CN210327778U - Image sensor and related chip and handheld device - Google Patents

Abstract

The application discloses an image sensor (100/200), comprising: a photodiode, a transfer gate (102), and a read circuit (112) having an input (Vin) and an output (Vout), the read circuit comprising: an integrator (114) for integrating with respect to an input of the read circuit and outputting to the output of the read circuit; and a switch (108) arranged in parallel with the integrator; wherein the transmission gate is coupled between the photodiode and the input terminal of the reading circuit.

Description

Image sensor and related chip and handheld device

Technical Field

The present disclosure relates to a touch controller and a related chip, a touch control system and a touch control method, and more particularly, to a touch controller and a related chip, a touch control system and a touch control method based on phase modulation.

Background

A conventional capacitive transimpedance amplifier (CTIA) pixel structure is different from an active-pixel sensor (APS) structure in that the conventional capacitive transimpedance amplifier (CTIA) pixel structure integrates capacitance of an integrator in a reading circuit in real time by using photocurrent generated by a photodiode, and a transfer gate is not required between the photodiode and the reading circuit to determine when the photocurrent generated by the photodiode is transmitted to the integrator of the reading circuit; in contrast, the active pixel sensor needs to accumulate charges by the photodiode and dump the accumulated charges into the rear source follower again, so that a transfer gate is needed to disconnect the photodiode from the source follower before the photodiode is exposed, and the transfer gate is turned on to dump the charges into the rear source follower after the photodiode is exposed.

However, in the pixel structure of the capacitive transimpedance amplifier, since there is no transmission gate, the photodiode is directly connected to the read circuit through a metal layer wire, which is inevitably connected to the photodiode through a via (via), and due to imperfections in the semiconductor process, the via on the photodiode often causes a certain degree of dark current, which results in noise.

SUMMERY OF THE UTILITY MODEL

An object of the present application is to disclose a touch controller based on phase modulation, a related chip, a touch control system and a touch control method, so as to solve the above problems.

An embodiment of the present application discloses an image sensor, including: photodiode transmission gate and reading circuit, reading circuit has input and output, reading circuit includes: the integrator is used for integrating the input end of the reading circuit and outputting the integrated input end to the output end of the reading circuit; and a switch arranged in parallel with the integrator; wherein the transmission gate is coupled between the photodiode and the input terminal of the reading circuit.

An embodiment of the present application discloses a chip, including: the image sensor described above.

An embodiment of the present application discloses an image sensor operating method, configured to operate the image sensor, where the image sensor operating method includes: in a reset phase, controlling the transmission gate and the switch to be conducted so as to reset the integrator; and in the exposure and sampling stage, the photodiode is exposed, the transmission gate is controlled to be conducted, the switch is not conducted, and the light current generated by the photodiode integrates the integrator.

An embodiment of the present application discloses an image sensor operating method, configured to operate the image sensor, where the image sensor operating method includes: in an exposure and reset stage, exposing the photodiode, and simultaneously controlling the switch to be conducted and the transmission gate to be not conducted so as to reset the integrator; and in the reference value sampling stage, the photodiode stops exposure, and the transmission gate and the switch are controlled to be not conducted at the same time, so that the output end of the reading circuit generates a reference value sampling result.

An embodiment of the present application discloses a handheld device for sensing a fingerprint of a specific object, comprising: a display panel; and the image sensor is used for obtaining the fingerprint information of the specific object.

The embodiment of the application utilizes an additional transmission gate to avoid forming a guide hole on the photodiode so as to reduce the occurrence of dark current.

Drawings

Fig. 1 is a schematic diagram of an image sensor according to a first embodiment of the disclosure.

Fig. 2 is a layout diagram of a part of a circuit of the image sensor of fig. 1.

Fig. 3 is a schematic diagram of an operation of the image sensor of fig. 1.

Fig. 4 is a schematic diagram of an image sensor according to a second embodiment of the disclosure.

Fig. 5 is a schematic diagram of the operation of the image sensor of fig. 4.

Fig. 6 is a schematic diagram of an embodiment of a handheld device of the present application.

Wherein the reference numerals are as follows:

100. 200 image sensor

102 photodiode

104 transmission gate

106 capacitor

108 switch

110 amplifier

112 read circuit

114 integrator

116 sampling circuit

120. 122 conducting wire

600 hand-held device

602 display screen assembly

Detailed Description

The following disclosure provides various embodiments or illustrations that can be used to implement various features of the disclosure. The embodiments of components and arrangements described below serve to simplify the present disclosure. It is to be understood that such descriptions are merely illustrative and are not intended to limit the present disclosure. For example, in the description that follows, forming a first feature on or over a second feature may include certain embodiments in which the first and second features are in direct contact with each other; and may also include embodiments in which additional elements are formed between the first and second features described above, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or characters in the various embodiments. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Moreover, spatially relative terms, such as "under," "below," "over," "above," and the like, may be used herein to facilitate describing a relationship between one element or feature relative to another element or feature as illustrated in the figures. These spatially relative terms are intended to encompass a variety of different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Although numerical ranges and parameters setting forth the broad scope of the application are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain standard deviations found in their respective testing measurements. As used herein, "about" generally refers to actual values within plus or minus 10%, 5%, 1%, or 0.5% of a particular value or range. Alternatively, the term "about" means that the actual value falls within the acceptable standard error of the mean, subject to consideration by those of ordinary skill in the art to which this application pertains. It is understood that all ranges, amounts, values and percentages used herein (e.g., to describe amounts of materials, length of time, temperature, operating conditions, quantitative ratios, and the like) are modified by the term "about" in addition to the experimental examples or unless otherwise expressly stated. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, these numerical parameters are to be understood as meaning the number of significant digits recited and the number resulting from applying ordinary carry notation. Herein, numerical ranges are expressed from one end to the other or between the two ends; unless otherwise indicated, all numerical ranges set forth herein are inclusive of the endpoints.

The area of a reading circuit of a traditional active-pixel sensor (APS) structure is small, so that small pixels are mostly collocated; compared with a conventional capacitive transimpedance amplifier (CTIA) pixel structure, the readout circuit area of the conventional capacitive transimpedance amplifier (CTIA) pixel structure is large, for example, the area of an integrator therein is large, so that when a pixel is small, the fill factor (fill factor) is obviously reduced, and therefore the pixel structure is generally used with a large photodiode.

In the application of fingerprint identification by using an image sensor, because light reflected into the image sensor is often darker when a fingerprint is pressed, compared with the image sensor for general photographing, a photodiode of the image sensor in the application is designed to be larger so as to increase the light-sensing capacity, and therefore the pixel structure of the capacitive transimpedance amplifier is suitable for being used in the fingerprint identification application. In addition, the reading circuit of the pixel structure of the capacitive transimpedance amplifier uses the integrator, so that the linearity of the reading circuit is better than that of the pixel structure of the active pixel sensor, and for fingerprint identification application, the requirement on the linearity is higher than that of common photographing, so that the pixel structure of the capacitive transimpedance amplifier just meets the requirement on the linearity.

In order to solve the dark current problem of the pixel structure of the capacitive transimpedance amplifier in the related art, the capacitive transimpedance amplifier pixel structure proposed in the present disclosure has a transmission gate disposed between the photodiode and the read circuit, wherein a source/drain of the transmission gate is directly connected to the photodiode through the substrate, and another source/drain of the transmission gate is connected to the read circuit, so that the photodiode can be connected to the read circuit through the transmission gate without being connected to the read circuit through a metal layer wire. Therefore, the capacitor transimpedance amplifier provided by the present disclosure does not need to connect the photodiode and the metal layer wire through a via (via), thereby avoiding dark current caused by the via on the photodiode, reducing the whole dark current and improving noise.

Fig. 1 is a schematic diagram of an image sensor according to a first embodiment of the disclosure. In the present embodiment, theimage sensor 100 is implemented by using a cmos process. Theimage sensor 100 includes aphotodiode 102, atransfer gate 104, aread circuit 112, and asampling circuit 116. Thetransmission gate 104 may be a transistor, and in the embodiment, thetransmission gate 104 is an N-type Complementary Metal Oxide Semiconductor (CMOS) transistor, but the application is not limited thereto. Theread circuit 112 has an input terminal Vin and an output terminal Vout, and thetransmission gate 104 is coupled between thephotodiode 102 and the input terminal Vin of theread circuit 112.

In the present embodiment, theread circuit 112 includes anintegrator 114 and aswitch 108. Theswitch 108 may be implemented by the same or similar to thetransmission gate 104, such as an nmos transistor, but the application is not limited thereto. Theintegrator 114 is used for integrating the signal at the input terminal Vin of thereadout circuit 112 and outputting the integrated signal to the output terminal Vout of thereadout circuit 112. In the present embodiment, theintegrator 114 includes anamplifier 110 and acapacitor 106, theamplifier 110 is coupled between the input terminal Vin and the output terminal Vout of thereadout circuit 112, and thecapacitor 106 is connected in parallel with theamplifier 110. Theamplifier 110 may be a single-ended amplifier or a double-ended differential amplifier.

Thesampling circuit 116 is used to convert the analog signal at the output terminal Vout into a digital signal Dout according to the sampling control signal Ss, and thesampling circuit 116 may be a Correlated Double Sampling (CDS) circuit.

In the present embodiment, thephotodiode 102 implemented by cmos process has a semiconductor substrate and a metal connection layer stacked on the semiconductor substrate, and the metal connection layer includes a dielectric layer and a conductive line therein. At least a portion of theimage sensor 100 is disposed in the semiconductor substrate. Fig. 2 is a layout diagram of a part of the circuit of theimage sensor 100 of fig. 1. As shown in fig. 2, the gate of thetransmission gate 104 is connected to the first reference voltage VDD through theconductive line 122 in the metal connection layer, so that thetransmission gate 104 keeps the conducting state, in this embodiment, since thetransmission gate 104 is an nmos transistor, the first reference voltage VDD should be high, i.e. the logic value is 1. The cathode of thephotodiode 102 is adjacent to one source/drain of thetransfer gate 104, such that the cathode of thephotodiode 102 is coupled to one source/drain of thetransfer gate 104 through the semiconductor substrate. The other source/drain of thetransmission gate 104 is connected to the input terminal Vin of thereading circuit 112 through theconductive line 120 in the metal connection layer. The anode of thephotodiode 102 is coupled to a second reference voltage VSS, which is low in the embodiment, i.e. the logic value is 0.

Thephotodiode 102 and the metal connection layer above it are not directly connected, that is, thephotodiode 102 and the metal connection layer are completely separated by a dielectric layer in a range overlapping each other, and there is no via connecting thephotodiode 102 and the wire in the metal connection layer above. Thephotodiode 102 and the metal connection layer are coupled only indirectly through thetransfer gate 104 outside the range where they overlap each other. For example, thephotodiode 102 is coupled to theconductive line 122 through the gate of thetransmission gate 104; and thephotodiode 102 is coupled to theconductive line 120 through the other source/drain of thetransmission gate 104. In addition, the gate of theswitch 108 is coupled to the control signal S1 through the metal connection layer.

Fig. 3 is a schematic diagram of the operation of theimage sensor 100 of fig. 1. The operations of fig. 3 include: a reset phase, an exposure and sensing value sampling phase and a reference value sampling phase. During the reset phase, thetransmission gate 104 remains on and controls theswitch 108 to be on by the control signal S1 to reset theintegrator 114. In the exposure and sensing value sampling phase, the photodiode is exposed tolight 102, thetransmission gate 104 is kept conductive, and theswitch 108 is controlled to be non-conductive by the control signal S1, so that the photocurrent generated by thephotodiode 102 integrates theintegrator 114 in real time, and the output terminal Vout of thereading circuit 112 is raised. Thesampling circuit 116 converts the analog signal at the output terminal Vout into a digital signal Dout as a sensing value according to the sampling control signal Ss, for example, when the sampling control signal Ss is high, thesampling circuit 116 performs digital double sampling on the output terminal Vout.

As mentioned above, thetransmission gate 104 is kept conductive in both of the above two stages, the present disclosure avoids using thetransmission gate 104 to connect thephotodiode 102 and the conductive line in the metal connection layer above, so that the dark current generated by the operation of fig. 3 can be effectively reduced to affect the integration result of theintegrator 114, thereby reducing the noise.

In the reference value sampling phase, the control signal S1 controls theswitch 108 to be turned on to reset theintegrator 114, and then thesampling circuit 116 reads the output Vout signal of theintegrator 114 at the time of resetting according to the sampling control signal Ss to serve as the reference value, and obtains the corrected sensing result according to the sensing value and the reference value.

Fig. 4 is a schematic diagram of an image sensor according to a second embodiment of the disclosure. The difference between theimage sensor 200 and theimage sensor 100 is that thetransmission gate 104 of theimage sensor 200 is selectively turned into a conductive state. Specifically, the gate of thetransmission gate 104 is controlled by the control signal S2 through the metal connection layer, rather than being fixedly connected to the first reference voltage VDD as in theimage sensor 100.

Fig. 5 is a schematic diagram of the operation of theimage sensor 200 of fig. 4. The operations of fig. 5 include: a reset phase, an exposure and sensing value sampling phase and a reference value sampling phase. In the reset phase, theswitch 108 is controlled to be turned on by the control signal S1 to reset theintegrator 114. During the exposure and sensing value sampling phase, the photodiode is exposed 102, theswitch 108 is controlled to be non-conductive by the control signal S1, and controls thetransmission gate 104 to be kept on through the control signal S2 in the early stage of the exposure and sensing value sampling phase, so that the photocurrent generated by thephotodiode 102 integrates theintegrator 114 in real time, the output terminal Vout of thereadout circuit 112 is raised, and controls thetransmission gate 104 to remain non-conductive by the control signal S2 in the later stage of the exposure and sensing value sampling phase, so that the photocurrent generated by thephotodiode 102 stops integrating theintegrator 114, and, thereafter, thesampling circuit 116 converts the analog signal at the output terminal Vout into a digital signal Dout as a sensing value according to the sampling control signal Ss, thesampling circuit 116 performs digital double sampling with respect to the output terminal Vout, for example, when the sampling control signal Ss is high. Therefore, one of the advantages of theimage sensor 200 over theimage sensor 100 is that thephotodiode 102 is prevented from outputting current to theintegrator 114 when thesampling circuit 116 is sampling.

During the reference value sampling phase, the control signal S1 controls theswitch 108 to be turned on to reset theintegrator 114, and the control signal S2 controls theswitch 104 to be turned on, after the reset of theintegrator 114 is completed, the control signal S1 controls theswitch 108 to be turned off, so as to copy the charge injection (charging) noise generated when theswitch 108 is turned on to off at the output terminal Vout of theintegrator 114, and thepost-sampling circuit 116 reads the noise as a reference value according to the sampling control signal Ss, and can obtain a corrected sensing result according to the sensing value and the reference value. Therefore, one of the advantages of the control method of theimage sensor 200 of fig. 5 over the control method of theimage sensor 100 of fig. 3 is that the charge injection noise from the on-to-off of theswitch 108 can be eliminated from the sensing result.

The present application also provides a chip including theimage sensor 100 or theimage sensor 200. In some embodiments, theimage sensor 100/200 may be applied to fingerprint recognition applications, for example, a handheld device is also provided, and fig. 6 is a schematic diagram of an embodiment of the handheld device. Thehandheld device 600 includes adisplay screen assembly 602 and animage sensor 100/200. Thehandheld device 600 may be used for optical underscreen fingerprint sensing to sense a fingerprint of a particular object. Thehandheld device 600 may be any handheld electronic device such as a smart phone, a personal digital assistant, a handheld computer system, or a tablet computer. Thedisplay screen assembly 602 may include a display panel and a protective cover disposed above the display panel, and theimage sensor 100/200 is disposed below the display panel, in this embodiment, the display panel may be an organic electroluminescent display panel (OLED), but the present application is not limited thereto.

The foregoing description has set forth briefly the features of certain embodiments of the present application so that those skilled in the art may more fully appreciate the various aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should understand that they can still make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.

Claims (10)

1. An image sensor, comprising:

a photodiode;

a transmission gate; and

a read circuit having an input and an output, the read circuit comprising:

the integrator is used for integrating the input end of the reading circuit and outputting the integrated input end to the output end of the reading circuit; and

a switch arranged in parallel with the integrator;

wherein the transmission gate is coupled between the photodiode and the input terminal of the reading circuit.

2. The image sensor of claim 1, wherein the photodiode has a metal connection layer over it, and the photodiode and the metal connection layer are in an overlapping range without a via connecting the photodiode and the metal connection layer.

3. The image sensor of claim 2, wherein the photodiode and the metal connection layer are completely separated by a dielectric layer in a range overlapping each other.

4. The image sensor of claim 3, wherein the photodiode and the metal connection layer are coupled to each other through the transfer gate outside a range overlapping each other.

5. The image sensor of claim 1, wherein the transfer gate has a gate coupled to a reference voltage that fixes the transfer gate in a conductive state.

6. The image sensor of claim 1, wherein the integrator comprises:

an amplifier coupled between the input and the output of the read circuit; and

a capacitor arranged in parallel with the amplifier.

7. The image sensor of claim 6, wherein the amplifier is a differential amplifier.

8. The image sensor of claim 1, wherein the photodiode has an anode and a cathode, the cathode coupled to the transfer gate.

9. A chip, wherein the chip comprises:

the image sensor as claimed in any one of claims 1 to 8.

10. A handheld device for sensing a fingerprint of a specific object, comprising:

a display panel; and

the image sensor of claims 1-8, configured to obtain fingerprint information of the particular object.

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