CN111083399A - Active pixel circuit capable of being read randomly and driving method thereof - Google Patents
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Abstract
The invention discloses an active pixel circuit capable of being read randomly and a driving method thereof, wherein the active pixel circuit comprises: a photodiode, a first transistor, a second transistor, a first power supply, and a second power supply; the first power supply is connected with the drain electrode of the second transistor and is connected with the drain electrode of the first transistor through the diode, the drain electrode of the first transistor is connected with the grid electrode of the first transistor and the top grid electrode of the second transistor, the source electrode of the first transistor is grounded, the bottom grid electrode of the second transistor is connected with the second power supply, and the source electrode of the second transistor is a signal output end. The invention makes the output current of the random reading active pixel sensor circuit and the photocurrent of the diode present a power function relationship, and the output signal and the light intensity of the circuit present a quasi-linear relationship, so the sensitivity and the dynamic response range of the sensor can be simultaneously optimized.
Description
Technical Field
The invention belongs to the technical field of circuits, and particularly relates to a randomly readable active pixel circuit and a driving method thereof.
Background
A conventional active pixel circuit generally includes three transistors (a reset switch transistor Trst, a source follower Tsf, and a selection switch transistor Tsel) and one photodiode. A Logarithmic Active Pixel Sensor (log.aps) like fig. 1 can be formed if the gate and drain of the reset switching transistor Trst are shorted. Aps has a log.aps output signal that varies logarithmically with the change in light intensity, and therefore has a wider dynamic response range, typically at least 100dB or more, than conventional active pixel circuits. In addition, the log.aps does not need to reset the sensor, the circuit is simple, the pixel fill factor is larger, and the operation is faster and simpler. Meanwhile, each pixel in the log.aps works independently and does not need to perform time integration on photo-generated charges in the photoelectric conversion process, so that the sensor can be read randomly in space and time, the random reading performance in space allows important signals to be read and processed independently, the sensor is more intelligent, and the random reading performance in time enables the signals to be read out and processed more quickly, so that the random reading performance in space and time enables the reading speed of effective signals to be faster.
However, the device connection manner inside the log.aps pixel causes the output signal to decrease with the increase of the illumination intensity, so that the signal reading and processing circuit at the back end needs to be redesigned. Also, the sensitivity of the sensor is low at low light, precisely because the log.aps output is logarithmic to the input. Finally, the design of an active pixel using three transistors also makes it difficult to further reduce the pixel size, which in turn affects the sensitivity of the pixel.
Disclosure of Invention
To overcome the above technical drawbacks, the present invention provides a randomly readable active pixel sensor circuit capable of improving the sensitivity and dynamic range of the randomly readable active pixel sensor circuit.
In order to solve the problems, the invention is realized according to the following technical scheme:
a randomly readable active pixel circuit comprising: a photodiode, a first transistor, a second transistor, a first power supply, and a second power supply;
the first power supply is connected with the drain electrode of the second transistor and is connected with the drain electrode of the first transistor through the diode, the drain electrode of the first transistor is connected with the grid electrode of the first transistor and the top grid electrode of the second transistor, the source electrode of the first transistor is grounded, the bottom grid electrode of the second transistor is connected with the second power supply, and the source electrode of the second transistor is a signal output end.
Compared with the prior art, the beneficial effect of this circuit is: the two transistors of the source follower and the selection switch tube are replaced by one transistor on the basis of the Log.APS, so that the sensor circuit keeps the random reading performance of the Log.APS, and simultaneously, the output and the input are in a linear-like relation, the sensitivity and the dynamic range of the sensor under weak illumination are improved, the number of active devices in a pixel is reduced, and the aperture ratio and the filling factor of the pixel are also improved.
As a further improvement of the present invention, the first transistor is a single-gate transistor, and the second transistor is a double-gate transistor.
As a further improvement of the present invention, the photodiode is a diode having an n-i-p structure, the first transistor and the second transistor are both n-type semiconductor devices, the first power supply is connected to a cathode of the photodiode, and an anode of the photodiode is connected to a drain of the first transistor.
As a further improvement of the present invention, the photodiode is a diode having a p-i-n structure, the first transistor and the second transistor are p-type semiconductor devices, the first power supply is connected to an anode of the photodiode, and a cathode of the photodiode is connected to a drain of the first transistor.
Meanwhile, the invention also provides another active pixel circuit capable of being read randomly, which comprises: a photodiode, a first transistor, a second transistor, a first power supply, and a second power supply;
the first power supply is connected with the drain electrode of the first transistor and the drain electrode of the second transistor, the drain electrode of the first transistor is connected with the grid electrode of the first transistor, the source electrode of the first transistor is connected with the top grid electrode of the second transistor and grounded through the photodiode, the bottom grid electrode of the second transistor is connected with the second power supply, and the source electrode of the second transistor is a signal output end.
As a further improvement of the present invention, the first transistor is a single-gate thin film transistor, and the second transistor is a double-gate thin film transistor.
As a further improvement of the present invention, the photodiode is a diode having an n-i-p structure, the first transistor and the second transistor are both n-type semiconductor devices, a cathode of the diode is connected to a source of the first transistor and a top gate of the second transistor, and an anode of the diode is grounded.
As a further improvement of the present invention, the photodiode is a p-i-n photodiode, the first transistor and the second transistor are both p-type semiconductor devices, an anode of the photodiode is connected to a source of the first transistor and a top gate of the second transistor, and a cathode of the photodiode is grounded.
The invention also provides a driving method of the active pixel circuit capable of being read randomly, which comprises the following steps:
when the active pixel circuit capable of being read randomly is in a working state, voltage is applied to the photodiode, the photodiode is in a reverse bias state, photocurrent is generated under illumination, the first transistor and the second transistor work in a subthreshold region, and therefore the output current of the active pixel circuit capable of being read randomly and the photocurrent of the photodiode are in a power function relationship.
Compared with the prior art, the method has the beneficial effects that: the output current of the active pixel circuit which can be read randomly and the photocurrent of the diode are in a power function relationship, so that the output signal of the sensor circuit and the light intensity are in a quasi-linear relationship to form a logarithm-exponential pixel circuit, and the sensitivity and the dynamic response range of the sensor can be optimized simultaneously.
Drawings
Embodiments of the invention are described in further detail below with reference to the attached drawing figures, wherein:
FIG. 1 is a schematic diagram of a conventional logarithmic active pixel circuit;
FIG. 2 is a schematic diagram of an active pixel circuit according to an embodiment;
FIG. 3 is a diagram of an active pixel circuit according to a second embodiment;
FIG. 4 is a schematic diagram of an active pixel circuit according to a third embodiment;
fig. 5 is a schematic diagram of an active pixel circuit according to the fourth embodiment.
Detailed Description
The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.
Example one
The embodiment discloses a random-readable active pixel circuit, as shown in fig. 2, including: photodiode D, single-gate TFT1, double-gate TFT2, and first power supply VDDConnected with the drain of the double-gate TFT2, the anode of the photodiode D is connected with the drain of the single-gate TFT1, and the cathode of the photodiode D is connected with the first power supply VDDThe drain of the single-gate TFT1 is connected to the gate of the single-gate TFT1 and the top gate of the double-gate TFT2, the source of the single-gate TFT1 is grounded, and the bottom gate of the double-gate TFT2 is connected to the second power supply VBGConnected, the source of the double-gate TFT2 is the signal output terminal, and the first power supply VDDA second power supply V for supplying a reverse bias voltage to the photodiode DBGFor operating a double-gate thin film transistor.
In the above embodiments, the photodiode D is a photodiode of an n-i-p structure, and various diodes such as an amorphous silicon diode or an organic diode or similar photodetectors may be used.
In the above embodiment, the active layer material of the single-gate thin film transistor TFT1 and the active layer material of the double-gate thin film transistor TFT2 are all one of n-type materials such as amorphous silicon, indium gallium zinc oxide, n-type organic semiconductor, and n-type low temperature polysilicon, and the double-gate thin film transistor TFT2 is used to replace a source follower and a selection switch tube in the Log APS, so as to reduce the number of devices in the pixel and improve the aperture ratio and the fill factor of the pixel.
The embodiment improves the circuit, so that the output and the input of the pixel have a quasi-linear positive correlation relationship while the random readability of the pixel in space and time is kept, and the design of a back-end signal reading and signal processing circuit is facilitated.
The present embodiment is further explained with reference to the specific implementation process, as follows:
when the sensor pixel circuit is in working state, the photodiode D needs to be reversely biased to sense light, so the first power supply VDDA second power supply VBGAre all externally biased ports; since a-Si, IGZO, an n-type organic semiconductor, and n-type low temperature polysilicon, which are used to fabricate the thin film transistor, are n-type materials and generally require a positive voltage to be applied for driving, the photodiode D having an n-i-p structure, i.e., a cathode as an external bias port and an anode connected to the gate of the TFT1, is used. When the sensor pixel circuit is in operation, VDDThe photodiode D is under reverse bias for forward bias, and the photogenerated carriers in the photodiode D generate electron-hole pairs under the action of external bias and move to the cathode and the anode respectively to form a photogenerated current Iphoto：
Wherein q is a meta charge, η0Is the quantum efficiency of diode D, P is the light intensity, APDFor the photosensitive area of diode D, λ is the wavelength, R is the reflection coefficient, α and t are the absorption coefficient and thickness, respectively, of the active layer of diode D, h is the planck constant, and c is the speed of light in vacuum, so the total current flowing through diode D is:
IPD＝IDS1＝Idark+Iphoto(2)
Idarkis in a dark stateThe lower diode D is in reverse biased leakage current.
In the single-gate thin film transistor TFT1, the gate and drain are shorted, so the gate voltage VGSAnd source drain voltage VDS1And (3) equality:
VGS＝VDS1(3)
when the single-gate thin film transistor TFT1 works in the sub-threshold region, the source-drain current I of the TFT1 can be obtained according to the current formula of the sub-threshold region of the thin film transistorDS1Comprises the following steps:
wherein, ID01Is a VGS＝VT1And V isDS1When > kT/q, the output current, V, of the single-gate thin film transistor TFT1T1Is the threshold voltage of a single gate thin film transistor TFT1
S1The subthreshold swing of the single-gate thin film transistor TFT1 is shown as k, the Boltzmann constant and T, the temperature. When in use
I.e. VDS1> 0.0258V (at room temperature), formula (4) can be simplified as:
the source-drain voltage V of the single-gate thin film transistor TFT1 can be obtained by converting the above formula (5)DS1Comprises the following steps:
since the anode of the photodiode D, the gate and drain of the single-gate thin-film transistor TFT1, and the top gate of the double-gate thin-film transistor TFT2 are connected together, there are:
VTG＝VDS1(7)
for the double-gate TFT2, its threshold voltage VT2Can be expressed as:
VT2＝VTH0+γVTG(8)
wherein, VTH0Is a VTGWhen the threshold voltage of the TFT2 is 0, γ is a control coefficient of the second gate voltage to the threshold voltage.
Regulating VDGThe output current I in the sub-threshold region of the dual-gate TFT2 can be obtained by operating the dual-gate TFT2 in the sub-threshold regionDS2Comprises the following steps:
wherein, ID02Is a VBG＝VT2And V isDS2At > kT/q, the output current of the double-gate thin film transistor TFT2,
S2is the sub-threshold swing of the double gate thin film transistor TFT 2. When in use
I.e. VDS2> 0.0258V (at room temperature), formula (9) can be simplified as:
therefore, the final output current I of the circuit device of the random-reading active pixel sensorDS2Photocurrent I of diode DphotoIn a power function relationship, namely:
for thin film transistors of the same active material and the same process, the sub-threshold swing is substantially unchanged, i.e. S1≈S2So that an output current I can be obtainedDS2Is in a power function relation with the light intensity P,namely:
IDS2∝P-γ
if the control coefficient gamma of the top gate voltage of the n-type double-gate thin film transistor to the threshold voltage is-0.9 to-2, the output current of the active pixel circuit and the light intensity are in a quasi-linear relationship. Therefore, for a general logarithmic active pixel sensor, the active pixel circuit based on the n-type semiconductor device designed by the embodiment retains the characteristic of random reading, and because the output of the pixel circuit has a quasi-linear relation with the light intensity, the output current changes more obviously with the light intensity under weak light intensity, thereby having higher sensitivity and wider dynamic response range.
Example two
The present embodiment discloses another randomly readable active pixel circuit, as shown in fig. 3, which is different from the first embodiment in that: the photodiode D is a p-i-n photodiode, and the first power supply VDDConnected with the anode of the photodiode D, the cathode of the photodiode D is connected with the drain of the single-gate thin film transistor TFT1, and a first power supply VDDA second power supply V for supplying a reverse bias voltage to the photodiode DBGIs the operating voltage of the double gate thin film transistor TFT 2.
In the above embodiments, the active layer material of the single-gate thin film transistor TFT1 and the active layer material of the double-gate thin film transistor TFT2 are both p-type low-temperature polysilicon or p-type organic semiconductor, and the double-gate thin film transistor TFT2 is used to replace the source follower and the selection switch tube in the Log APS, so as to reduce the use of devices inside the pixel, improve the aperture ratio of the pixel, and simplify the production process.
The present embodiment is further explained with reference to the specific implementation process, as follows:
when the sensor pixel circuit is in operation, the first power supply VDD must apply a negative bias voltage to place the photodiode D in a reverse bias state and the thin film transistor in operation, because it is composed of a p-i-n type diode and a p-type thin film device. The total current flowing through the photodiode D is:
IPD＝ISD1＝Idark+Iphoto(11)
the gate voltage and the source-drain voltage of the single-gate thin film transistor TFT1 are also the same as in equation (3), i.e., the gate voltage and the source-drain voltage are equal. The sub-threshold current I of the TFT1 can be obtained from the current formula of the sub-threshold region of the p-type thin film transistorSD1Comprises the following steps:
wherein,
β1is an ideal parameter for the single gate thin film transistor TFT 1. When V isDS1＜＜-Vsth1Then, equation (12) can be simplified as:
the source-drain voltage V of the single-gate thin film transistor TFT1 can be obtained by converting the formula (13)DS1Comprises the following steps:
the top gate voltage V of the double gate TFT2 can be obtained from the formulas (7) and (8)TGAnd a threshold voltage VT2. Likewise, adjust VDGThe output current I in the sub-threshold region of the dual-gate TFT2 can be obtained by operating the dual-gate TFT2 in the sub-threshold regionSD2Comprises the following steps:
when V isDS2＜＜-Vsth2Equation (14) can be simplified as:
therefore, it can followMachine-reading final output current I of active pixel sensor circuitSD2Photocurrent I of diode DphotoIn a power function relationship, namely:
for thin film transistors of the same active material and the same process, the ideality factor is substantially unchanged, i.e., β1≈β2Therefore, the output current ISD2 is obtained as a power function of the light intensity P, i.e.:
ISD2∝P-γ
if the control coefficient gamma of the top gate voltage of the double-gate thin film transistor with the active layer material being the p-type material to the threshold voltage is-0.9-2, the output current of the pixel circuit and the light intensity are in a quasi-linear relationship. Therefore, the active pixel circuit has the characteristics of random reading, high sensitivity and wide dynamic range.
EXAMPLE III
The present embodiment discloses another randomly readable active pixel circuit, as shown in fig. 4, including: photodiode D, single-gate thin film transistor TFT1, double-gate thin film transistor TFT2, and first power supply VDDA second power supply VBGFirst power supply VDDThe drain of the single-gate TFT1 and the drain of the double-gate TFT2, the drain of the single-gate TFT1 is connected to the gate of the single-gate TFT1, the source of the single-gate TFT1 is connected to the cathode of the diode D, the anode of the photodiode D is grounded, the source of the single-gate TFT1 is connected to the gate of the double-gate TFT2, and the double-gate TFT2 is connected to the second power supply VBGConnected, the source of the double-gate TFT2 is the signal output terminal, and the first power supply VDDA second power supply V for supplying an operating voltage to the single gate TFT1BGFor operating the double gate thin film transistor TFT 2.
In the above embodiment, the photodiode D is a photodiode of an n-i-p structure.
In the above embodiments, the active layer material of the single-gate thin film transistor TFT1 and the active layer material of the double-gate thin film transistor TFT2 are all one of n-type materials such as amorphous silicon, indium gallium zinc oxide, n-type organic semiconductor, and n-type low temperature polysilicon, and the double-gate thin film transistor TFT2 is used to replace a source follower and a selection switch tube in the Log APS, so that the use of devices inside the pixel is reduced, the aperture ratio of the pixel is improved, and the production process is simplified.
The present embodiment is further explained with reference to the specific implementation process, as follows:
when the sensor pixel circuit is in working state, the photodiode D needs to be reversely biased to make it sense light, so the first power supply VDDA second power supply VBGAre all externally biased ports; since a-Si, IGZO, n-type organic semiconductor, and n-type low temperature polysilicon used to fabricate the thin film transistor are n-type materials and generally require application of a positive voltage to drive, the photodiode D having an n-i-p structure, i.e., the cathode is used as an external bias port and the anode is grounded. When the sensor pixel circuit is in operation, VDDFor forward bias, the photodiode D is in a reverse bias state, and at this time, the photo-generated carriers in the photodiode D generate electron-hole pairs due to the external bias and move to the cathode and the anode respectively, and the photocurrent and the total current flowing through the photodiode D are the same as those of equations (1) (2). The gate-drain voltage, the sub-threshold region current, and the source-drain voltage of the single-gate thin film transistor TFT1 are the same as those of equations (3), (4), and (6), respectively.
Since the three ports of the cathode of the photodiode D, the source of the single-gate thin film transistor TFT1, and the top gate of the double-gate thin film transistor TFT2 are connected together, there are:
VTG＝VDD-VDS1(17)
the threshold voltage V of the double-gate TFT2 can be obtained from the formula (8)T2. Regulating VDGThe output current I in the sub-threshold region of the dual-gate TFT2 can be obtained by operating the dual-gate TFT2 in the sub-threshold regionDS2Comprises the following steps:
wherein, ID02Is a VBG＝VT2And V isDS2At > kT/q, the output current of the double-gate thin film transistor TFT2,
S2is the sub-threshold swing of the double gate thin film transistor TFT 2. When in use
I.e. VDS2> 0.0258V (at room temperature), equation (18) can be simplified as:
therefore, the final output current I of the circuit device of the random-reading active pixel sensorDS2Photocurrent I of diode DphotoIn a power function relationship, namely:
for thin film transistors of the same active material and the same process, the sub-threshold swing is substantially unchanged, i.e. S1≈S2So that an output current I can be obtainedDS2In a power function relationship with the light intensity P, namely:
IDS2∝Pγ
if the active layer material is n-type double-gate thin film transistor, the control coefficient gamma of the top gate voltage to the threshold voltage is-0.9-2, the output current of the pixel circuit and the light intensity are in quasi-linear relation, for the general logarithmic active pixel sensor, the active pixel image sensor designed by the embodiment keeps the characteristic of random reading, and because the output of the sensor and the light intensity are in quasi-linear relation, the output current changes obviously with the light intensity under the weak light intensity, so that the active pixel image sensor has higher sensitivity and wider dynamic response range.
Example four
The present embodiment discloses another randomly readable active pixel circuit, as shown in fig. 5, which is different from the third embodiment in that: the photodiode D is a p-i-n structure diode, the anode of the photodiode D is connected with the source electrode of the single-gate thin film transistor TFT1, the cathode of the photodiode D is grounded, and the first power supply VDDFor supplying an operating voltage to the single gate thin film transistor TFT1, a second power supply VBGAn operating voltage is supplied to the double gate thin film transistor TFT 2.
In the above embodiments, the active layer material of the single-gate thin film transistor TFT1 and the active layer material of the double-gate thin film transistor TFT2 are both p-type low-temperature polysilicon or p-type organic semiconductor, and the double-gate thin film transistor TFT2 is used to replace the source follower and the selection switch tube in the Log APS, so as to reduce the use of devices inside the pixel, improve the aperture ratio of the pixel, and simplify the production process.
The present embodiment is further explained with reference to the specific implementation process, as follows:
when the sensor pixel circuit is in operation, the first power supply VDD must apply a negative bias to place the tft in operation and the photodiode D in a reverse bias state, because it is composed of a p-i-n type photodiode and a p-type thin film device. The total current flowing through the photodiode D is the same as equation (11). The gate voltage and the source-drain voltage of the single-gate thin film transistor TFT1 are also the same as in equation (3), i.e., the gate voltage and the source-drain voltage are equal. The gate-drain voltage, the sub-threshold region current, and the source-drain voltage of the single-gate thin film transistor TFT1 are the same as those of equations (3), (4), and (14), respectively.
Since the three ports of the anode of the photodiode D, the source of the single-gate thin film transistor TFT1, and the top gate of the double-gate thin film transistor TFT2 are connected together, there are:
VTG＝VDD-VDS1(20)
the threshold voltage V of the double-gate TFT2 can be obtained from the formula (8)T2. Regulating VDGThe size of (3) is such that the dual-gate TFT2 operates in the sub-threshold region, thereby obtaining the sub-threshold region output of the dual-gate TFT2Output current ISD2Comprises the following steps:
when V isDS2＜＜-Vsth2Equation (21) can be simplified as:
thus, the resulting output current I of the randomly readable active pixel sensor circuitSD2Photocurrent I of diode DphotoIn a power function relationship, namely:
for thin film transistors of the same active material and the same process, the ideality factor is substantially unchanged, i.e., β1≈β2Therefore, the output current ISD2 is obtained as a power function of the light intensity P, i.e.:
ISD2∝Pγ
if the control coefficient gamma of the top gate voltage of the double-gate thin film transistor with the active layer material being the p-type material to the threshold voltage is-0.9-2, the output current of the pixel circuit and the light intensity are in a quasi-linear relationship. Therefore, the active pixel circuit has the characteristics of random reading, high sensitivity and wide dynamic range.
EXAMPLE five
The embodiment discloses a driving method of an active pixel circuit capable of being read randomly, which is applicable to the first embodiment to the fourth embodiment and comprises the following steps:
when the active pixel circuit capable of being randomly read is in a working state, voltage is applied to the photodiode, the photodiode is in a reverse bias state, photocurrent is generated under illumination, the first transistor and the second transistor work in a sub-threshold region, and therefore the output current of the active pixel circuit capable of being randomly read and the photocurrent of the photodiode are in a power function relationship, the output signal of the active pixel sensor circuit capable of being randomly read and the light intensity are in a quasi-linear relationship, and therefore sensitivity and a dynamic response range can be optimized simultaneously.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, so that any modification, equivalent change and modification made to the above embodiment according to the technical spirit of the present invention are within the scope of the technical solution of the present invention.
Claims (9)
1. A randomly readable active pixel circuit, comprising: a photodiode, a first transistor, a second transistor, a first power supply, and a second power supply;
the first power supply is connected with the drain electrode of the second transistor and is connected with the drain electrode of the first transistor through the diode, the drain electrode of the first transistor is connected with the grid electrode of the first transistor and the top grid electrode of the second transistor, the source electrode of the first transistor is grounded, the bottom grid electrode of the second transistor is connected with the second power supply, and the source electrode of the second transistor is a signal output end.
2. The active pixel circuit of claim 1, wherein the first transistor is a single-gate transistor and the second transistor is a double-gate transistor.
3. The active pixel circuit according to claim 2, wherein the photodiode is a photodiode of an n-i-p structure, the first transistor and the second transistor are both n-type semiconductor devices, the first power source is connected to a cathode of the photodiode, and an anode of the photodiode is connected to a drain of the first transistor.
4. The active pixel circuit according to claim 2, wherein the photodiode is a p-i-n photodiode, the first transistor and the second transistor are p-type semiconductor devices, the first power source is connected to an anode of the photodiode, and a cathode of the photodiode is connected to a drain of the first transistor.
5. A randomly readable active pixel circuit, comprising: a photodiode, a first transistor, a second transistor, a first power supply, and a second power supply;
the first power supply is connected with the drain electrode of the first transistor and the drain electrode of the second transistor, the drain electrode of the first transistor is connected with the grid electrode of the first transistor, the source electrode of the first transistor is connected with the top grid electrode of the second transistor and grounded through the photodiode, the bottom grid electrode of the second transistor is connected with the second power supply, and the source electrode of the second transistor is a signal output end.
6. The active pixel circuit of claim 5, wherein the first transistor is a single-gate thin film transistor and the second transistor is a double-gate thin film transistor.
7. The active pixel circuit according to claim 6, wherein the photodiode is a photodiode of an n-i-p structure, the first transistor and the second transistor are both n-type semiconductor devices, a cathode of the photodiode is connected to a source of the first transistor and a top gate of the second transistor, and an anode of the diode is grounded.
8. The active circuit according to claim 6, wherein the photodiode is a p-i-n photodiode, the first transistor and the second transistor are both p-type semiconductor devices, an anode of the photodiode is connected to a source of the first transistor and a top gate of the second transistor, and a cathode of the diode is grounded.
9. A method of driving a randomly readable active pixel circuit as claimed in any one of claims 1 to 8, comprising the steps of:
when the active pixel circuit capable of being read randomly is in a working state, voltage is applied to the photodiode, the photodiode is in a reverse bias state, photocurrent is generated under illumination, the first transistor and the second transistor work in a subthreshold region, and therefore the output current of the active pixel circuit capable of being read randomly and the photocurrent of the photodiode are in a power function relationship.
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| CN201911378964.9A CN111083399A (en) | 2019-12-27 | 2019-12-27 | Active pixel circuit capable of being read randomly and driving method thereof |
| PCT/CN2020/078925 WO2021128595A1 (en) | 2019-12-27 | 2020-03-12 | Active pixel circuit capable of being read randomly and driving method therefor |
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| CN114046881B (en) * | 2021-11-15 | 2024-05-28 | 深圳知微创新技术有限公司 | High-sensitivity color sensor based on thin film transistor |
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| CN101556962A (en) * | 2008-04-11 | 2009-10-14 | 三星电子株式会社 | Image sensor with sensing transistor having two gates and method of operating the same |
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