ELECTRONIC DEVICE AND OPERATING METHOD THEREOF

An electronic device and an operating method thereof are provided. The electronic device includes a driving transistor and a preset transistor. The operating method includes the following steps: turning on the preset transistor, and providing a first voltage to a control terminal of the driving transistor; turning off the preset transistor, and providing a second voltage to the driving transistor, wherein the first voltage is greater than the second voltage; executing a sensing process; and executing a scan process to provide an output signal.

BACKGROUND

Technical Field

The disclosure relates a device; particularly, the disclosure relates to an electronic device and an operating method thereof.

Description of Related Art

For a general active pixel sensor (APS), since the active pixel sensor has the threshold voltage (Vth) problem of the driving transistor, such as in-plain Vth variation due to process and Vth degradation caused by various factors (e.g. static destruction, irradiation etc.), which greatly affects the sensing quality of image sensing results.

SUMMARY

The operating method of the disclosure is adapted to the electronic device. The electronic device includes a driving transistor and a preset transistor. The operating method includes the following step: turning on the preset transistor, and providing a first voltage to a control terminal of the driving transistor; turning off the preset transistor, and providing a second voltage to the driving transistor, wherein the first voltage is greater than the second voltage; executing a sensing process; and executing a scan process to provide an output signal.

The electronic device of the disclosure includes a preset transistor and a driving transistor. The driving transistor is electrically connected to the preset transistor. A first voltage is provided to a control terminal of the driving transistor when the preset transistor is turned on. A second voltage is provided to the driving transistor when the preset transistor is turned off. The first voltage is greater than the second voltage.

Based on the above, according to the operating method and the electronic device of the disclosure, the electronic device can provide a good image sensing function.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the exemplary embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numbers are used in the drawings and the description to refer to the same or like components.

Certain terms are used throughout the specification and appended claims of the disclosure to refer to specific components. Those skilled in the art should understand that electronic device manufacturers may refer to the same components by different names. This article does not intend to distinguish those components with the same function but different names. In the following description and rights request, the words such as “comprise” and “include” are open-ended terms, and should be explained as “including but not limited to . . . ”.

The term “coupling (or connection)” used throughout the whole specification of the present application (including the appended claims) may refer to any direct or indirect connection means. For example, if the text describes that a first device is coupled (or connected) to a second device, it should be interpreted that the first device may be directly connected to the second device, or the first device may be indirectly connected through other devices or certain connection means to be connected to the second device. The terms “first”, “second”, and similar terms mentioned throughout the whole specification of the present application (including the appended claims) are merely used to name discrete elements or to differentiate among different embodiments or ranges. Therefore, the terms should not be regarded as limiting an upper limit or a lower limit of the quantity of the elements and should not be used to limit the arrangement sequence of elements. In addition, wherever possible, elements/components/steps using the same reference numerals in the drawings and the embodiments represent the same or similar parts. Reference may be mutually made to related descriptions of elements/components/steps using the same reference numerals or using the same terms in different embodiments.

FIG.1is a schematic diagram of an electronic device according to an embodiment of the disclosure. Referring toFIG.1, the electronic device100may be an active pixel sensor (APS), and may be manufactured by thin-film transistor (TFT) process, but the disclosure is not limited thereto. The electronic device100includes an active area and a peripheral area, a (active matrix (AM)) pixel array110is located in the active area, and a peripheral circuit120is located in the peripheral area. The pixel array110is electrically connected to the peripheral circuit120. The pixel array110includes a plurality of pixel units p(1,1) to p(N,M), a plurality of reset signal lines101_1to101_N, a plurality of read signal lines102_1to102_N and a plurality of data signal lines103_1to103_M, wherein M and N are positive integers. The peripheral circuit120includes a plurality of readout circuits121_1to121_M, a preset signal line104, a preset voltage line105and a readout control line106. In the embodiment of the disclosure, one row of the pixel units p(1,1) to p(N,M) is electrically connected to corresponding one of the reset signal lines101_1to101_N and corresponding one of the read signal lines102_1to102_N. One column of the pixel units p(1,1) to p(N,M) is electrically connected to corresponding one of the readout circuits121_1to121_M through a corresponding one of the data signal lines103_1to103_M. In the embodiment of the disclosure, the readout circuits121_1to121_M are electrically connected to the preset signal line104, the preset voltage line105and the readout control line106.

FIG.2is a schematic diagram of a pixel circuit and a readout circuit according to an embodiment of the disclosure. Referring toFIG.1andFIG.2, the specific circuit architecture of at least one of the pixel units p(1,1) to p(N,M) and corresponding one of the readout circuits121_1to121_M ofFIG.1may be implemented as the pixel unit211and readout circuit221ofFIG.2. The pixel unit211may be a pixel at n-th row and m-th column in the pixel array110. In the embodiment of the disclosure, the pixel unit211includes a read transistor M1, a driving transistor M2, a reset transistor M3and a sensing unit PD. A first terminal of the read transistor M1is electrically connected to the driving transistor M2and the reset transistor M3through a circuit node P. A second terminal of the read transistor M1is electrically connected to the readout circuit221through a circuit node N2and the data signal line103_m, wherein m is an integer between 1 and M. A control terminal of the read transistor M1is configured to receive a read signal RD(n) from the read signal line102_n, wherein n is an integer between 1 and N. A first terminal of the driving transistor M2is configured to receive an adjustable voltage Va. A second terminal of the driving transistor M2is electrically connected to the read transistor M1and the reset transistor M3through the circuit node P. A control terminal of the driving transistor M2is electrically connected to the sensing unit PD and the reset transistor M3through a circuit node N1. A first terminal of the reset transistor M3is electrically connected to the read transistor M1and the driving transistor M2through the circuit node P. A second terminal of the reset transistor M3is electrically connected to the sensing unit PD and the driving transistor M2through the circuit node N1. To be more specific, reset transistor M3is electrically connected between the second terminal and the control terminal of the driving transistor M2. A control terminal of the reset transistor M3is configured to receive a reset signal RS(n) from the reset signal line101_n. An anode of the sensing unit PD is electrically connected to a bias voltage Vbias. A cathode of the sensing unit PD is electrically connected to the driving transistor M2and the reset transistor M3through the circuit node N1.

In the embodiment of the disclosure, the peripheral circuit120includes a preset transistor Tprst, a readout transistor Tro, an amplifier circuit221_1and a current source221_2. The preset transistor Tprst is included in the peripheral circuit120, but the disclosure is not limited thereto. A first terminal of the preset transistor Tprst is configured to receive a preset voltage Vprst from the preset voltage line105. A second terminal of the preset transistor Tprst is electrically connected to the circuit node N2and the readout transistor Tro. A control terminal of the preset transistor Tprst is configured to receive a preset signal Prst from the preset signal line104. A first terminal of the readout transistor Tro is electrically connected to the circuit node N2and the preset transistor Tprst. A second terminal of the readout transistor Tro is electrically connected to the amplifier circuit221_1and the current source221_2through a circuit node N3. A control terminal of the readout transistor Tro is configured to receive a readout signal RO from the readout control line106. An input terminal of the amplifier circuit221_1is electrically connected to the readout transistor Tro and the current source221_2through the circuit node N3. The current source221_2is electrically connected between the circuit node N3and a ground or a power supply, and configured to generate a constant current Ics flowing from the circuit node N3toward the ground or the power supply.

In the embodiment of the disclosure, the read transistor M1, the driving transistor M2, the reset transistor M3, the preset transistor Tprst and the readout transistor Tro may be N-type transistors, but the disclosure is not limited thereto. In the embodiment of the disclosure, the first terminal and the second terminal of one of the above transistors may be a drain terminal and a source terminal respectively, and the control terminal of the transistor may be a gate terminal, but the disclosure is not limited thereto. In one embodiment of the disclosure, at least one of the read transistor M1, the driving transistor M2, the reset transistor M3, the preset transistor Tprst and the readout transistor Tro may be a P-type transistor. In the embodiment of the disclosure, the sensing unit PD may be a photodiode, but the disclosure is also not limited thereto.

FIG.3is a schematic diagram of voltage variation according to the embodiment ofFIG.2of the disclosure.FIG.4is a flowchart of an operating method according to an embodiment of the disclosure. Referring toFIG.1toFIG.4, the pixel unit211and the readout circuit221ofFIG.2may perform the following steps S410to S440. In step S410, the preset transistor Tprst may be turned on, and a first voltage (voltage VBEof the circuit node N1) may be provided to the control terminal of the driving transistor M2. As shown inFIG.3, the pixel unit211may operate a reset process during a reset period RP from time t1to time t4, and the reset process includes a preset process during the period from time t1to time t2. During the period from time t0to time t3, the adjustable voltage Va may be changed from a reset voltage Vrst to an operation voltage Vdd. However, in one embodiment of the disclosure, the first terminal of the driving transistor M2may also be changed to a floating state (i.e. high impedance). During the period from time t1to time t2, the reset signal RS(n), the preset signal Prst and the read signal RD(n) may be changed from a low voltage level to a high voltage level respectively, and the readout signal RO may be maintained at the low voltage level. Thus, the read transistor M1, the reset transistor M3and the preset transistor Tprst may be turned on, and the readout transistor Tro may be turned off, and the preset voltage Vprst (i.e. the first value) may be provided to the control terminal of the driving transistor M2. In other words, the voltage value of the first voltage (i.e. voltage VBEof the circuit node N1) is at a first value equal to the preset voltage Vprst. The preset transistor Tprst is turned on during at least a part of the reset process. It should be noted that inFIG.3, both the preset transistor Tprst and the read transistor M1are turned on during a part of the reset process, but since the preset voltage Vprst may be provided to the control terminal of the driving transistor M2when the preset transistor Tprst, the read transistor M1and the reset transistor M3are all turned on, it may be that only one of the preset transistor Tprst and the read transistor M1is turned on during a part of the reset process, another one of them is turned on during all the reset process. On the other hand, the control terminal and the second terminal of the driving transistor M2may be short-circuited by the turned on reset transistor M3, since the driving transistor M2has a symmetrical structure in principle, the driving transistor M2can be regarded as an equivalent diode with exchanged source and drain. A cathode terminal of the equivalent diode corresponds to the first terminal of the driving transistor M2. An anode terminal of the equivalent diode corresponds to the control terminal and the second terminal of the driving transistor M2. Thus, due to the operation voltage Vdd is greater than the preset voltage Vprst, the equivalent diode is operated in reverse bias, and there is no current flowing through the equivalent diode. Therefore, a voltage VBE(i.e. the first voltage) of the circuit node N1is equal to the preset voltage Vprst during the period from time t1to time t3. It should be noted that since the transistors in the disclosure are N-type transistors, the term “low voltage level” in the disclosure is referred to a voltage level to turn off the N-type transistor (for example, a ground), and the term “high voltage level” in the disclosure is referred to a voltage level high enough to turn on the N-type transistor.

In step S420, the preset transistor Tprst may be turned off, and a second voltage may be provided to a first terminal of the driving transistor M2. As shown inFIG.3, during the period from time t3to time t4, the adjustable voltage Va may be changed from the operation voltage Vdd to the reset voltage Vrst. During the period from time t2to time t4, the preset signal Prst and the read signal RD(n) may be changed from the high voltage level to the low voltage level respectively, the reset signal RS(n) may be maintained at the high voltage level, and the readout signal RO may be maintained at the low voltage level. Thus, the reset transistor M3may be turned on, and the read transistor M1, the preset transistor Tprst and the readout transistor Tro may be turned off, and the reset voltage Vrst (i.e. the second voltage) may be provided to the first terminal of the driving transistor M2. More specifically, the control terminal and the second terminal of the driving transistor M2may also be short-circuited by the turned on reset transistor M3, and the driving transistor M2may also be operated as the equivalent diode. Thus, due to the reset voltage Vrst is smaller than the preset voltage Vprst, the equivalent diode is operated in forward bias, and there is a diode current flowing through the equivalent diode. Therefore, the voltage VBE(i.e. the first voltage) of the circuit node N1is pulled down after time t3, and after certain time, the voltage VBE(i.e. the first voltage) of the circuit node N1is equal to the voltage (i.e. the second value) of the reset voltage Vrst plus a threshold voltage Vth (i.e. Vrst+Vth) of the driving transistor M2. That is, the voltage VBE(i.e. the first voltage) of the circuit node N1is reduced from the preset voltage Vprst (i.e. the first value) to the voltage (i.e. the second value) of the reset voltage Vrst plus a threshold voltage Vth (i.e. Vrst+Vth) when the reset voltage Vrst is provided to the driving transistor M2. Therefore, the second value of the first voltage (Vrst+Vth) is greater than a voltage value of the second voltage (Vrst).

Moreover, during the period from time t1to time t5, the voltage Vdata(m) of the circuit node N2is equal to the preset voltage Vprst. Then, during a data initialization period DIP from time t5to time t6, the electronic device100may operate a data initialization process. During the data initialization period DIP from time t5to time t6, the reset signal RS(n), the preset signal Prst and the read signal RD(n) may be maintained at the low voltage level respectively, and the readout signal RO may be changed from the low voltage level to the high voltage level. Thus, the read transistor M1, the reset transistor M3and the preset transistor Tprst may be turned off, and the readout transistor Tro may be turned on, and the voltage Vdata(m) of the circuit node N2is pulled down from the preset voltage Vprst to a low voltage level (i.e. ground voltage).

In step S430, the pixel unit211executes a sensing process. As shown inFIG.3, the electronic device100may operate the sensing process during an exposure period EP from time t7to time t8, and the sensing unit PD may provide a sensing signal (sensing current) corresponding to a sensing result to the control terminal of the driving transistor M2. During the exposure period EP from time t7to time t8, the reset signal RS(n), the preset signal Prst, the read signal RD(n) and the readout signal RO may be maintained at the low voltage level. Thus, the voltage VBE(i.e. the first voltage) of the circuit node N1is further reduced from the voltage (i.e. the second value) of the reset voltage Vrst plus a threshold voltage Vth (i.e. Vrst+Vth) to the voltage (i.e. the third value) of the reset voltage Vrst minus a sensing voltage ΔVBEand plus a threshold voltage Vth (i.e. Vrst−ΔVBE+Vth). The sensing voltage ΔVBErepresents a voltage variation due to the sensing result of the sensing unit PD.

In step S440, the pixel unit211executes a scan process to provide an output signal. As shown inFIG.3, the pixel unit211may operate a scan process during a scan period SP from time t9to time t12. During the scan period SP from time t9to time t12, the adjustable voltage Va may be changed from the reset voltage Vrst to the operation voltage Vdd. During a readout period ROP from time t10to time t11, the read signal RD(n) and the readout signal RO may be changed from the low voltage level to the high voltage level respectively, and the reset signal RS(n) and the preset signal Prst may be maintained at the low voltage level. Thus, the read transistor M1and the readout transistor Tro may be turned on, and the reset transistor M3and the preset transistor Tprst may be turned off, and the readout circuit221may readout the output signal with the voltage Vdata(m) through the circuit node N2according to the voltage VBE(i.e. the first voltage) of the circuit node N1. More specifically, the constant current Ics is flowing through the driving transistor M2, the read transistor M1and the readout transistor Tro and toward the current source221_2. The driving transistor M2may act as a source follower in the saturation region, and the voltage Vdata(m) of the circuit node N2is pulled up from the low voltage level to the voltage of the reset voltage Vrst minus the sensing voltage ΔVBEand minus a transistor voltage β (i.e. (Vrst−ΔVBE+Vth)-Vth-β=Vrst-ΔVBE-β). That is, the threshold voltage Vth can be excluded in the voltage Vdata(m). The transistor voltage β may be expressed in the following equation (1), wherein the symbol L represents a gate width of the driving transistor M2, the symbol W represents a channel width of the driving transistor M2, the symbol u represents an electron mobility and the symbol Cox represents a capacitance per unit area of the gate insulator of the driving transistor M2.

Therefore, the input terminal of the amplifier circuit221_1may receive an input voltage Vin from the circuit node N3, and the input voltage Vin is equal to the voltage Vdata(m) (i.e. Vrst-ΔVBE-β). That is, the readout circuit221may generate the sensing data that is not affected by the threshold voltage Vth of the driving transistor M2.

FIG.5is a schematic diagram of an electronic device according to another embodiment of the disclosure. Referring toFIG.5, the electronic device500may be an APS, and includes a (active matrix (AM)) pixel array510and a peripheral circuit520. The pixel array510is electrically connected to the peripheral circuit520. The pixel array510includes a plurality of pixel units p(1,1) to p(N,M), a plurality of reset signal lines501_1to501_N, a plurality of read signal lines502_1to502_N, a plurality of preset signal lines503_1to503_N and a plurality of data signal lines504_1to504_M, wherein M and N are positive integers. The peripheral circuit520includes a plurality of readout circuits521_1to521_M, a reset control line505, a reset voltage line506and a readout control line507. In the embodiment of the disclosure, one row of the pixel units p(1,1) to p(N,M) is electrically connected to corresponding one of the reset signal lines501_1to501_N, corresponding one of the read signal lines502_1to502_N and corresponding one of the preset signal lines503_1to503_N. One column of the pixel units p(1,1) to p(N,M) is electrically connected to corresponding one of the readout circuits521_1to521_M through a corresponding one of the data signal lines504_1to504_M. In the embodiment of the disclosure, the readout circuits521_1to521_M are electrically connected to the reset control line505, the reset voltage line506and the readout control line507.

FIG.6is a schematic diagram of a pixel circuit and a readout circuit according to another embodiment of the disclosure. Referring toFIG.5andFIG.6, the specific circuit architecture of at least one of the pixel units p(1,1) to p(N,M) and corresponding one of the readout circuits521_1to521_M ofFIG.5may be implemented as the pixel unit611and readout circuit621ofFIG.6. The pixel unit611may be a pixel at n-th row and m-th column in the pixel array510. In the embodiment of the disclosure, the pixel unit611includes a read transistor M1, a driving transistor M2, a reset transistor M3, a preset transistor M4and a sensing unit PD. A first terminal of the read transistor M1is electrically connected to the driving transistor M2through a circuit node P. A second terminal of the read transistor M1is electrically connected to the readout circuit621through a circuit node N2and the data signal line504_m, wherein m is an integer between 1 and M. A control terminal of the read transistor M1is configured to receive a read signal RD(n) from the read signal line502_n, wherein n is an integer between 1 and N. A first terminal of the driving transistor M2is electrically connected to the preset transistor M4and the reset transistor M3. A second terminal of the driving transistor M2is electrically connected to the read transistor M1through the circuit node P. A control terminal of the driving transistor M2is electrically connected to the sensing unit PD and the reset transistor M3through a circuit node N1. A first terminal of the reset transistor M3is electrically connected to the sensing unit PD and the driving transistor M2through the circuit node N1. A second terminal of the reset transistor M3is electrically connected to the driving transistor M2and the preset transistor M4. A control terminal of the reset transistor M3is configured to receive a reset signal RS(n) from the reset signal line501_n. A first terminal of the preset transistor M4is configured to receive an operation voltage Vdd. A second terminal of the preset transistor M4is electrically connected to the driving transistor M2and the reset transistor M3. A control terminal of the preset transistor M4is configured to receive a preset signal Prst(n) from the preset signal line503_n. An anode of the sensing unit PD is electrically connected to a bias voltage Vbias. A cathode of the sensing unit PD is electrically connected to the driving transistor M2and the reset transistor M3through the circuit node N1.

In the embodiment of the disclosure, the readout circuit621in the peripheral circuit520includes a reset control transistor Trcr, a readout transistor Tro, an amplifier circuit621_1and a current source621_2. A first terminal of the reset control transistor Trcr is configured to receive a reset voltage Vrst from the reset voltage line506. A second terminal of the reset control transistor Trcr is electrically connected to the circuit node N2and the readout transistor Tro. A control terminal of the reset control transistor Trcr is configured to receive a reset control signal Rst_ctrl from the reset control line505. A first terminal of the readout transistor Tro is electrically connected to the circuit node N2and the reset control transistor Trcr. A second terminal of the readout transistor Tro is electrically connected to the amplifier circuit621_1and the current source621_2through a circuit node N3. A control terminal of the readout transistor Tro is configured to receive a readout signal RO from the readout control line507. An input terminal of the amplifier circuit621_1is electrically connected to the readout transistor Tro and the current source621_2through the circuit node N3. The current source621_2is electrically connected between the circuit node N3and a ground or a power supply, and configured to generate a constant current Ics flowing from the circuit node N3to the ground or a power supply.

In the embodiment of the disclosure, the read transistor M1, the driving transistor M2, the reset transistor M3, the preset transistor M4, the reset control transistor Trcr and the readout transistor Tro may be N-type transistors, but the disclosure is not limited thereto. In the embodiment of the disclosure, the first terminal and the second terminal of the above transistors may be a drain terminal and a source terminal respectively, and the control terminal of the transistor may be a gate terminal, but the disclosure is not limited thereto. In one embodiment of the disclosure, at least one of the read transistor M1, the driving transistor M2, the reset transistor M3, the preset transistor M4, the reset control transistor Trcr and the readout transistor Tro may be a P-type transistor. In the embodiment of the disclosure, the sensing unit PD may be a photodiode, but the disclosure is also not limited thereto.

FIG.7is a schematic diagram of voltage variation according to the embodiment ofFIG.6of the disclosure. Referring toFIG.4toFIG.7, the pixel unit611and the readout circuit621ofFIG.6may perform the following steps S410to S440. In step S410, the preset transistor M4may be turned on, and a first voltage may be provided to the control terminal of the driving transistor M2. As shown inFIG.7, the pixel unit611may operate a reset process during a reset period RP from time t0to time t3, and the reset process includes a preset process during the period from time t0to time t1. During the period from time t0to time t1, the reset signal RS(n) and the preset signal Prst(n) may be changed from a low voltage level to a high voltage level respectively, and the read signal RD(n), the readout signal RO and the reset control signal Rst_ctrl may be maintained at the low voltage level. Thus, the reset transistor M3and the preset transistor M4may be turned on, and the read transistor M1, the reset control transistor Trcr and the readout transistor Tro may be turned off, and the operation voltage Vdd (i.e. the first value) may be provided to the control terminal of the driving transistor M2. The preset transistor M4is turned on during the reset process. More specifically, the control terminal and the first terminal of the driving transistor M2may be short-circuited by the turned on reset transistor M3, and the driving transistor M2may be operated as an equivalent diode. A cathode terminal of the equivalent diode corresponds to the second terminal (drain terminal) of the driving transistor M2. An anode terminal of the equivalent diode corresponds to the control terminal and the first terminal of the driving transistor M2. Because the Read transistor M1is turned off, there is no current flowing through the equivalent diode. Therefore, a voltage VBE(i.e. the first voltage) of the circuit node N1is equal to the operation voltage Vdd during the period from time t0to time t2.

In step S420, the preset transistor M4may be turned off, and a second voltage may be provided to the driving transistor M2. As shown inFIG.7, during the period from time t2to time t3, the preset signal Prst(n) may be changed from the high voltage level to the low voltage level, the reset signal RS(n) may be maintained at the high voltage level, and the read signal RD(n) and the reset control signal Rst_ctrl may be changed from the low voltage level to the high voltage level. Thus, the read transistor M1, the reset transistor M3and the reset control transistor Trcr may be turned on, and the preset transistor M4and the readout transistor Tro may be turned off, and the reset voltage Vrst (i.e. the second voltage) may be provided to the driving transistor M2. More specifically, the control terminal and the first terminal of the driving transistor M2may also be short-circuited by the turned on reset transistor M3, and the driving transistor M2may also be operated as the equivalent diode. Thus, due to the reset voltage Vrst is smaller than the voltage of the first terminal of the driving transistor M2, the equivalent diode is operated in forward bias, and there is a diode current flowing through the equivalent diode. Therefore, the voltage VBE(i.e. the first voltage) of the circuit node N1is pulled down after time t3, and after certain time, the voltage VBE(i.e. the first voltage) of the circuit node N1is equal to the voltage (i.e. the second value) of the reset voltage Vrst plus a threshold voltage Vth (i.e. Vrst+Vth) of the driving transistor M2. That is, the voltage VBE(i.e. the first voltage) of the circuit node N1is reduced from the operation voltage Vdd (i.e. the first value) to the voltage (i.e. the second value) of the reset voltage Vrst plus a threshold voltage Vth (i.e. Vrst+Vth) when the reset voltage Vrst is provided to the driving transistor M2.

Moreover, during the period from time t2to time t5, the voltage Vdata(m) of the circuit node N2is equal to the reset voltage Vrst. Then, during a data initialization period DIP from time t5to time t6, the electronic device500may operate a data initialization process. During the data initialization period DIP from time t5to time t6, the reset signal RS(n), the preset signal Prst(n), the read signal RD(n) and the reset control signal Rst_ctrl may be maintained at the low voltage level respectively, and the readout signal RO may be changed from the low voltage level to the high voltage level. Thus, the read transistor M1, the reset transistor M3, the preset transistor M4and the reset control transistor Trcr may be turned off, and the readout transistor Tro may be turned on, and the voltage Vdata(m) of the circuit node N2is pulled down from the reset voltage Vrst to a low voltage level (i.e. ground voltage).

In step S430, the pixel unit611executes a sensing process. As shown inFIG.7, the electronic device500may operate the sensing process during an exposure period EP from time t7to time t8, and the sensing unit PD may provide a sensing signal (sensing current) corresponding to a sensing result to the control terminal of the driving transistor M2. During the exposure period EP from time t7to time t8, the reset signal RS(n), the preset signal Prst(n), the read signal RD(n) and the readout signal RO may be maintained at the low voltage level. Thus, the voltage VBE(i.e. the first voltage) of the circuit node N1is further reduced from the voltage (i.e. the second value) of the reset voltage Vrst plus a threshold voltage Vth (i.e. Vrst+Vth) to the voltage (i.e. the third value) of the reset voltage Vrst minus a sensing voltage ΔVBEand plus a threshold voltage Vth (i.e. Vrst−ΔVBE+Vth). The sensing voltage ΔVBErepresents a voltage variation due to the sensing result of the sensing unit PD.

In step S440, the pixel unit611executes a scan process to provide an output signal. As shown inFIG.7, the pixel unit611may operate a scan process during a scan period SP from time t9to time t12. During the scan period SP from time t9to time t12, the preset signal Prst(n) may be changed from the low voltage level to the high voltage level to turn on the preset transistor M4. During a readout period ROP from time t10to time t11, the read signal RD(n) and the readout signal RO may be changed from the low voltage level to the high voltage level respectively, and the reset signal RS(n), and the reset control signal Rst_ctrl may be maintained at the low voltage level. Thus, the read transistor M1, the preset transistor M4and the readout transistor Tro may be turned on, and the reset transistor M3and the reset control transistor Trcr may be turned off, and the readout circuit621may readout the output signal with the voltage Vdata(m) through the circuit node N2according to the voltage VBE(i.e. the first voltage) of the circuit node N1. More specifically, the constant current Ics is flowing through the preset transistor M4, the driving transistor M2, the read transistor M1and the readout transistor Tro and toward the current source621_2. The driving transistor M2may act as a source follower in the saturation region, and the voltage Vdata(m) of the circuit node N2is pulled up from the low voltage level (i.e. ground voltage) to the voltage of the reset voltage Vrst minus the sensing voltage ΔVBEand minus a transistor voltage β (i.e. (Vrst−ΔVBE+Vth)-Vth-β=Vrst-ΔVBE-β). That is, the threshold voltage Vth can be excluded in the voltage Vdata(m). The transistor voltage β may be expressed in the above equation (1).

Therefore, the input terminal of the amplifier circuit621_1may receive an input voltage Vin from the circuit node N3, and the input voltage Vin is equal to the voltage Vdata(m) (i.e. Vrst-ΔVBE-β). That is, the readout circuit621may generate the sensing data that is not affected by the threshold voltage Vth of the driving transistor M2.

In summary, the electronic device and the operating method thereof of the disclosure can effectively eliminate or reduce the threshold voltage (Vth) problem of the driving transistor, so as to effectively improve the sensing quality of image sensing results.