CN115942135A

CN115942135A - Device and method for improving dynamic range of CMOS (complementary Metal oxide semiconductor) and photon statistical method

Info

Publication number: CN115942135A
Application number: CN202211569811.4A
Authority: CN
Inventors: 周丽萍; 胡星宇
Original assignee: Individual
Current assignee: Individual
Priority date: 2022-12-08
Filing date: 2022-12-08
Publication date: 2023-04-07

Abstract

The application relates to the field of photoelectricity, and provides a device and a method for improving dynamic range and a photon statistical method for a CMOS (complementary metal oxide semiconductor), wherein the CMOS comprises a plurality of pixel structures, a control circuit and a photosensitive element array, the pixel structures at least comprise photoelectric conversion elements, and the device comprises a voltage identification controller; the voltage identification controller is arranged in the pixel structure and is configured to measure the voltage Vn of the photoelectric conversion element in real time; when it is recognized that the voltage of the photoelectric conversion element reaches saturation, a voltage saturation signal is transmitted to the control circuit. According to the embodiment of the disclosure, the maximum number of photons which can be received by the photoelectric conversion element is increased by re-exposing when the voltage of the photoelectric conversion element reaches saturation, and the equivalent well depth is increased, so that the dynamic range is expanded.

Description

Device and method for improving dynamic range of CMOS (complementary Metal oxide semiconductor) and photon statistical method

Technical Field

The invention relates to the field of photoelectricity, in particular to a device and a method for improving dynamic range of a CMOS and a photon statistical method.

Background

The image sensor is widely applied to various fields, such as digital cameras, unmanned planes, video monitoring equipment, automatic driving and the like. In recent years, CMOS image sensor and CCD image sensor technologies have been developed, and have become mainstream image sensor chips due to their advantages of low power consumption, high integration, low cost, and random access.

Exposure refers to the process of converting a certain intensity and quantity of optical signals into electrical signals within a certain time. The effect of exposure on image quality is very obvious, and overexposure can make the image too bright and look like bleaching; underexposure results in too dark an image, and both underexposure and overexposure result in loss of image detail. The exposure amount is a comprehensive statistical value of the aperture size, the exposure time, the analog gain and the digital gain which affect the image brightness. The dynamic range is an important index of the imaging quality of the image sensor, and the larger the dynamic range is, the wider the light intensity range capable of detecting the scene information is, that is, the more information contained in the image is. The maximum amount of charge that each photosensitive or output channel pixel element can store on the image sensor is called the well depth.

At present, the output of a CMOS image sensor and a CCD image sensor in the field is in a linear form, the sampling precision of a part of the output is sacrificed when the output is fitted with the visual experience of human eyes, and the pixel size is overlarge to expand the trap depth when the output is pursuing a high dynamic range. The low-trap-depth small-pixel CMOS image sensor cannot obtain a high dynamic range due to the linear property.

Disclosure of Invention

The following presents a simplified summary in order to provide a basic understanding of some aspects of the disclosed embodiments. This summary is not an extensive overview nor is intended to identify key/critical elements or to delineate the scope of such embodiments but rather as a prelude to the more detailed description that is presented later.

The embodiment of the disclosure provides a device and a method for improving a dynamic range of a CMOS (complementary metal oxide semiconductor) and a photon statistical method, so as to solve the problem of low sampling precision caused by an excessively small high dynamic range in an image sensor in the prior art.

In some embodiments, there is provided an improved dynamic range device for CMOS comprising a plurality of pixel structures, a control circuit, and a photosensitive element array, the pixel structures including at least a photoelectric conversion element, the device comprising a voltage identification controller;

the voltage identification controller is arranged in the pixel structure and is configured to measure the voltage Vn of the photoelectric conversion element in real time; when it is recognized that the voltage of the photoelectric conversion element reaches saturation, a voltage saturation signal is transmitted to the control circuit.

Preferably, the apparatus further comprises an accumulator;

the voltage identification controller is further configured to identify and send an accumulation signal to the accumulator once when the voltage of the photoelectric conversion element is identified to be saturated;

and an accumulator arranged in the pixel structure and configured to receive the accumulated signal to count.

Preferably, the photoelectric conversion element is a PN-type photodiode.

Preferably, the voltage identification controller is arranged in the pixel structure and is configured to acquire a P-junction voltage or an N-junction voltage of the photodiode.

In some embodiments, a method for improving dynamic range of CMOS is provided, which is applied to the device, and the exposure speed of the image sensor is adjusted by adjusting the light quantity entering the photoelectric conversion element.

Preferably, the adjusting of the exposure speed of the image sensor by adjusting the amount of light entering the photoelectric conversion element includes:

s11, in the exposure process of the photoelectric conversion element, the voltage identification controller measures the voltage Vn of the photoelectric conversion element in real time;

s12, when the voltage of the photoelectric conversion element reaches saturation, the voltage identification controller sends a voltage saturation signal to the control circuit;

s13, the control circuit controls the photoelectric conversion element to restart exposure;

s14, repeatedly executing S11 to S13 for multiple times;

and S15, after the exposure of the photoelectric conversion element is finished, biasing the photoelectric conversion element.

In some embodiments, there is provided an improved dynamic range photon statistics method for CMOS, applied to a device further comprising an accumulator, the method comprising:

s21, when the voltage of the photoelectric conversion element reaches saturation, the voltage identification controller generates an accumulation signal to an accumulator, and the count of the accumulator is increased by one;

s22, repeatedly executing S21;

s23, after the exposure of the photoelectric conversion element is finished, the control circuit outputs voltage data of all pixel structures in the photosensitive element array, and therefore the photon number corresponding to Vn is calculated;

s24, acquiring a counting number n of the accumulator;

s25, calculating the number of photons received by the photoelectric conversion element to be m; m = n + well depth + Vn.

The disclosed embodiment provides a device and a method for improving dynamic range and a photon statistical method for CMOS (complementary metal oxide semiconductor), wherein the CMOS comprises a plurality of pixel structures, a control circuit and a photosensitive element array, the pixel structures at least comprise photoelectric conversion elements, and the device comprises a voltage identification controller; the voltage identification controller is arranged in the pixel structure and is configured to measure the voltage Vn of the photoelectric conversion element in real time; when it is recognized that the voltage of the photoelectric conversion element reaches saturation, a voltage saturation signal is transmitted to the control circuit. According to the embodiment of the disclosure, the maximum number of photons which can be received by the photoelectric conversion element is increased by re-exposing when the voltage of the photoelectric conversion element reaches saturation, and the equivalent well depth is increased, so that the dynamic range is expanded.

The foregoing general description and the following description are exemplary and explanatory only and are not restrictive of the application.

Drawings

One or more embodiments are illustrated by way of example in the accompanying drawings, which correspond to the accompanying drawings and not in limitation thereof, in which elements having the same reference numeral designations are shown as like elements and not in limitation thereof, and wherein:

fig. 1 is a schematic diagram of a CMOS provided in an embodiment of the present disclosure;

FIG. 2-1 is a schematic diagram of an apparatus for improving dynamic range for CMOS according to an embodiment of the present disclosure;

fig. 2-2 is a schematic backside-illuminated view of a pixel structure according to an embodiment of the disclosure;

reference numerals:

1: a horizontal shifter; 2: a vertical shifter; 3: an output amplifier; 4: a sense amplifier; 5: a control circuit; 6: a sequential circuit; 7: a pixel structure; 711: a voltage identification controller; 712: an accumulator; 72: a photoelectric conversion element; 73; an MOS tube; 8: an array of photosensitive elements.

Detailed Description

So that the manner in which the features and advantages of the embodiments of the present disclosure can be understood in detail, a more particular description of the embodiments of the disclosure, briefly summarized above, may be had by reference to the appended drawings, which are included to illustrate, but are not intended to limit the embodiments of the disclosure. In the following description of the technology, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the disclosed embodiments. However, one or more embodiments may be practiced without these details. In other instances, well-known structures and systems may be shown in simplified form in order to simplify the drawing.

The terms "first," "second," and the like in the description and in the claims, and the above-described drawings of embodiments of the present disclosure, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It should be understood that the data so used may be interchanged under appropriate circumstances such that embodiments of the present disclosure described herein may be made. Furthermore, the terms "comprising" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions.

In the embodiments of the present disclosure, the terms "upper", "lower", "inner", "middle", "outer", "front", "rear", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings. These terms are used primarily to better describe the disclosed embodiments and their embodiments, and are not used to limit the indicated systems, elements or components to a particular orientation or to be constructed and operated in a particular orientation. Moreover, some of the above terms may be used to indicate other meanings besides the orientation or positional relationship, for example, the term "on" may also be used to indicate some kind of attachment or connection relationship in some cases. The specific meanings of these terms in the embodiments of the present disclosure can be understood by those of ordinary skill in the art as appropriate.

In addition, the terms "disposed," "connected," and "secured" are to be construed broadly. For example, "connected" may be a fixed connection, a detachable connection, or a unitary construction; can be a mechanical connection, or an electrical connection; may be directly connected, or indirectly connected through intervening media, or may be in communication between two systems, components or parts. Specific meanings of the above terms in the embodiments of the present disclosure can be understood by those of ordinary skill in the art according to specific situations.

The term "plurality" means two or more unless otherwise specified.

In the embodiment of the present disclosure, the character "/" indicates that the preceding and following objects are in an or relationship. For example, A/B represents: a or B.

The term "and/or" is an associative relationship that describes objects, meaning that three relationships may exist. For example, a and/or B, represents: a or B, or A and B.

It should be noted that, in the case of no conflict, the embodiments and features in the embodiments of the present disclosure may be combined with each other.

In the prior art, the output of a CMOS image sensor and a CCD image sensor is in a linear form, the sampling precision of a part of the output is sacrificed when the output is fitted with the visual experience of human eyes, and the pixel size is overlarge to expand the well depth when the output is pursuing a high dynamic range. The low-trap-depth small-pixel CMOS image sensor cannot obtain a high dynamic range due to the linear property.

Referring to fig. 1, a CMOS schematic is provided for an embodiment of the present disclosure, with a horizontal shifter 1 shown in fig. 1; the circuit comprises a vertical shifter 2, an output amplifier 3, a sensitive amplifier 4, a control circuit 5, a time sequence circuit 6, a pixel structure 7 and a photosensitive element array 8. The photosensitive cell array 8 has an ADC module therein.

Referring to fig. 2-1, a schematic diagram of an apparatus for improving dynamic range for CMOS is provided for the embodiments of the present disclosure. Referring to fig. 2-2, a backside illuminated schematic diagram of a pixel structure is provided for the embodiments of the present disclosure. Among them, fig. 2-1 and 2-2 show the voltage recognition controller 711, the accumulator 712, the photoelectric conversion element 72, and the MOS tube 73.

The image sensor includes a plurality of pixel structures 7, the pixel structure 7 including at least a photoelectric conversion element 72, the pixel structure including an accumulator 712 and a voltage identification controller 711; wherein the voltage identification controller 711, provided at the pixel structure 7, is configured to measure the voltage Vn of the photoelectric conversion element 72 in real time; when recognizing that the voltage of the photoelectric conversion element 72 reaches saturation, it sends a voltage saturation signal to the control circuit 5, and generates an accumulation signal to the accumulator 712; the accumulator 712, which is arranged in picture element structure 7, is configured to receive the accumulated signal and to count accordingly.

The photoelectric conversion element 72 is a PN type photodiode. The light transmission controller 711 is configured to acquire a P junction voltage or an N junction voltage of the photodiode.

Correspondingly, the embodiment of the present disclosure provides a method for improving a dynamic range of a CMOS, which is applied to the above image sensor, and the method includes:

s14, repeatedly executing S11 to S13 for multiple times;

It is to be understood that, among others, the photoelectric conversion element is a photodiode. The principle is that the voltage identification controller continuously measures the photodiode voltage Vn during the exposure process, and resets the photodiode, i.e. clears its charge, when the voltage reaches a set value, such as the photodiode saturation voltage. At this point the photodiode can resume exposure, i.e. overexposure is avoided.

The dynamic range is an important evaluation index in the CMOS image sensor. The dynamic range indicates the range of the maximum light intensity signal and the minimum light intensity signal that the CMOS image sensor can detect simultaneously in the same frame image.

The method achieves the purpose of increasing the charge of the photodiode relative to the full well. The range of the maximum light intensity signal received by the corresponding CMOS is enlarged, and the dynamic range is enlarged.

In addition, the embodiments of the present disclosure further provide a method for improving dynamic range photon statistics for CMOS, including:

s22, repeatedly executing S21;

s24, acquiring a counting number n of the accumulator;

s25, calculating the number of photons received by the photoelectric conversion element to be m; m = n + the number of photons corresponding to the well depth + Vn.

It will be appreciated that the accumulator is used to count the number of voltages that saturate, and that n is obtained by counting up by one without stopping. After exposure, the control circuit outputs the voltage data of all the pixels in the photosensitive element array and the counting number n of the corresponding accumulator, and the number of the received photons of the photodiode is the number of the photons corresponding to the sum of the trap depth n and Vn. All accumulators and photodiodes are then cleared.

In CMOS, there is an ADC block. The ADC module is used for converting the voltage analog signal into a corresponding digital signal. Each pixel structure in the CMOS circuit is provided with an ADC conversion module. The ADC converts the voltage to a corresponding image readout luminance, which is equivalent to the number of carriers captured in the diode. The carriers represent the number of photons.

A specific example is a photodiode with a charge of 50000 electrons in a full well, which reaches the full well for the first time after exposure is started, and then it cannot receive any more photons, and then its output voltage Vn reaches an extreme value, and when it is detected that Vn reaches the extreme value, the voltage identification controller adds the count value of the accumulator from 0 to 1, and simultaneously clears the photodiode, so that it can continue to receive photons. The second time it reaches the full well, the accumulator is incremented from 1 to 2. Assuming that the exposure process is finally stopped, the accumulator value is 3 and the amount of charge read out by the photodiode is 20000 electrons. That is to say that during this exposure, 50000 x 3+20000=170000 photons are received by this diode.

Instead of the CMOS of the method, the diode can only receive the photon amount of the full trap corresponding to the diode at most after the exposure is finished.

The above description and the drawings sufficiently illustrate embodiments of the disclosure to enable those skilled in the art to practice them. Other embodiments may include structural and other changes. The examples merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others. The embodiments of the present disclosure are not limited to the structures that have been described above and shown in the drawings, and various modifications and changes may be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. An improved dynamic range device for a CMOS comprising a plurality of pixel structures, a control circuit and an array of photosensitive elements, the pixel structures comprising at least a photoelectric conversion element, characterized in that the device comprises a voltage identification controller;

2. The improved dynamic range device for CMOS of claim 1 further comprising an accumulator;

and the accumulator is arranged in the pixel structure and is configured to receive the accumulation signal so as to count.

3. The improved dynamic range device for CMOS of claim 1 wherein said photoelectric conversion element is a PN-type photodiode.

4. The improved dynamic range device for CMOS of claim 3, wherein the voltage discrimination controller is configured to obtain a P-junction voltage or an N-junction voltage of the photodiode.

5. A method for improving dynamic range of CMOS, applied to the apparatus of claim 1, the method comprising:

s14, repeatedly executing S11 to S13 for multiple times;

6. An improved dynamic range photon statistics method for CMOS, applied to the apparatus of claim 1, further comprising an accumulator, the method comprising:

s22, repeatedly executing S21;

s24, acquiring a counting number n of an accumulator;