TWI745014B - Optical sensing circuit and touch display apparatus including the same - Google Patents

Abstract

An optical sensing circuit is provided, which includes a driving transistor, an optical sensing element, a first transistor, a second transistor, and a storage capacitor. The driving transistor includes a control terminal coupled with a first node. The optical sensing element is coupled with the first node, and is configured to generate a sensing current flowing between the first node and a first power terminal according to received light. The driving transistor is configured to generate a driving current corresponding to the sensing current. The first transistor is configured to transmit the driving current to a reading line according to a first control signal. The second transistor is configured to transmit, according to a second control signal, a reference voltage on the reading line to the first node when the first transistor is conducted. The second transistor is further configured to form a diode connection with the driving transistor to compensate for the threshold voltage of the driving transistor when the first transistor is switched off. The storage capacitor is coupled with the first node.

Description

Light sensing circuit and touch display

This disclosure relates to a light sensing circuit and its related touch display, in particular to a light sensing circuit that can share control signals with the pixel circuit in the touch display.

Organic light-emitting diode (OLED) pixel circuits and embedded light sensing circuits are often used together to implement touch displays of mobile devices to obtain a narrow or borderless product appearance, such as the common optical devices on the market. A smart phone with fingerprint touch function. In the current display manufacturing process, the device characteristics of the transistor will vary depending on the region, so that the organic light-emitting diode pixel circuit and the light sensing circuit require more complicated control signals to compensate for the variation of the device characteristics. If the organic light emitting diode pixel circuit and the light sensing circuit cannot share the control signal, and it is necessary to provide multiple sets of shift registers for both in the display, it is not conducive to reducing the frame width of the display.

The present disclosure provides a light sensing circuit, which includes a driving transistor, a light sensing element, a first transistor, a second transistor, and a storage capacitor. The driving transistor includes a control terminal coupled to the first node. The light sensing element is coupled to the first node and used for generating a sensing current flowing between the first node and the first power terminal according to the received light. The driving transistor is used to generate a driving current corresponding to the sensing current. The first transistor is used for transmitting the driving current to the read line according to the first control signal. The second transistor is used for transmitting the reference voltage on the read line to the first node when the first transistor is turned on according to the second control signal. The second transistor is also used to form a diode connection with the driving transistor when the first transistor is turned off to compensate for the critical voltage of the driving transistor. The storage capacitor is coupled to the first node.

The present disclosure provides a touch display, which includes a plurality of read lines, a plurality of pixel circuits, and a plurality of light sensing circuits. Each light sensing circuit includes a driving transistor, a light sensing element, a first transistor, a second transistor, and a storage capacitor. The driving transistor includes a control terminal coupled to the first node. The light sensing element is coupled to the first node and used for generating a sensing current flowing between the first node and the first power terminal according to the received light. The driving transistor is used to generate a driving current corresponding to the sensing current. The first transistor is used for transmitting the driving current to one of the plurality of read lines according to the first control signal. The second transistor is used for transmitting the reference voltage on one of the read lines to the first node when the first transistor is turned on according to the second control signal. The second transistor is also used to form a diode connection with the driving transistor when the first transistor is turned off to compensate for the threshold voltage of the driving transistor. The storage capacitor is coupled to the first node. In addition, the corresponding ones of the plurality of pixel circuits and the corresponding ones of the plurality of light sensing circuits are used to receive the first control signal and the second control signal.

One of the advantages of the above embodiments is that the sensing result of the light sensing circuit is hardly affected by the variation of the element characteristics.

Another advantage of the above embodiments is that the touch display can have a narrow frame.

The embodiments of the present disclosure will be described below in conjunction with related drawings. In the drawings, the same reference numerals indicate the same or similar elements or method flows.

FIG. 1 is a schematic diagram of a light sensing circuit 100 according to an embodiment of the present disclosure. The light sensing circuit 100 includes a driving transistor Td, a first transistor T1, a second transistor T2, a storage capacitor C1, and a light sensing element PS. One end of the light sensing element PS is coupled to the control end of the driving transistor Td through the first node N1, and the other end is coupled to the first power terminal 110, wherein the first power terminal 110 is used to provide the first operating voltage FVSS . When the light sensing element PS does not receive light, the light sensing element PS maintains the first node N1 and the first power terminal 110 in an open circuit state. On the other hand, when the light sensing element PS is illuminated by light, the light sensing element PS will generate a sensing current Is flowing between the first node N1 and the first power terminal 110, for example, flowing from the first node N1 to the first node N1. One power terminal 110.

The driving transistor Td, the first transistor T1 and the second transistor T2 each include a first terminal, a second terminal and a control terminal. The first terminal and the second terminal of the driving transistor Td are respectively coupled to the second power terminal 120 and the second node N2, wherein the second power terminal is used to provide the second working voltage FVDD, and the second working voltage FVDD is higher than the first A working voltage FVSS. The control terminal of the driving transistor Td is coupled to the first node N1, and the driving transistor Td is used to generate a corresponding drive current Id according to the voltage of its control terminal (hereinafter referred to as the control terminal voltage Vg). In other words, the driving transistor Td is used to generate the driving current Id corresponding to the sensing current Is, that is, the driving transistor Td is used to amplify the sensing current Is.

The first terminal and the second terminal of the first transistor T1 are respectively coupled to the read line 101[m] and the second node N2, and the control terminal of the first transistor T1 is used to receive the first control signal S1[n] . The reading line 101 [m] is used to transmit the driving current Id to an external reading circuit (for example, the reading circuit 530 [m] in FIG. 5). In some embodiments, the reading circuit can integrate the driving current Id, convert analog to digital, and/or amplify the signal. The first transistor T1 is also used to transfer the reference voltage Vbias on the read line 101 [m] to the inside of the photo sensing circuit 100 to reset the voltage of each node.

The first terminal and the second terminal of the second transistor T2 are respectively coupled to the second node N2 and the first node N1, and the control terminal of the second transistor T2 is used to receive the second control signal S2[n]. The second transistor T2 is used to reset the voltage of each node together with the first transistor T1. In addition, the second transistor T2 is also used to form a diode connection with the driving transistor Td to compensate for the threshold voltage of the driving transistor Td.

In addition, the storage capacitor C1 is coupled between the first node N1 and the second power terminal 120. In some embodiments, a display with in-screen optical fingerprint sensing function can be realized by combining the array formed by the light sensing circuit 100 and a plurality of organic light emitting diode (OLED) pixel circuits. In some embodiments, the light sensing element PS may be realized by a transistor in the form of a diode connection, or may be realized by a photodiode.

Figure 2 is a simplified waveform diagram of the first control signal S1[n] and the second control signal S2[n]. As shown in FIG. 2, the operation of the light sensing circuit 100 in a frame time includes a reset stage 210-1, a compensation stage 220-1, a sensing stage 230-1 and an output stage 240-1. Please refer to Figure 2 and Figure 3A at the same time. In the reset phase 210-1, the first control signal S1[n] and the second control signal S2[n] both have a logic high level (Logic High Level, for example, sufficient Turn on the low voltage of the P-type transistor). Therefore, the driving transistor Td, the first transistor T1, and the second transistor T2 are turned on, and the second transistor T2 transmits the reference voltage Vbias to the first node N1, so that the control terminal voltage Vg is substantially equal to the reference voltage Vbias.

Next, please refer to Figure 2 and Figure 3B at the same time. In the compensation phase 220-1, the first control signal S1[n] has a logic low level (for example, a high voltage enough to turn off the P-type transistor), and The second control signal S2[n] has a logic high level. Therefore, the first transistor T1 will be turned off and the second transistor T2 will be turned on. At this time, the driving transistor Td and the second transistor T2 form a diode connection, so that the control terminal voltage Vg at the end of the compensation phase 220-1 can be substantially represented by the following "Equation 1", where the symbol "Vth" represents The threshold voltage for driving the transistor Td.

Vg = FVDD -| Vth | "Formula 1"

Please refer to Figure 2 and Figure 3C at the same time. In the sensing phase 230-1, the first control signal S1[n] and the second control signal S2[n] both have a logic low level, so that the first transistor T1 Both and the second transistor T2 are turned off. In this case, if the light sensing element PS receives light, the light sensing element PS will generate a sensing current Is, causing the control terminal voltage Vg to change, which can be represented by the following "Equation 2", where the symbol "△ "Vsig" represents the amount of change in the control terminal voltage Vg in the sensing phase 230-1.

Vg = FVDD -| Vth |-△ Vsig 《Formula 2》

Next, please refer to Figure 2 and Figure 3D at the same time. In the output stage 240-1, the first control signal S1[n] has a logic high level and the second control signal S2[n] has a logic low level, so that the first control signal S1[n] has a logic low level. One transistor T1 is turned on and the second transistor T2 is turned off. In this case, the driving transistor Td will generate a driving current Id corresponding to the control terminal voltage Vg, and the driving current Id will be output to the read line 110 [m] through the first transistor T1. The size of the driving current Id can be represented by the following "Equation 3", where the symbol "k" represents the carrier mobility of the driving transistor Td, the unit capacitance of the gate oxide layer, and the gate width-to-length ratio. The product of those.

After the output stage 240-1 ends, the light sensing circuit 100 can repeat the similar operations according to the above-mentioned process. For example, the light sensing circuit 100 can perform another reset stage 210-2, which will not be repeated here. It can be seen from "Equation 3" that the driving current Id is hardly affected by the element variation of the light sensing circuit 100, and therefore can accurately reflect the light intensity received by the light sensing element PS.

Figure 4 is a light sensing circuit according to an embodiment of the present disclosure 400 schematic diagram. The light sensing circuit 400 is similar to the light sensing circuit 100. The difference is that the light sensing circuit 400 further includes a third transistor T3, and the storage capacitor C1 is coupled between the first node N1 and the third transistor T3. In detail, the first terminal of the third transistor T3 is coupled to the second power terminal 120, and the second terminal of the third transistor T3 is coupled to the storage capacitor C1 and the light sensing element PS through the third node N3. In addition, the control terminal of the third transistor T3 is used to receive the second control signal S2[n].

The waveforms of the first control signal S1[n] and the second control signal S2[n] described in the second figure are also applicable to the light sensing circuit 400. Therefore, the third node N3 will be set to the second operating voltage FVDD during the reset phase 210-1. If the light sensing element PS receives light in the sensing phase 230-1, the light sensing element PS will generate a sensing current Is flowing between the third node N3 and the first power terminal 110, for example by the third node N3 and the first power terminal 110. The node N3 flows to the first power terminal 110. The remaining corresponding operations, components, connection methods, and advantages of the aforementioned photo-sensing circuit 100 are all applicable to the photo-sensing circuit 400, and for the sake of brevity, they will not be repeated here.

In some embodiments, the first terminal of the third transistor T3 may not be coupled to the second power terminal 120, but is used to receive another reset voltage different from the second operating voltage FVDD.

In the above-mentioned multiple embodiments, the transistors of the light sensing circuits 100 and 400 can be implemented by various suitable P-type transistors, but the present disclosure is not limited to this. If the first control signal S1[n] and the second control signal S2[n] in Figure 2 are respectively converted to have opposite waveforms, the transistors of the photo-sensing circuits 100 and 400 can also be made of various suitable N-types. Transistor Lysaght now.

FIG. 5 is a simplified functional block diagram of the touch display 500 according to an embodiment of the present disclosure. The touch display 500 includes a plurality of light sensing circuits 100, a plurality of pixel circuits PX, a first shift register 510, a second shift register 520, a plurality of reading circuits, and a plurality of reading lines. The plurality of reading circuits are respectively coupled to the plurality of reading lines. The plurality of light sensing circuits 100 are arranged in a matrix with multiple columns and rows, and the plurality of pixel circuits PX are also arranged in a matrix with multiple rows and columns. The photo sensing circuit 100 and the pixel circuit PX located in the same column can share control signals, and the photo sensing circuit 100 located in the same row will pass through one of the multiple reading lines (for example, the reading line 101[m]) It is coupled to one of a plurality of reading circuits (for example, reading circuit 530 [m]). For the convenience of description, FIG. 5 only shows one photo sensor circuit 100 and one pixel circuit PX in the same column, and one corresponding read line 101 [m] and one read circuit 530 [m].

The pixel circuit PX includes the third transistor T3, the fourth transistor T4, the fifth transistor T5, the sixth transistor T6, the seventh transistor T7, the eighth transistor T8, the ninth transistor T9, and the storage capacitor C2 And the light-emitting element LE. The control terminal of the eighth transistor T8 is used to receive the first control signal S1[n], and the control terminals of the fifth transistor T5, the sixth transistor T6, and the ninth transistor T9 are used to receive the second control signal S2[ n]. In addition, the control ends of the fourth transistor and the seventh transistor T7 are used to receive the third control signal EM[n]. In some embodiments, the third control signal EM[n] has a logic high level in the sensing phase 230-1 of FIG. 2, and in the reset phase 210-1, compensation There are logic low levels in the phase 220-1 and the output phase 240-1.

The pixel circuit PX can perform related operations of node voltage reset and threshold voltage compensation according to the first control signal S1[n] and the second control signal S2[n], and determine the light-emitting unit LE according to the third control signal EM[n] The timing of the light. In addition, the pixel circuit PX receives the third operating voltage OVDD and the fourth operating voltage OVSS to generate a current for driving the light-emitting unit LE, and determines the brightness of the light-emitting unit LE according to the data voltage Vdata and the reference voltage Vref. In some embodiments, the light emitting unit LE may be realized by an organic light emitting diode or a micro light emitting diode (Micro LED). The relevant content is known by those with ordinary knowledge in the relevant technical field, and for the sake of brevity, it will not be repeated here.

It can be seen from FIG. 5 that the driving current Id is transmitted to the reading circuit 530 [m] via the reading line 101 [m]. In detail, the reading circuit 530 [m] includes at least one integrating circuit, and the integrating circuit includes an amplifier 532. The amplifier 532 includes a first terminal (for example, an inverting input terminal), a second terminal (for example, a non-inverting input terminal), and an output terminal. The first end of the amplifier 532 is coupled to the read line 101 [m] to receive the driving current Id. The second terminal of the amplifier 532 is used to receive the reference voltage Vbias. Through the virtual short circuit (Virtual Ground) characteristic between the first end and the second end of the amplifier 532, the reference voltage Vbias will be mirrored from the second end of the amplifier 532 to the first end, so that the read line 101 [m] The voltage of is substantially maintained at the reference voltage Vbias. The output terminal of the amplifier 532 provides the output voltage Vout corresponding to the driving current Id to other subsequent circuits, such as an analog-to-digital conversion circuit.

As shown in Figure 5, the first shift register 510 generates the first The control signal S1[n] and the second control signal S2[n] can be shared by the photo sensor circuit 100 and the pixel circuit PX located in the same row, and the second shift register 520 is used to generate the third control signal EM[n]. Therefore, the touch display 500 does not need to additionally provide other shift registers for the light sensing circuit 100, which helps to reduce the frame width of the touch display 500.

In some embodiments, the multiple light sensing circuits 100 in the touch display 500 can be replaced with light sensing circuits 400. In this case, the light sensing circuit 400 and the pixel circuit PX located in the same column can still share the first control signal S1[n] and the second control signal S2[n]. Therefore, the touch display 500 still has an operation mode and advantages similar to the foregoing content, and for the sake of brevity, the details are not repeated here.

In the specification and the scope of the patent application, certain words are used to refer to specific elements. However, those with ordinary knowledge in the technical field should understand that the same element may be called by different terms. The specification and the scope of patent application do not use the difference in names as a way of distinguishing components, but the difference in function of the components as the basis for distinguishing. The "including" mentioned in the specification and the scope of the patent application is an open term, so it should be interpreted as "including but not limited to". In addition, "coupling" here includes any direct and indirect connection means. Therefore, if it is described in the text that the first element is coupled to the second element, it means that the first element can be directly connected to the second element through electrical connection, wireless transmission, optical transmission, or other signal connection methods, or through other elements or connections. The means is indirectly connected to the second element electrically or signally.

The description of "and/or" used here includes the enumerated Any combination of one or more of the items. In addition, unless otherwise specified in the specification, any term in the singular case also includes the meaning of the plural case.

The above are only preferred embodiments of the present disclosure, and all equal changes and modifications made in accordance with the requirements of the present disclosure should fall within the scope of the disclosure.

100, 400: light sensing circuit

101[m]: Reading line

110: The first power supply terminal

120: second power terminal

Td: drive transistor

T1: The first transistor

T2: second transistor

T3: third transistor

T4: The fourth transistor

T5: fifth transistor

T6: sixth transistor

T7: seventh transistor

T8: Eighth Transistor

T9: Ninth Transistor

PS: light sensing element

C1, C2: storage capacitor

N1: the first node

N2: second node

N3: second node

LE: Light-emitting element

S1[n]: The first control signal

S2[n]: The second control signal

EM[n]: The third control signal

Id: drive current

Is: sense current

FVSS: first working voltage

FVDD: second working voltage

OVDD: third working voltage

OVSS: Fourth working voltage

Vbias, Vref: reference voltage

Vg: Control terminal voltage

210-1, 210-2: Reset phase

220-1: Compensation phase

230-1: Sensing phase

240-1: output stage

500: Touch display

510: first shift register

520: Second shift register

530[m]: Reading circuit

532: Amplifier

Vout: output voltage

FIG. 1 is a schematic diagram of a light sensing circuit according to an embodiment of the present disclosure. Figure 2 is a simplified waveform diagram of the first control signal and the second control signal. FIG. 3A is a schematic diagram of the equivalent circuit operation of the photo sensing circuit of FIG. 1 in the reset stage. FIG. 3B is a schematic diagram of the equivalent circuit operation of the photo sensing circuit of FIG. 1 in the compensation stage. FIG. 3C is a schematic diagram of the equivalent circuit operation of the photo-sensing circuit of FIG. 1 in the sensing phase. FIG. 3D is a schematic diagram of the equivalent circuit operation of the light sensing circuit of FIG. 1 in the output stage. FIG. 4 is a schematic diagram of a light sensing circuit according to an embodiment of the present disclosure. FIG. 5 is a simplified functional block diagram of the touch display according to an embodiment of the present disclosure.

100: light sensing circuit

101[m]: Reading line

110: The first power supply terminal

120: second power terminal

Td: drive transistor

T1: The first transistor

T2: second transistor

PS: light sensing element

C1: storage capacitor

N1: the first node

N2: second node

S1[n]: The first control signal

S2[n]: The second control signal

Id: drive current

Is: sense current

FVSS: first working voltage

FVDD: second working voltage

Vbias: Reference voltage

Vg: Control terminal voltage

Claims (11)

A light sensing circuit includes: a driving transistor, including a control terminal coupled to a first node; a light sensing element, coupled to the first node, and used for generating in response to received light A sensing current flowing between the first node and a first power terminal, wherein the driving transistor is used to generate a driving current corresponding to the sensing current; a first transistor is used to generate a driving current corresponding to the sensing current; The control signal transmits the driving current to a read line; a second transistor, wherein when the first transistor is turned on, the second transistor is turned on according to a second control signal to a reference on the read line The voltage is transmitted to the first node through the first transistor and the second transistor, and when the first transistor is turned off, the second transistor is turned on according to the second control signal to form a pair with the driving transistor. The pole body is connected to compensate the threshold voltage of the driving transistor; and a storage capacitor is coupled to the first node. The light sensing circuit of claim 1, wherein a first terminal of the driving transistor is coupled to a second power terminal, and a second terminal of the driving transistor is coupled to the first transistor and Between the second transistor. The light sensing circuit of claim 2, wherein a first end of the first transistor is coupled to the read line, and a second end of the first transistor is coupled to the driving transistor The second end, the first transistor A control terminal is used to receive the first control signal. The light sensing circuit according to claim 3, wherein a first end of the second transistor is coupled to the second end of the first transistor, and a second end of the second transistor is coupled to At the first node, a control terminal of the second transistor is used to receive the second control signal. The light sensing circuit according to claim 4, further comprising: a third transistor, wherein a first terminal of the third transistor is coupled to the second power terminal or used to receive a reset voltage, the A second end of the third transistor is coupled to the light sensing element and the storage capacitor, and a control end of the third transistor is used for receiving the second control signal. A touch display includes: a plurality of read lines; a plurality of pixel circuits; and a plurality of light sensing circuits, wherein each light sensing circuit includes: a driving transistor, including a first node coupled to A control terminal; a light sensing element, coupled to the first node, and used to generate a sensing current flowing between the first node and a first power terminal according to the received light, wherein the drive The transistor is used for generating a driving current corresponding to the sensing current; a first transistor is used for transmitting the driving current to one of the plurality of read lines according to a first control signal; A second transistor, wherein when the first transistor is turned on, the second transistor is turned on according to a second control signal to transmit a reference voltage on the one of the plurality of read lines through the first The transistor and the second transistor are transmitted to the first node. When the first transistor is turned off, the second transistor is turned on according to the second control signal to form a diode connection with the driving transistor to compensate The threshold voltage of the driving transistor; and a storage capacitor coupled to the first node; wherein the corresponding ones of the plurality of pixel circuits and the corresponding ones of the plurality of light sensing circuits are used for receiving the The first control signal and the second control signal. The touch display according to claim 6, wherein a first terminal of the driving transistor is coupled to a second power terminal, and a second terminal of the driving transistor is coupled to the first transistor and the Between the second transistor. The touch display according to claim 7, wherein a first end of the first transistor is coupled to the one of the plurality of read lines, and a second end of the first transistor is coupled to At the second end of the driving transistor, a control end of the first transistor is used to receive the first control signal. The touch display according to claim 8, wherein a first end of the second transistor is coupled to the second end of the first transistor, and a second end of the second transistor is coupled to A control terminal of the first node and the second transistor is used to receive the second control signal. The touch display according to claim 9, further comprising: a third transistor, wherein a first terminal of the third transistor is coupled to the second power terminal or used to receive a reset voltage, the A second end of the three transistor is coupled to the light sensing element and the storage capacitor, and a control end of the third transistor is used for receiving the second control signal. The touch display according to claim 6, further comprising a plurality of reading circuits respectively coupled to the plurality of reading lines, wherein each of the plurality of reading circuits includes: an amplifier including a first One end, a second end, and an output end, wherein the first end of the amplifier is coupled to a corresponding one of the plurality of read lines, and the second end of the amplifier is used to pass through a virtual short circuit (Virtual Ground) The reference voltage is provided to the first terminal of the amplifier.

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