JP2002343954A - Solid-state image sensing element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enlarge the dynamic range of an output signal to a light receiving amount by ensuring linear characteristics of an output of an output part of a CCD linear sensor. SOLUTION: An overflow control gate 162 and an overflow drain 164 are arranged on an N-th register gate 142N of one transfer register 140A out of two transfer registers 140A, 140B which have the same characteristics. When the amount of signal charges of the transfer register 140A becomes at least a definite threshold value (Qc), an excessive amount of the signal charges is discharged to the outside. Consequently, an output signal from an output part 150 is increased with gently linear characteristic in a region where the light receiving amount of a sensor part approaches a saturation region. As a result, the light receiving amount of the sensor can ensure linear characteristics of an output signal in the vicinity of the saturation region, and the dynamic range of the output signal to the light receiving amount can be enlarged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image sensor such as a linear sensor using a CCD, and more particularly to a solid-state image sensor capable of expanding a dynamic range of an output with respect to a received light amount.

[0002]

2. Description of the Related Art Conventionally, a CCD linear sensor having a structure as shown in FIG. 3 has been known. The arrows in the figure indicate the direction in which the signal charges are transferred. This C
The CD linear sensor includes a pair of sensor arrays 20A and 20B, a pair of readout gates (readout gates) 30A and 30B, a pair of transfer registers 40A and 40B, and a common output unit 50 on a semiconductor substrate 10. It is provided. Each of the sensor rows 20A and 20B is composed of a plurality of photosensors 22 arranged in one direction, and is provided adjacent to and parallel to each other. Each photo sensor 22
Has a structure as, for example, a photodiode, and usually accumulates signal charges according to the amount of received light. Each of the read gates 30A and 30B reads the signal charges accumulated in each of the photosensors 22 by a read pulse, and sets the signal charges in each of the transfer registers 40A and 40B.

Each transfer register 40A, 40B transfers a signal charge to the output section 50 in synchronization with a transfer clock pulse, and the final output stage of each transfer register 40A, 40B has each transfer register 40A, 40B. A junction gate 44 for joining the signal charges is provided. The signal charges transferred by the transfer registers 40A and 40B are merged by the merge gate unit 44, and the added signal charges are transferred from the final horizontal output gate unit (HOG) 46 to the charge-voltage converter (FD) of the output unit 50. A floating diffusion portion).

The output unit 50 detects the signal charge generated in the FD unit and converts the signal charge into an image signal. For example, the output unit 50 periodically resets the detected value of the signal charge by a reset clock corresponding to a transfer clock. Meanwhile, a new signal charge is sequentially detected and appropriately amplified, thereby outputting a voltage signal (imaging signal) corresponding to the signal charge. For example,
The N-th photo sensor 22A of the sensor rows 20A and 20B
The signal charges of N and 22BN are added and output, and each of the photosensors 22AN and 22BN can be regarded as one pixel in total.

[0005]

By the way, in the conventional CCD linear sensor as described above, the output signal obtained from the output section 50 has a single linear characteristic with respect to the light receiving amount within a certain range of the photo sensor. It has become something. FIG. 4 is an explanatory diagram showing the output characteristics with respect to such a light receiving amount. The vertical axis indicates the signal charge amount transferred by the transfer register, and the horizontal axis indicates the light receiving amount in the photo sensor. Then, for example, the above-described sensor row 2
0A, 20B Nth photo sensor 22AN, 22B
When the signal charges of N are AN and BN, the curve d in FIG.
Indicates the values of the signal charges AN and BN.

That is, each photo sensor 22AN, 22
Since the BNs are adjacent to each other, the signal charges AN and BN
Are almost the same value, and each photo sensor 22AN, 2
Up to the same saturation region of 2BN, each rises with a linear characteristic, and when approaching the saturation region, the rise is suppressed. On the other hand, a curve e in FIG. 4 shows the signal charge amount at the merging gate section 44, that is, the added value of the signal charge AN and the signal charge BN. Until the saturation region is approached, the increase is suppressed. Therefore, in the conventional CCD linear sensor, if the amount of light received by each photosensor 22 becomes large and becomes close to the saturation region, there arises a problem that an accurate output signal cannot be obtained.

On the other hand, in an image input apparatus such as a scanner using a CCD linear sensor, signal processing (γ correction) is performed by software processing.
In the light receiving region where the output from the CD linear sensor is saturated,
Even if software signal processing is performed, it is difficult to secure the gradation.

Accordingly, an object of the present invention is to increase the dynamic range of an output signal with respect to the amount of received light while securing the linear characteristics of the output even when the amount of light received by the photosensor is close to the saturation region. It is to provide a solid-state imaging device which can perform the above.

[0009]

In order to achieve the above object, the present invention provides a semiconductor device comprising a plurality of photosensors, a transfer register for sequentially transferring signal charges detected by the photosensors, and a transfer register. In a solid-state imaging device provided with an output unit for converting the transferred signal charges into an output signal, the solid-state imaging device includes a plurality of photosensors arranged in one direction, and at least one pair of parallel sensor rows adjacent to each other, A pair of transfer registers that are provided corresponding to the pair of sensor rows, respectively, and transfer signal charges along the arrangement direction of the photosensor units of each sensor row; a merging gate unit where the pair of transfer registers merge; An output unit for detecting a signal charge generated in the junction gate unit and converting the signal charge into an output signal, wherein one of the transfer registers of the pair of transfer registers is provided. A solid-state imaging device characterized in that a limiting means for limiting the amount of charges.

In the solid-state imaging device of the present invention, when the amount of light received by the photo sensor increases, the amount of charge handled by one transfer register is limited by the operation of the limiting means for limiting the amount of charge handled by one transfer register. As a result, of the signal charge amounts obtained by summing up the signal charge amounts of the respective sensor rows generated at the merging gate section, the signal charge amount of one transfer register is limited, and the change amount of the signal charge amount corresponding to the other transfer register is corresponding. It changes with the changed characteristics. As a result, even when the amount of light received by the photo sensor is close to the saturation region, the linear characteristic of the signal charge at the junction gate is secured by limiting the amount of charge handled by one of the transfer registers, and Since the linear characteristics of the output in the section can be secured, the dynamic range of the output signal with respect to the amount of received light can be expanded.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the solid-state imaging device according to the present invention will be described below. In the present embodiment, the present invention is applied to a CCD linear sensor having a pair of sensor rows. FIG. 1 shows a CCD according to the present embodiment.
FIG. 3 is a schematic plan view illustrating a configuration of a linear sensor. The arrows in the figure indicate the direction in which the signal charges are transferred. This C
The CD linear sensor includes a pair of sensor arrays 120A and 120B and a pair of read gates 1 on a semiconductor substrate 110.
30A, 130B and a pair of transfer registers 140A, 1
40B and a common output unit 150.
In the CCD linear sensor of the present embodiment, an overflow control gate (OFCG) 162 and an overflow drain (OF) as a means for restricting the amount of charge to be handled are provided to a register gate in the middle of one transfer register 140A.
D) 164 is provided.

That is, in the CCD linear sensor of this embodiment, the overflow control gate (OFCG) 1
62 and an overflow drain (OFD) 164 eliminate a part of the signal charge transferred by one transfer register 140A and limit the amount of charge handled by the transfer register 140A, thereby reducing the amount of charge handled by the other transfer register 140A.
The difference is made with the handling charge amount of 0B. Thereby, the output unit 150 is provided in a portion where the amount of light received by the photo sensor is close to the saturation region.
The linear characteristic of the output is secured in order to expand the dynamic range of the output signal with respect to the amount of received light. Hereinafter, the configuration of each unit in the CCD linear sensor of this example will be described in order.

First, each of the sensor arrays 120A, 120B
A plurality of photo sensors 122 each arranged in one direction
And are provided in parallel adjacent to each other.
Each photosensor 122 has, for example, a structure as a photodiode, and normally accumulates signal charges according to the amount of received light. Each read gate 130A, 130B
Reads out the signal charges accumulated in each photosensor 122 by a readout pulse, and reads out each transfer register 140
A and 140B are set in each register gate.

Each of the transfer registers 140A and 140B transfers a signal charge to the output unit 150 in synchronization with a transfer clock pulse.
In the final output stage of B, each transfer register 140A, 140
A merging gate 144 for merging the B signal charges is provided. The signal charges transferred by the transfer registers 140A and 140B are merged at the merge gate 144,
The signal charges added to each other are applied to the charge-voltage converter (FD) of the output unit 150 from the horizontal output gate unit (HOG) 146 at the final stage. In this example, each sensor row 120A, 120B, each read gate 130A, 1
The transfer register 30B and the transfer registers 140A and 140B have the same characteristics.

The output unit 150 detects the signal charge generated in the FD unit and converts the signal charge into an image pickup signal. For example, the output unit 150 periodically resets the detected value of the signal charge by a reset clock corresponding to a transfer clock. Meanwhile, a new signal charge is sequentially detected and appropriately amplified, thereby outputting a voltage signal (imaging signal) corresponding to the signal charge. For example, the signal charges of the N-th photosensors 122AN and 122BN of the sensor arrays 120A and 120B are added and output, and the respective photosensors 122AN and 122BN are output.
2BN can be regarded as one pixel in total.

In the CCD linear sensor of this embodiment, an overflow control gate 162 and an overflow drain 164 are provided in the Nth register gate 142N of one transfer register 140A. The overflow control gate 162 forms a barrier having a predetermined potential by performing, for example, ion implantation of impurities into the semiconductor substrate 110, and a signal charge transferred to the register gate 142N of the transfer register 140A is constant. When the signal charge exceeds the threshold (Qc described later), the excess of the signal charge leaks over the barrier of the overflow control gate 162 and is discharged to the outside from the overflow drain 164. Further, the threshold value limited by the overflow control gate 162 can be variably controlled by an external control circuit or the like by controlling a bias or the like. By providing the overflow control gate 162 and the overflow drain 164, the amount of charge handled is limited downstream of the register gate 142N of the transfer register 140A.

FIG. 2 is an explanatory diagram showing the output characteristics with respect to the amount of received light in the CCD linear sensor having such a configuration. The ordinate indicates the amount of signal charges transferred by the transfer register, and the abscissa indicates the amount of received light in the photosensor. Indicates the amount. Then, for example, the sensor rows 120A, 1
20B Nth photo sensor 122AN, 122BN
Are the signal charges AN and BN, the curve a1 in FIG. 2 shows the signal charge AN of the photosensor 122AN, and the curve a
2 indicates the value of the signal charge BN of the photo sensor 122BN. Note that a portion where the signal charges AN and BN of the photosensors 122AN and 122BN have substantially common characteristics is indicated by a.

That is, in this embodiment, the overflow control gate 1 is provided in one transfer register 140A.
Since the amount of handled electric charge is suppressed by providing 62, when the signal electric charge AN of the photosensor 122AN becomes equal to or larger than the threshold value (Qc), all the excess amount is discharged from the overflow control gate 162, and the curve a1 Is constant at the line of Qc. On the other hand, the photo sensor 122BN
The signal charge BN has a linear characteristic until approaching the saturation region, as in the related art, because the amount of charge handled by the transfer register 140B is not suppressed. Therefore, the value obtained by adding these signal charges has a gradual linear characteristic that is equal to or more than the threshold value (Qc) as shown by the curve b in FIG.

As a result, the signal charge applied to the merging gate section 144 and the output signal output from the output section 150 rise with a gentle linear characteristic in a region where the amount of light received by the sensor portion approaches a saturation region. Therefore, even when the amount of received light is close to the saturation region, the output unit 150
Can secure the linear characteristic of the output, and can expand the dynamic range of the output signal with respect to the amount of received light (indicated by an arrow D in FIG. 2). Further, in this example, as described above, the threshold value (Q
c) can be variably controlled from a control circuit or the like,
For example, by changing the threshold value in consideration of the actual condition of the amount of received light, more appropriate control can be realized.
In this example, the output characteristic of the signal charge with respect to the amount of received light (the slope of the linear characteristic curve) has a different value (slope) with the threshold Qc as a boundary. It will be dealt with by appropriately performing arithmetic processing by a circuit or the like.

[0020]

As described above, in the solid-state imaging device according to the present invention, the amount of charge handled by one of the pair of transfer registers for reading out signal charges from the pair of sensor rows and transferring the signal charges to the output unit is limited. Restriction means were provided. For this reason, when the amount of light received by the photo sensor in each sensor row increases, the amount of charge handled by one transfer register is limited by the action of the limiting means that limits the amount of charge handled by one transfer register. As a result, even when the amount of light received by the photo sensor is close to the saturation region, the linear characteristic of the signal charge at the junction gate is secured by limiting the amount of charge handled by one of the transfer registers, and Since the linear characteristics of the output in the section can be secured, the dynamic range of the output signal with respect to the amount of received light can be expanded.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing a configuration of a CCD linear sensor according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing output characteristics with respect to a light receiving amount of the CCD linear sensor shown in FIG.

FIG. 3 is a schematic plan view showing a configuration of a conventional CCD linear sensor.

FIG. 4 is an explanatory diagram showing output characteristics with respect to a light receiving amount of the CCD linear sensor shown in FIG. 3;

[Explanation of Reference Symbols] 110: semiconductor substrate, 120A, 120B: sensor row, 122: photo sensor, 130A, 130B ...
Read gates, 140A, 140B transfer registers, 144 merge gates, 146 horizontal output gates, 150 output units, 162 overflow control gates, 164 overflow drains.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4M118 AA02 AB01 BA08 CA02 DD04 DD08 FA08 FA17 FA21 FA33 FA44 5B047 BB02 CB05 CB17 CB22 5C024 CX43 EX01 GY01 GZ02 5C051 AA01 BA02 DA06 DB01 DB08 DC03 DC07 DE17

Claims (6)

[Claims] 1. A plurality of photosensors, a transfer register for sequentially transferring signal charges detected by the photosensors on a semiconductor substrate, and an output unit for converting the signal charges transferred by the transfer registers into output signals. A solid-state imaging device comprising: a plurality of photosensors each arranged in one direction, at least a pair of parallel sensor rows adjacent to each other, and a plurality of photosensors provided corresponding to the pair of sensor rows, respectively. A pair of transfer registers for transferring signal charges along the array direction of the photosensor units in a row; a merge gate unit where the pair of transfer registers merge; and a signal charge generated in the merge gate unit, and an output signal is detected. An output unit for converting the transfer register into a transfer register; A solid-state imaging device characterized by the above-mentioned. 2. The solid-state imaging device according to claim 1, wherein the solid-state imaging device is a linear sensor that reads a substantially linear image using the pair of sensor arrays. 3. The solid-state imaging device according to claim 1, wherein said means for limiting the amount of handled charges comprises an overflow control gate and an overflow drain provided in the middle of one transfer register. 4. The overflow control gate is a potential barrier that, when the signal charge transferred to the one transfer register exceeds a certain value, leaks the signal charge exceeding the certain value to the overflow drain side. The solid-state imaging device according to claim 3, wherein: 5. The solid-state imaging device according to claim 4, further comprising control means for variably controlling a constant value of a signal charge transferred to said one transfer register by said overflow control gate. 6. A read gate between the sensor row and the transfer register, wherein a signal charge of the sensor row is read out to the transfer register side via the read gate by a read pulse, and a signal charge of the transfer register is read by a transfer clock pulse. 2. The data is transmitted to an output unit.
The solid-state imaging device according to any one of the preceding claims.