WO2021012071A1

WO2021012071A1 - Image sensor, related chip, and electronic apparatus

Info

Publication number: WO2021012071A1
Application number: PCT/CN2019/096658
Authority: WO
Inventors: 徐荣贵
Original assignee: 深圳市汇顶科技股份有限公司
Priority date: 2019-07-19
Filing date: 2019-07-19
Publication date: 2021-01-28
Also published as: CN110972518B; CN110972518A

Abstract

Disclosed are an image sensor (10), a related chip, and an electronic apparatus (20). The image sensor comprises: a pixel (12) for sensing light and generating an analog sensing signal; a gain amplifier (14) coupled to the pixel and used for adjusting a gain value according to the intensity of the light, and for amplifying, on the basis of the gain value, the analog sensing signal to generate a gained analog sensing signal; and an analog-to-digital converter (16) coupled to the gain amplifier and used for sampling the gained analog sensing signal by using a relevant multi-sampling technique, and for converting the gained analog sensing signal into a digital sensing signal, wherein the number of sampling times varies in real time according to the analog sensing signal.

Description

Image sensor and related chip and electronic device

Technical field

This application relates to a pixel sensing technology, and in particular to an image sensor and related chips and electronic devices.

Background technique

CMOS image sensors have been mass-produced and applied. Generally speaking, a CMOS image sensor includes a pixel array, which is composed of a plurality of pixels arranged in an array, and the pixel includes a photosensitive component and a conversion circuit. The photosensitive element includes, for example, a photosensitive diode (photodiode) or a photosensitive transistor (phototransistor). The photosensitive component will generate electric charge after receiving light and store the generated electric charge. The conversion circuit converts the charge stored in the photosensitive component into a potential signal, where the potential signal is the pixel value corresponding to the photosensitive component. Then, the analog-to-digital converter samples the potential signal, and performs analog-to-digital conversion on the sampled potential signal to obtain the analog-to-digital conversion result. The practice of the analog-to-digital converter often directly affects the noise level generated by the analog-to-digital converter, but in pursuit of speed, the complexity of the analog-to-digital converter cannot be increased without limit.

Therefore, being able to take into account the cost and accuracy of image sensing results at the same time has become an important work item.

Summary of the invention

One of the objectives of the present application is to disclose a pixel sensing technology, especially an image sensor and related chips and electronic devices, to solve the above problems.

An embodiment of the present application discloses an image sensor. The image sensor includes: a pixel for sensing light and generating an analog sensing signal; a gain amplifier, coupled to the pixel, for generating an analog sensing signal according to the light Intensity adjusts the gain value, and amplifies the analog sensing signal based on the gain value to generate a post-gain analog sensing signal; and an analog-to-digital converter, coupled to the gain amplifier, for sensing the post-gain analog The measurement signal is sampled using the correlated multi-sampling technique, and the gain-enhanced analog sensing signal is converted into a digital sensing signal, wherein the number of sampling is changed in real time according to the analog sensing signal.

An embodiment of the present application discloses a chip including the aforementioned image sensor.

An embodiment of the present application discloses an electronic device including the aforementioned image sensor.

The ramp generator of the image sensor disclosed in the present application can generate different ramp signals based on the different intensities of light, thereby changing the sampling method and the analog-to-digital conversion method, thereby alleviating the negative impact caused by quantization noise or high-frequency noise, thereby improving The accuracy of image sensing results.

Description of the drawings

FIG. 1 is a schematic block diagram of an embodiment of the chip of the application.

FIG. 2A is a schematic diagram illustrating the operation of the image sensor shown in FIG. 1 when light is at the first intensity.

FIG. 2B is a signal timing diagram of the ramp signal generated by the ramp generator of FIG. 2A.

FIG. 3A is a schematic diagram illustrating the operation of the image sensor shown in FIG. 1 when light is at the second intensity.

3B is a signal timing diagram of the ramp signal generated by the ramp generator of FIG. 3A.

4 is a schematic diagram of an embodiment in which the image sensor shown in FIG. 1 is applied to an electronic device.

Wherein, the reference signs are explained as follows:

10 Image sensor

12 Pixel

14 Gain amplifier

16 Analog-to-digital converter

18 Digital signal processor

20 Electronic device

160 Ramp generator

162 Comparator

164 Counter

SA Analog signal

SD Digital sensing signal

SG Simulate sensing signal after gain

Sout Image processing signal

S_RAMP Ramp signal

S_com Digital comparison signal

GL Gain value

G1 The first gain value

G2 The second gain value

S1 First paragraph

S2 Second paragraph

S3 The third paragraph

S4 Paragraph 4

V Voltage

T Time

L1 First strength

L2 Second Intensity

Detailed ways

The following disclosure provides various embodiments or examples, which can be used to realize different features of the disclosure. The specific examples of components and configurations described below are used to simplify the present disclosure. When it is conceivable, these narratives are only examples and are not intended to limit the content of this disclosure. For example, in the following description, forming a first feature on or on a second feature may include some embodiments where the first and second features are in direct contact with each other; and may also include In some embodiments, additional components are formed between the above-mentioned first and second features, so that the first and second features may not be in direct contact. In addition, the present disclosure may reuse component symbols and/or labels in multiple embodiments. Such repeated use is based on the purpose of brevity and clarity, and does not in itself represent the relationship between the different embodiments and/or configurations discussed.

Furthermore, the use of spatially relative terms here, such as "below", "below", "below", "above", "above" and similar, may be used to facilitate the description of the drawing The relationship between one component or feature relative to another component or feature is shown. In addition to the orientation shown in the figure, these spatially relative terms also cover a variety of different orientations in which the device is in use or operation. The device may be placed in other orientations (for example, rotated by 90 degrees or in other orientations), and these spatially-relative description words should be explained accordingly.

Although the numerical ranges and parameters used to define the broader scope of the present application are approximate numerical values, the relevant numerical values in the specific embodiments are presented here as accurately as possible. However, any value inherently inevitably contains the standard deviation due to individual test methods. Here, "same" usually means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a specific value or range. Or, the term "same" means that the actual value falls within the acceptable standard error of the average value, depending on the consideration of a person with ordinary knowledge in the technical field of the application. It should be understood that all ranges, quantities, values and percentages used herein (for example, to describe the amount of material, time length, temperature, operating conditions, quantity ratio and other Similar ones) are all modified with "same". Therefore, unless otherwise stated to the contrary, the numerical parameters disclosed in this specification and the accompanying patent scope are approximate values and can be changed according to requirements. At least these numerical parameters should be understood as the indicated effective number of digits and the value obtained by applying the general carry method. Here, the numerical range is expressed from one end point to the other end point or between the two end points; unless otherwise specified, the numerical range described here includes the end points.

Generally speaking, a pixel includes a photosensitive component and a conversion circuit. The photosensitive component generates electric charge after receiving light and stores the generated electric charge. The conversion circuit converts the charge stored in the photosensitive component into a potential signal, the potential signal is an analog electric signal, and the analog electric signal generally has noise added to it. When the analog electrical signal is amplified, the noise will also be amplified. In addition, the analog-to-digital converter uses quantization technology to convert analog electrical signals into digital signals, and quantization noise is generated during the conversion process. Because there are at least the above two noise sources, to improve the accuracy of the image sensing result of the image sensor, the above two noises can be eliminated. The image sensor disclosed in this application can allow the analog-to-digital converter to adjust the conversion mode in real time and adaptively under different light intensities, so as to optimally reduce the negative effects caused by the above two kinds of noises and improve image transmission. The details of the accuracy of the sensory results are as follows.

FIG. 1 is a schematic block diagram of an embodiment of an image sensor 10 of this application. Referring to FIG. 1, FIG. 1 includes an image sensor 10 and a digital signal processor 18. The image sensor 10 is used for sensing light and generating a digital sensing signal SD accordingly. The digital signal processor 18 is used to process an image based on the digital sensing signal SD, and output an image processing signal Sout.

In some embodiments, the image sensor 10 and the digital signal processor 18 may be located on different chips. However, this disclosure is not limited to this. In some embodiments, the image sensor 10 and the digital signal processor 18 are integrated into a single chip.

The image sensor 10 includes a pixel array. The pixel array includes a plurality of pixels 12 arranged in rows and columns. For the convenience of description and the simplicity of the drawing, FIG. 1 only shows a single pixel 12. The pixel 12 is used for sensing light and generating an analog sensing signal SA. In detail, the pixel 12 includes a photosensitive element and a conversion circuit. The photosensitive element receives light to form a photocharge or photocurrent. Then, the photosensitive component stores the charge corresponding to the photoelectron or photocurrent. The conversion circuit converts the charge stored in the photosensitive component into a potential signal, and the potential signal is an analog sensing signal SA. In some embodiments, the photosensitive component may include a photodiode. In addition, in some embodiments, the light may be generated by a laser diode (LD), a light emitting diode (LED), or other light emitting unit that can generate light, or it may be natural light.

In the present disclosure, the pixel array may be an active pixel (active pixel) array, or a dark pixel (dark pixel) array. Correspondingly, the pixels 12 may include effective pixels and/or dark pixels. In addition, in addition to the pixel array, the image sensor 10 also includes a gain amplifier 14 and an analog-to-digital converter 16.

The gain amplifier 14 is coupled between the pixel 12 and the analog-to-digital converter 16, for adjusting the gain value GL according to the intensity of the light sensed by the photosensitive element of the pixel 12, and amplifying the analog sensing signal SA based on the gain value GL to After generating the gain, the sensing signal SG is simulated. It should be noted that the gain value GL is negatively related to the intensity of the light sensed by the photosensitive element of the pixel 12. For example, when the light sensing element of the pixel 12 detects the weaker light, the photoelectron or photocurrent generated by the pixel 12 is smaller, so the analog sensing signal SA is weaker, that is, the voltage swing is smaller, in order to increase the subsequent modulus The efficiency of the conversion, the larger the gain value GL selected by the gain amplifier 14 is. Conversely, when the light is stronger, the gain value GL selected by the gain amplifier 14 is smaller. In some embodiments, the gain amplifier 14 is an adjustable gain amplifier with a limited number of stages, and has more than two different gain values for selection to provide analog sensing signals SA of different strengths. In some embodiments, the gain amplifier 14 may also have an infinite number of segments.

The analog-to-digital converter 16 is coupled between the gain amplifier 14 and the digital signal processor 18 for converting the gain analog sensing signal SG into a digital sensing signal SD. In this embodiment, the analog-to-digital converter 16 uses correlated multiple sampling (CMS) technology to sample the gain analog sensing signal SG. In some embodiments, the analog-to-digital converter 16 uses the correlated double sampling (CDS) technique to sample the gain analog sensing signal SG.

The analog-to-digital converter 16 includes a ramp generator 160, a comparator 162, and a counter 164. The ramp generator 160 is used to generate the ramp signal S_RAMP to the comparator 162. In this embodiment, the ramp generator 160 can change the ramp signal S_RAMP in real time and adaptively under different light intensities. Specifically, the ramp generator 160 can change the waveform of the ramp signal S_RAMP, including the bit resolution and the number of ramps, in real time and adaptively according to the gain value GL, so that the analog-to-digital converter 16 can adjust in real time and adaptively. The conversion method is used for the purpose of optimally reducing noise. In this embodiment, the bit resolution is a power of two. For example, when the power is a value of 10, the bit resolution is 1024; and when the power is a value of 11, the bit resolution is 2048, and so on.

The bit resolution of the ramp signal S_RAMP is related to the quantization noise. In detail, the greater the bit resolution of the ramp signal S_RAMP, the smaller the quantization noise. For example, the quantization noise when the bit resolution is 2048 is smaller than the quantization noise when the bit resolution is 1024.

The number of ramps of the ramp signal S_RAMP is related to the high frequency part of the noise on the analog sensing signal SG after gain. In detail, since the slope of the ramp signal S_RAMP is used as the sampling reference of the analog-to-digital converter 16, the more the number of ramps of the ramp signal S_RAMP, the more sampling times. Generally speaking, as the number of sampling times increases, the high frequency part (for example, thermal noise) of the noise on the analog sensing signal SG after gain will be more suppressed. For example, when the number of sampling times is 4, the degree of suppression of the high frequency part of the noise on the analog sensing signal SG after gain is higher than that when the number of sampling times is 2 times. The degree to which the high-frequency part of the noise on the measurement signal SG is suppressed.

To sum up, in this disclosure, depending on the characteristics of different analog sensing signals SA caused by different light intensities, the analog-to-digital converter 16 can select the partial quantization noise or the noise on the analog sensing signal SG after gain. The high frequency part is suppressed, the details of which will be described in the embodiment in FIGS. 2A and 2B and FIGS. 3A and 3B.

It should be noted that the analog to digital converter 16 has an equivalent number of bits, that is, the number of bits of the digital sensing signal SD. In order to simplify the design of the circuit (such as the digital signal processor 18) after the analog-to-digital converter 16, even if the analog-to-digital converter 16 in this embodiment adjusts the conversion mode in real time and adaptively, the equivalent of the analog-to-digital converter 16 is The number of bits actually remains constant. The details will be described in the embodiments of FIGS. 2A and 2B and FIGS. 3A and 3B.

The comparator 162 is used to compare the gain analog sensing signal SG and the ramp signal S_RAMP, and generate a digital comparison signal S_com. For example, the positive terminal of the comparator 162 receives the ramp signal S_RAMP, and the negative terminal receives the gain analog sensing signal SG. In one case, initially, the voltage value of the ramp signal S_RAMP is smaller than the analog sensing signal SG after the comparison gain, and the digital comparison signal S_com generated by the comparator 162 is at a low level at this time. After that, the voltage value of the ramp signal S_RAMP gradually rises. At a certain point in time, the voltage value of the ramp signal S_RAMP begins to be greater than the analog sensing signal SG after the comparison gain, and the digital comparison signal S_com generated by the comparator 162 changes from a low level to a high level. This level of change is called transition. In other words, the transition from a logic low state to a logic high state is called a transition, and vice versa. In addition, based on the operating principle of the comparator, when the bit resolution of the ramp signal S_RAMP is larger, the quantization noise generated when the comparator 162 simulates the sensing signal SG for analog-to-digital conversion after the quantization gain is smaller. In some embodiments, the comparator 162 includes an operational amplifier.

The counter 164 is used for generating a digital sensing signal SD according to the digital comparison signal S_com. In detail, the counter 164 marks the time point when the digital comparison signal S_com transitions by counting the number of times. In some embodiments, the number of bits of the counter 164 is not limited to any value, as long as the number of bits of the counter 164 is greater than or equal to the equivalent number of bits of the analog-to-digital converter 16 is a feasible implementation manner.

In order to facilitate the understanding of the concept of the present invention, actual numerical values are used to illustrate in the embodiments of FIGS. 2A and 2B and FIGS. 3A and 3B. The equivalent number of bits of the analog-to-digital converter 16 is 12, but this application does not take this as limit.

The schematic diagram of FIG. 2A illustrates the operation of the image sensor 10 shown in FIG. 1 when the light is the first intensity L1; the schematic diagram of FIG. 3A illustrates the image sensor shown in FIG. 1 when the light is the second intensity L2 10 operations. 2B is a signal timing diagram of the ramp signal S_RAMP generated by the ramp generator 160 of FIG. 2A, and FIG. 3B is a signal timing diagram of the ramp signal S_RAMP generated by the ramp generator 160 of FIG. 3A, wherein the horizontal axis represents time T, and The axis represents the voltage V.

Please refer to FIGS. 2A and 3A at the same time. In FIG. 2A, the pixel 12 is illuminated by light with a first intensity L1, and in FIG. 3A, the pixel 12 is illuminated by light with a second intensity L2, where the first intensity L1 is higher than the first intensity L1. The second intensity L2 makes the voltage swing of the analog sensing signal SA in FIG. 2A greater than the voltage swing of the analog sensing signal SA in FIG. 3A. In response to the voltage swing of the analog sensing signal SA, the gain value GL (first gain value G1) of the gain amplifier 14 in FIG. 2A will be smaller than the gain value GL (second gain value G2) of the gain amplifier 14 in FIG. 3A. The ramp generator 160 generates different ramp signals S_RAMP according to the first gain value G1 and the second gain value G2. The details are described below.

Since the voltage swing of the analog sensing signal SA in FIG. 2A is greater than the voltage swing of the analog sensing signal SA in FIG. 3A, the signal-to-noise ratio of the analog sensing signal SA in FIG. 3A is greater than that of the analog sensing signal SA in FIG. 2A The signal-to-noise ratio is poor, and since the analog sensing signal SA of FIGS. 2A and 3A will pass through the gain amplifier 14 to adjust the gain before entering the analog-to-digital converter 16, the degree of quantization noise generated in FIGS. 2A and 3A Are the same or similar. In other words, in Figure 2A, the quantization noise will have a greater degree of influence than the noise of the analog sensing signal SA; on the contrary, in Figure 3A, the noise of the analog sensing signal SA will be more affected than the quantization noise. The impact is greater.

In view of this, in the embodiment of FIG. 2A, since quantization noise is the main noise source, the ramp generator 160 sets the bit resolution of the ramp signal S_RAMP to be higher than that of FIG. 3A, for example, 2 ¹¹ , that is, 2048. In the 3A embodiment, the ramp generator 160 sets the bit resolution of the ramp signal S_RAMP to be lower than that in FIG. 2A, for example, 2 ¹⁰ , which is 1024.

In addition, the equivalent bit number of the analog-to-digital converter 16 is related to the bit resolution of the ramp signal S_RAMP and the number of samplings. In detail, the order of the equivalent bit number is the product of the bit resolution and the number of samples. In this embodiment, since the equivalent number of bits is kept at 12 (that is, 4096 steps), in the embodiment of FIG. 2A, the ramp generator 160 sets the number of sampling times to 2, so that the bit resolution (2048 ) And the number of samples (2) are kept at 4096; in the embodiment of FIG. 3A, the ramp generator 160 sets the number of samples to 4, so that the bit resolution (1024) and the number of samples (4) The product of is maintained at 4096, and the high frequency part of the noise on the analog sensing signal SG after gain can be further suppressed.

When the ramp generator 160 selects two sampling times SN, as shown in FIG. 2B, the ramp signal S_RAMP generated by the ramp generator 160 includes a continuous first segment S1 and a second segment S2, wherein the slope of the first segment S1 The absolute value of is equal to the absolute value of the slope of the second segment S2, and the polarity of the slope of the first segment S1 is opposite to the polarity of the slope of the second segment S2. In this embodiment, the first segment S1 is increasing, and the second segment S2 is decreasing.

When the ramp generator 160 selects four sampling times SN, as shown in FIG. 3B, the ramp signal S_RAMP generated by the ramp generator 160 includes consecutive first segment S1, second segment S2, third segment S3, and fourth segment S_RAMP. Segment S4, where the absolute values of the slopes of the first segment S1, the second segment S2, the third segment S3, and the fourth segment S4 are equal, and the polarity of the slopes of the first segment S1 and the third segment S3 is the same as that of the second segment S2 And the polarity of the slope of the fourth segment S4 is opposite. In this embodiment, the first section S1 and the third section S3 are increasing, and the second section S2 and the fourth section S4 are decreasing.

The operation schemes of FIGS. 2A and 2B and FIGS. 3A and 3B are summarized in Table 1 below. The relative adjectives used in Table 1 below all refer to the relative degree between FIGS. 2A and 2B and FIGS. 3A and 3B.

Table 1

4 is a schematic diagram of an embodiment in which the image sensor 10 shown in FIG. 1 is applied to an electronic device 20. 4, the electronic device 20 includes an image sensor 10, which can be used to perform pixel sensing technology for image sensing or under-screen fingerprint sensing. The electronic device 20 can be, for example, a smart phone, a personal digital assistant, or a handheld computer system. Or any handheld electronic device such as a tablet computer.

In some embodiments, a chip includes the image sensor 10, for example, the chip may be a semiconductor chip implemented by a different process. In some embodiments, the pixel 12 and other circuits of the image sensor 10 are arranged in the same chip, for example, the pixel 12, the gain amplifier 14, and the analog-to-digital amplifier are arranged in the same chip. In some embodiments, for example, under the requirement of ultra-high pixels, the gain amplifier 14 and the analog-to-digital amplifier are provided in one chip, and the pixel 12 is separately provided in another chip.

The above description briefly presents the features of certain embodiments of the present application, so that those with ordinary knowledge in the technical field to which the present application belongs can more fully understand the various aspects of the present disclosure. Those who have ordinary knowledge in the technical field to which this application belongs can understand that they can easily use this disclosure as a basis to design or modify other processes and structures to achieve the same purpose and/or as the embodiments described herein. To achieve the same advantages. Those with ordinary knowledge in the technical field to which this application belongs should understand that these equal implementations still belong to the spirit and scope of the disclosure, and various changes, substitutions and alterations can be made without departing from the spirit of the disclosure. With scope.

Claims

An image sensor, characterized in that the image sensor comprises:

Pixels to sense light and generate analog sensing signals;

A gain amplifier, coupled to the pixel, for adjusting a gain value according to the intensity of the light, and amplifying the analog sensing signal based on the gain value to generate a gain analog sensing signal; and

An analog-to-digital converter, coupled to the gain amplifier, for sampling the post-gain analog sensing signal using correlated multi-sampling technology, and converting the post-gain analog sensing signal into a digital sensing signal,

Wherein the number of times of sampling is changed in real time according to the analog sensing signal.
The image sensor of claim 1, wherein the analog-to-digital converter comprises:

A ramp generator is coupled to the gain amplifier and used to change the ramp signal in real time and adaptively based on the gain value.
3. The image sensor of claim 2, wherein the bit resolution of the ramp signal generated by the ramp generator is negatively related to the gain value.
3. The image sensor according to claim 2, wherein the bit resolution of the ramp signal generated by the ramp generator is negatively related to the number of samplings.
The image sensor according to claim 2, wherein the analog-to-digital converter further comprises:

The comparator is used to compare the gain analog sensing signal and the ramp signal, and generate a digital comparison signal.
8. The image sensor of claim 5, wherein the analog-to-digital converter further comprises:

The counter is used for generating the digital sensing signal according to the digital comparison signal.
The image sensor according to claim 3, wherein the equivalent number of bits of the analog-to-digital converter is related to the bit resolution of the ramp signal and the number of samplings.
7. The image sensor of claim 6, wherein the bit resolution of the ramp signal changes in real time according to the analog sensing signal.
7. The image sensor according to claim 6, wherein when the number of times of sampling changes in real time according to the analog sensing signal, the equivalent bit number of the analog-to-digital converter is kept at a constant value.
7. The image sensor according to claim 7, wherein when the bit resolution of the ramp signal is changed in real time according to the analog sensing signal, the equivalent bit number of the analog-to-digital converter is maintained at a constant value.
10. The image sensor according to claim 10, wherein the ramp generator selects the sampling times as two or four times according to the gain value.
11. The image sensor according to claim 11, wherein when the number of sampling times selected by the slope generator is twice, the slope signal generated by the slope generator includes consecutive first and second segments, The absolute value of the slope of the first segment is equal to the absolute value of the slope of the second segment, and the polarity of the slope of the first segment is opposite to the polarity of the slope of the second segment.
The image sensor of claim 12, wherein the first segment is increasing, and the second segment is decreasing.
The image sensor according to claim 11, wherein when the number of times that the slope generator selects the sampling is four times, the slope signal generated by the slope generator includes consecutive first segment, second segment, The third section and the fourth section, wherein the absolute values of the slopes of the first section, the second section, the third section, and the fourth section are equal, and the first section and the third section The polarities of the slopes of the second section and the fourth section are the same, and the polarities of the slopes of the first section and the third section are the same as those of the second section and The polarity of the slope of the fourth segment is opposite.
15. The image sensor of claim 14, wherein the first segment and the third segment are both increasing, and the second segment and the fourth segment are both decreasing.
The image sensor according to claim 11, wherein the bit resolution of the ramp signal generated by the ramp generator when the number of sampling times is two is four The bit resolution of the ramp signal generated at the second time is twice the bit resolution.
3. The image sensor of claim 1, wherein the gain value is negatively related to the intensity of the light.
A chip, characterized in that it comprises:

A gain amplifier, coupled to the pixel, is used to adjust the gain value according to the intensity of the light sensed by the pixel, and amplify the analog sensing signal based on the gain value to generate a gain analog sensing signal, wherein the pixel passes the sensing Measuring the light to generate the analog sensing signal; and

An analog-to-digital converter, coupled to the gain amplifier, for sampling the post-gain analog sensing signal using correlated multi-sampling technology, and converting the post-gain analog sensing signal into a digital sensing signal,

Wherein the number of times of sampling is changed in real time according to the analog sensing signal.
The chip of claim 18, wherein the pixels are provided in the chip.
An electronic device, characterized in that it comprises:

The image sensor according to any one of claims 1-17.