Fingerprint identification circuit and method, display panel, and display device

Abstract

The application discloses a kind of fingerprint identification circuit and method, display panel, display device, including current reading unit, photodiode and current amplification unit, current amplification unit is for the current amplification that passes through current reading unit;The anode of photodiode is connected to bias voltage, and current reading unit is used to read the current signal that flows through the unit under the control of first signal line.According to the technical scheme provided in the embodiment of the application, in order to ensure that the current signal received by the current reading unit is large enough, the effective identification of the optical signal collected by the photodiode is realized, the effective differentiation of the valley ridge signal of the fingerprint is ensured, and the accuracy of the fingerprint identification is improved, the current amplification unit is arranged between the current reading unit and the photodiode in the embodiment, so that the photodiode device with thin I layer can work in strong light environment and weak light environment.

Description

TECHNICAL FIELD

[0001] The present application generally relates to the field of fingerprint identification technology, and in particular to a fingerprint identification circuit and method, a display panel, and a display device. BACKGROUND

[0002] Currently, the in-screen fingerprint identification technology combining optical sensing and display mostly adopts a structure of a display backplane plus an amorphous silicon photodiode device. The structure combining a LTPS (Low Temperature Poly-Silicon) process with a high mobility and good stability and the amorphous silicon photodiode device has a great development prospect in the field of mobile phones.

[0003] The current device has good performance in a low-brightness environment such as indoors, but in a high-brightness environment such as outdoors on a sunny day, the natural light as stray light has a huge impact on the light sensor device, easily causing the device to saturate and unable to distinguish the signal difference between the fingerprint valleys and ridges, interfering with normal fingerprint identification. Therefore, a photodiode device structure with a low external quantum efficiency (EQE) is adopted to ensure that it is not easily saturated under strong light irradiation, so as to achieve the purpose of distinguishing between bright and dark states.

[0004] Currently, the most effective solution for the photodiode device to reduce its EQE is to reduce the thickness of the I layer. However, the photodiode device using a small thickness of the I layer has a very low EQE in a weak light environment, resulting in a small photocurrent and a low signal-to-noise ratio, which cannot effectively distinguish the fingerprint valley and ridge signals, and reduces the accuracy and effectiveness of fingerprint identification. SUMMARY

[0005] In view of the above defects or deficiencies in the prior art, it is desirable to provide a fingerprint identification circuit and method, a display panel, and a display device.

[0006] In a first aspect, a fingerprint identification circuit is provided, comprising a current reading unit, a photodiode, and a current amplification unit, wherein,

[0007] The current amplification unit is arranged between the photodiode and the current reading unit, and is configured to amplify the current flowing through the current reading unit.

[0008] The anode of the photodiode is connected to a bias voltage,

[0009] The current reading unit is configured to read the current signal flowing through the unit under the control of a first signal line.

[0010] In a second aspect, a fingerprint identification method for the fingerprint identification circuit is provided, and the method comprises:

[0011] The first state recognition: under the control of the second signal of the second signal line, the third transistor is closed, and the current reading unit reads a first current, the first current being a current flowing through the photodiode;

[0012] The second state recognition: under the control of the second signal of the second signal line, the third transistor is turned on, and the current reading unit reads a second current, the second current being a current flowing through the photodiode plus a current flowing through the third transistor.

[0013] In a third aspect, a display panel is provided, comprising the fingerprint recognition circuit.

[0014] In a fourth aspect, a display device is provided, comprising the display panel.

[0015] According to the technical scheme provided by the embodiment of the present application, the photodiode collects the light signal, converts the light signal into an electric signal, and reads the current signal flowing through the current reading unit. The current signal is used to judge the light signal received by the photodiode. In order to ensure that the current signal received by the current reading unit is large enough, the light signal collected by the photodiode can be effectively identified, the valley ridge signal of the fingerprint can be effectively distinguished, and the accuracy of the fingerprint recognition is improved. The current amplification unit is arranged between the current reading unit and the photodiode, so that the photodiode device with a thin I layer can work in a strong light environment and a weak light environment to meet the requirements. The current is amplified and read by the current reading unit, which meets the requirements of fingerprint recognition. BRIEF DESCRIPTION OF DRAWINGS

[0016] Other features, objects, and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments, read in conjunction with the accompanying drawings:

[0017] Figure 1 FIG. 1 is a schematic diagram of a fingerprint recognition circuit structure in the embodiment;

[0018] Figure 2 FIG. 2 is a schematic diagram of a fingerprint recognition circuit in the embodiment;

[0019] Figure 3 FIG. 3 is a schematic diagram of strong light recognition of a fingerprint recognition circuit in the embodiment;

[0020] Figure 4 FIG. 4 is a schematic diagram of weak light recognition of a fingerprint recognition circuit in the embodiment. DETAILED DESCRIPTION

[0021] The application will be described in further detail below with reference to the drawings and embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the application and are not intended to limit the application. In addition, it should be noted that only parts related to the application are shown in the drawings for ease of description.

[0022] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and embodiments.

[0023] Please refer to Figure 1 The present embodiment provides a kind of fingerprint identification circuit, it is characterized in that, including current reading unit 10, photodiode 30 and current amplification unit 20, wherein,

[0024] The current amplification unit 20 is arranged between the photodiode 30 and the current reading unit 10, for amplifying the current flowing through the current reading unit 10;

[0025] The anode of the photodiode 30 is connected to bias voltage VBias,

[0026] The current reading unit 10 is used to read the current signal flowing through the unit under the control of the first signal line Gate1.

[0027] In the fingerprint identification circuit provided by the present embodiment, the light signal is collected by the photodiode, the light signal is converted into the electric signal, and the current signal flowing through is read by the current reading unit. The light signal received by the photodiode is judged through the current signal. In order to ensure that the current signal received by the current reading unit is large enough, the effective identification of the light signal collected by the photodiode is realized, the valley ridge signal of the fingerprint is effectively distinguished, and the accuracy of the fingerprint identification is improved. The current amplification unit is arranged between the current reading unit and the photodiode, so that the photodiode device with thin I layer can work in strong light environment and weak light environment to meet the demand. The current is read by the current reading unit after amplification, which meets the demand of fingerprint identification.

[0028] Optionally, the current amplification unit 20 includes a first transistor T1, a second transistor T2 and a third transistor T3, wherein,

[0029] The source of the first transistor T1 and the source of the second transistor T2 are connected to the current reading unit, the gate of the first transistor T1 is connected to the first pole of the third transistor T3, the gate of the second transistor T2 is connected to the second pole of the third transistor T3, the drain of the first transistor T1 is connected to the negative pole of the photodiode, and the drain of the second transistor T2 is connected to bias voltage.

[0030] The drain of the first transistor T1 is connected to its gate, and the gate of the third transistor T3 is connected to the second signal line Gate2.

[0031] like Figure 2 As shown, this embodiment uses a current amplification unit 20 composed of three transistors to achieve the current amplification function. The source of the first transistor T1 and the source of the second transistor T2 are both connected to the first terminal of the current reading unit, i.e., the fourth transistor T4. The drain of the first transistor T1 is connected to the negative terminal of the photodiode, and the positive terminal of the photodiode is connected to the bias voltage. The drain of the second transistor T2 is also directly connected to the bias voltage. The drain and gate of the first transistor T1 are connected to ensure that the first transistor T1 operates in the saturation region. At the same time, by connecting the gate of the first transistor T1 and the gate of the second transistor T2 to the third transistor T3, when in a low light environment, the third transistor T3 is turned on, and the first transistor T1 and the second transistor T2 form a common source and common gate structure, ensuring that the second transistor T2 also operates in the saturation region.

[0032] The current amplification unit 20 provided in this embodiment operates in different modes under different lighting conditions. Specifically, in strong light mode, the third transistor T3 is turned off under the control of the second signal line Gate2, and the current in the current reading unit of the entire fingerprint recognition circuit is the current I1 on path 1. Figure 3 As shown, this current is the photocurrent generated by the photodiode device; when in low-light mode, the third transistor T3 is turned on under the control of the second signal line Gate2. At this time, the current of the circuit reading unit is the sum of the currents of path 1 and path 2, I1 + I2, as shown. Figure 4 As shown, the current read by the circuit reading unit is amplified, where both the first transistor T1 and the second transistor T2 are operating in the saturation region. At this time, the current in path 1 is: The current in path 2 is: Since the first transistor T1 and the second transistor T2 have a common source and common gate structure... In the above formula, W is the width of the transistor and L is the length of the transistor. Therefore, this circuit structure can proportionally replicate the current on path 1 into path 2. Furthermore, by designing the width and length of the first transistor T1 and the second transistor T2, it is possible to determine how many times the current on path 2 amplifies the current on path 1, ultimately achieving overall current amplification in the entire circuit, enhancing the optical signal, and solving the problem of insufficient signal in low-light environments.

[0033] The second signal used to control the third transistor T3 to open and close in the above embodiment is determined according to the ambient light state in which the photodiode is currently located, wherein the strong light and weak light conditions involved can be determined according to the actual needs of the fingerprint identification circuit; meanwhile, a thin I layer photodiode device is used in the above embodiment, wherein the thickness of the I layer is generally 2K-3K nanometers.

[0034] Further, the current reading unit is a fourth transistor T4.

[0035] The first electrode of the fourth transistor T4 is connected to the source of the first transistor T1 and the source of the second transistor T2, the second electrode of the fourth transistor T4 is connected to a reading signal line, and the gate of the fourth transistor T4 is connected to the first signal line.

[0036] In the embodiment, the fourth transistor T4 is used as a current reading unit, the second electrode of the fourth transistor T4 is connected to a reading signal line, the current flowing through the fourth transistor T4 is read through the reading signal line, the gate of the fourth transistor T4 is connected to the first signal line, and the opening and closing of the fourth transistor T4 is controlled under the control of the first signal line, thereby realizing the reading of the current signal.

[0037] In the embodiment, a current amplification system composed of a group of three transistors is used, under strong light, the current amplification unit 20 only extracts the photocurrent of the thinned photodiode device, which can avoid the problem that the difference between the fingerprint ridge and valley signals is small due to too high EQE, and at the same time, under weak light, the current of the diode can be controllably amplified by several times to meet the demand for signal-to-noise ratio under weak light.

[0038] The embodiment also provides a fingerprint identification circuit identification method for the above fingerprint identification circuit, and the method comprises the following steps.

[0039] First state identification: under the control of the second signal of the second signal line Gate2, the third transistor T3 is closed, the current reading unit reads a first current, and the first current is the current flowing through the photodiode;

[0040] Second state identification: under the control of the second signal of the second signal line Gate2, the third transistor T3 is turned on, the current reading unit reads a second current, and the second current is the current flowing through the photodiode plus the current flowing through the third transistor T3.

[0041] The embodiment provides two fingerprint identification circuit identification methods, including a first state and a second state, the first state is a strong light state, the third transistor T3 is closed, and the fingerprint identification circuit forms as shown in Figure 3As shown in the current flow direction, at this time, the current read by the current reading unit is the current in path 1; the second state is in a weak light state, the third transistor T3 is turned on, and the fingerprint recognition circuit forms as Figure 4 As shown in the current flow direction, at this time, the current read by the current reading unit is the current in path 1 and path 2, realizing amplification of the read current signal in a weak light state, and the amplification multiple of the current is controllable, meeting the demand for signal-to-noise ratio in weak light.

[0042] The embodiment also provides a display panel comprising the fingerprint recognition circuit.

[0043] Further, the photoelectric sensor is further included for detecting light intensity, and when the light intensity is greater than a set value, the third transistor T3 is controlled to be turned off through the second signal line, or when the light intensity is less than or equal to the set value, the third transistor T3 is controlled to be turned on through the second signal line.

[0044] In the embodiment, the third transistor T3 is turned on and turned off according to different light intensities, realizing that the third transistor T3 is turned on in a weak light state, and the read current is amplified, improving the effect of the light signal. Preferably, the photoelectric sensor is arranged to detect the corresponding light intensity, and when the detected light intensity is greater than a set value, the third transistor T3 is turned off through the control of the second signal line. In a weak light condition, the photoelectric sensor quantitatively detects the light intensity, which can be calculated and determined according to the thickness of the I layer in the actual photodiode and the length and width of the corresponding first transistor T1 and second transistor T2, to realize quantitative selection.

[0045] The embodiment also provides a display device comprising the display panel.

[0046] It should be understood that the above-mentioned terms such as "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application; the orientation terms "inner" and "outer" refer to the inner and outer of the contour of each component itself. In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features limited by "first", "second" can explicitly or implicitly include one or more of the features.

[0047] For purposes of the description hereinafter, spatial or directional terms, for example, "above", "below", "upper", "lower", "top", "bottom", "over", "under", "left", "right" and the like, relate to the application as it is shown in the drawings and are used in connection with the exemplary embodiments of the application. It is to be understood, however, that the application can assume many different variations and that the exemplary terminology used herein is for the purpose of description only. For example, spatially relative terms are intended to encompass different orientations of the device in use or operation, for example, device can be inverted or rotated by 90 degrees or at other orientations and the spatially relative terms used herein are intended to encompass such variations. Thus, an object or structure that would be denoted an "above" another object or structure in one orientation of the device can potentially be denoted as "below" the other object or structure when the device is oriented differently. Accordingly, the term "above" encompasses both a position above and a position below. The device can be otherwise oriented (rotated at 90 degrees or at other orientations) and the spatially relative terms used herein interpreted accordingly.

[0048] The above description is only preferred embodiments of the present application and the technical principles used. Those skilled in the art should understand that the scope of the application involved in the present application is not limited to the technical solutions formed by the specific combinations of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features can be replaced with the technical features disclosed in the present application (but not limited to) having similar functions to form technical solutions.

Claims

1. A fingerprint recognition circuit, characterized by, The current reading unit, the photodiode and the current amplification unit are included, wherein, The current amplification unit is arranged between the photodiode and the current reading unit, and is used for amplifying the current flowing through the current reading unit; The anode of the photodiode is connected to a bias voltage, and the thickness of the photodiode is 2K-3K nanometers; The current reading unit is used for reading the current signal flowing through the unit under the control of the first signal line, The current amplification unit includes a first transistor, a second transistor and a third transistor, and the first transistor and the second transistor are in a common-source common-gate structure, The source of the first transistor and the source of the second transistor are connected to the current reading unit, the gate of the first transistor is connected to the first pole of the third transistor, the gate of the second transistor is connected to the second pole of the third transistor, the drain of the first transistor is connected to the negative pole of the photodiode, and the drain of the second transistor is connected to a bias voltage; The drain of the first transistor is connected to the gate, and the gate of the third transistor is connected to the second signal line, when in a strong light mode, the third transistor is closed under the control of the second signal line; when in a weak light mode, the third transistor is opened under the control of the second signal line.

2. The fingerprint recognition circuit according to claim 1, characterized in that, The current reading unit is a fourth transistor; The first pole of the fourth transistor is connected to the source of the first transistor and the source of the second transistor, the second pole of the fourth transistor is connected to a reading signal line, and the gate of the fourth transistor is connected to the first signal line.

3. A method of identification for a fingerprint identification circuit, for a fingerprint identification circuit as claimed in any of the claims 1-2, characterized in that, The method includes: First state recognition: under the control of the second signal of the second signal line, the third transistor is closed, the current reading unit reads a first current, and the first current is the current flowing through the photodiode; Second state recognition: under the control of the second signal of the second signal line, the third transistor is turned on, the current reading unit reads a second current, and the second current is the current flowing through the photodiode plus the current flowing through the third transistor.

4. A display panel, characterized by, The fingerprint recognition circuit includes any one of claims 1-2.

5. The display panel of claim 4, wherein, The method further includes a photoelectric sensor for detecting light intensity, and when the light intensity is greater than a set value, the third transistor is controlled to be closed through the second signal line, or when the light intensity is less than or equal to the set value, the third transistor is controlled to be turned on through the second signal line.

6. A display device, characterized by comprising: The display panel includes the display panel of claim 4 or 5.

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