CN107563361B - Sensor pixel and optical sensor - Google Patents
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- CN107563361B CN107563361B CN201710920202.1A CN201710920202A CN107563361B CN 107563361 B CN107563361 B CN 107563361B CN 201710920202 A CN201710920202 A CN 201710920202A CN 107563361 B CN107563361 B CN 107563361B
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Abstract
The embodiment of the invention discloses a sensor pixel and an optical sensor, wherein the sensor pixel comprises: the collimating layer is internally provided with an optical tunnel, and the optical tunnel is used for receiving light in the approximately vertical direction in the light reflected by the target finger; at least two photosensitive elements for outputting an electrical signal according to the light received by the optical tunnel; the signal detection circuit is electrically connected with one or more photosensitive elements and is used for acquiring the electric signals output by the gated photosensitive elements; and the control unit is used for controlling the gating quantity of the photosensitive elements. The technical scheme provided by the embodiment of the invention solves the problem of low quality of fingerprint images caused by overexposure or underexposure, and realizes the dynamic adjustment of the size of the electronic aperture of the sensor pixels, namely the dynamic adjustment of the exposure of the sensor pixels, so as to obtain better image quality and improve the signal to noise ratio.
Description
Technical Field
The embodiment of the invention relates to a fingerprint identification technology, in particular to a sensor pixel and an optical sensor.
Background
Fingerprint sensors are currently mainly divided into two categories, namely optical fingerprint sensors and capacitive fingerprint sensors. The capacitive fingerprint sensor images a fingerprint by measuring a difference in magnitude of a connection capacitance formed between a fingerprint valley line, a fingerprint ridge line and a planar sensing electrode array unit. When the dielectric layer between the sensing electrode array and the finger is thicker, the capacitance will be attenuated and the imaging of the sensor will be blurred. As technology evolves, the thickness of the dielectric layer between the sensing electrode and the target electrode increases from the order of 10um to the order of 100um for fingerprint sensors. Furthermore, in view of the integrity of the industrial design of mobile phone screens, it is desirable that the fingerprint sensor penetrate directly through the screen glass, i.e. chemically strengthened glass having a thickness of 400um to 500 um. Therefore, the penetration force of the optical fingerprint sensor has great advantages over the capacitive fingerprint sensor.
However, when the conventional optical fingerprint sensor is applied to intelligent devices such as mobile phones, the optical fingerprint sensor has a great disadvantage that the thickness of the optical fingerprint sensor is generally large, because the optical fingerprint sensor usually needs to place a finger on an optical lens, the angle of refraction of the emitted light on the uneven line of the fingerprint on the surface of the finger and the brightness of the reflected light are different when the finger is irradiated by a built-in light source, so that a light intensity space distribution image is formed, and devices such as a lens focus the image projection on the image sensor to obtain a multi-gray fingerprint image. Optical structures such as lenses are required, so that the optical path length is long, and the overall thickness of the sensor is large, so that the industrial design of the mobile phone is not facilitated.
If the optical fingerprint sensor is directly arranged at the bottom of the screen, the light receiving range of each pixel is large due to refraction and diffuse reflection, and the light reflected by adjacent ridges or valleys is received by the same pixel, so that the image is blurred. This problem is solved in the prior art by providing a collimator on the optical fingerprint sensor. However, the electronic aperture of the pixel of the improved fingerprint sensor cannot be adjusted, and the problem of low quality of the acquired fingerprint image due to overexposure or underexposure can occur.
Disclosure of Invention
The invention provides a sensor pixel and an optical sensor, which are used for solving the problem of low image quality caused by overexposure or underexposure, realizing dynamic adjustment of the size of an electronic aperture of the sensor pixel and dynamic adjustment of the exposure of the sensor pixel, obtaining better image quality and improving the signal to noise ratio.
In a first aspect, an embodiment of the present invention provides a sensor pixel, including:
the collimating layer is internally provided with an optical tunnel, and the optical tunnel is used for receiving light in the approximately vertical direction in the light reflected by the target finger;
at least two photosensitive elements for outputting an electrical signal according to the light received by the optical tunnel;
a control unit for controlling the number of gates of the photosensitive elements;
and the signal detection circuit is electrically connected with one or more photosensitive elements and is used for acquiring the electric signals output by the gated photosensitive elements.
Preferably, the collimation layer comprises at least one mask layer; the mask layer includes a light-transmitting region and a light-opaque region.
Preferably, the number of the mask layers is at least two;
the light-transmitting areas adjacent to the mask layers are staggered, and the projection area of the formed optical tunnel is smaller than the area of the light-transmitting area.
Preferably, each photosensitive element corresponds to one of the optical tunnels.
Preferably, the apparatus further comprises a load circuit, at least one first switch and at least one second switch;
the load circuit is used for providing a driving voltage or a driving current;
each sensor pixel comprises M rows and N columns of photosensitive elements, wherein M and N are integers greater than or equal to 1;
the first poles of the photosensitive elements of each row are electrically connected to the load circuit through a first switch, and the second poles of the photosensitive elements of each column are electrically connected to the input end of the signal detection circuit through a second switch.
Preferably, the signal detection circuit includes:
the input end of the integrating circuit is electrically connected to the second pole of the photosensitive element through the second switch, and the output end of the integrating circuit is electrically connected with the control unit;
the control unit is used for controlling the gating quantity of the photosensitive elements according to the output of the integrating circuit.
Preferably, the integrating circuit includes:
an amplifier; the same-direction input end is used for inputting a first reference voltage, the reverse input end is electrically connected with the input end of the integrating circuit, and the output end is electrically connected with the control unit;
an integrating capacitor, a first pole of which is electrically connected with the reverse input end of the amplifier, and a second pole of which is electrically connected with the output end of the amplifier;
and the first reset switch is connected with the integrating capacitor in parallel.
Preferably, the signal detection circuit further includes:
and the first input end of the comparator is electrically connected with the output end of the amplifier, the second input end of the comparator is used for inputting a second reference voltage, and the output end of the comparator is used for outputting a turnover signal.
Preferably, the signal detection circuit further includes:
at least one second reset switch, a first end of each second reset switch is electrically connected with a second pole of the photosensitive element, and a second end of each second reset switch is grounded;
preferably, the signal detection circuit further comprises a compensation circuit, and the compensation circuit is electrically connected with the input end of the integration circuit and is used for injecting charges into the integration circuit to adjust the charge accumulation amount of the integration circuit.
Preferably, the compensation circuit comprises a current source and a third switch, the current source being electrically connected to the inverting input of the amplifier via the third switch.
Preferably, the control unit is configured to increase the number of the photosensitive elements electrically connected to gate the signal detection circuit by controlling the conduction of the first switch and the second switch if the voltage value of the signal output by the integration circuit is smaller than a first set threshold; and if the voltage value of the signal output by the integrating circuit is larger than a second set threshold value, the first switch and the second switch are controlled to be turned off, so that the number of the photosensitive elements electrically connected with the signal detection circuit is reduced.
In a second aspect, embodiments of the present invention further provide an optical sensor, including a sensor pixel array, where the sensor pixel array includes a plurality of sensor pixels provided in any of the embodiments of the present invention.
Preferably, the optical sensor further comprises light sources located on both sides of the sensor pixel array.
The embodiment of the invention provides a sensor pixel comprising a collimation layer, wherein an optical tunnel is formed in the collimation layer, light in the approximately vertical direction in light reflected by a target finger can be received, the gating quantity of photosensitive elements is controlled by a control unit, namely, the gating quantity of the photosensitive elements is controlled, and the electronic aperture of the sensor pixel can be adjusted. The problems that the quality of acquired images is low due to overexposure or underexposure of the electronic aperture of the existing sensor pixels cannot be adjusted are solved, the size of the electronic aperture of the sensor pixels is dynamically adjusted, the quality of the acquired images is improved, and the signal to noise ratio is improved.
Drawings
FIG. 1 is a schematic cross-sectional view of a sensor pixel according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a discrete structure of a sensor pixel according to an embodiment of the present invention;
FIG. 3 is a schematic cross-sectional view of another sensor pixel according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of another sensor pixel according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of another sensor pixel according to an embodiment of the present invention;
fig. 6 is a schematic cross-sectional view of an optical sensor according to an embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting thereof. It should be further noted that, for convenience of description, only some, but not all of the structures related to the present invention are shown in the drawings. The invention takes a fingerprint sensor as an example to explain the working principle of the integral adjusting circuit, but the invention is not limited to the protection scope of the invention, and the protection scope of the invention is subject to the contents of the claims.
Fig. 1 is a schematic cross-sectional view of a sensor pixel according to an embodiment of the present invention, and a specific structure of the sensor pixel 100 is as follows:
a collimation layer 110, wherein an optical tunnel 111 is formed in the collimation layer 110, and the optical tunnel 111 is used for receiving light in a substantially vertical direction in the light reflected by the target finger; at least two photosensitive elements 120 are used to output electrical signals based on light received by the optical tunnel 111.
And a control unit for controlling the number of gates of the photosensitive elements 120.
The signal detection circuit is electrically connected with the one or more photosensitive elements 120 and is used for acquiring the electric signals output by the gated photosensitive elements 120.
The photosensitive elements 120 may be photodiodes or photoresistors, and each photosensitive element 120 corresponds to an optical tunnel 111.
Light reflected by an object to be detected, such as a finger, impinges on the sensor pixel 100 from a plurality of angles. Wherein only light in a substantially vertical direction is received by the optical tunnel 111 in the collimating layer 110 and emitted from the optical tunnel 111 of the collimating layer 110, e.g. light 11 may be emitted from the optical tunnel 111, impinging on the photosensitive element 120, whereas light 12 at a smaller angle to the side of the collimating layer 110 remote from the photosensitive element 120 may not be emitted from the optical tunnel 111. Therefore, the light receiving range of the pixels is limited, so that the light reflected by the adjacent ridge lines or valley lines of the target finger fingerprint is generally received by the same pixel, and the interference of the light in different directions on the fingerprint image is reduced to enhance the definition of the obtained fingerprint image. And the alignment layer 110 provided by the embodiment of the present invention may be thin enough to provide an ultra-thin fingerprint recognition device. Upon receiving the light 11, the photosensitive element 120 outputs an electrical signal to the signal detection circuit. The signal detection circuit obtains the electric signal output by the photosensitive element 120, and the intensity of the electric signal corresponds to different light intensities. The control unit may include a logic circuit, and in one implementation of the embodiment of the present invention, the control unit may be electrically connected to an output terminal of the signal detection circuit, and control the number of the gated photosensitive elements 120 according to the magnitude of the signal output by the signal detection circuit. The control unit may also receive an external control signal, for example, a control signal from an external processor, and control the number of photosensitive elements that are gated according to the control signal.
Specifically, the number of photosensitive elements 120 may be selected according to a certain rule, for example, when the ambient light is weak, the light obtained by the photosensitive elements 120 is weak, the value of the electrical signal output by the photosensitive elements 120 is small, at this time, the voltage value of the electrical signal output by the signal detection circuit is small, and when the voltage value is smaller than the set first threshold, the control unit may control to increase the number of the photosensitive elements 120 that are selected; when the ambient light is stronger, the light obtained by the photosensitive element 120 is stronger, the value of the electrical signal output by the photosensitive element 120 is larger, at this time, the voltage value output by the signal detection circuit is larger, and when the voltage value is larger than the set second threshold value, the control unit can control to reduce the number of the gated photosensitive elements 120.
Therefore, the control unit can control the number of the gating photosensitive elements 120 to achieve the effect of adjusting the electronic aperture of the fingerprint sensor pixels, so that the quality of an image acquired according to the image data output by the sensor pixels can be improved, for example, the sensor pixels are applied to the fingerprint sensor, the quality of the acquired fingerprint image can be improved, and the signal to noise ratio can be improved.
According to the technical scheme, the sensor pixel comprises the collimation layer, at least two photosensitive elements, the signal detection circuit and the control unit for controlling the quantity of gating photosensitive elements, the problems that the electronic aperture of the existing sensor pixel cannot be adjusted, the acquired image quality is low due to overexposure or underexposure are solved, the size of the electronic aperture of the sensor pixel is dynamically adjusted, and the effect of obtaining better image quality and improving the signal to noise ratio is achieved, wherein the size of the electronic aperture of the sensor pixel is equivalent to that of dynamically adjusting the exposure of the sensor pixel.
FIG. 2 is a schematic diagram showing a discrete structure of a sensor pixel according to an embodiment of the present invention, wherein the collimating layer 110 includes at least one mask layer 113; the mask layer 113 includes a light-transmitting region 113A and a light-opaque region 113B. Light reflected to the light-transmitting region 113A of the mask layer 113 may be emitted from the light-transmitting region 113A, and light reflected to the light-opaque region 113B will not be emitted.
The material of the mask layer 113 may be a metal, a metal oxide, or a carbonate. Further, the mask layer 113 may be black, so that the light irradiated to the opaque region 113B may be absorbed, and the influence of the light in other directions on the light in the substantially vertical direction received by the collimation layer may be further reduced, so as to improve the quality of the fingerprint image.
Specifically, fig. 3 is a schematic cross-sectional view of another sensor pixel according to an embodiment of the present invention, where the collimating layer 110 includes at least two mask layers 113; the light-transmitting areas 113A of adjacent mask layers 113 are staggered, and the projected area of the formed optical tunnel 111 is smaller than the area of the light-transmitting areas 113A, for example, the area 122 of the optical tunnel 111 projected on the sensor is smaller than the area of the light-transmitting areas 113A, that is, the area 122 of the optical tunnel 111 projected on the sensor is smaller than the area 121 of the light-transmitting areas 113 projected on the sensor.
Adjacent mask layers 113 are arranged in a staggered configuration; accordingly, the light-transmitting regions 113A of the adjacent mask layers 113 are offset from each other, and the light-impermeable regions 113B of the adjacent mask layers 113 are offset from each other, so that the inner wall structure of the optical tunnel 111 is formed in a stepwise shape. The opaque region 113B of one of the adjacent two mask layers 113 blocks a portion of the light-transmitting region 113A of the other such that the projected area of the optical tunnel 111 is smaller than the area of the light-transmitting region 113A. The advantage of this arrangement of the mask layer 113 is that it is advantageous to further increase the collimation effect of the collimation layer, resulting in a smaller light receiving range of the whole pixel. When a mask layer 113 is used, the collimation effect is generally improved by reducing the area of the transparent area 113A of the mask layer 113, and when the transparent area 113A is smaller, the process difficulty is relatively high, and even the existing process cannot be realized. However, at least two or more mask layers 113 are interlaced to form a smaller optical tunnel cross section, so as to improve the collimation effect, and the light-transmitting area of each mask layer 113 is not required to be small, so that the process difficulty of forming the mask layers 113 can be reduced.
Fig. 4 is a schematic structural diagram of a sensor pixel according to an embodiment of the present invention, where on the basis of the above embodiment, the sensor pixel further includes:
a load circuit 180, at least one first switch S10 and at least one second switch S20.
The load circuit 180 is used to provide a driving voltage or a driving current.
Each sensor pixel includes M rows and N columns of photosensitive elements 120, where M and N are integers greater than or equal to 1.
The first pole of each row of photosensitive elements 120 is electrically connected to the load circuit 180 through a first switch S10, and the second pole of each column of photosensitive elements 120 is electrically connected to the input terminal of the signal detection circuit 140 through a second switch S20. The first switch S10 and the second switch S20 may be switching transistors, and the control unit 150 may be electrically connected to gates of the switching transistors and may control on or off of the switching transistors.
The number of the first switches S10 corresponding to the M rows and N columns of the photosensitive elements 120 may be M, and the number of the second switches S20 may be N. One or more photosensitive elements 120 may be gated by controlling the on or off of the first switch S10 and controlling the on or off of the second switch S20. Illustratively, when the switch S10 of the ith row and the switch S20 of the jth column are closed, the photosensitive element 120 of the jth column of the ith row is gated, and the photosensitive element 120 transmits the generated electrical signal to the signal detection circuit 140. When all the first switches S10 are controlled to be turned on, the leftmost second switch S20 shown in fig. 4 is turned on, and the photosensitive element 120 of the leftmost column is turned on.
According to the technical scheme, the sensor pixel formed by the photosensitive element array is provided, the first switch is controlled to be turned on or off, and the second switch is controlled to be turned on or off, so that the gating quantity of the photosensitive elements can be controlled, and the electronic aperture adjustment can be performed on the fingerprint image. The problems that the quality of the acquired fingerprint image is low due to the fact that the electronic aperture of the existing fingerprint sensor pixel cannot be adjusted, overexposure or underexposure are solved, the size of the electronic aperture of the sensor pixel is dynamically adjusted, namely the exposure of the sensor pixel is dynamically adjusted, better image quality can be obtained, and the signal to noise ratio is improved are solved.
Wherein the signal detection circuit 140 may comprise:
the input end of the integrating circuit 142 is electrically connected to the second pole of the photosensitive element 120 through the second switch S20, and the output end is electrically connected to the control unit 150.
The control unit 150 is used for controlling the gating quantity of the photosensitive element 120 according to the output of the integration circuit 142. Preferably, the integrating circuit 142 includes:
an amplifier a10; the amplifier a10 has a common input terminal for inputting the first reference voltage V10, a reverse input terminal electrically connected to the input terminal of the integrating circuit 142, and an output terminal electrically connected to the control unit 150.
The first pole of the integrating capacitor C10 is electrically connected to the inverting input terminal of the amplifier a10, and the second pole is electrically connected to the output terminal of the amplifier a 10.
The first reset switch S30 is connected in parallel with the integrating capacitor C10.
The reverse input terminal of the amplifier a10 receives the electric signal transmitted from the photosensitive element 120, and accumulates the electric signal in the integrating capacitor C10. Light of different intensities enters the photosensitive element 120, for example, light reflected by ridges of the fingerprint has high intensity, light reflected by valleys has weak intensity, and when light reflected by ridges of the fingerprint and light reflected by valleys are irradiated to the photosensitive element 120 of the sensor pixel, the output of the photosensitive element 120 is different. Specifically, if the light received by the optical tunnel is strong, the electrical signal (current) output by the photosensitive element 120 will be large, and thus the integrator output reaches the preset voltage for a relatively short time, for example, the time to reach saturation is relatively short. If the intensity of the received light of the optical tunnel is smaller, the electrical signal (current) output by the photosensitive element 120 will be smaller, and thus the time for the integrator output to reach the preset voltage will be longer. When the first reset switch S30 is closed, the integrating capacitor C10 is reset. The signal detection circuit can accurately obtain the time corresponding to the quantity of light rays in the optical tunnel in the sensor pixel, so that a clear fingerprint image is obtained according to the time. For example, the processor obtains the fingerprint image by obtaining the time when the output voltage of the integrator reaches the preset voltage.
On the basis of the above embodiment, the signal detection circuit 140 further includes:
at least one second reset switch S40, a first end of each second reset switch S40 is electrically connected to a second pole of the photosensitive element 120, and a second end of the second reset switch S40 is grounded.
A current source 141 and a third switch S50, the current source 141 being electrically connected to the inverting input terminal of the amplifier a10 through the third switch S50.
The second reset switch S40 is set to reset the integrator to release the charge of the photosensitive element 120, reducing the influence on the next frame data output by the sensor pixels.
Further, in the sensor pixel provided by the embodiment of the invention, the signal detection circuit may further include a compensation circuit, and the compensation circuit is electrically connected to the input end of the integration circuit and is used for injecting charges into the integration circuit to adjust the charge accumulation amount of the integration circuit.
Referring to fig. 5, fig. 5 is a schematic structural diagram of another sensor pixel according to an embodiment of the present invention. On the basis of the above embodiment, the sensor pixel further includes a current source 141 and a third switch S50 that constitute a compensation circuit, and the current source 141 is electrically connected to the input terminal of the integration circuit 142 through the third switch S50.
When the third switch S50 is closed, the charge of the current source 141 is injected into the integrating circuit 142 to compensate the integrating speed of the integrating circuit 142, and the two working states of the compensating circuit are a compensating state and a reset state, and when the third switch S50 is closed, the charge of the current source 141 is injected into the integrating circuit 142 to be in the compensating state. The compensation switch is in a reset state when being disconnected. When the amount of charge accumulated by the integration circuit 142 is compensated using the current source 141, the integration circuit may be compensated to be continuous or discontinuous in time according to the process of integration.
The overall operation and principle of the sensor pixel incorporating the compensation circuit is further described below.
Referring to the sensor pixel shown in fig. 5, in order to make the photosensitive element 120 form a measurable voltage signal with respect to the charge amounts of the ridge lines and the valley lines, the other end of the second switch S20 electrically connected to the sensing element 120 is connected to the input end of the integrating circuit 142 through the fourth switch S60, i.e. the charge transfer switch, and the fingerprint sensor comprises the following steps:
s1, resetting an integrating circuit 142;
s2, resetting the photosensitive element 120 and resetting the compensation circuit;
s3, closing the fourth switch S60, opening the second reset switch S40, and closing the third switch S50;
s4 returns to step S2.
In step S1, the integrating circuit 142 needs to reset the integrating capacitor C10 in advance before integrating in order to ensure the consistency of measurement, the resetting process is that the integrating capacitor C10 has an initial charge, for example, assuming that the reference voltages at the two ends of the integrating capacitor C10 are Vref3 and Vref5, respectively, and the reset charge of the integrating capacitor 522 is qrst= (Vref 3-Vref 5) ×cr, where Cr is the capacitance value of the integrating capacitor. In the sensor pixel shown in fig. 5, the first reset switch S30 may be directly connected to two ends of the integrating capacitor C10 for simplifying the structure of the reset circuit, that is, the electric quantity qrst=0 of the integrating capacitor C10 after reset. The integrating circuit 142 repeats the process of re-integrating a plurality of times, that is, the process of charging the integrating capacitor C10 a plurality of times with the electric charge generated by the photosensitive element 120. And each time the integrating capacitor C10 is charged, the compensation circuit is electrically connected to the integrating circuit through the third switch S50, and charges are injected into the integrating circuit.
The step S2 includes: step S21, closing a second reset switch S40 to reset; in step S22, the compensation circuit resets by opening the third switch S50.
In step S3, the fourth switch S60 is closed, the gated photosensitive element 120 is electrically connected to the integrating circuit, and the compensating circuit injects charge into the integrating circuit 142 to adjust the accumulated amount of integrated charge in the integrating circuit 142. The integrating circuit 142 outputs a magnitude responsive to the amount of charge generated by the photosensitive element 120.
On the basis of the above embodiment, the signal detection circuit 140 further includes:
the first input end of the comparator A20 is electrically connected with the output end of the amplifier A10, the second input end of the comparator A20 is used for inputting the second reference voltage V20, and the output end of the comparator A is used for outputting the turnover signal.
The first input end of the comparator A20 is electrically connected with the output end of the amplifier A10, and when the output voltage of the integrator reaches the voltage of the second input end of the comparator, the output voltage signal of the comparator A20 is inverted, and the time of the inverted signal is used as the output of the sensor pixel. Then in step S3, the fourth switch S60 is closed, the gated photosensitive element 120 is connected to the input terminal of the integrating circuit through the charge transfer switch 420, the output terminal of the integrating circuit is connected to the input terminal of the comparator a20, the output terminal of the comparator a20 is used as the output of the sensor, and the time T of the comparator a20 outputting the flipped voltage signal reflects the magnitude of the charge generation amount of the photosensitive element 120.
When the value change of the integrating circuit output voltage crosses the reference voltage value in comparator a20, the comparator inverts the output signal.
The flip time of the comparator is t= (qr. End-qr. Rst)/Δq, where qr. End is the amount of charge of the integrating capacitor when the comparator is flipped, qr. Rst is the initial amount of charge of the integrating capacitor, is a constant value for a given fingerprint sensor design (qr. End-qr. Rst), and is related to the amount of charge initialized by the compensating capacitor according to equation Δq. In engineering practice, T rounding is output as a result for simplicity.
On the basis of the above embodiment, the control unit 150 is configured to increase the number of photosensitive elements 120 electrically connected to the gate signal detection circuit 140 by controlling the conduction of the first switch S10 and the second switch S20 if the voltage value of the signal output by the integration circuit 142 is smaller than the first set threshold; if the voltage value of the signal output by the integrating circuit 142 is greater than the second set threshold, the number of photosensitive elements 120 electrically connected to the gate signal detecting circuit 140 is reduced by controlling the first switch S10 and the second switch S20 to be turned off.
When the voltage value output by the integrator is smaller than the first set threshold, for example, the control unit 150 controls the first switch S10 and the second switch S20 to gate one or more photosensitive elements 120 to increase the output current of the photosensitive element array, which is equivalent to increasing the electronic aperture; when the voltage value output by the integrator is greater than the second set threshold, for example, the voltage output by the integrator 142 is close to or equal to the saturation voltage of the integrator, the control unit 150 controls the first switch S10 and the second switch S20 to close the one or more photosensitive elements 120 to reduce the output current of the photosensitive element array, which is equivalent to reducing the electron aperture.
According to the technical scheme, the sensor pixel comprises the collimation layer, the photosensitive element signal detection circuit and the control unit, the problems that an electronic aperture of an existing sensor pixel cannot be adjusted, the acquired image quality is low due to overexposure or underexposure are solved, the size of the electronic aperture of the sensor pixel is dynamically adjusted, namely, the exposure of the sensor pixel is dynamically adjusted, so that better image quality is obtained, and the signal-to-noise ratio is improved.
In other implementations of the embodiments of the present invention, the control unit may receive an external control signal to control the number of gates of the photosensitive elements 120. For example, an external processor receives the output of the sensor pixels, obtains an image, and sends a control signal to the control unit 150 in the sensor pixels according to the quality of the image, so as to control the number of gates of the photosensitive elements 120. Specifically, when the processor detects that the quality of the image is poor, it may send a control signal to the control unit 150, and the control unit 150 controls to increase the number of the sensing elements that are gated according to the control signal. The processor may also send a control signal to the control unit 150 according to the light of the environment, when the light of the environment is strong, and the control unit 150 controls to reduce the number of the gated photosensitive elements 120 according to the control signal; when the ambient light is weak, a control signal is sent to the control unit 150, and the control unit 150 controls the number of the light sensing elements 120 to be increased according to the control signal.
The embodiment of the invention also provides an optical sensor. Fig. 6 is a schematic cross-sectional view of an optical sensor according to an embodiment of the present invention, and referring to fig. 6, the sensor pixel array includes a plurality of sensor pixels 100 according to any embodiment of the present invention. The sensor pixel is located on the chip 101 of the sensor, and the optical sensor has the functional modules and beneficial effects of the included sensor pixel 100. The optical sensor may be an optical fingerprint sensor arranged at the bottom of the terminal, for example at the bottom of the OLED terminal. After the light emitted by the terminal irradiates the finger, the light reflected by the finger fingerprint enters the optical tunnel of the collimation layer on the sensor pixel 100 through the glass of the terminal, and the sensor pixel outputs a signal, so that fingerprint identification is performed according to the signal of the fingerprint sensor.
If the optical sensor includes a plurality of sensor pixels, the plurality of sensor pixels in the optical sensor may share one signal detection circuit 140, and the signal detection circuit 140 detects the electrical signals output from the photosensitive elements 120 of the respective sensor pixels in a time-sharing manner.
In addition, the optical sensor further comprises a light source 300, the light source 300 being located on both sides of the sensor pixel array, i.e. on both sides of the chip 101. The light source 300 is used to provide illumination, which may be an LED, for example. The light source 300 emits light outward to the finger surface, and the finger surface reflects or scatters the light of the light source 300 into the sensor pixel array. Such an arrangement of the light source 300 may make the formed image clearer.
The optical sensor further includes a protective layer 200, a package substrate 400, and a PCB 500 on the basis of the above-described embodiment. The protective layer 200 is made of a material with good transmittance, for example, glass, screen, sapphire or ceramic material. In use, an object to be measured, such as a finger, is placed on the surface of the protective layer 200 on the side remote from the sensor pixel array, and light reflected from the finger fingerprint is emitted through the protective layer 200 onto the sensor pixel array. The optical sensor may be disposed at the bottom of the terminal, and the optical sensor may not be provided with the protective layer 200, and the protective layer 200 may be replaced with glass of the terminal. The light emitted by the terminal can irradiate the finger fingerprint, and the light reflected by the finger fingerprint penetrates through the glass of the terminal to enter the sensor pixel on the optical sensor.
Note that the above is only a preferred embodiment of the present invention and the technical principle applied. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, while the invention has been described in connection with the above embodiments, the invention is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the invention, which is set forth in the following claims.
Claims (12)
1. A sensor pixel, comprising:
the optical tunnel is used for receiving light in the vertical direction in the light reflected by the target finger;
at least two photosensitive elements for outputting an electrical signal according to the light received by the optical tunnel;
a control unit for controlling the number of gates of the photosensitive elements;
the signal detection circuit is electrically connected with one or more photosensitive elements and is used for acquiring the electric signals output by the gated photosensitive elements;
a load circuit, at least one first switch and at least one second switch; wherein the signal detection circuit includes: the input end of the integrating circuit is electrically connected to the second pole of the photosensitive element through the second switch, and the output end of the integrating circuit is electrically connected with the control unit; the control unit is used for controlling the gating quantity of the photosensitive elements according to the output of the integrating circuit;
the control unit is used for increasing the number of the photosensitive elements electrically connected with the signal detection circuit by controlling the conduction of the first switch and the second switch if the voltage value of the signal output by the integration circuit is smaller than a first set threshold value; if the voltage value of the signal output by the integrating circuit is larger than a second set threshold value, the first switch and the second switch are controlled to be turned off, so that the number of the photosensitive elements electrically connected with the signal detection circuit is reduced;
wherein each sensor pixel comprises M rows and N columns of photosensitive elements, and M and N are integers greater than or equal to 1; the first poles of the photosensitive elements of each row are electrically connected to the load circuit through a first switch, and the second poles of the photosensitive elements of each column are electrically connected to the input end of the signal detection circuit through a second switch; the number of the first switches corresponding to the M rows and the N columns of the photosensitive elements is M, and the number of the second switches corresponding to the M rows and the N columns of the photosensitive elements is N; one or more of the photosensitive elements are turned on by controlling the first switch to be turned on or off and controlling the second switch to be turned on or off.
2. The sensor pixel of claim 1, wherein the collimation layer comprises at least one mask layer; the mask layer includes a light-transmitting region and a light-opaque region.
3. The sensor pixel of claim 2, wherein the number of mask layers is at least two;
the light-transmitting areas adjacent to the mask layers are staggered, and the projection area of the formed optical tunnel is smaller than the area of the light-transmitting area.
4. The sensor pixel of claim 1, wherein each photosensitive element corresponds to one of the optical tunnels.
5. The sensor pixel of claim 1, wherein the load circuit is configured to provide a drive voltage or a drive current.
6. The sensor pixel of claim 5, wherein the integration circuit comprises:
an amplifier; the same-direction input end is used for inputting a first reference voltage, the reverse input end is electrically connected with the input end of the integrating circuit, and the output end is electrically connected with the control unit;
an integrating capacitor, a first pole of which is electrically connected with the reverse input end of the amplifier, and a second pole of which is electrically connected with the output end of the amplifier;
and the first reset switch is connected with the integrating capacitor in parallel.
7. The sensor pixel of claim 6, wherein the signal detection circuit further comprises:
and the first input end of the comparator is electrically connected with the output end of the amplifier, the second input end of the comparator is used for inputting a second reference voltage, and the output end of the comparator is used for outputting a turnover signal.
8. The sensor pixel of claim 6, wherein the signal detection circuit further comprises:
and the first end of each second reset switch is electrically connected with the second pole of the photosensitive element, and the second end of each second reset switch is grounded.
9. The sensor pixel of claim 5, wherein the signal detection circuit further comprises a compensation circuit electrically coupled to the input of the integration circuit for injecting charge into the integration circuit to adjust the integration circuit charge accumulation.
10. The sensor pixel of claim 9, wherein the compensation circuit comprises a current source and a third switch, the current source being electrically connected to the input of the integration circuit through the third switch.
11. An optical sensor comprising an array of sensor pixels comprising a plurality of sensor pixels as claimed in any one of claims 1 to 10.
12. The optical sensor of claim 11, further comprising light sources located on either side of the sensor pixel array.
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