JP2893625B2 - Photo sensor system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photo sensor system, and more particularly, to a photo sensor system for detecting the amount of irradiation light with high accuracy.

[0002]

2. Description of the Related Art Conventionally, a photo sensor system is usually
A plurality of photosensors are arranged in a matrix using a photodiode or a thin film transistor (TFT) as a light receiving element (photosensor). And
Each photosensor generates an electric charge according to the amount of irradiated light, and the luminance can be known by checking the amount of the electric charge. A scanning voltage is applied from the horizontal scanning circuit and the vertical scanning circuit to the photosensors arranged in a matrix to detect the charge amount of each photosensor, amplify the charge amount, and detect the amount of irradiation light. doing.

Further, when trying to express a gradation of an object to be detected, the level of an analog signal corresponding to the detected charge amount is divided and processed in accordance with the gradient, and converted into a gradation corresponding to the detection signal level. ing.

[0004]

However, in such a conventional photosensor system, the analog output of the photosensor is taken out as it is, amplified once, and then the output signal is divided according to the gradation. As a result, the grayscale expression required an external amplifier circuit, which not only increased the size of the photosensor system, but also reduced the output of the photosensor, especially in dark areas to be detected, and provided a stable output. However, there is a problem that accurate gradation expression is difficult to obtain.

Therefore, the present invention is based on a critical sensing time until the output of the photosensor is inverted by changing the sensing time of the photosensor whose output is inverted at a time corresponding to the amount of light in the sensing state. It is an object of the present invention to provide a photosensor system capable of accurately expressing a gradation by detecting the amount of light.

[0006]

SUMMARY OF THE INVENTION A photosensor system according to the present invention has a sense state and a non-sense state, and when in the sense state, its output is inverted at a time corresponding to the amount of light irradiated. In the photo sensor system using the photo sensor, the photo sensor is alternately switched between a sense state and a non-sense state, and the length of the sense time in the sense state is changed to detect the inversion of the output of the photo sensor. The above object is achieved by repeating the detection operation a plurality of times and detecting the light amount of the irradiation light based on the critical sensing time at which the output of the photosensor is inverted.

In this case, the photo sensor is, for example,
As described in claim 2, the source electrode and the drain electrode are disposed opposite to each other with the semiconductor layer interposed therebetween, and the semiconductor layer, the source electrode and the drain electrode are interposed with insulating films on both sides of the semiconductor layer. A first gate electrode and a second gate electrode opposed to the semiconductor layer are provided, and one of the first gate electrode side and the second gate electrode side is a light irradiation side, and light emitted from the light irradiation side is provided. Is transmitted through the insulating film on the light irradiation side, is irradiated on the semiconductor layer, and the voltage applied to the gate electrode on the light irradiation side is controlled,
The sense state and the non-sense state may be controlled.

Further, the sense time may be set to be shorter at predetermined time intervals sequentially from a preset longest sense time, for example, as set forth in claim 3;
Further, as set forth in claim 4, it may be set to be sequentially longer at predetermined time intervals from a preset shortest sense time.

[0009]

According to the photo sensor system of the present invention, the photo sensor is alternately switched between the sense state and the non-sense state, the length of the sense time in the sense state is changed, and the output of the photo sensor is inverted. The detection operation is repeated several times to detect the amount of irradiation light based on the critical sense time when the output of the photo sensor is inverted, so that the amount of light can be digitized and extracted, and amplified externally. The amount of light can be accurately detected without providing a circuit. As a result, gradation expression can be performed with high accuracy.

In this case, the photo sensor is provided with a source electrode and a drain electrode opposed to each other with a semiconductor layer interposed therebetween.
On both sides of the semiconductor layer, the source electrode and the drain electrode, a first gate electrode and a second gate electrode opposed to the semiconductor layer with an insulating film interposed therebetween, respectively, are arranged. One of the gate electrode sides is a light irradiation side, and light irradiated from the light irradiation side is irradiated on the semiconductor layer through the insulating film on the light irradiation side, and the light is irradiated on the gate electrode on the light irradiation side. Assuming that the sense state and the non-sense state are controlled by controlling the applied voltage, the sense state of the photosensor can be easily controlled, and the photosensor itself has an amplifying function. A photo sensor function and a photo sensor selection function can be provided, which can further improve detection accuracy and further reduce the size of the photo sensor system itself. Rukoto can.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

FIGS. 1 to 8 show an embodiment of a photosensor system. FIG. 1 is a circuit block diagram of a photosensor system, FIG. 2 is a circuit diagram showing an example of a photosensor array, and FIG. FIG. 4 is a side sectional view of a photo sensor used in the photo sensor system, FIG. 4 is an equivalent circuit of the photo sensor of FIG. 3, FIG. 5 is an explanatory diagram of voltages applied to each electrode of the photo sensor of FIG. FIG. 6 is a characteristic curve diagram showing output characteristics in the voltage applied state of FIG. 5, FIG. 7 is a timing diagram showing a relationship between applied voltages and output signals of each part of the photosensor array of FIG. 2, and FIG. FIG.

In FIG. 1, a photo sensor system 1
Includes a pixel section drive circuit 2, a sensor section 3, a clock generation section 4, a signal inversion detection section 5, a gradation determination section 6, and the like.

As shown in FIG. 2, the sensor section 3 has a large number of photo sensors PS arranged in a matrix, and includes 1 to n photo sensors PS in a row direction and 1 to m photo sensors PS in a column direction. Are arranged. Each photosensor PS has a drive line 3 whose bottom gate electrode (BG) is arranged in the row direction.
1 and its drain electrode (D) is connected to a signal line 32 arranged in the column direction. Each photosensor PS has its top gate electrode (TG) connected to a top electrode line 33 arranged in the row direction. That is,
Each photosensor PS has a top gate electrode (TG), a drain electrode (D), and a source electrode (S), as described later.
And a bottom gate electrode (BG).

As shown in FIG. 2, the pixel section driving circuit 2 of FIG. 1 includes a row address decoder 34 as a vertical scanning circuit connected to a driving line 31 of the sensor section 3 and a signal line 32 of the sensor section 3. It includes a column switch 35 as a connected horizontal scanning circuit, and a top address decoder 36 connected to the top electrode line 33 of the sensor unit 3.

The row address decoder 34 applies bottom gate voltages φBG 1 to φBG to the bottom gate electrodes (BG) of the photosensors PS arranged for each row via the drive line 31.
BGn is applied.

A drain voltage (Vdd) is input to the column switch 35 via a precharge transistor 37, and an output signal V _OUT is output from the column switch 35 via a buffer 38. That is, the column switch 35 outputs the output of each photo sensor PS connected to each signal line 32 via the buffer 38 every time the precharge transistor 37 is turned on when the precharge voltage φPG is input to the precharge transistor 37. And outputs it as an output signal V _OUT .

The top address decoder 36 is a top gate electrode (TG) of each photo sensor PS arranged for each row.
, Top gate voltages φTG1 to φTGn are applied via top electrode line 33.

The source electrode (S) of the photo sensor PS is grounded.

Referring again to FIG. 1, the clock generator 4
Includes a transmitting circuit, a frequency dividing circuit, and the like, and outputs a clock signal and a reset signal of a predetermined frequency to the pixel unit driving circuit 2 and the signal inversion detecting unit 5. Then, the pixel unit driving circuit 2
A top gate voltage (φTG) and a bottom gate voltage (φBG) are output as a sense signal and a reset signal to the sensor unit 3 based on the clock signal and the reset signal input from the clock generation unit 4. Driving of each photo sensor PS is performed.

The signal inversion detecting section 5 further includes a sensor section 3
Is input the output signal V _OUT from the signal inversion detecting unit 5, the time from the clock generation unit 4 from the time the reset signal is input until the next reset signal, i.e., sense time of the photosensor PS to be described later τ The number of clock signals input from the clock generator 4 is counted
The count number and the address data of the photosensor PS whose output signal V _OUT is inverted are output to the gradation judging unit 6.

The gradation judging section 6 has a CPU (Central Processes).
sing unit), RAM (Random Access Memory) and R
An OM (Read Only Memory) or the like is provided, and its RAM or ROM has a table showing the relationship between the time until the output signal V _OUT is inverted (critical sense time τ) and the gradation, and the photo sensor system 1 as the photo sensor system 1. The program is stored in advance. The gradation determining unit 6 searches the ROM based on the count number input from the signal inversion detecting unit 5 and directly converts the converted gradation data into gradation data while controlling the driving of the sensor unit 3. Output to external image memory.

Each photosensor PS shown in FIG.
As shown in (1), basically, an inverted staggered thin film transistor and a coplanar thin film transistor are combined in a single semiconductor layer.

That is, in the photosensor PS, a bottom gate electrode (BG) 11 is formed on a transparent insulating substrate 10 made of glass or the like, and the bottom gate electrode (BG) 11 and the insulating substrate 10 are A bottom gate insulating film 12 made of silicon nitride (SiN) is formed to cover. A semiconductor layer 13 is formed on the bottom gate insulating film 12 at a position facing the bottom gate electrode (BG) 11, and the semiconductor layer 13 is made of i-type amorphous silicon (ia-Si). Is formed.
A source electrode (S) 14 and a drain electrode (D) 15 are formed on the semiconductor layer 13 at positions facing each other at a predetermined interval with the semiconductor layer 13 interposed therebetween. ) 14 and the drain electrode (D) 15 are connected to the semiconductor layer 13 via n ⁺ silicon layers 16 and 17 made of amorphous silicon in which a dopant such as phosphorus is diffused. These constitute a bottom transistor (inverted staggered thin film transistor).

The portion between the source electrode (S) 14 and the drain electrode (D) 15 and the semiconductor layer 13 between the source electrode (S) 14 and the drain electrode (D) 15 is a top gate insulating layer made of transparent silicon nitride. A top gate electrode (TG) 19 made of a transparent conductive material is formed on the top gate insulating film 18 at a position facing the bottom gate electrode (BG) 11 on the top gate insulating film 18. . The top gate electrode (TG) 19 is provided with an electron-
In order to generate hole pairs, not only the channel region of the semiconductor layer 13 but also the n ⁺ silicon layer 16 as shown in FIG.
17 is preferably formed to have a size that also covers the upper surface. Although not shown, this top gate electrode (TG) 1
A transparent overcoat film made of silicon nitride is formed so as to cover 9 and the top gate insulating film 18 to protect them. The above top gate electrode (TG) 1
9, a top transistor (coplanar thin film transistor) is formed by the top gate insulating film 18, the semiconductor layer 13, the source electrode (S) 14, and the drain electrode (D) 15.

In this embodiment, the photo sensor PS is:
As shown in FIG. 3, irradiation light A is irradiated from the top gate electrode (TG) 19 side, and the irradiation light A passes through the top gate electrode (TG) 19 and the top gate insulating film 18 and is applied to the semiconductor layer 13. Irradiated. Note that the photo sensor P
As is clear from the above configuration, S is not limited to the irradiation of the irradiation light A from the top gate electrode 1 side, and is not limited to the irradiation from the bottom gate electrode (BG) 11 side. Can be performed in a similar manner.

In this photosensor PS, for example, the bottom gate electrode (BG) 11 is 500 angstroms, the bottom gate insulating film 12 is 2000 angstroms, the semiconductor layer 13 is 1500 angstroms, the source electrode (S) 14 and the drain electrode (D). 15 is formed at 500 Å, n ⁺ silicon layers 16 and 17 are formed at 250 Å, top gate insulating film 18 is formed at 2,000 Å, top gate electrode (TG) 19 is formed at 500 Å, and overcoat film is formed at 2,000 Å. 13, the distance between the source electrode (S) 14 and the drain electrode (D) 15
It is formed to 7 μm.

As described above, the photosensor PS has a configuration in which the inverted staggered thin film transistor and the coplanar thin film transistor are combined, and an equivalent circuit thereof can be shown in FIG.

Next, the operation of the photo sensor PS will be described.

When a positive voltage, for example, +10 [V] is applied to the bottom gate electrode (BG) 11 of the photosensor PS shown in FIG. 3, an n-channel is formed in the bottom transistor. Here, when a positive voltage, for example, +5 [V] is applied between the source electrode (S) 14 and the drain electrode (D) 15, electrons are supplied from the source electrode (S) 14 side, and a current flows. In this state, the top gate electrode (TG) 19
A negative voltage of a level that annihilates the channel due to the electric field of the bottom gate electrode (BG) 11, for example, -20 [V]
Is applied, the electric field from the top gate electrode (TG) 19 acts to reduce the influence of the electric field of the bottom gate electrode (BG) 11 on the channel layer. As a result, the depletion layer extends in the thickness direction of the semiconductor layer 13. , N channels. At this time, the top gate electrode (TG) 19
When the irradiation light A is irradiated from the side, electron-hole pairs are induced on the side of the top gate electrode (TG) 19 of the semiconductor layer 13. Since −20 [V] is applied to the top gate electrode (TG) 19, the induced holes are accumulated in the channel region and cancel the electric field of the top gate electrode (TG) 19. Therefore, an n-channel is formed in the channel region of the semiconductor layer 13 and a current flows. The current (hereinafter, drain current I _DS ) flowing between the source electrode (S) 14 and the drain electrode (D) 15 changes according to the amount of irradiation light A.

As described above, the photosensor PS is controlled so that the electric field from the top gate electrode (TG) 19 acts in a direction that prevents the electric field from the bottom gate electrode (BG) 11 from forming a channel. Since the n-channel is pinched off, the drain current I _DS flowing when no light is irradiated can be extremely small, for example, about 10 ⁻¹⁴ A. As a result, the photo sensor PS
The difference between the drain current I _DS of the drain current I _DS and the light non-irradiation time during the light irradiation can sufficiently increase it. In addition,
At this time, the amplification factor of the bottom transistor changes depending on the amount of irradiated light, and the S / N ratio can be increased.

In addition, the photo sensor PS applies a positive voltage (+10 [V]) to the bottom gate electrode (BG) 11 and, for example,
When the voltage is set to 0 [V], holes can be discharged from the trap level between the semiconductor layer 13 and the top gate insulating film 18 to refresh, that is, reset. That is, if the photosensor PS is used continuously, the trap level between the top gate insulating film 18 and the semiconductor layer 13 is a hole and a drain electrode (D) 1 generated by light irradiation.
Filled with holes injected from No. 5, the channel resistance in the non-light irradiation state also decreases, and the drain current I _DS increases in the no light irradiation state. Therefore, 0 [V] is applied to the top gate electrode (TG) 19 to discharge the holes and reset.

Further, in the photosensor PS, when a positive voltage is not applied to the bottom gate electrode (BG) 11, a channel is not formed in the bottom transistor, and the drain current _IDS flows even if light irradiation is performed. Instead, it can be in a non-selected state. That is, the photo sensor PS
By controlling the voltage (bottom gate voltage V _BG ) applied to the bottom gate electrode (BG) 11, the selected state and the non-selected state can be controlled. When 0 [V] is applied to the top gate electrode (TG) 19 in this non-selected state, holes are discharged from the trap level between the semiconductor layer 13 and the top gate insulating film 18 as described above. Can be reset.

Next, the above operation will be described with reference to FIG. 5 showing a relationship between voltages applied to the respective electrodes of the photosensor PS and FIG. 6 showing a drain current characteristic curve at that time. FIG. 6 shows that the top gate voltage V _TG applied to the top gate electrode (TG) 19 is changed by using the bottom gate voltage V _BG applied to the bottom gate electrode (BG) 11 and the presence or absence of the irradiation light A as parameters. The graph shows the drain current characteristics when the device is turned on.

Now, as shown in FIG. 5A and FIG.
The state is common in that the bottom gate voltage V _BG is 0 [V]. This state corresponds to the drain current characteristic curve T1 when the irradiation light A is irradiated (when bright) and the drain current characteristic curve T2 when the irradiation light A is not irradiated (when dark) in FIG. That is, this state corresponds to the top gate voltage V _TG
Is changed from 0 [V] to −20 [V], and the drain current _IDS is 1 regardless of the irradiation of the irradiation light A.
0 [pA] or less, and the photosensor PS is in a non-selected state.

The states shown in FIGS. 5C and 5D are common in that the bottom gate voltage V _BG is +10 [V]. In this state, light is radiated and the top gate voltage V
_{Even if TG} is changed from 0 [V] to -20 [V], the drain current I _DS is always 1 [μA] or more as shown in FIG. _IDS flows and light irradiation is detected. When the photosensor PS is not irradiated with the irradiation light A, the top gate voltage V _TG is -14 [V] or less and 10 [pA] or less, as shown in FIG. When the drain current I _DS flows and the top gate voltage V _TG becomes higher, the drain current I _DS increases.

Therefore, as shown in FIG. 5, the photo sensor PS _changes the top gate voltage V _TG to, for example, 0
By controlling to [V] and -20 [V], the sense state and the reset state can be controlled, and the bottom gate voltage V _{BG is set} to, for example, 0 [V] and +10 [V].
Thus, the selected state and the non-selected state can be controlled. As a result, the top gate voltage V _TG
In addition, by controlling the bottom gate voltage V _BG , the photo sensor PS can operate as a photo sensor having both a function as a photo sensor and a function as a selection transistor.

In this embodiment, the photosensor PS is applied to a photosensor array as shown in FIG. 2 by utilizing the fact that it has both a function as a photosensor and a function as a selection transistor. The photo sensor system 1 shown in FIG. 1 is configured using the photo sensor array.

Next, the operation will be described.

In the photo sensor system 1 described above,
Each of the photo sensors PS arranged in a matrix is alternately switched between a sense state and a non-sense state, and the length of the sense time in the sense state is changed.
It is checked whether or not the output of each photosensor PS is inverted within this sense time, and based on the critical sense time at which the output of each photosensor PS is inverted, the amount of irradiation light,
That is, the gradient of the detection target is detected.

That is, in FIG. 1, the clock generating section 23 outputs a clock signal of a predetermined frequency and a reset signal to the pixel section driving circuit 21 and the signal inversion detecting section 24,
The pixel unit driving circuit 2 detects the sensor unit 3 based on the clock signal and the reset signal input from the clock generation unit 4.
Outputs a top gate voltage (φTG) and a bottom gate voltage (φBG) as a sense signal and a reset signal,
The sensor unit 3 is driven for each photo sensor PS. At this time, as shown in FIG. 2, the pixel portion drive circuit 21 uses the row address decoder 34, the top address decoder 36, and the column switch 35 to control each photo sensor P.
The bottom gate voltages φBG1 to φBGn applied to the bottom gate electrode (BG) 11 of the S, the top gate electrode (T
G) Top gate voltages φTG1 to φTG applied to 19
The n and the drain voltages φd1 to φdm (precharge voltage φPG) applied to the drain electrode (D) 15 are controlled as shown in FIG.

That is, as shown in FIG. 7, in the photosensor system 1, first, the bottom gate voltage φBG1 is applied to each photosensor PS connected to the first row.
Is reset to 0 [V] and the top gate voltage φTG1 is set to +5 [V]. During the reset, the precharge transistor 37 is charged with a precharge voltage (φPG) for a predetermined time.
Is applied to the signal line 32 to apply the drain voltages φd1 to φdm.
Is precharged by applying. Thereafter, the photo sensor PS is set to the sensing state by setting the top gate voltage φTG1 to −20 [V], and the bottom gate voltage φBG1 is set to +10 [V] during this sensing state (sense time τ).
Then, the photo sensor PS is in the selected state. When the photosensor PS is in the selected state, the output signal V _OUT changes to 0 [V] according to the length of the predetermined sense time τ1 and the light irradiation amount (light amount) within the sense time τ1. +10 [V].

The above operation is performed from the bottom gate voltage φBG1 and the top gate voltage φTG1 to the bottom gate voltage φBGn.
And the top gate voltage φTGn, that is, from the photosensors in the first row to the nth row of the photosensors PS arranged in a matrix,
The operation is performed at the same sense time τ1, and the output signal V _OUT of the photo sensor PS connected to each row at this time is output from the column switch 35 to the signal inversion detection unit 5 via the buffer 38.

When the above operation is performed from the first row to the n-th row, reset is performed, and then, as shown in FIG. 7, the sense time τ2 is shorter than the sense time τ1 by a predetermined time τ2 as shown in FIG. And for this sense time τ2,
The same processing is repeated from the first line to the n-th line. Then, the output signal V _OUT of each photosensor PS at this time is output to the signal inversion detection unit 5 in the same manner as described above.

Similarly, the sensing time τ is successively shortened by a predetermined time, and the above processing is repeated. The above processing is repeated a preset number of times. At this time, the number of repetitions is set to be at least the number of tones to be expressed.

[0046] In this manner, the output signal V _{OU T} of each photosensor PS is sequentially input to the signal inversion detecting unit 5,
The signal inversion detection unit 5 detects whether or not the output signal V _OUT is inverted for each photosensor PS,
The clock signal input from the clock generation unit 4 is counted within the sense time τ, and the count number and the address data of the photosensor PS in which the output signal V _OUT is inverted are output to the gradation determination unit 6. And each photo sensor PS
As described above, the time until the output signal V _OUT is inverted depends on the amount of irradiation light applied to each photosensor PS, and is counted by the clock generator 4 (that is, the count of the photosensor PS). The critical sense time τ) at which the output signal V _OUT is inverted corresponds to the amount of irradiation light applied to each photosensor PS.

The gradation judging section 6 searches a table showing the relationship between the critical sense time and the gradation stored in the built-in ROM based on the count number input from the signal inversion detecting section 5 and converts the table into gradation data. The converted gradation data is output to an image memory (not shown).

As described above, each photo sensor PS is alternately switched between the sense state and the non-sense state, and the length of the sense time τ in the sense state is changed, so that the output signal V _OUT of the photo sensor PS is inverted. The detection operation for detecting the critical sense time τ is repeated a plurality of times, and the light amount (gradation) of the irradiation light is detected based on the critical sense time τ when the output signal V _{OUT of the} photosensor PS is inverted. Therefore, the amount of light (gradation) can be extracted as a digital signal, and the amount of light (gradation) can be accurately detected without providing an external amplifier circuit. As a result, gradation expression can be performed with high accuracy.

For example, as shown in FIG. 8, for example, in a circular figure Z, there are a region Z ₀ , a region Z ₁ , a region Z _M and a region Z _N from inside to outside, and the outside region Z _N is pure white. When the inner area Z ₀ is completely black, the signal inversion detector 5 detects the outer area Z _N of the photo sensor PS that detects the outer area Z _N in all the detection operations from the first detection operation to the final detection operation. Detecting the inversion of the output signal V _OUT ,
Also, for example, starting from the third detection operation and
One eye region Z _M by detecting the inversion of the output signal V _OUT of the photosensor PS to detect, to detect a reversal of all the output signals V _OUT in the detection operation after about this region Z _M. In addition, the signal inversion detection unit 5 detects the inversion of the output signal V _OUT of the photo sensor PS that detects the area Z ₁ in the detection operation performed later than the area Z _M , and this area Z ₁
For all the output signals V
Detects inversion of _OUT . Further, the signal inversion detection unit 5
In the final detection operation, the inversion of the output signal V _OUT of the photo sensor PS for detecting the inner area Z ₀ is detected.
Then, the signal inversion detection unit 5 counts the clock signal input from the clock generation unit 4 for each photosensor PS within the sense time τ when the output signal V _OUT is first detected to be inverted. Then, the count result and the address data of the photosensor PS in which the output signal V _OUT is inverted are output to the gradation determination unit 6. Therefore, based on the count result as a digital signal, the gradation judging section 6 determines each of the region regions Z ₀ , Z ₁ , Z _M and Z _N.
Can be accurately determined.

Further, according to this embodiment, as each photosensor PS, the source electrode (S)
14 and a drain electrode (D) 15 are opposed to each other, and the insulating film 1 is formed on both sides of the semiconductor layer 13, the source electrode (S) 14, and the drain electrode (D) 15.
A bottom gate electrode (BG) 11 and a top gate electrode (TG) 1 opposed to the semiconductor layer 13 via the first and second semiconductor layers 2 and 18;
The top gate electrode (TG) 19 is used as a light irradiation side, and the light irradiated from the light irradiation side is transmitted through the top gate insulating film 18 on the light irradiation side to irradiate the semiconductor layer 13. Since the voltage applied to the top gate electrode (TG) 19 on the light irradiation side is controlled so that the sense state and the non-sense state are controlled, the sense state of the photosensor PS is changed. In addition to being able to control easily, the photosensor PS itself can be provided with a photosensor function having an amplification function and a selection function of the photosensor PS, so that the detection accuracy can be further improved, and The size of the sensor system 1 itself can be further reduced.

In the above embodiment, the photosensor PS is formed by combining an inverted staggered thin film transistor and a coplanar thin film transistor with a single semiconductor layer. However, the present invention is not limited to this. A photosensor PS having a sense state and a non-sense state and inverting the output thereof in a time corresponding to the amount of light irradiated when in the sense state can be used.

In the above-described embodiment, the sense time τ is set to be shorter at predetermined time intervals from the longest sense time. However, the present invention is not limited to this. For example, the sense time τ is sequentially set at predetermined time intervals from the shortest sense time. It may be set longer, and the rate of decrease or increase in the sense time may be changed.

[0053]

According to the photo sensor system of the present invention, the photo sensor is alternately switched between the sense state and the non-sense state, and the length of the sense time in the sense state is changed, so that the output of the photo sensor is changed. The detection operation for detecting the inversion is repeated a plurality of times, and the light amount of the irradiation light is detected based on the critical sense time at which the output of the photosensor is inverted, so that the light amount can be digitized and extracted. It is possible to accurately detect the amount of light without providing an amplifier circuit. As a result, gradation expression can be performed with high accuracy.

In this case, the photo sensor is arranged such that the source electrode and the drain electrode face each other with the semiconductor layer interposed therebetween.
On both sides of the semiconductor layer, the source electrode and the drain electrode, a first gate electrode and a second gate electrode opposed to the semiconductor layer with an insulating film interposed therebetween, respectively, are arranged. One of the gate electrode sides is a light irradiation side, and light irradiated from the light irradiation side is irradiated on the semiconductor layer through the insulating film on the light irradiation side, and the light is irradiated on the gate electrode on the light irradiation side. Assuming that the sense state and the non-sense state are controlled by controlling the applied voltage, the sense state of the photosensor can be easily controlled, and the photosensor itself has an amplifying function. A photo sensor function and a photo sensor selection function can be provided, which can further improve detection accuracy and further reduce the size of the photo sensor system itself. Rukoto can.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing one embodiment of a photosensor system according to the present invention.

FIG. 2 is a circuit diagram showing a sensor array of the sensor unit of FIG.

FIG. 3 is a side sectional view of the photosensor of FIG. 2;

FIG. 4 is an equivalent circuit of the photosensor of FIG.

FIG. 5 is an explanatory diagram of voltages applied to respective electrodes of the photosensor of FIG. 4 and changes in the state thereof.

6 is a characteristic curve diagram showing output characteristics in a voltage application state of FIG.

FIG. 7 is a timing chart showing a relationship between an applied voltage of each section to the photosensor of FIG. 2 and an output signal.

FIG. 8 is an explanatory diagram of a gradation detecting operation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photosensor system 2 Pixel part drive circuit 3 Sensor part 4 Clock generation part 5 Signal inversion detection part 6 Gradation judgment part 10 Insulating substrate 11 Bottom gate electrode (BG) 12 Bottom gate insulating film 13 Semiconductor layer 14 Source electrode (S 15) Drain electrode (D) 16, 17 n ⁺ silicon layer 18 Top gate insulating film 19 Top gate electrode (TG) 34 Row address decoder 35 Column switch 36 Top address decoder PS Photo sensor

Claims (4)

(57) [Claims] 1. A photo sensor system using a photo sensor having a sense state and a non-sense state, and in a sense state, the output of which is inverted at a time corresponding to the amount of light irradiated. While alternately switching between the sense state and the non-sense state, and changing the length of the sense time in the sense state, the detection operation of detecting the inversion of the output of the photo sensor is repeated a plurality of times. A photosensor system for detecting the amount of irradiation light based on the critical sense time for inversion. 2. The photosensor according to claim 1, wherein a source electrode and a drain electrode are opposed to each other with a semiconductor layer interposed therebetween, and both sides of the semiconductor layer, the source electrode and the drain electrode with an insulating film interposed therebetween. A first gate electrode and a second gate electrode facing the semiconductor layer are provided, and one of the first gate electrode side and the second gate electrode side is a light irradiation side, and irradiation is performed from the light irradiation side. Light is transmitted through the insulating film on the light irradiation side to irradiate the semiconductor layer, and by controlling a voltage applied to the gate electrode on the light irradiation side, the sense state and the non-sense state are controlled. The photo sensor system according to claim 1, wherein 3. The photo sensor system according to claim 1, wherein the sense time is set to be shorter at predetermined time intervals sequentially from a preset longest sense time. 4. The photo sensor system according to claim 1, wherein the sense time is set to be longer at predetermined time intervals sequentially from a preset shortest sense time.