JP4396023B2 - Solid-state imaging device and driving method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid-state imaging apparatus that directly reads out discrete data of a signal corresponding to accumulated charges by performing a plurality of readings within a certain period and a driving method thereof.
[0002]
[Prior art]
Solid-state imaging devices are applied in many fields such as camera systems for moving images and still images, image input systems such as scanners, copying machines, and image recognition devices. In recent years, with the advancement of digital technology, there is an increasing demand for discrete data (digital data) as an output signal even in a solid-state imaging device.
[0003]
In order to digitize an output signal in a conventional solid-state imaging device, a method is used in which after a certain period of exposure, a signal proportional to the output is A / D converted at the output unit of the solid-state imaging device.
[0004]
For example, in a CCD (Charge Coupled Device), charges accumulated in one field period are transferred, converted into a voltage corresponding to the amount of accumulated charges by an output circuit at a subsequent stage, and then analogized via a separately provided A / D conversion circuit. The output is converted to digital output.
[0005]
[Problems to be solved by the invention]
However, such a solid-state imaging device and its driving method have the following problems. That is, an A / D conversion circuit for obtaining a digital output from an analog output is large in scale and is not suitable for downsizing of a solid-state imaging device. In addition, there is a noise component generated in the A / D conversion circuit, which causes a problem when incorporated in a solid-state imaging device.
[0006]
[Means for Solving the Problems]
The present invention has been made to solve such problems. That is, the solid-state imaging device according to the present invention includes a light receiving unit that accumulates charges for a certain period with respect to incident light, and a read control unit that performs charge readout a plurality of times within one field period in which charges are accumulated in the light receiving unit. And a differential amplifier that compares and outputs a signal corresponding to the charge read out by the read control unit and a predetermined reference value, and makes it possible to divide a plurality of charge reads performed within one field period equally or unevenly. You can choose what to do .
[0007]
The solid-state imaging device driving method of the present invention includes a step of accumulating charges for a certain period of time with respect to incident light, a step of reading out charges a plurality of times within one field period for accumulating charges, And a step of comparing and outputting a signal corresponding to the charge and a predetermined reference value, so that it is possible to select whether the charge read-out multiple times within one field period is equally divided or non-uniform. It is .
[0008]
In the present invention, the charge is read out in a plurality of times while the charge is accumulated for a certain period. By comparing the signal corresponding to each read charge and a predetermined reference value, the reference value is exceeded at an early stage of the readout timing divided into a plurality of times within one field period as the charge amount increases. The smaller the charge amount, the higher the reference value is exceeded at a later stage. That is, by performing 0 or 1 determination at each read timing, a signal corresponding to the accumulated charge can be directly converted into discrete data.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a basic circuit diagram for explaining the solid-state imaging device of the present embodiment. That is, this solid-state imaging device mainly includes a MOS sensor 1, a capacitor 2 for temporarily accumulating charges obtained by photoelectric conversion by the sensor 1, and a read transistor 3 for performing control for reading the accumulated charges. And a differential amplifier 4 that compares a signal corresponding to the amount of the read charge with a reference value, and a reset transistor 5 that performs control to discharge the charge accumulated in the capacitor 2.
[0010]
The sensor 1 performs photoelectric conversion on incident light, and the converted electric charge is accumulated in the capacitor 2. The capacitor 2 accumulates electric charges according to the amount of incident light photoelectrically converted by the sensor 1 for a certain period.
[0011]
The electric charge accumulated in the capacitor 2 is read out by applying a read pulse to the gate of the read transistor 3 and is sent as a signal voltage to one input terminal of the differential amplifier 4. A predetermined reference value is input to the other input terminal of the differential amplifier 4. As a result, the differential amplifier 4 compares the signal voltage corresponding to the read charge with the reference value, and outputs a digital signal of 0 or 1.
[0012]
When the reset pulse is applied to the gate of the reset transistor 5 after the signal output for a certain period is completed, the electric charge accumulated in the capacitor 2 is discharged.
[0013]
The present embodiment is characterized in that a plurality of read pulses are applied to the gate of the read transistor 3 within one field period. 2A and 2B are diagrams for explaining the read pulse, in which FIG. 2A shows the timing of the conventional read pulse, and FIG. 2B shows the timing of the read pulse of this embodiment.
[0014]
In the conventional read pulse, one read pulse is generated in one field period. In the present embodiment, eight read pulses are generated in one field period.
[0015]
That is, in this solid-state imaging device, one field period is divided into eight to generate a readout pulse, which is sequentially applied to the gate of the readout transistor 3 and the charge accumulated in the one field period is output as an 8-bit digital signal. Here, each readout pulse generated within one field period is referred to as a divided field.
[0016]
In the case of the MOS type sensor 1, the electric charge obtained by photoelectric conversion is accumulated in the capacitor 2 and can be read out any number of times without resetting until reset. That is, the amount of charge read by each readout pulse is the amount of charge accumulated for the total of each divided field from the start of one field to the generation of the readout pulse.
[0017]
Therefore, for example, a signal corresponding to the charge accumulated for 1/8 field by the read pulse generated in the 1/8 field is input to the differential amplifier 4, and the signal corresponding to 2/8 field is output by the read pulse generated in the 2/8 field. A signal corresponding to the accumulated charge is input to the differential amplifier 4, and similarly, a signal corresponding to the accumulated charge for each divided field is sequentially input to the differential amplifier 4 until a read pulse generated in the 8/8 field. Entered.
[0018]
A predetermined reference value is input to the differential amplifier 4 and is compared with a signal corresponding to the charge accumulated for the total of each divided field described above. If the signal corresponding to the amount of charge is smaller than the reference value, 0 is output, and otherwise (1 or more), 1 is output.
[0019]
FIG. 3 is a diagram illustrating the relationship between the signal level input to the sensor and the output signal. Here, light of each intensity is input to the six sensors 1a to 1f, and the outputs (outputs from the differential amplifier) in each divided field at that time are shown.
[0020]
For example, if the signal level of the output from the sensor 1a is “5”, “0” is output from the differential amplifier from the 1/8 field to the 3/8 field, and the differential amplifier after the 4/8 field. Outputs “1”.
[0021]
If the signal level of the output from the sensor 1b is “8”, “1” is output from the differential amplifier in all of the 1/8 field to 8/8 field.
[0022]
If the signal level of the output from the sensor 1c is “7”, “0” is output from the differential amplifier for 1/8 field, and “1” is output from the differential amplifier after 2/8 field. Is done.
[0023]
If the signal level of the output from the sensor 1d is “3”, “0” is output from the differential amplifier from the 1/8 field to the 5/8 field, and the differential amplifier after the 6/8 field. Outputs “1”.
[0024]
If the signal level of the output from the sensor 1e is "1", "0" is output from the differential amplifier from 1/8 field to 7/8 field, and only 8/8 field is output from the differential amplifier. “1” is output.
[0025]
If the signal level of the output from the sensor 1 f is “6”, “0” is output from the differential amplifier from the 1/8 field to the 2/8 field, and the differential amplifier after the 3/8 field. Outputs “1”.
[0026]
As described above, in the solid-state imaging device of the present embodiment, a digital signal corresponding to the signal level is output from the differential amplifier according to each signal level, and a digital output is obtained without the need to provide a complicated A / D conversion circuit. be able to.
[0027]
FIG. 4 is a diagram for explaining the change in the amount of incident light with respect to the exposure time and the output signal corresponding to each amount of incident light. When driving the solid-state imaging device of the present embodiment, a plurality of read pulses are applied to the gate of the read transistor 3 (see FIG. 1) within one field period. At this time, a read pulse is generated by dividing one field period into eight equal parts.
[0028]
In this case, in the incident light amounts L1 to L8 shown in FIG. 4, output signals of each bit are generated at equal intervals by read pulses corresponding to the equally divided divided fields. Here, the amount of incident light L1 to L8 increases linearly, but the transition of the output signal changes in a Log manner. Thus, a high dynamic range can be realized when the amount of incident light is small, and saturation of the output signal can be suppressed when the amount of incident light is large.
[0029]
FIG. 5 is a diagram for explaining the relationship between each incident light quantity and the output signal in the case of unequal divided fields. Here, the period of the divided field after the first divided field is increased in a Log manner. As a result, the generation timing of the read pulse becomes Log, but the output signal changes linearly.
[0030]
That is, even in a single solid-state imaging device, the change of the output signal is made logarithmic or linear depending on whether the timing of the readout pulse applied to the gate of the readout transistor is equally divided or made logarithmic. It becomes possible to choose.
[0031]
FIG. 6 is a configuration diagram illustrating an example of a solid-state imaging device including a CCD. Here, a plurality of sensors 1 arranged in a matrix, a vertical transfer unit 10 formed corresponding to the columns of the sensors 1 in the figure, and a horizontal transfer unit provided on the lower end side of the vertical transfer unit 10 in the figure 20, an output unit 30 provided in a subsequent stage of the horizontal transfer unit 20, and a differential amplifier 4 in which a signal from the output unit 30 is an input on one side and a reference value is an input on the other side.
[0032]
In such a solid-state imaging device composed of a CCD, the electric charge obtained by photoelectric conversion by the sensor 1 in a predetermined period is sent to the vertical transfer unit 10 by a read pulse generated at a predetermined timing, and sequentially in the vertical direction by a vertical transfer pulse. Forward. Further, after the transfer in the vertical direction, the horizontal transfer unit 20 sequentially transfers in the horizontal direction. Thereafter, each charge transferred by the output unit 30 is converted into a voltage corresponding to the amount of charge and output.
[0033]
The differential amplifier 4 compares the voltage output from the output unit 30 with a predetermined reference value and outputs a digital signal of 0 or 1.
[0034]
The solid-state imaging device according to the present embodiment including such a CCD is also characterized in that a readout pulse is applied a plurality of times within one field period, as before. In the CCD, since the readout of charges is destructive readout, by applying readout pulses at Log intervals as shown in FIG. 5, each divided field is gradually widened and accumulated in each divided field. Increase the time gradually.
[0035]
As a result, even if a read pulse is generated in a divided field within one field period and the charge is read out and discharged, the charge is accumulated in the next divided field for a longer period than in the previous divided field. For this reason, the charge amount corresponding to each divided field gradually increases.
[0036]
Therefore, by comparing the signal of the amount of charge corresponding to each divided field, which sequentially increases, with the reference value by the differential amplifier 4, a digital output corresponding to the amount of incident light can be obtained even in destructive readout. become.
[0037]
In the solid-state imaging device according to the present embodiment including such a CCD, since the readout is performed a plurality of times within one field period, the amount of charge handled by one readout can be reduced, and the size and vertical of the sensor 1 can be reduced. The sizes of the transfer unit 10 and the horizontal transfer unit 20 can be reduced. Furthermore, low voltage driving of the vertical transfer unit 10 and the horizontal transfer unit 20 can be achieved.
[0038]
Note that even in a solid-state imaging device such as a CCD that performs destructive readout, the reference value given to the differential amplifier 4 can be varied in each divided field, so that the amount of incident light can be reduced even in equally divided readout as shown in FIG. The corresponding digital output can be obtained.
[0039]
That is, in the equally divided readout shown in FIG. 4, since the period of each divided field is equal, the amount of charge accumulated in any divided field is the same for the same amount of light. On the other hand, there is a certain difference in the amount of charge accumulated in any divided field at different light quantities.
[0040]
Therefore, the reference value given to the differential amplifier 4 is gradually reduced from the first read pulse to the last read pulse in one field. This makes it possible to obtain a digital output corresponding to the amount of incident light even if the divided fields are equally spaced.
[0041]
Here, in the present embodiment described above, when a plurality of sensors are provided, a bit output corresponding to each sensor is sequentially obtained in one divided field within one field period. Therefore, when storing this bit output in the memory, the storage destination address of the memory is shifted and stored by an address corresponding to the number of divided fields in one field.
[0042]
For example, when one field is divided into eight, each bit output of each sensor obtained in one divided field is stored in the order of memory addresses (1, 9, 17,...), That is, at eight address intervals. Then, each bit output of each sensor obtained in the next divided field is stored in the order of memory addresses (2, 10, 18,...). When such storage is sequentially performed within one field period, the bit output of one field period obtained by the same sensor is stored at eight consecutive addresses.
[0043]
The MOS-type solid-state imaging device described above can be applied to either a line-type or an area-type, and the CCD-type solid-state imaging device can be applied to a line-type.
[0044]
Such a solid-state imaging device can be applied to a camera system for moving images and still images, an image input system such as a scanner and a copying machine, and an image recognition system that performs pattern matching and the like.
[0045]
Here, in the solid-state imaging device of the present embodiment, the higher the input level, the more “1” is set in the output bit at an earlier stage. Therefore, when the solid-state imaging device of this embodiment is applied to an image recognition system, a portion with a high input level can be detected at an early stage of one field period, and high-speed pattern matching processing can be realized.
[0046]
In the solid-state imaging device according to the present embodiment, if the output bit corresponding to the divided field in one field is “1”, the subsequent output bit is automatically handled as “1”, and then It becomes possible to speed up the processing.
[0047]
In the present embodiment, an example in which one field period is divided into eight and eight read pulses are generated in one field period has been described. However, the present invention is not limited to this, and the number of read pulses is appropriately set. You only have to set it. Further, the number of read pulses in one field period may be varied according to the usage form of the digital signal to be output.
[0048]
【The invention's effect】
As described above, the present invention has the following effects. That is, the signal obtained by photoelectric conversion in the light receiving unit can be digitized by a differential amplifier having a simple configuration without using a complicated A / D conversion circuit, and the solid-state imaging device can be reduced in size and speeded up. Can be achieved. In addition, since the amount of charge handled in one reading is small, it is possible to reduce the size of the pixel and the transfer unit, and it is possible to achieve higher density of the pixel, lower amplitude of the drive unit, and lower voltage. Become.
[Brief description of the drawings]
FIG. 1 is a basic circuit diagram illustrating a solid-state imaging device according to an embodiment.
FIG. 2 is a diagram illustrating a read pulse.
FIG. 3 is a diagram illustrating a relationship between a signal level input to a sensor and an output signal.
FIG. 4 is a diagram for explaining a change in an incident light amount with respect to an exposure time and an output signal corresponding to each incident light amount.
FIG. 5 is a diagram illustrating the relationship between each incident light quantity and an output signal in the case of unequal divided fields.
FIG. 6 is a configuration diagram illustrating an example of a solid-state imaging device including a CCD.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Sensor, 2 ... Capacitor, 3 ... Reading transistor, 4 ... Differential amplifier, 5 ... Reset transistor, 10 ... Vertical transfer part, 20 ... Horizontal transfer part, 30 ... Output part

Claims (10)

A light receiving unit that accumulates charges for a certain period of time with respect to incident light;
A readout control unit that performs charge readout a plurality of times within one field period in which charges are accumulated in the light receiving unit;
A differential amplifier that compares and outputs a signal corresponding to the electric charge read by the read control unit and a predetermined reference value ;
A solid-state imaging device characterized in that a plurality of charge readings performed within the one field period can be selected to be equally divided or non-uniform . When the output result of the differential amplifier by a plurality of charge readouts performed within the one field period exceeds the predetermined reference value, the output result of the differential amplifier by the subsequent charge readouts within the one field period is obtained. 2. The solid-state imaging device according to claim 1, wherein the solid-state imaging device is automatically handled as exceeding the predetermined reference value . The read control unit performs a plurality of charge readings with gradually changing intervals within the one field period when performing a selection in which a plurality of charge reading intervals performed within the one field period are unequal. The solid-state imaging device according to claim 1. The solid-state imaging device according to claim 1, wherein the differential amplifier outputs discretized data corresponding to a charge amount. The solid-state imaging device according to claim 1, wherein the predetermined reference value input to the differential amplifier is varied for each of the plurality of charge readouts. Storing charges for a certain period of time with respect to incident light;
A step of performing charge readout a plurality of times within one field period in which the charge is accumulated;
A step of comparing and outputting a signal corresponding to the read electric charge and a predetermined reference value ,
A method of driving a solid-state imaging device, wherein it is possible to select whether the plurality of charge readouts performed within one field period are equally divided or non-uniform . When the output result of the differential amplifier by a plurality of charge readouts performed within the one field period exceeds the predetermined reference value, the output result of the differential amplifier by the subsequent charge readouts within the one field period is obtained. 7. The method for driving a solid-state imaging device according to claim 6 , wherein the predetermined reference value is automatically handled as being exceeded . The charge readout is performed a plurality of times while the intervals are gradually changed in the one field period when selection is made such that the plurality of charge readout intervals performed within the one field period are unevenly adjacent. 6. A driving method of a solid-state imaging device according to 6. The method of driving a solid-state imaging device according to claim 6, wherein the charge is compared with a predetermined reference value and discretized data corresponding to the charge amount of the charge is output. The method for driving a solid-state imaging device according to claim 6, wherein the predetermined reference value is varied for each of the plurality of charge readings.

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