CN109348150B - Pixel circuit for realizing CMOS active pixel flexible image sensor based on organic thin film phototransistor - Google Patents
Pixel circuit for realizing CMOS active pixel flexible image sensor based on organic thin film phototransistor Download PDFInfo
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- CN109348150B CN109348150B CN201811217307.1A CN201811217307A CN109348150B CN 109348150 B CN109348150 B CN 109348150B CN 201811217307 A CN201811217307 A CN 201811217307A CN 109348150 B CN109348150 B CN 109348150B
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- film transistor
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/70—SSIS architectures; Circuits associated therewith
- H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/70—SSIS architectures; Circuits associated therewith
- H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
- H04N25/77—Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
Abstract
The invention discloses a pixel circuit for realizing a CMOS active pixel flexible image sensor based on an organic thin film phototransistor, which comprises the organic phototransistor PH, and five organic thin film transistors T1, T2, T3, T4 and T5; the source electrode of the T1 is connected with VDD, the grid electrode is connected with a first scanning control line VSCAN1, the drain electrode of the T2 is connected with the source electrode of PH, and the grid electrode is connected with a second scanning control line VSCAN 2; the source of the T3 is connected to the drain of the T1, the drain is used as an output end, the drain is connected to a Column selection scanning line Column select, the gate is connected to a Row selection scanning line Row select, the source of the T4 is connected to the controllable voltage source VLL, the drain is connected to the gate of PH, and the gate is connected to a third scanning control line VSCAN 3; the source of T5 is connected to the capacitor C, the drain is connected to the ground line VSS, and the gate is connected to the fourth scanning control line VSCAN 4. According to the invention, the silicon-based thin film transistor is replaced by the organic thin film transistor, and the flexible image sensor can be realized according to the special flexibility of the organic material.
Description
Technical Field
The invention belongs to the technical field of electronic circuits, and particularly relates to a pixel circuit for realizing a CMOS (complementary metal oxide semiconductor) active pixel flexible image sensor based on an organic thin film phototransistor.
Background
When a smart phone or a digital camera takes a picture, an optical image generated by imaging an object through various optical lenses is transmitted to an image sensor, and an optical signal is converted into an electric signal to be read out according to the property of the image sensor. Conventional CMOS image sensor pixel circuit designs are based on the photoelectric conversion properties of silicon-based photodiodes. However, in consideration of the responsivity of the silicon-based photodiode, the sensitivity is not ideal, and the flexible device based on the organic semiconductor is the mainstream of the future electronic products, so that the organic thin film phototransistor is used for replacing the silicon-based photodiode, and the design of the pixel circuit of the image sensor is realized.
Experiments show that the threshold voltage of the phototransistor can drift due to illumination, and the threshold voltage changes, which shows that the light and the threshold voltage have a certain relation.
Disclosure of Invention
The invention aims to overcome the technical defects of the existing silicon-based photoelectric sensor and provides a pixel circuit for realizing a CMOS (complementary metal oxide semiconductor) active pixel flexible image sensor based on an organic thin-film photoelectric transistor, which utilizes the characteristic property of the photoelectric transistor and the property of threshold voltage change generated by photoelectric conversion to realize the pixel circuit design of the image sensor and acquire and read signals. The method can be applied to the fields of mobile payment fingerprint identification, unmanned driving and the like in the camera of the mobile phone.
The invention is realized by the following technical scheme:
a pixel circuit for realizing a CMOS active pixel flexible image sensor based on an organic thin film phototransistor comprises the organic phototransistor PH, a capacitor c, a first organic thin film transistor T1, a second organic thin film transistor T2, a third organic thin film transistor T3, a fourth organic thin film transistor T4 and a fifth organic thin film transistor T5;
the source electrode of the first organic thin film transistor T1 is connected with a power supply voltage VDD, the grid electrode of the first organic thin film transistor T1 is connected with a first scanning control line VSCAN1, and the drain electrode of the first organic thin film transistor T1 is connected with a first node A; the source electrode of the second organic thin film transistor T2 is connected with a second node B, the drain electrode of the second organic thin film transistor T2 is connected with the source electrode of the phototransistor PH, and the grid electrode of the second organic thin film transistor T2 is connected with a second scanning control line VSCAN 2; the first node A is connected with the second node B; the source electrode of the third organic thin film transistor T3 is connected to the drain electrode of the first organic thin film transistor T1, the drain electrode is used as an output end, the drain electrode is connected to a Column selection scanning line Column select, the gate electrode is connected to a Row selection scanning line Row select, the source electrode of the fourth organic thin film transistor T4 is connected to a controllable voltage source VLL, the drain electrode is connected to the gate electrode of the organic phototransistor PH, and the gate electrode is connected to a third scanning control line VSCAN 3; a source electrode of the fifth organic thin film transistor T5 is connected to one end of a capacitor C, a drain electrode is connected to a ground line VSS, a gate electrode is connected to a fourth scanning control line VSCAN4, and the other end of the capacitor C is connected to the first node a;
the first organic thin film transistor T1, the second organic thin film transistor T2, the third organic thin film transistor T3, the fourth organic thin film transistor T4 and the fifth organic thin film transistor T5 are all p-type organic thin film transistors.
The working method of the pixel circuit is as follows:
in the first stage, the third control scan line VSCAN3 is at a low level, the fourth organic thin film transistor T4 is turned on, VLL performs reset initialization on the organic phototransistor PH, and at this time, other scan control lines are at a high level, so that other organic thin film transistors are turned off;
in the second stage, the first scan control line VSCAN1 is at a low level, the first organic thin film transistor T1 is turned on, at this time, VDD charges the capacitor C, the third scan control line VSCAN3 is at a high level, the fourth organic thin film transistor T4 is turned off, the fourth scan control line VSCAN4 is at a low level, and the fifth organic thin film transistor T5 is turned on;
in the third stage, the first scan control line VSCAN1 is at a high level, the first organic thin film transistor T1 is turned off, the second scan control line VSCAN2 is at a low level, the second organic thin film transistor T2 is turned on, and the voltage at the point a passes through the second organic thin film transistor T2 to discharge the organic phototransistor PH until the voltage at the point a reaches the threshold voltage of the phototransistor PH, the detected threshold voltage may be output through the drain of the third organic thin film transistor T3, and the threshold voltage of the phototransistor at each pixel point may be successfully detected according to the row and column selection requirements.
The invention has the advantages and beneficial effects that:
1. the pixel circuit of the image sensor designed by the invention uses the organic phototransistor to replace the traditional silicon-based photodiode, uses the organic thin film transistor to replace the silicon-based thin film transistor, and can realize a flexible image sensor according to the special flexibility of organic materials.
2. According to the high responsivity and the high sensitivity of the organic photoelectric transistor, the working efficiency of the circuit can be greatly improved.
3. According to the design of the circuit and the property aiming at the organic photoelectric transistor, the change of the threshold voltage of the organic photoelectric transistor can be accurately read, and further the specific relation between the threshold voltage and light is analyzed.
Drawings
Fig. 1 is a circuit diagram of the present invention.
Fig. 2 is a circuit control timing diagram of the present invention.
For a person skilled in the art, other relevant figures can be obtained from the above figures without inventive effort.
Detailed Description
In order to make the technical solution of the present invention better understood, the technical solution of the present invention is further described below with reference to specific examples.
Referring to fig. 1, the pixel circuit of the image sensor of the present invention includes an organic phototransistor PH, a capacitor c, a first p-type organic thin film transistor T1, a second p-type organic thin film transistor T2, a third p-type organic thin film transistor T3, a fourth p-type organic thin film transistor T4, and a fifth p-type organic thin film transistor T5.
The source electrode of the first p-type organic thin film transistor T1 is connected with a power supply voltage VDD, the grid electrode of the first p-type organic thin film transistor T1 is connected with a first scanning control line VSCAN1, and the drain electrode of the first p-type organic thin film transistor T1 is connected with a first node A; the source electrode of the second p-type organic thin film transistor T2 is connected with a second node B, the drain electrode of the second p-type organic thin film transistor T2 is connected with the source electrode of the phototransistor PH, and the grid electrode of the second p-type organic thin film transistor T2 is connected with a second scanning control line VSCAN 2; the source electrode of the third p-type organic thin film transistor T3 is connected to the drain electrode of the first p-type organic thin film transistor T1, the drain electrode is used as an output end and is connected to a Column selection scanning line Column select, the gate electrode is connected to a Row selection scanning line Row select, the source electrode of the fourth p-type organic thin film transistor T4 is connected to a controllable voltage source VLL, the drain electrode is connected to the gate electrode of the organic phototransistor PH, and the gate electrode is connected to a third scanning control line VSCAN 3; the fifth p-type organic thin film transistor T5 has a source connected to the capacitor C, a drain connected to the ground line VSS, and a gate connected to the fourth scan control line VSCAN 4.
Further, the first scan control signal, the second scan control signal, the third scan control line, the fourth scan control line, and the row selection control signal are provided through an external timing controller.
The working principle of the present invention is explained in detail below with reference to fig. 2, and the driving process of the pixel circuit is divided into three stages: an initialization phase, a threshold voltage programming phase and a threshold voltage signal reading phase.
In the first phase (initialization phase), the third control scan line VSCAN3 is at low level, T4 is turned on, VLL performs reset initialization on the organic phototransistor PH, and at this time, other scan control lines are at high level, so that other organic tfts are turned off.
In the second phase (threshold voltage programming phase), the first scan control line VSCAN1 is low, T1 is on, at which time VDD charges the capacitor C, and the third scan control line VSCAN3 is high, T4 is off, the fourth scan control line VSCAN4 is low, and T5 is on.
In the third stage (threshold voltage signal reading stage), the first scanning control line VSCAN1 is at a high level, at this time, T1 is turned off, the second scanning control line VSCAN2 is at a low level, T2 is turned on, at this time, the voltage at the point a passes through T2, so that the organic phototransistor PH is discharged until the voltage at the point a is the threshold voltage of the phototransistor PH, the detected threshold voltage can be output through the drain of the organic thin film transistor T3, and the threshold voltage of the phototransistor of each pixel point can be successfully detected according to the requirements of row and column selection, thereby realizing the function of collecting and reading data after the image sensor is illuminated.
The invention has been described in an illustrative manner, and it is to be understood that any simple variations, modifications or other equivalent changes which can be made by one skilled in the art without departing from the spirit of the invention fall within the scope of the invention.
Claims (2)
1. A pixel circuit for realizing a CMOS active pixel flexible image sensor based on an organic thin film phototransistor comprises the organic phototransistor PH, a capacitor c, a first organic thin film transistor T1, a second organic thin film transistor T2, a third organic thin film transistor T3, a fourth organic thin film transistor T4 and a fifth organic thin film transistor T5;
the source electrode of the first organic thin film transistor T1 is connected with a power supply voltage VDD, the grid electrode of the first organic thin film transistor T1 is connected with a first scanning control line VSCAN1, and the drain electrode of the first organic thin film transistor T1 is connected with a first node A; the source electrode of the second organic thin film transistor T2 is connected with a second node B, the drain electrode of the second organic thin film transistor T2 is connected with the source electrode of the phototransistor PH, and the grid electrode of the second organic thin film transistor T2 is connected with a second scanning control line VSCAN 2; the first node A is connected with the second node B; the source electrode of the third organic thin film transistor T3 is connected to the drain electrode of the first organic thin film transistor T1, the drain electrode is used as an output end, the drain electrode is connected to a Column selection scanning line Column select, the gate electrode is connected to a Row selection scanning line Row select, the source electrode of the fourth organic thin film transistor T4 is connected to a controllable voltage source VLL, the drain electrode is connected to the gate electrode of the organic phototransistor PH, and the gate electrode is connected to a third scanning control line VSCAN 3; a source electrode of the fifth organic thin film transistor T5 is connected to one end of a capacitor C, a drain electrode is connected to a ground line VSS, a gate electrode is connected to a fourth scanning control line VSCAN4, and the other end of the capacitor C is connected to the first node a;
the first organic thin film transistor T1, the second organic thin film transistor T2, the third organic thin film transistor T3, the fourth organic thin film transistor T4 and the fifth organic thin film transistor T5 are all p-type organic thin film transistors.
2. Method of operating a pixel circuit according to claim 1, characterized in that it comprises the following phases:
in the first stage, the third control scan line VSCAN3 is at a low level, the fourth organic thin film transistor T4 is turned on, VLL performs reset initialization on the organic phototransistor PH, and at this time, other scan control lines are at a high level, so that other organic thin film transistors are turned off;
in the second stage, the first scan control line VSCAN1 is at a low level, the first organic thin film transistor T1 is turned on, at this time, VDD charges the capacitor C, the third scan control line VSCAN3 is at a high level, the fourth organic thin film transistor T4 is turned off, the fourth scan control line VSCAN4 is at a low level, and the fifth organic thin film transistor T5 is turned on;
in the third stage, the first scan control line VSCAN1 is at a high level, the first organic thin film transistor T1 is turned off, the second scan control line VSCAN2 is at a low level, the second organic thin film transistor T2 is turned on, the first node a voltage passes through the second organic thin film transistor T2 at this time, so that the organic phototransistor PH is discharged until the first node a voltage is the threshold voltage of the phototransistor PH, the detected threshold voltage can be output through the drain of the third organic thin film transistor T3, and the threshold voltage of the phototransistor of each pixel point can be successfully detected according to the row and column selection requirements.
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| CN110728254B (en) * | 2019-10-22 | 2022-03-01 | 武汉华星光电半导体显示技术有限公司 | Optical fingerprint identification circuit and display device |
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| CN104751798B (en) * | 2015-04-10 | 2016-03-30 | 京东方科技集团股份有限公司 | Pixel-driving circuit, display device and image element driving method |
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