JPH02296470A - Photoelectric converter - Google Patents

Abstract

PURPOSE:To decrease the destruction of a sensor by providing an amplifier means amplifying a signal subjected to photoelectric conversion between plural photoelectric conversion means and a charge storage means. CONSTITUTION:The output of the plural photoelectric conversion means connected in common is connected to a gate of a 1st MOS transistor(TR) M1, a drain of the 1st MOS TR M1 is connected to a source of a 2nd MOS TR M2, the drain of the 2nd MOS TR M2 is connected to a power voltage VCC and the gate of the 2nd MOS TR M2 is controlled by a pulse phiTO to control the conduction of the amplifier. Capacitors CT1, CT2 being temporary storage means are provided at the post stage of the amplifier to store the offset signal tentatively and an offset signal is transferred together with a sensor signal and both the signals are subjected to subtraction processing to eliminate the offset signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a photoelectric conversion device, and particularly to a photoelectric conversion device having a plurality of photoelectric conversion elements and a charge storage means for accumulating signals from these photoelectric conversion elements. Regarding equipment.

[Prior art and problems to be solved by the invention] Conventionally,
A method for reading sensor signals transferred from a sensor of a photoelectric conversion device such as a solid-state imaging device is to temporarily store the read signal in a storage capacitor CA, and then output it to an output line having a stray capacitance C□ for direct reading. There are two methods: a method of reading the data through a buffer, and a method of reading the data through a buffer.

In the former method, the level of the output signal is determined by the capacitance division between the negative storage capacitor C7 and the stray capacitor CH, so the output signal becomes small. If the output signal level is low, there is a problem that the noise charge generated by the output signal line becomes larger than the noise charge of the sensor and deteriorates the S/N ratio.

In recent years, there has been a tendency for the number of sensor pixels in photoelectric conversion devices to increase as images become more precise. However, as the value of stray capacitance C1 increases in proportion to the number of sensor pixels, the output signal becomes smaller and smaller.

Furthermore, let us consider the case where the sensor signal reading method is applied to a color factory sensor. In a color sensor, for example, a gold transmission filter (W) is used to obtain a luminance signal, a red transmission filter is used to obtain a color signal red (R), and a blue transmission filter is used to obtain a color signal (B). There is.

In this case, the output of the R and B signals will be at a level approximately ⅓ or less compared to the output of the W signal, and if the reduction in signal level due to capacitance division is included, the signals will be quite small.

In order to increase the output signal, it is conceivable to significantly reduce the value of the negative storage capacitance co.

However, there is a problem in that increasing the value of the negative time storage capacitor C7 increases the chip area. In addition, when a large number of sensors are connected to a common vertical signal line, such as area sensors used in solid-state imaging devices, each sensor has parasitic capacitance, so the capacitance value of the vertical signal line usually increases over time. It becomes larger than the value of capacitance C7, and the degree of damage to the sensor itself increases, but the - time storage capacitance C
If the value of 7 is increased, the degree of damage to the sensor itself becomes greater.

In this way, considering the degree of destruction of the sensor, the chip area, etc., it is desirable that the - time accumulation and capacitance C7 be small;
There is a contradictory demand that in order to increase the output level, it is desirable that the storage capacitance CT be large.

The latter method is to provide a buffer for amplifying the output signal from the negative storage capacitor CT, and by inputting the output signal to the base of the bipolar transistor,
Amplification can be performed, and the readout gain is large (although
There is a problem with high speed.

[Means for Solving the Problems] A photoelectric conversion device of the present invention includes a plurality of photoelectric conversion elements and a charge storage means for accumulating signals from these photoelectric conversion elements.

between the plurality of photoelectric conversion elements and the charge storage means,
It is characterized by providing an amplification means for amplifying the photoelectrically converted signal.

[Function] The photoelectric conversion device of the present invention includes an amplification means for amplifying a photoelectrically converted signal between a plurality of photoelectric conversion elements (one unit of a sensor that performs photoelectric conversion) and a charge storage means. The signal from the photoelectric conversion element is amplified and stored in the charge storage means, and the signal is output from the charge storage means.

Therefore, the output signal level can be increased, the degree of destruction of the sensor can be reduced, and a photoelectric conversion device excellent in high-speed operation can be constructed.

[Example] Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of a signal readout circuit of an embodiment of the photoelectric conversion device of the present invention.

As shown in the figure, the amplifier used in this embodiment is composed of a first MOS transistor M1 and a second MOS transistor M2.

The sensor used in this embodiment is an area sensor in which a plurality of photoelectric conversion elements are arranged in a matrix, and one row of the plurality of photoelectric conversion elements is connected to the amplifier through a common vertical signal line.

The output side of the plurality of commonly connected photoelectric conversion elements is the first M
OS connected to the gate of the transistor M1, and connected to the gate of the first M
The drain of the OS transistor MI is connected to the source of the second MOS transistor M2, the drain of the second MOS transistor M2 is connected to the power supply voltage Vcc, and the gate of the second MOS transistor M2 is connected to the pulse φ
To controls the conduction of the amplifier.

Note that when an amplifier is provided after a plurality of commonly connected photoelectric conversion elements, there is a slight change (offset) in the C level between the amplifiers. In solid-state imaging devices whose purpose is to detect minute signals, such differences in offset also cause deterioration in image quality as offset noise. Therefore, in this embodiment, a capacitor CT, , CT, which is a temporary storage means is provided after the above-mentioned amplifier, and the offset signal is temporarily stored.The offset signal is transferred together with the sensor signal, and both signals are subjected to subtraction processing to offset the offset signal. The signal is removed.

That is, the sensor signal and offset signal output from the amplifier are pulses φA1. MOS controlled by φa
l-transistor T1. Capacitor CT1 via Tt
．． MOS stored in CTa and controlled by pulse φH1
The signals are output to output lines s, , S2 through transistors THI and Toa, respectively, and subjected to subtraction processing. Note that the output lines St and S2 are pulses φ□. It is cleared to a predetermined potential (8) by the MOS transistors T IIcI and TM01 controlled by .

Note that the above amplifier transfers the sensor signal to the capacitor CT, and also transfers the offset noise signal to the capacitor C.
It is controlled so that it functions as an amplifier when transferring to T. This is because heat is generated when the amplifier is operated while signal charges are being accumulated in the sensor, and this heat causes an increase in dark current noise in the sensor.

The operation of the photoelectric conversion device will be described below.

FIG. 2 is a timing chart for explaining the operation of the signal readout circuit.

In the figure, first, in section T, pulses φ1° and φT1 are set to high level, and the MOS transistor M
2. By turning on T+, the residual charge remaining in the capacitor C□ is cleared. After that, the pulse ψVe
is set to low level, and the MOS transistor T vc is turned off.

Next, in period T2, the control pulse φVRI applied to the sensor is set to high level to read out the sensor signal accumulated in the sensor, and the second MOS of the amplifier
Input to the gate of transistor M2. The sensor signal amplified by the amplifier is read out to a capacitor CT. After that, pulse φ7. As the low level, MO
S) Turn off the transistor T1.

Next, in period T, the control pulse φvl11 applied to the sensor is set at high level, the pulses φra and φvc are set at high level, and the MOS transistors Tfi, T
Turn on VC to refresh the sensor and clear the capacitor CT2 and vertical signal line.

Next, in interval T4, the pulse φvc is set to low level to turn off the MOS transistor Tvc, and in interval T, the residual signal (sensor noise) of the refreshed sensor is read out, and the second MOS transistor M, input into the gate. The sensor signal amplified by the amplifier is read out to a capacitor CT.

Next, in period T, pulse φ□1 is set to high level to turn on MOS transistors T, , T□2, and the signals temporarily stored in capacitors CT, , CT2 are output by pulses from the horizontal shift register.・Read out the force signal. The offset noise of the amplifier is the sensor signal and the sensor noise is connected to the capacitor CT7. Although they are taken in at the same time when read out to CTz, the sensor noise is removed from the sensor signal at the same time by subtracting the signals obtained from the output lines S, , S.

Note that the amplifier gain of this embodiment is determined by setting the sizes of the first MOS transistor and the second MOS transistor to W l / L 1. If W 2 / L 2 and the channel lengths are the same (Ll = L2) K = '7
Therefore, if W, /W2=16/1, then K=4.

For example, if the value of capacitor CT is 2 pF, capacitor C
The value of I4 is 4. In the case of pF, the conventional readout gain is 1/3, but the readout gain in this embodiment is 4/3.
It becomes 3.

It should be noted that although the amplifier in the above embodiment is composed of MOS transistors, the amplifier may be composed of other elements. for example,
A bipolar transistor may be a base input/collector output type, or an emitter input/collector output type.

Alternatively, an FET or the like may be used.

The present invention is applicable not only to the area sensor of the above embodiment but also to other sensors, such as line sensors.

As already mentioned, when the sensor is a color sensor,
The output level of the R and B signals may be approximately 1/3 or less of the output level of the W signal, but by using the present invention and changing the amplifier gain for each color, the color signal output level can be adjusted to the desired level. can be set to a value of

FIG. 3 is a schematic configuration diagram of a solid-state imaging device to which the present invention is applied.

In the figure, an image sensor 201 in which optical sensors are arranged in an area is subjected to television scanning by a vertical scanning section 202 and a horizontal scanning section 203.

The signal output from the horizontal scanning section 203 is sent to the processing circuit 20.
4 and output as a standard television signal.

Drive pulses and the like for the vertical and horizontal scanning sections 202 and 203 are supplied by a driver 205.

The driver 205 is also limited by the controller 206.

[Effects of the Invention] As described in detail above, according to the photoelectric conversion device of the present invention, the following effects can be obtained.

(2) The degree of sensor destruction can be reduced.

(2) Since the readout gain can be increased, deterioration of the S/N ratio due to noise charges on the output signal line can be prevented.

(2) In the case of a color sensor, the color signal output level can be set to a desired value by changing the amplifier gain for each color.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a signal readout circuit of an embodiment of the photoelectric conversion device of the present invention. FIG. 2 is a timing chart for explaining the operation of the signal readout circuit. FIG. 3 is a schematic configuration diagram of a solid-state imaging device to which the present invention is applied. CT,,CT2. : Capacitor, φTO1φTl, φT2. φM+, φvc
, φVRI + φVR2φH1; Pulse, T lr T z + THII 'r,,,
THCI THC2Tvc, M, , M,
: MOS transistor, S2; output line. Figure 1

Claims (3)

[Claims] (1) In a photoelectric conversion device having a plurality of photoelectric conversion elements and a charge accumulation means for accumulating signals from these photoelectric conversion elements, between the plurality of photoelectric conversion elements and the charge accumulation means,
A photoelectric conversion device comprising an amplifying means for amplifying a photoelectrically converted signal. (2) The photoelectric conversion device according to claim 1, wherein a plurality of said charge storage means are provided. (3) The photoelectric conversion device according to claim 1, wherein the plurality of photoelectric conversion elements constitute a color sensor, and the amplification degree of the amplification means differs depending on the color signal.