminance sensor 701, and the headlight switch 702 output control signals. Only one of them may be provided.

  In addition, the control signal output from the ISO sensitivity setting mechanism 700, the illuminance sensor 701, and the sensitivity setting means such as the headlight switch 702 may be a binary signal or a continuous signal. Further, the number of stages of the control signal is not particularly limited.

  Furthermore, in this embodiment, as a specific example of the sensitivity setting means, an ISO sensitivity setting mechanism 700, an illuminance sensor 701, and a headlight switch 702 are shown, but they are used for switching the column amplifier gain and the clamp capacity. Other control means may be used as the sensitivity setting means as long as possible information can be output.

  Furthermore, the camera system according to the present embodiment may include a solid-state imaging device having only a storage capacity switching function. In this case, the signal output from the sensitivity setting means is input to the storage capacitor switching terminal of the solid-state imaging device. According to such a camera system, it is possible to achieve an effect of adjusting the gain attenuation regardless of the presence or absence of the column signal amplification means.

  According to the solid-state imaging device according to the present invention, it is possible to significantly reduce noise particularly when imaging under low illuminance as compared with the conventional solid-state imaging device. Also, an image with a high S / N ratio can be taken. For this reason, the solid-state imaging device according to the present invention is used in, for example, a high-quality single-lens reflex digital still camera, a consumer or professional digital still camera, and is required to have a high S / N image quality at low illuminance. This is particularly useful for a MOS solid-state imaging device, a broadcasting MOS solid-state imaging device mainly for high-definition video imaging, an astronomical observation camera, an in-vehicle camera, or the like.

The figure which shows schematic structure of the solid-state imaging device which concerns on the 1st Embodiment of this invention. The figure which shows the detail of A part shown by FIG. The figure which shows typically one signal path | route in a solid-state imaging device Diagram showing signal and noise levels when output amplifier gain is increased Diagram showing signal and noise levels when increasing column amplifier gain The figure which shows schematic structure of the solid-state imaging device which concerns on the 2nd Embodiment of this invention. The figure which shows the detail of B part shown by FIG. The figure which shows schematic structure of a noise removal circuit The figure which shows the timing of the signal which is supplied to the noise removal circuit The figure which shows schematic structure of the camera system which concerns on the 3rd Embodiment of this invention. Schematic diagram of a conventional MOS solid-state imaging device The figure which shows the relationship between the incident light quantity and output characteristic (photoelectric conversion characteristic) in the conventional MOS type solid-state imaging device.

Explanation of symbols

500 Solid-state imaging device 501 Unit pixel 502 Vertical signal line 503 Row selection means 504 Column selection means 505 Column signal amplification means 506 Noise removal circuit 507 Horizontal signal line 508 Output amplifier 509 Signal output terminal 510 Gain switching terminal 511 Storage capacitor switching terminal 600 601 Inversion means 610 Clamp capacitor 611 Clamp power supply 612 Sampling capacitor 699 Camera system 700 ISO sensitivity setting mechanism 701 Illuminance sensor 702 Headlight switch 703 CDS / AD conversion unit 704 DSP (signal processing unit)
800 headlights

Claims (16)

A solid-state imaging device,
A plurality of unit pixels including a light receiving element and arranged two-dimensionally;
A column amplifying unit provided for each column of the unit pixels and amplifying a signal output from the unit pixel;
A solid-state imaging device comprising: gain switching means for switching the gain of the column amplification means. The column amplifying means includes two or more amplifier circuits each having a different gain and each connected in parallel,
2. The solid state according to claim 1, wherein the gain switching means includes at least one gain switching terminal, and selects one of the amplifier circuits according to a signal input to the gain switching terminal. Imaging device. Each of a plurality of unit pixels aligned in the same column, and a plurality of vertical signal lines electrically connected to the column amplification means;
A noise removal circuit that is electrically connected to each of the vertical signal lines and removes noise contained in a signal output from the column amplification means;
A horizontal signal line electrically connected to each of the noise removal circuits;
The solid-state imaging device according to claim 1, further comprising an output amplifier electrically connected to the horizontal signal line. A noise removal circuit that includes storage means for holding a signal output from the column amplification means, and that removes noise included in the signal output from the column amplification means;
The solid-state imaging device according to claim 1, further comprising storage capacity switching means for switching the capacity of the storage means. The storage means includes
Two or more first storage units each having a different capacity and each connected in parallel;
A second storage unit,
The storage capacitor switching means includes a storage capacitor switching terminal, and selects one of the first storage units according to a signal input to the storage capacitor switching terminal. Solid-state imaging device.   6. The solid-state imaging device according to claim 4, wherein the gain switching unit and the storage capacity switching unit are controlled independently of each other.   6. The solid-state imaging device according to claim 4, wherein the gain switching unit and the storage capacity switching unit are controlled simultaneously.   The solid-state imaging device according to claim 1, wherein the solid-state imaging device is a MOS solid-state imaging device. A camera system,
A solid-state imaging device according to any one of claims 1 to 8,
Sensitivity setting means for outputting a control signal for designating sensitivity,
The gain switching means switches the gain of the column amplification means based on a control signal output from the sensitivity setting means.   The camera system according to claim 9, wherein the sensitivity setting unit detects illuminance and outputs the control signal based on the detected illuminance. The camera system is mounted on a vehicle having a light,
The camera system according to claim 9, wherein the sensitivity setting unit outputs the control signal in accordance with switching between turning on and off of the light. A solid-state imaging device,
A plurality of unit pixels including a light receiving element and arranged two-dimensionally;
A noise removal circuit that includes storage means for holding a signal output from the unit pixel, and that removes noise included in the signal output from the unit pixel;
A solid-state imaging device comprising storage capacity switching means for switching the capacity of the storage means. The storage means includes
Two or more first storage units each having a different capacity and each connected in parallel;
A second storage unit,
The storage capacitor switching unit includes a storage capacitor switching terminal, and selects one of the first storage units according to a signal input to the storage capacitor switching terminal. Solid-state imaging device. A camera system,
A solid-state imaging device according to claim 12 or 13,
Sensitivity setting means for outputting a control signal for designating sensitivity,
The storage capacity switching means switches the capacity of the storage means based on a control signal output from the sensitivity setting means.   The camera system according to claim 14, wherein the sensitivity setting unit detects illuminance and outputs the control signal based on the detected illuminance. The camera system is mounted on a vehicle having a light,
The camera system according to claim 14, wherein the sensitivity setting unit outputs the control signal in accordance with switching between turning on and off of the light.

Images