JPH05215602A - Optical sensor and optical sensor unit using the same - Google Patents

Abstract

PURPOSE:To make it possible to sustain linear optoelectric conversion characteristics upto a low quantity of light region by converting photocurrent, delivered from an optoelectric converting means such as a photodiode, into a voltage by means of a differential amplifier and an integrating capacitor. CONSTITUTION:The optical sensor comprises a photodiode 1, an operational amplifier 2 having an inverted input receiving an output from the photodiode 1 and a non-inverted input receiving a voltage reference Vref, an integrating capacitor 3 connected in parallel with the operational amplifier 2 and connecting the output from the photodiode 1 with the output from the operational amplifier 2, a capacitor 4, and an output switch 5. In accordance with the quantity of light, the optoelectric converting means (photodiode 1) produces charges which are led to the input side of a differential amplifier circuit(circuit employing a CMOS) and then the charges are stored in the integrating capacitor 3 connected in parallel with the differential amplifier circuit. Consequently, a constant potential is kept at the input side of the differential amplifier circuit and the variation at the output side thereof is amplified and outputted therefrom.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device (optical sensor) equipped with a photoelectric conversion element used in a facsimile document reading device or the like.

[0002]

2. Description of the Related Art As a method of a document reading apparatus used for a facsimile or the like, there are two methods, a reduction type for reading an image from a document by forming a reduced image and a contact type for reading the original image in its original size. In recent years, a contact type reading device has been actively developed because the device can be downsized and the optical system can be easily adjusted. The optical sensor used in this device is generally one using a thin film of amorphous silicon, CdS-Se, or the like, or one using a charge coupled device (CCD) and a silicon single crystal such as a MOS type. Has been adopted. this house,
A high-performance element such as a photodiode or a phototransistor can be used as a photoelectric element in the case of using a silicon single crystal. A MOS type photosensor using a phototransistor is relatively inexpensive and can obtain high performance, and thus is being put to practical use.

FIG. 14 shows an M using a phototransistor.
The circuit configuration of the OS type optical sensor is shown. This device includes a plurality of sensors 20.1-20. n, the base-collector capacitances 22.1 to 22. n, switches 21.1 to 21. for reading out signals from each sensor. n and each sensor and a reset switch 24 for resetting the output section. In such a circuit, first, the reset switch 24 and the switches 21.1 to 21.1 are
21. n is turned on and each sensor is reset. In this state, the capacitance between the base and collector of each sensor is 2
2.1-22. n is reverse biased to a constant voltage. Then, the switches 21.1 to 21. n is turned off and the sensors 20.1-20. When n detects light, electric charges are generated according to the amount of light, and the base-collector capacitance 22.1 to 2
2. The electric charge held in n is discharged. Next, the switches 21.1 to 21. n is sequentially turned on / off according to the signal 25 from the scanning circuit. At this time, the base-collector capacitances 22.1 to 22. Since n is recharged, a current flows between the base and the emitter. Then, due to the action of the transistor, a current multiplied by the amplification factor h _fe flows between the emitter and the collector. In this way, the light detected by each sensor is converted into a current, amplified, and appears on the output side.

[0004]

The photosensor device using the above-mentioned phototransistor can obtain a highly sensitive output due to the amplifying action of the phototransistor. However, the phototransistor has the characteristics shown in FIG. 15, and when the potential difference V _BE between the base and the emitter at the time of outputting is small, it becomes difficult for the base and emitter current I _BE to flow exponentially. Therefore, when the amount of light detected by the sensor is small, a fixed read time (equation 1
In 00 nsec to several μsec), the current between the base and the emitter corresponding to the electric charge discharged by the capacitance 22 between the base and the emitter does not flow. As a result, the output of the optical sensor sharply decreases in the region where the amount of light is small, as shown in the area IX of FIG. For this reason, the linearity of the photoelectric conversion characteristic is lost, and it is difficult to obtain a highly sensitive sensor.

In such an optical sensor device, it is possible to maintain the linearity of the photoelectric conversion characteristic by lengthening the reading time, but since the reading time of the original becomes long, there is a problem in increasing the speed of the device. Becomes

Therefore, in view of the above problems, an object of the present invention is to realize an optical sensor in which a linear photoelectric conversion characteristic is maintained in a region where the light amount is small in a short reading time.

[0007]

In order to solve the above problems, the photosensor of the present invention employs photoelectric conversion means for generating electric charges according to the amount of light and accumulates the electric charges for a certain period of time. The potential fluctuation is used as the light output potential according to the light quantity. Then, a photoelectric conversion unit that generates electric charges according to the amount of light according to the present invention, an integration unit that outputs a potential fluctuation in which the electric charges are accumulated for a certain time as a light output potential, and a potential setting that initializes the light output potential. In the optical sensor having the means, the integrating means is connected in parallel between a differential amplifier circuit that operates with respect to a predetermined reference voltage using the output of the photoelectric conversion means as an input, and the input and output of the differential amplifier circuit. It is characterized by having an integration capacity. A photodiode can be used as the photoelectric conversion means.

Further, it is preferable that the differential amplifier circuit can be constructed by a circuit using CMOS, and that the differential amplifier circuit be a comparison circuit constructed by CMOS. As the potential setting means, a switch circuit connected in parallel between the input and output of the differential amplifier circuit can be used.

Then, in an optical sensor device having a plurality of the above-mentioned optical sensors and a buffer circuit to which the optical output potentials from the optical sensors are sequentially input, the optical output potential is applied to the gate electrode in the buffer circuit. FET for output
It is desirable to have. Further, it is also effective to provide, as the buffer circuit, a transmission capacitance to which the optical output potential is input, and a transmission potential initialization means for initializing the transmission potential generated at the output of this transmission capacitance. As the transfer potential initialization means, it is desirable to adopt potential conversion initialization means for initializing the transfer potential prior to the initialization of the light output potential. Further, it is also effective to use a threshold potential setting means for initializing the transmission potential to the threshold potential of the output FET as the transmission potential initialization means. As the threshold potential setting means, a potential setting FET having the same configuration as the output FET can be used, and it is effective to use the potential setting FET with the drain and gate electrode short-circuited.

Further, when the output FET is provided, it is effective to provide an output potential reset means for initializing the potential on the output side of the output FET.
It is desirable to install switch means at the output end of the output FET for shutting off the through current during the operation of the output potential resetting means.

[0011]

In the optical sensor of the present invention, the charges generated by the photoelectric conversion means according to the amount of light are guided to the input side of the differential amplifier circuit used as the integrating means and connected in parallel with the differential amplifier circuit. Is accumulated in the integrating capacitance. Therefore, the potential on the input side of the differential amplifier circuit is constant and the potential on the output side changes, and this change is amplified and output from the differential amplifier circuit. In the photosensor of the present invention, since the signal from the photoelectric conversion means is voltage-converted by using the integration means as described above, it is possible to adopt the photoelectric conversion means that maintains linearity even in a region where the amount of light is small. Becomes further,
When a signal is read from the sensor of the present invention, the signal from the photoelectric conversion means is read while being held in the integration capacitor, so that the signal corresponding to the detected light is not destroyed.

Therefore, it is possible to repeatedly read out the signal from the sensor of the present invention.

Further, since the output voltage from the optical sensor of the present invention depends on the value of the integrated capacitance, the sensitivity of the sensor can be easily adjusted. Furthermore, in the differential amplifier circuit, since the charge from the photoelectric conversion means is converted into a voltage change, the influence on the sensor output due to the deviation of the junction capacitance unique to each photoelectric conversion means or the deviation of the individual wiring capacitance is affected. Suppressed.

By using a plurality of such optical sensors, it becomes possible to construct an optical sensor device having excellent linearity which is used in a facsimile or the like. Then, in the buffer circuit to which the optical output potential from the optical sensor is sequentially input, the source follower is configured by using the output FET in which the optical output potential is applied to the gate electrode.

Further, in an optical sensor device using a plurality of optical sensors adopting such a differential amplifier circuit,
By eliminating the effect of the offset potential peculiar to the differential amplifier, more accurate information can be obtained. For this purpose, a transmission capacitance may be inserted on the output side of each optical sensor, but by installing the transmission capacitance in the buffer circuit to which the optical output potential from the optical sensor is sequentially input, the device can be simplified. Planned. Furthermore, by initializing the transfer capacitance prior to the initialization of the light output potential of each photosensor, it is possible to transfer the potential fluctuation that initializes the light output potential of each photosensor. Therefore, the optical sensor outputs a high-level optical output potential when the amount of light is small, but this polarity is converted by this transfer capacitance, and a transfer potential that becomes a high-level potential is output when the amount of light is large. It Therefore, by using this transfer capacitance, the output from the optical sensor device according to the present invention can be more highly accurate, and at the same time, it can be output with the same characteristics as the conventional optical sensor device. Also, the output FET
When the source follower using is used, the output potential difference of the output FET can be effectively used by initially setting the transmission potential from the transmission capacitance to the threshold potential of the output FET.

When the output FET is used as a source follower in order to reduce the load on the operational amplifier, the potential at the output end of the output FET is reset after transmitting the output from each optical sensor. , Confusion with the output from other optical sensors is avoided. Then, at the time of this reset, the optical output potential or the transmission potential applied to the output FET may be set to be equal to or lower than a threshold value at which the through current does not flow, but the through current at the output end of the output FET is prevented at the time of reset. By installing the switch means, it is possible to shorten the time for recharging the current path applied to the output FET, so that high speed operation becomes possible.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit configuration of an optical sensor device according to an embodiment of the present invention. The sensor device of this example is
n optical sensors 10.1 to 10. Each optical sensor 10 is connected in parallel with the photodiode 1, the operational amplifier 2 and the operational amplifier 2 to which the output of the photodiode 1 is input to the inverting input, and the reference voltage Vref is input to the non-inverting input. It is composed of an integrating capacitor 3 and a reset switch 6 which are connected to each other and which connect the output of the photodiode 1 and the output of the operational amplifier 2, and a capacitor 4 and an output switch 5 which are connected to the output of the operational amplifier 2. These optical sensors 10.1 to 10.
n are connected in parallel, and the output switches 5.1-5. n is an n-channel MOS 8 used as a source follower of the buffer circuit 11 via a reset switch 7 that resets the output from each sensor.
Is connected to the gate 8G. The output of the source follower is connected to the external circuit 12 via the output reset switch 9. Each switch 5.1 of this example
n, 6.1 to n, 7, and 9 are driven by signals from the scanning circuit 13.

FIG. 2 shows a timing chart for explaining the operation of this optical sensor device. In the device of this example, the reset switch 7 connected to the gate input 8G of the source follower 8 and the output 8O of the source follower 8.
The other end of the reset switch 9 connected to is grounded, and these switches 7 and 9 are repeatedly turned on and off at time intervals T0. When these switches 7 and 9 are off, the output from each sensor is applied to the gate 8G, and the potential based on this is output from the output 8O to the external circuit. Note that the time intervals of repeating on / off are not limited to the same time, and each time interval may of course be set appropriately.

The output switch 5 of the sensor 10 is
It is turned on only for the time T0, and this operation is repeated with the time interval T1 as one cycle. The output of the sensor is supplied to the source follower 8 when the output switch 5 is turned on. Therefore, the output switch 5.1 of each sensor
~ 5. n is turned on and off with a delay of 2 × T0 each. That is, the output switch 5.1 of the sensor 10.1.
The output switch 5.2 of the sensor 10.2 is turned on 2 × T0 hours after the switch is turned on.

The reset switch 6 of the sensor 10 is turned on for the time T2, and this operation is repeated with the time T1 as one cycle, like the output switch 5. The operation timings of the reset switches 6.1 to n of the respective sensors 10.1 to n are the same as those of the output switches 5.1 to n described above.
Is the same as.

The state of each sensor of this example that repeats such an operation is as follows. First, the input and output of the operational amplifier 2.1 are short-circuited by the reset switch 6.1 turned on at the time t1, and the input potential Vin Has the same value as the output potential Vout of the operational amplifier 2 and is reset to the reference potential Vref input to the non-inverting input. That is, the following relationship holds for each input / output potential of the operational amplifier 2.

Vin = Vout (1) Vout = A (Vref−Vin) (2) From Equations (1) and (2) Vin = Vref (1 / (1 + 1 / A)) (3) Here, A is the amplification factor of the operational amplifier 2, and when the amplification factor A is much larger than 1, Vin and Vout are V
Initialized to ref.

At time t2, when the reset switch 6.1 is turned off, the operational amplifier 2.1 starts the accumulation operation. That is, when the photodiode 1.1 detects light, electric charge is generated, so that the electric charge is generated by the integration capacitor 3.
Accumulated in 1. Therefore, a potential difference of ΔV occurs between Vin and Vout. In this state, the output switch is at time t3.
If the current Ip flows from the photodiode 1.1 according to the amount of light during the time Tst until turning on, the ΔV is represented by the following equation.

ΔV = Vin−Vout = Ip × Tst / C (4) Here, C is the capacitance value of the integral capacitance 3.1. Vin and Vout in this state are (2) and (4)
It is expressed as follows from the formula.

Vout = (Vref−ΔV) / (1 + 1 / A) (5) Vin = Vref− (Vref−ΔV) / (A + 1) ·· (6) where the amplification factor A is greater than 1. When it is large, Vout = Vref−ΔV (7) Vin = Vref (8) That is, the output potential Vou of the operational amplifier is changed by the current Ip corresponding to the amount of light from the photodiode 1.1.
t decreases by Ip × Tst / C, and the input potential Vin
Is found to be held at Vref.

When the output switch 5.1 is turned on at time t3, the operational amplifier 2.1 outputs the above-mentioned output potential Vout. In this way, the operational amplifier 2.1 outputs the voltage-converted potential of the current Ip according to the amount of light,
This potential Vout is applied to the gate 8G of the source follower 8. At this time, the reset switches 7 and 9 are off. The buffer circuit 11 is for reducing the load of the operational amplifier 2, and an n-channel type FET is used as a source follower.

In this circuit 11, since the source potential, which is the output 8O, follows the gate potential, a potential corresponding to the output of each photosensor 10.1 to n applied to the gate 8G is output. FIG. 2 shows an output waveform when the capacitance is a load, as an example of the output 8O of the source follower.
In addition, in order to reduce the load of the operational amplifiers 2.1 to n, the output of each sensor 10.1 to n has a source follower 8
Capacitances 4.1 to n corresponding to the gate capacity of are connected, and the other end is grounded.

At time t4, the reset switches 7 and 9 are turned on and the output switch 5.1 is turned off. Therefore, the gate potential and the source potential of the source follower are reset to the ground potential. Then, time t
In 1 ', the reset switch 6.1 is turned on in the optical sensor 10.1, and a new cycle is started.
On the other hand, in the next optical sensor 10.2, the output switch 5.2 is turned on and the reset switches 7 and 9 of the source follower 8 are turned off.
The output of 0.2 is applied to the gate 8G and the sensor 10.
An electric potential proportional to the detected light amount of 2 is output.

FIG. 3 shows the photoelectric conversion characteristics of this device. In the device of this example, when the light intensity is 0, the current Ip
Is 0, the potential V0 at this time is a value obtained by subtracting the voltage drop Vth at the source follower from Vref. Since the current Ip increases as the light amount increases, the output potential from the photosensor of this example decreases in proportion to the light amount. Then, the linearity according to the light amount is secured until the lower limit value _VL determined from the normal operation range of the operational amplifier is reached. As described above, in the optical sensor of this example, linearity can be secured even in a weak light amount region where it was difficult to secure linearity in the conventional optical sensor using the phototransistor. Further, even in a region where the amount of light is small, there is no difference in response time, and it is possible to operate in a short reading time. Further, in general, since the difference between the potential V0 and the lower limit value V _L is about 2V, a sufficient dynamic range can be secured.

FIG. 4 shows how the photoelectric conversion characteristics of the optical sensor of the present invention are changed. Since the output potential of the sensor of the present invention is inversely proportional to the integral capacitance, the sensitivity of the sensor can be easily adjusted by changing the value of the integral capacitance. Therefore, it is possible to inexpensively provide an optical sensor device having sensitivity according to the application.

Further, since the photocurrent from the photodiode is accumulated in the integrating capacitance and then output as an output voltage from the operational amplifier, variations in the junction capacitance of the photodiode or variations in the wiring capacitance from the diode to the operational amplifier are caused. The output side is not affected by the resulting characteristics of the individual photosensors. Further, since the potential applied to the photodiode is kept constant, all the current generated by light is stored in the integrating capacitor. Therefore, since a potential difference proportional to the photocurrent of the photodiode is always obtained as an output, it is possible to suppress problems such as variations in sensitivity depending on the reading position of the reading device.

FIG. 5 shows an example in which the operational amplifier used in the optical sensor of this example is constituted by using CMOS. The circuit shown in FIG. 5 is a CMOS-based comparator, and is provided between the power supply potential V _DD and the ground potential.
P-channel MOS1 to form a current mirror circuit
10, 111 and n-channel MOS 112, 113
Are installed in parallel. After the two are connected, the n-channel MOS 114 is installed to set the potential V
_LMT is input to make it a constant current source. The input potential Vin and the reference potential Vref are applied to the gates of the n-channel MOSs 112 and 113, respectively, and the output potential Vout is taken from between the p-channel MOS 110 and the n-channel MOS 112.

FIG. 6 shows the input / output characteristics of the above comparator. Since the photosensor device of this example is used as an integrating circuit having a storage time Tst of about 0.1 msec to 10 sec, it does not need to be a high-speed operational amplifier using a bipolar element and has the circuit configuration as described above. It is possible to obtain sufficient characteristics with a comparator. Therefore, the sensor device of this example can be manufactured at low cost.

In addition to the operational amplifier described above, the reset switch and the like can all be composed of MOS transistors, and the photosensor device of this example including the photodiode can be composed on one semiconductor substrate. For this reason, it can be incorporated in various devices like a conventional photosensor using a phototransistor.

[Embodiment 2] FIG. 7 shows a circuit configuration of an optical sensor device according to the present embodiment. The sensor device of this example is also an optical sensor 1 including n photodiodes 1.
0.1-10. n. Also in each of the optical sensors 10, as in the first embodiment, from the photodiode 1, the operational amplifier 2 to which the output of the photodiode 1 is input, the integration capacitance 3 and the reset switch 6 connected in parallel with the operational amplifier 2, and the like. It is configured.
Of these configurations, those parts that are common to the first embodiment are designated by the same reference numerals, and description thereof will be omitted. The optical sensor device according to the present example includes the optical sensors 10.1 to 10. In the buffer circuit 11 to which n outputs are sequentially input, a transmission capacitance 30 for transmission is inserted in a portion where the output from each photosensor is introduced. That is, each sensor 10.1-1
0. The output potential from n is the output switch of each sensor 5.1-5. It is selected by n and applied to the input side 30a of the transfer capacitor 30.

As a result, the transfer potential appearing on the output side 30b of the transfer capacitor 30 is the gate 8G of the n-channel MOS 8 used as the source follower of the buffer circuit 11.
Is applied to. Furthermore, the output side 30b
Between the gate and the gate 8G, one end of the reset switch 7 for initializing the potential of the output side 30b is connected. Then, at the other end of the reset switch 7, an n-channel MOS 3 having the same structure as the MOS 8 which is a source follower is formed.
1 is connected. Further, since the gate electrode 31g and the drain 31d of the MOS 31 are short-circuited, the reset switch 7 causes the potential of the output side 30b to be MO.
The threshold potential Vth of S31, that is, the source follower 8
Is set to the threshold potential Vth.

As described in the first embodiment, by adopting the optical sensor 10 using the photodiode 1, the operational amplifier 2, the integrating capacitor 3 and the reset switch 6, the linear type is ensured and the optical sensor has high sensitivity. The device can be realized. The operational amplifier 2 generally has a minute offset potential. Therefore, in a region where the amount of light is small, the output potentials from the individual photosensors may vary due to these minute offset potentials. Therefore, in order to obtain high-quality and highly accurate image data, it is desirable to remove the influence of this offset potential. That is, as shown in FIG. 9, even if the reference potential Vref is input to the non-inverting input of the operational amplifier by the offset potential Vof peculiar to each operational amplifier, the reset initial potential Vin of the optical sensor is set.
t is as follows.

Vint = Vref + Vof (11) Therefore, the output potential V from the optical sensor shown in equation (7)
out becomes Vout = Vref + Vof−ΔV (12), and the potential shifted by Vof is output. Although this Vof is minute, it is unique to each operational amplifier and appears as a variation in the output from each optical sensor. Therefore, by removing the offset potential Vof, the linearity can be ensured even in a minute light amount region, and an optical sensor device with higher accuracy can be realized.

Therefore, in this device, the transmission capacitance 30 is inserted in the buffer circuit 11, and the transmission capacitance 30 is used to detect each of the optical sensors 10.1 to 10. n offset potential Vof. 1-Vof. n can be canceled. Further, in this device, each optical sensor 10.
1-10. By obtaining the potential fluctuation at the time of initialization of n through the transmission capacitor 30, the potential proportional to the light amount can be output from the buffer circuit 11 to the external circuit. Therefore, the device of this example, like the conventional optical sensor device,
Since a signal with a high potential can be output when the amount of light is large,
The device is easier to use.

Next, the operation of each part of this apparatus will be described based on the timing chart of FIG.

Also in the apparatus of this embodiment, the switches 7 and 9 are repeatedly turned on and off by the pulse at the time interval T0 as in the first embodiment. Therefore, when the switches 7 and 9 are in the off state, the output from each sensor is applied to the gate 8G via the transmission capacitance 30, and the potential based on this is output from the output 8O to the external circuit. Note that, as in the first embodiment, the time intervals may be set as appropriate without being limited to the case where the times of repeating on / off are the same. In addition, the output switch 5 and the reset switch 6 of each optical sensor
Is driven in a cycle of time T1 as in the first embodiment. In this device, optical sensors 10.1-1
0. Since the potential change at the time of initialization of n is transmitted to the buffer circuit 11, first, the output switch 5 is turned on. Then, the potential of the input side 30a of the transmission capacitance 30 is set to the respective optical sensors 10.1 to 10. At n, the light quantity is initialized to a value converted by voltage. Then, after the time T0, the reset switch 6 is set to the time T0 while keeping the output switch 5 in the ON state.
It is turned on for a while and the output potential of the optical sensor is initialized. At the same time, the potential on the input side 30a of the transfer capacitance increases by the amount of voltage conversion of the light amount. After that, that is, after the time T0 × 2 has elapsed since the output switch 5 was turned on, the output switch 5 is turned off, and the optical sensor restarts the measurement of the light amount,
The following optical sensor is connected to the buffer circuit.

These operations will be described with time. At time t11, the optical switch 10.1 is selected by turning on the output switch 5.1. This time t
11, the output potential Vou of the optical sensor 10.1
t. 1 is as follows from the expression (12).

Vout. 1 = Vref + Vof. 1-ΔV1 (13) Here, Vof. 1 is an offset potential peculiar to the optical sensor 10.1, and ΔV1 is a value obtained by potential conversion of the amount of light sensed by the optical sensor 10.1 shown in Expression (4). Since the output switch 5.1 is turned on, the potential of the input side 30a of the transfer capacitance 30 is Vout. Set to 1. On the other hand, the potential of the output side 30b of the transfer capacitor 30 is MO because the reset switch 7 is on.
The threshold potential Vth of the source follower 8 is set via S31.

Next, at time t12, the optical sensor 1
When the reset switch 6.1 of 0.1 is turned on, the output of the operational amplifier 2.1 is initialized to the reference potential. At this time, as described above, since the offset potential exists for each operational amplifier, the output of the operational amplifier 2.1, that is, the output of the optical sensor 10.1 is Vout. 1 ′ = Vref + Vof. 1 ... (14) is reset. At the same time, the input side 3 of the transfer capacitance
0a is also Vout. It is set to 1 '. Therefore, input side 3
The potential of 0a increases by ΔV1 as can be seen from the equations (13) and (14). On the other hand, the potential Vtr of the output side 30b
Since the reset switch 7 is open, Vtr = Vth + ΔV1 (15) in response to the potential fluctuation on the input side 30a. In this way, the potential fluctuation Vtr output from the transfer capacitance 30 of the present device is not affected by the offset potential of each photosensor. Further, in the source follower 8 to which this potential fluctuation Vtr is applied, V at the time t11.
Since tr is the threshold value Vth, the output potential is 0. Further, at time t12, Vth + ΔV1 is applied to the gate electrode, and thus the source follower 8 outputs a potential increased by ΔV1. Therefore, the output of this device is such that a high potential is output when the amount of light is large, which is similar to that of the conventionally used optical sensor device.
Since the output characteristic has a general polarity, it can be easily incorporated into a facsimile or the like.

Further, when the output switch 5.1 is turned off and the output switch 5.2 is turned on at time t13, as described in the first embodiment, the optical sensor 1 is turned on.
The accumulation operation according to the light amount is started in the operational amplifier 2.1 of 0.1. Further, the output of the optical sensor 10.2 is applied to the buffer circuit 11, and the input side 30 of the transfer capacitance is applied.
a is an output potential Vou of the optical sensor 10.2 shown below.
t. Set to 2.

Vout. 2 = Vref + Vof. 2-ΔV2 (16) Then, at time t14, when the output potential of the optical sensor 10.2 is reset, the potential of the input side 30a of the transfer capacitance also rises, similar to the equation (14), and Vout. 2 ′ = Vref + Vof. 2 ... (17) Therefore, at the time t13, the transfer potential Vt of the output side 30b of the transfer capacitor which has been reset to Vth again.
Vtr = Vth + ΔV2 (18) appears in h. As a result, ΔV2 is output from the source follower 8.

In this device, each optical sensor 10.1 to
10. These operations are repeated with time T1 as one cycle for n, and continuous image data can be input.

That is, t after time T1 from time t11
11 ', the output switch of the optical sensor 10.1.
1 is turned on again, and the amount of light accumulated from time t13 is converted into a potential and transmitted to the buffer circuit 11. Time t1 which is T0 time after time t12, t13, t14
Also at 2 ', t13', and t14 ', time t
The operations at 12, t13, and t14 are repeated.

As described above, in the device of this example, by inserting the transfer capacitance in the buffer circuit, it is possible to extract the potential fluctuation from which the influence of the offset potential is removed from the output of each optical sensor. Therefore, it is possible to eliminate the influence of the minute offset potential peculiar to the operational amplifier used in each optical sensor, prevent the variation even in the weak light quantity, and output the potential fluctuation according to the light quantity. It is possible to As described above, in the optical sensor device of this example, the linearity is maintained even in the low light amount region where the influence of the offset potential is likely to occur, and further, highly accurate image data without variations can be output. Further, as an output signal, a signal of a high level can be output when the amount of light is large as in the conventional device, so that a device having high compatibility and being easy to use can be realized.

[Embodiment 3] FIG. 10 shows a circuit configuration of an optical sensor device according to the present embodiment. The sensor device of this example also includes the optical sensors 10.1 to 10. n. Also in each of the optical sensors 10, as in the first embodiment, from the photodiode 1, the operational amplifier 2 to which the output of the photodiode 1 is input, the integration capacitance 3 and the reset switch 6 connected in parallel with the operational amplifier 2, and the like. It is configured. Of these configurations, those parts that are common to the first embodiment are designated by the same reference numerals, and description thereof will be omitted. The optical sensor device of the present example is configured so that the optical sensors 10.1 to 10. In the source follower 8 for impedance-converting and outputting the output of n, the reset switch 7 provided on the gate electrode 8G thereof is omitted, so that the photosensor device can output at a higher speed.

On the output side of the source follower 8, in order to prevent confusion with the output corresponding to the next optical sensor, each optical sensor 10.1 to 10. After transmitting the output from n, it is reset to a low potential by the reset switch 9. At this time, if the output potential from the optical sensor applied to the source follower 8 exceeds the threshold potential of the MOSFET that is the source follower 8, a large amount of through current will flow through the reset switch 9, This is a big problem in terms of current consumption. Therefore, when the reset switch 9 on the output side of the source follower 8 is turned on, the photosensor output side, that is, the gate potential of the source follower 8 is turned on to a low potential by turning on the reset switch 7, and this shoot-through current is To prevent.

While the reset switches 7 and 9 are on, the optical sensors 10.1 to 10. n output switches 5.1-5. Since n is off, the potentials of the common line 41 and the gate electrode 8G drop to 0V. As a result, each of the optical sensors 10.1 to 10. n operational amplifiers 2.1-2. n is the output switch 5.1-5. n
To the gate electrode 8G of the source follower 8 to the common line 4
It becomes necessary to charge 1 each time. The wiring capacitance of the common line 41 has a value of about 1 pF, and the optical sensors 10.1 to 10. Output potential from n is 0V → 2-3V
And big. Therefore, when the number of optical sensors 10 included in the optical sensor device increases, the charging time cannot be ignored.

FIG. 13 shows the results of simulating the changes over time in the gate potential Vg of the source follower 8 and the potential change Vo on the output side of the source follower 8 in the optical sensor device of the first embodiment. .. In this simulation, the common line 41 has a capacitance of 1 pF and each operational amplifier transistor size is about several μm.
The clock frequency is 500 KHz. As can be seen from this figure, the gate potential Vg drops to 0V each time the reset switch 9 is turned on, so the source follower 8
Output potential Vo rises sharply and is not stable.

Therefore, in the present embodiment, in order to speed up the rise of the output potential Vo of the source follower 8 and enable high speed operation, the reset switch on the gate electrode 8G side is omitted and the drop of the gate potential Vg is prevented. I am trying to do it. On the other hand, in order to prevent a through current from flowing when the output side of the source follower 8 is reset, a cutoff switch 40 is installed at the output end 8O of the source follower 8. Then, when the reset switch 9 that resets the output side of the source follower 8 is turned on, the cutoff switch 40 is turned off to prevent a through current.

The operation of this apparatus will be described based on the timing chart of this embodiment shown in FIG. In addition, each optical sensor 10.1-10. Since the operation of n and the output of the operational amplifier are the same as those in the first embodiment, description thereof will be omitted. First, time t
21, when the output switch 5.1 is turned on, the common line 41
Potential, that is, the potential of the input 8G of the source follower 8 becomes equal to the output potential of the operational amplifier 2.1, and the gate potential of the source follower 8 is changed from the reference potential Vref to Δ.
A value lower by V1 is set. At the same time, the reset switch 9 is turned on and reset on the output side of the source follower 8.

However, since the breaking switch 40 installed at the output end of the source follower 8 is off,
No through current flows. Next, at time t22, when the reset switch 9 is turned off and the cutoff switch 40 is turned on, the gate potential at that time, that is, the output voltage corresponding to ΔV1 appears on the output side of the source follower 80. At this time, unlike the first embodiment shown in FIG. 2, since the gate electrode 8G of the source follower 8 is already connected to the output of the operational amplifier 2.1 from the time t21, the time t22.
, The input potential of the source follower 8 is substantially the same as the output potential of the operational amplifier 2.1. Therefore, there is no time delay for charging the common line 41 and the gate electrode 8G, and the rise of the output potential from the source follower 8 becomes sharp. Therefore, the operating speed of this device can be improved.

Next, at time t23, the output switch 5.1 and the switch 10 are turned off, and the reset switch 6.1 of the optical sensor 10.1 and the optical sensor 10.
The second output switch 5.2 and the reset switch 9 are turned on. Therefore, the common line 41 and the source follower 8
The output ΔV2 of the operational amplifier 2.2 is applied to the gate electrode 8G of the. Then, the output side of the source follower 8 is reset, but since the cutoff switch 10 is off, a through current does not flow. Thus, unlike the first embodiment, the common line 41 and the gate electrode 8 are different in the present embodiment.
The output potential ΔV1 of the operational amplifier 2.1 to the output potential ΔV2 of the operational amplifier 2.2 is directly applied to G. Therefore, after the voltage once drops to 0V, the output potential ΔV of the operational amplifier 2.2
Compared to the device of Example 1 to which 2 is applied, the amount of change in potential is small and the gate potential of the source follower 8 can immediately follow. Further, since the charge amount is small, the power consumption of the operational amplifier 2.2 may be small.

Next, at time t24, the switch 9 is turned off and the cutoff switch 10 is turned on, so that the output potential ΔV of the operational amplifier 2.2 is output to the output side of the source follower.
An output voltage corresponding to 2 appears. The optical sensor 1
0.1 is the reset switch 6.1 as in the first embodiment.
Is turned off at time t25, the reset is completed, and the integration operation is started again.

FIG. 12 shows the result of simulating the change of the gate potential Vg of the source follower 8 and the time change of the output side potential change Vo of the source follower 8 in this embodiment. In this simulation, the capacitance of the common line 41 is set to 1 pF and each transistor size of the operational amplifier is set to about several μm, and the clock frequency is 500 KH, as in the simulation result described above.
z. As can be seen from this figure, unlike the simulation result shown in FIG. 13, the gate potential Vg is 0V.
When the reset switch 9 is turned off, the output potential Vo has already risen to a predetermined potential, the output potential Vo rises sharply, and a good output waveform is obtained.

As described above, in this embodiment, by providing the cutoff switch at the output end of the source follower,
Prevents shoot-through current when the source follower is reset. Therefore, the gate potential of the source follower is not reset to 0V each time after the output of each sensor, and the gate potential can be set to the output potential of each sensor in a short time. Furthermore, it is possible to apply the output potential of the next photosensor as the gate potential of the source follower while the source follower is being reset, that is, while the reset switch on the output side of the source follower is on. Become. Therefore, when the reset of the output side of the source follower is completed and the output potential corresponding to each photosensor is output, the gate potential of the source follower has already been changed to
The output potential of the selected photosensor can be established. Therefore, it is possible to improve the rise of the output signal from the source follower, as compared with the device of the first embodiment in which the output potential of each photosensor is applied after the reset of the source follower is completed. As described above, in the present embodiment, the output waveform from the source follower has a sharp rise and stabilizes to a value corresponding to the output potential of each optical sensor in a short time. The device can be realized, and even a photosensor device using a large number of photosensors can be realized with a fast operation.

Although the photodiode is used in the present embodiment and the first embodiment, the device can be constructed using various photodiodes such as a pin photodiode or an avalanche photodiode.

[0063]

As described above, in the optical sensor of the present invention and the optical sensor device using the same, a photocurrent from a photoelectric conversion means such as a photodiode is converted into a voltage by using a differential amplifier and an integrating capacitance. It is characterized by converting and outputting. Therefore, even in the low illuminance region, it is possible to configure the optical sensor by using the photoelectric conversion means such as the photodiode whose linearity is ensured.

Furthermore, the sensitivity of the sensor can be easily adjusted by changing the value of the integral capacitance. Since the photocurrent of the photodiode is converted into a voltage by using the differential amplifier and is output, it is possible to suppress the influence on the sensitivity of the photosensor device due to each photodiode. Therefore, the sensor device according to the present invention can be a device with less variation in sensitivity.

Further, in a buffer circuit to which optical output potentials from a plurality of optical sensors are sequentially input, by inserting a transfer capacitance for transmitting these optical output potentials, the operational amplifier peculiar to each optical sensor is provided. The influence of the offset potential can also be eliminated. Therefore, even when the amount of light is small, it is possible to prevent variations in sensitivity due to minute offset potentials, and it is possible to realize a highly accurate optical sensor device. at the same time,
By inserting this transmission capacitance, it is possible to realize an optical sensor device that supplies a high-level output signal when the amount of light is large as in the conventional optical sensor device. For this reason,
It is possible to provide a device that is highly compatible with the conventional optical sensor device and is easy to use.

Further, the output F which constitutes the buffer circuit
By installing a cutoff switch at the output end of ET to prevent a through current when resetting the output side of the output FET, resetting of the input side of the output FET can be omitted. Therefore, the optical output potential of each optical sensor is
The gate potential of the output FET can be established prior to the output state of the output FET. This allows
By sharpening the rising edge of the output signal from the output FET, an optical sensor device capable of high-speed operation can be realized.

The optical sensor according to the present invention is a MOS
Because it can be realized with a circuit composed of transistors,
It can be formed on one semiconductor substrate including a photodiode. Therefore, like a conventional optical device such as a phototransistor, it can be incorporated in a facsimile device or the like.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a circuit configuration of an optical sensor device according to a first embodiment of the invention.

FIG. 2 is a timing chart showing the operation of the optical sensor device shown in FIG.

FIG. 3 is a graph showing photoelectric conversion characteristics of the optical sensor shown in FIG.

FIG. 4 is a graph illustrating a change in photoelectric conversion characteristics of the optical sensor shown in FIG.

5 is a circuit diagram showing a circuit configuration of an operational amplifier used in the optical sensor shown in FIG.

6 is a graph showing the operating characteristics of the operational amplifier shown in FIG.

FIG. 7 is a circuit diagram showing a circuit configuration of an optical sensor device according to a second embodiment of the invention.

8 is a timing chart showing the operation of the optical sensor device shown in FIG.

9 is a graph illustrating the photoelectric conversion characteristics of the optical sensor shown in FIG.

FIG. 10 is a circuit diagram showing a circuit configuration of an optical sensor device according to a third embodiment of the invention.

11 is a timing chart showing an operation of the optical sensor device shown in FIG.

FIG. 12 is a graph showing a result of simulating a time variation of an input potential and an output potential of a buffer circuit in the optical sensor device shown in FIG.

FIG. 13 is a graph showing the result of simulating the time variation of the input potential and the output potential of the buffer circuit in the optical sensor device according to the first embodiment.

FIG. 14 is a circuit diagram showing a circuit configuration of a conventional photosensor device using a phototransistor.

FIG. 15 is a graph showing operating characteristics of the phototransistor shown in FIG.

16 is a graph showing photoelectric conversion characteristics of the optical sensor shown in FIG.

[Explanation of symbols]

1.1-1. n ... Photodiode 2.1-2. n ... Operational amplifier 3.1 to 3. n ... Integral capacity 4.1 to 4. n ... Condenser 5.1-5. n ... Output switch 6.1 to 6. n ... Reset switch 7 ... Reset switch 8 ... N channel MOS 8G ... MOS gate input 8O ... MOS output 9 ... Reset switch 10.1-10. n ... Optical sensor 11 ... Buffer circuit 12 ... External circuit 13 ... Scanning circuit 20.1-20. n ... Photodiodes 21.1-21. n ... Switch 22.1-22. n ... Base-collector capacitance 24 ... Reset switch 25 ... Signal from scanning circuit 30 ... Transfer capacitance 31 ... Reset FET 40 ... Breaking switch 41 ... Common line 110, 111 ... p-channel MOS 112, 113, 114 ... n-channel MOS Vin ... operational amplifier input potential Vout ... operational amplifier output potential Vref ... reference potential Vof ... offset potential V0 ... Initial potential of operational amplifier _VL ... Lower limit value of operational amplifier T0, T1, T2 ... Time interval Tst ... Accumulation time t1, t2, t3, t4 ... Time t11, t12, t13, t14 ... ·Times of Day

Claims (12)

[Claims] 1. A photoelectric conversion means for generating an electric charge according to the amount of light, an integrating means for outputting a potential fluctuation in which the electric charge is accumulated for a predetermined time as a light output potential, and a potential setting means for initializing the light output potential. And a differential amplifier circuit that operates with respect to a predetermined reference voltage with the output of the photoelectric conversion means as an input, and the integrator means is connected in parallel between the input and output of the differential amplifier circuit. An optical sensor having an integrated capacitance. 2. The optical sensor according to claim 1, wherein the photoelectric conversion means is a photodiode. 3. The optical sensor according to claim 1, wherein the differential amplifier circuit is composed of a CMOS circuit. 4. The method according to any one of claims 1 to 3,
The optical sensor, wherein the differential amplifier circuit is a comparison circuit composed of CMOS. 5. The method according to any one of claims 1 to 4,
The optical sensor, wherein the potential setting means is a switch circuit connected in parallel between the input and output of the differential amplifier circuit. 6. An optical sensor device comprising a plurality of optical sensors according to claim 1, and a buffer circuit to which the optical output potentials from these optical sensors are sequentially input. An optical sensor device in which the buffer circuit includes an output FET for applying the optical output potential to a gate electrode. 7. An optical sensor device comprising: a plurality of optical sensors according to claim 1; and a buffer circuit to which the optical output potentials from these optical sensors are sequentially input. An optical sensor device, wherein the buffer circuit includes a transfer capacitance to which the optical output potential is input, and a transfer potential initializing unit that initializes a transfer potential generated at the output of the transfer capacitor. 8. The optical sensor device according to claim 7, wherein the transmission potential initialization means is potential conversion initialization means for initializing the transmission potential prior to initialization of the optical output potential. .. 9. The buffer circuit according to claim 7, wherein the buffer circuit includes an output FET to which the transfer potential is applied to the gate potential, and the transfer potential initializing means sets the transfer potential to the output FET. An optical sensor device, which is a threshold potential setting means for initializing to a threshold potential of 1. 10. The threshold potential setting means according to claim 9, which is a potential setting FET having the same configuration as the output FET, and the drain of the potential setting FET is short-circuited to the gate electrode. Optical sensor device. 11. The optical sensor device according to claim 6, further comprising an output potential resetting unit that initializes a potential on an output side of the output FET. 12. The output FE according to claim 11.
An optical sensor device characterized in that a switch means for interrupting a through current during operation of the output potential resetting means is installed at an output end of T.