JP2002152607A - Solid-state imaging device and driving method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize and simplify a solid-state imaging unit capable of providing a digital output. SOLUTION: This solid-state imaging unit is provided with a sensor 1 storing electric charge for fixed period in regard to incident light, a read transistor 3 reading the electric charge a plurality of times within one field period during which the sensor 1 stores the electric charge, and a differential amplifier 4 comparing the electric charge read by the transistor 3 with a prescribed reference value and outputting these comparison results.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a solid-state imaging device for performing a plurality of readings within a predetermined period to directly obtain discretized data of a signal corresponding to accumulated charges, and a driving method thereof.

[0002]

2. Description of the Related Art Solid-state imaging devices have been applied in many fields, such as camera systems for moving images and still images, and image input systems such as scanners, copiers, and image recognition devices. In recent years, with the progress of digital technology, there has been an increasing demand for discrete data (digital data) as an output signal even in a solid-state imaging device.

In order to digitize an output signal in a conventional solid-state imaging device, a method is used in which a signal proportional to the output is subjected to A / D conversion at an output section of the solid-state imaging device after exposure for a certain period. .

For example, a CCD (Charge Coupled Device)
In e), the charges accumulated for one field period are transferred, and the output circuit in the subsequent stage converts the charges into a voltage corresponding to the accumulated charge amount, and then converts the analog output to a digital output via an A / D conversion circuit provided separately. are doing.

[0005]

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 has a large scale and is not suitable for miniaturization of a solid-state imaging device. In addition, there is noise generated in the A / D conversion circuit, and there is a problem in incorporating the noise into a solid-state imaging device.

[0006]

SUMMARY OF THE INVENTION 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 electric charge with respect to incident light for a certain period of time, and a read control unit that performs electric charge reading a plurality of times within one field period in which electric charge is accumulated in the light receiving unit. A differential amplifier that compares a signal corresponding to the charge read by the read control unit with a predetermined reference value and outputs the result.

Further, according to the method for driving a solid-state image pickup device of the present invention, a step of accumulating charges for a predetermined period with respect to incident light;
The method includes a step of performing charge reading a plurality of times within one field period for storing charges, and a step of comparing a signal corresponding to the read charge with a predetermined reference value and outputting the signal.

According to the present invention, the charge is read out plural times while the charge is accumulated for a certain period. By comparing the read signal corresponding to each charge with a predetermined reference value, the larger the charge amount, the more the value
In the field period, the timing exceeds the reference value at an earlier stage in the timing of reading out a plurality of times, and conversely, the smaller the charge amount, the later the reference value. That is, by performing the 0 and 1 determination at each readout timing, a signal corresponding to the accumulated charge can be directly converted to discrete data.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a basic circuit diagram illustrating the solid-state imaging device according to the present embodiment. That is, this solid-state imaging device mainly includes the MOS type sensor 1,
A capacitor 2 for temporarily storing the charge obtained by photoelectric conversion by the sensor 1, a read transistor 3 for controlling the reading of the stored charge, and a difference between a signal corresponding to the charge amount of the read charge and a reference value. It comprises a dynamic amplifier 4 and a reset transistor 5 for controlling discharge of the electric charge accumulated in the capacitor 2.

The sensor 1 performs photoelectric conversion on incident light, and the converted charge is stored in the capacitor 2. The capacitor 2 accumulates charges corresponding to the amount of incident light photoelectrically converted by the sensor 1 for a certain period.

The charge stored in the capacitor 2 is read out by applying a readout pulse to the gate of the readout transistor 3, and is read out as a signal voltage by the differential amplifier 4.
To one of the input terminals. Further, 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.

When a reset pulse is applied to the gate of the reset transistor 5 after the output of the signal for a certain period has ended, the electric charge accumulated in the capacitor 2 is discharged.

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 a read pulse. FIG. 2A shows the timing of a conventional read pulse, and FIG. 2B shows the timing of the read pulse of the present embodiment.

In the conventional read pulse, one read pulse is generated in one field period. In this embodiment, eight read pulses are generated in one field period.

That is, in this solid-state imaging device, a read pulse is generated by dividing one field period into eight, and the charges accumulated in one field period by sequentially applying the read pulses to the gate of the read transistor 3 are output as an 8-bit digital signal. I do. Here, the interval between each read pulse generated within one field period is referred to as a divided field.

In the case of the MOS sensor 1, charges obtained by photoelectric conversion are accumulated in the capacitor 2 and can be read out many times without destruction until resetting. In other words, the amount of charge read out by each readout pulse is the amount of charge accumulated for each divided field from the start of one field to the generation of the readout pulse.

Therefore, for example, a signal corresponding to the charge accumulated for 1/8 field by the read pulse generated in 1/8 field is input to the differential amplifier 4, and
The read pulse generated in 2/8 field causes 2
A signal corresponding to the charge accumulated for field is input to the differential amplifier 4, and similarly, a signal corresponding to the charge accumulated for the total of each divided field is sequentially subtracted until a read pulse generated in 8/8 field. Input to the dynamic amplifier 4.

A predetermined reference value is input to the differential amplifier 4, and is compared with a signal corresponding to the electric charge accumulated for the total of each divided field described above. Then, when the signal corresponding to the charge amount is smaller than the reference value, 0 is output, and otherwise (1 or more), 1 is output.

FIG. 3 is a diagram for explaining the relationship between the signal level input to the sensor and the output signal. Here, the light of each intensity is input to the six sensors 1a to 1f, and the output (output from the differential amplifier) in each divided field at that time is shown.

For example, assuming that the signal level of the output from the sensor 1a is "5", １ ／ field to ／ field
Until the field, “0” is output from the differential amplifier and 4
After / 8 field, "1" is output from the differential amplifier.

Assuming that the signal level of the output from the sensor 1b is "8", "1" is output from the differential amplifier in all the fields from 1/8 field to 8/8 field.

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 output.

If the signal level of the output from the sensor 1d is "3", "0" is output from the differential amplifier from 1/8 field to 5/8 field, and
After eight fields, "1" is output from the differential amplifier.

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
"1" is output from the differential amplifier for eight fields.

If the signal level of the output from the sensor 1f is "6", the differential amplifier outputs "0" from 1/8 field to 2/8 field, and
After eight fields, "1" is output from the differential amplifier.

As described above, in the solid-state imaging device according to the present embodiment, a digital signal corresponding to the signal level is output from the differential amplifier in accordance with each signal level, and the digital signal is not required to provide a complicated A / D conversion circuit. You can get the output.

FIG. 4 is a diagram for explaining the amount of incident light with respect to the exposure time and the change of 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) in one field period. At this time, a read pulse obtained by dividing one field period into eight is generated.

In this case, the incident light amounts L1 to L8 shown in FIG.
In this case, an output signal of each bit is generated at equal intervals by a read pulse corresponding to each equally divided field. Here, although the amount of incident light L1 to L8 increases linearly, the transition of the output signal changes like Log. 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.

FIG. 5 is a diagram for explaining the relationship between each incident light amount and an output signal in the case of an uneven divided field. Here, the period of the divided field after the first divided field is logarithmically increased. As a result, although the generation timing of the read pulse becomes Log-like, the output signal changes linearly.

That is, even with one solid-state imaging device,
Depending on whether the timing of the read pulse applied to the gate of the read transistor is divided equally or in a log manner, it is possible to select whether the change of the output signal is in a log or linear manner.

FIG. 6 is a block diagram showing an example of a solid-state imaging device comprising a CCD. Here, a plurality of sensors 1 arranged in a matrix, a vertical transfer unit 10 formed corresponding to a column of the sensors 1 in the figure, and a horizontal transfer unit provided at the lower end side of the vertical transfer unit 10 in the figure 20; an output unit 30 provided downstream 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.

In such a solid-state imaging device comprising a CCD, electric charges obtained by photoelectric conversion by the sensor 1 during a predetermined period are sent to the vertical transfer section 10 by a read pulse generated at a predetermined timing, and are vertically transferred by a vertical transfer pulse. Transfer sequentially in the direction. After the transfer in the vertical direction,
The data is sequentially transferred in the horizontal direction by the horizontal transfer unit 20. After that, each charge transferred by the output unit 30 is converted into a voltage corresponding to the charge amount and output.

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.

The solid-state imaging device of this embodiment comprising such a CCD is also characterized in that a plurality of readout pulses are applied within one field period, as described above. Since charge reading is destructive reading in the CCD, a reading pulse is applied at a log-like interval as shown in FIG. 5 to gradually widen each divided field and accumulate in each divided field. Increase the time gradually.

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 next divided field accumulates the charge for a longer period than the previous divided field. Therefore, the amount of charge corresponding to each divided field gradually increases.

Therefore, by comparing the signal of the amount of charge corresponding to each of the sequentially increasing divided fields with the reference value by the differential amplifier 4, it is possible to obtain a digital output according to the amount of incident light even in the case of destructive reading. Will be able to

In the solid-state imaging device according to the present embodiment including such a CCD, a plurality of readings are performed within one field period, so that the amount of charge handled in one reading can be reduced. The size and the size of the vertical transfer unit 10 and the horizontal transfer unit 20 can be reduced. Further, the vertical transfer unit 10 and the horizontal transfer unit 20
Can be driven at a low voltage.

Note that even in a solid-state imaging device such as a CCD which performs destructive reading, even if the reading is equally divided as shown in FIG. 4 by changing the reference value given to the differential amplifier 4 in each divided field. A digital output corresponding to the amount of incident light can be obtained.

That is, in the equal division readout shown in FIG. 4, since the period of each divided field is equal, the amount of electric charge accumulated in any divided field is the same with the same light amount. On the other hand, at different light amounts, there is a certain difference in the amount of charge stored in any of the divided fields.

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. As a result, a digital output corresponding to the amount of incident light can be obtained even when the divided fields are at equal intervals.

Here, in the present embodiment described above, when a plurality of sensors are provided, bit outputs corresponding to each sensor are sequentially obtained in one divided field within one field period. Therefore, when storing this bit output in a 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.

For example, when one field is divided into eight, each bit output of each sensor obtained in one divided field is arranged in the order of memory addresses (1, 9, 17,...), That is, at eight address intervals. Store. Then, each bit output of each sensor obtained in the next divided field is stored in the order of memory addresses (2, 10, 18,...). If such storage is sequentially performed within one field period, the bit output of one field period obtained by the same sensor is continuous.
It will be stored at the address.

The above-described MOS type solid-state imaging device can be applied to both the line type and the area type, and the CCD type solid-state imaging device can be applied to the line type.

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 for performing pattern matching and the like.

Here, in the solid-state imaging device of this embodiment,
The higher the input level, the earlier the output bit becomes “1”
Will stand. Therefore, if the solid-state imaging device of the present embodiment is applied to an image recognition system, a portion having a high input level can be detected at an early stage of one field period, and high-speed pattern matching processing can be realized.

In the solid-state imaging device according to the present embodiment, 1
When the output bit corresponding to the divided field in the field becomes "1", the subsequent output bits are automatically set to "1".
If it is handled as, the subsequent processing can be speeded up.

In this embodiment, an example has been described in which one field period is divided into eight and eight read pulses are generated within one field period. However, the present invention is not limited to this, and the read pulse may be appropriately changed. What is necessary is just to set the number of times. Further, the number of read pulses in one field period may be varied according to the use form of the output digital signal.

[0048]

As described above, the present invention has the following effects. That is, a 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 size and speed of the solid-state imaging device can be reduced. Can be achieved. In addition, since the amount of charge handled in one read operation is small, the size of the pixels and the transfer unit can be reduced, and it is possible to increase the density of the pixels and the amplitude and voltage of the drive unit. 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 illustrating an incident light amount with respect to an exposure time and a change in an output signal corresponding to each incident light amount.

FIG. 5 is a diagram illustrating a relationship between each incident light amount and an output signal in the case of an uneven divided field.

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 ... Read-out transistor 4 ... Differential amplifier 5 ... Reset transistor 10
... vertical transfer section, 20 ... horizontal transfer section, 30 ... output section

Claims (10)

[Claims] 1. A light receiving unit for accumulating charges for a certain period of incident light, a read control unit for reading electric charges a plurality of times within one field period for accumulating charges in the light receiving units, and the read control. A solid-state imaging device comprising: a differential amplifier that compares a signal corresponding to the charge read by the unit with a predetermined reference value and outputs the result. 2. The solid-state imaging device according to claim 1, wherein the read control unit performs the charge read a plurality of times at equal intervals within the one field period. 3. The solid-state imaging device according to claim 1, wherein the read control unit performs a plurality of charge read operations at intervals gradually changed within the one field period. 4. The solid-state imaging device according to claim 1, wherein the differential amplifier outputs discretized data corresponding to a charge amount. 5. The solid-state imaging device according to claim 1, wherein a predetermined reference value input to the differential amplifier is changed every time the plurality of charges are read. 6. A step of accumulating charge for a predetermined period with respect to incident light; a step of reading electric charges a plurality of times within one field period for accumulating the electric charges; and a signal corresponding to the read electric charges. And comparing and outputting the reference value with a predetermined reference value. 7. The driving method for a solid-state imaging device according to claim 6, wherein a plurality of charges are read out at equal intervals within the one field period. 8. The driving method for a solid-state imaging device according to claim 6, wherein charge reading is performed a plurality of times at intervals gradually changed within the one field period. 9. Comparing the electric charge with a predetermined reference value,
7. The driving method of a solid-state imaging device according to claim 6, further comprising outputting discretized data according to an amount of the electric charge. 10. The driving method of a solid-state imaging device according to claim 6, wherein the predetermined reference value is changed every time the charge is read out a plurality of times.