KR20200042725A - Evaluation method of noise characteristics in lens-free cmos photonic array sensor - Google Patents

Abstract

The present invention discloses a method for evaluating noise characteristics of a lens-free CMOS photon array sensor. The method comprises: a step of setting an exposure time and an analog amplification rate according to a test item and an evaluation method; a step of checking uniformity and maximum roughness of a measurement system; a step of placing a sensor board at a distance of about 1.5 M from a light source of the measurement system; a step of modifying the exposure time and analog gain according to the test item and the evaluation method; a step of capturing a raw image according to the evaluation method and the test item; a step of measuring test data according to the evaluation method and the test item; and a test report.

Description

Method for evaluating noise characteristics of a lens-free CMOS photon array sensor {EVALUATION METHOD OF NOISE CHARACTERISTICS IN LENS-FREE CMOS PHOTONIC ARRAY SENSOR}

The present invention relates to a method for evaluating noise characteristics of a lens-free CMOS photon array sensor.

The CMOS photon array sensor detects information in the form of light or electromagnetic waves and generates an image that displays the information. The CMOS photon array sensor consists of an integrated circuit that detects the information and converts the information into a current or voltage corresponding to the information. The current or voltage corresponding to the above information is later converted into digital data.

When a new CMOS photon array sensor was developed, the sensor's capabilities depended on a number of factors (microlens, color filter, photodiode, fill factor, circuit, sensor pixel size, sensor technology, manufacturing procedure). Therefore, a problem occurs that noise of the CMOS photon array sensor is generated by a number of factors.

Patent Publication No. 10-2015-0096728, 2015.07.07

The problem to be solved by the present invention is to provide a method for evaluating noise characteristics of a lens-free CMOS photon array sensor.

The problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

The noise characteristic evaluation method of the lens-free CMOS photon array sensor according to an aspect of the present invention for solving the above-described problems comprises setting exposure time and analog amplification factor according to test items and evaluation methods, and measuring system uniformity and maximum illuminance. Checking, placing the sensor board at a distance of about 1.5M from the light source of the measurement system, correcting the exposure time and analog gain according to the test item and evaluation method, capturing the raw image according to the evaluation method and test item Includes steps to measure test data according to evaluation methods and test items, and test reports.

Other specific matters of the present invention are included in the detailed description and drawings.

According to the noise characteristic evaluation method of the lens-free CMOS photon array sensor of the present invention, the noise characteristic of the lens-free CMOS photon array sensor can be measured.

The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

1 is a conceptual diagram of a CMOS photon array sensor according to an embodiment of the present invention.
2 is a conceptual diagram of a CMOS photon array sensor according to an embodiment of the present invention.
3 is a conceptual diagram of a measurement system of a CMOS photon array sensor according to an embodiment of the present invention.
4 is a flowchart of a method for evaluating noise characteristics of a CMOS photon array sensor according to an embodiment of the present invention.
5 is a test item embodiment of a measurement system of a CMOS photon array sensor according to an embodiment of the present invention.
6 is an example of an evaluation method of a measurement system of a CMOS photon array sensor according to an embodiment of the present invention.
7 is an example of a test report of a measurement system of a CMOS photon array sensor according to an embodiment of the present invention.

Advantages and features of the present invention, and methods for achieving them will be clarified with reference to embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, only the present embodiments allow the disclosure of the present invention to be complete, and are common in the technical field to which the present invention pertains. It is provided to fully inform the skilled person of the scope of the present invention, and the present invention is only defined by the scope of the claims.

The terminology used herein is for describing the embodiments and is not intended to limit the present invention. In this specification, the singular form also includes the plural form unless otherwise specified in the phrase. As used herein, “comprises” and / or “comprising” does not exclude the presence or addition of one or more other components other than the components mentioned. Throughout the specification, the same reference numerals refer to the same components, and “and / or” includes each and every combination of one or more of the mentioned components. Although "first", "second", etc. are used to describe various components, it goes without saying that these components are not limited by these terms. These terms are only used to distinguish one component from another component. Therefore, it goes without saying that the first component mentioned below may be the second component within the technical spirit of the present invention.

Unless otherwise defined, all terms (including technical and scientific terms) used in the present specification may be used as meanings commonly understood by those skilled in the art to which the present invention pertains. In addition, terms defined in the commonly used dictionary are not ideally or excessively interpreted unless explicitly defined.

Terms and definitions

Noise: Unwanted changes in the response of an imaging system

Spatial noise: consistent unwanted deformation for all exposures

Temporal noise: sensor dark current, photon shot noise, random noise due to analog processing and quantization

Illuminance: total radiant intensity incident on the surface, spectral weighting according to human vision

Exposure index: A value that is inversely proportional to the exposure provided to the image sensor to obtain an image.

Uniformity: Uniformity of the image area expected to be uniform, i.e., the degree of uniformity without grain, streaks, banding, spot defects, etc.

Sharpness: the degree to which the edges of the image change quickly with minimal contrast (minimum blur)

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a conceptual diagram of a CMOS photon array sensor according to an embodiment of the present invention.

Referring to FIG. 1, the CMOS photon array sensor is composed of a photon output, a photodiode, a capacitor, and an analog-to-digital converter.

The CMOS photon array sensor detects information in the form of light or electromagnetic waves and generates an image that displays the information. The CMOS photon array sensor consists of an integrated circuit that detects the information and converts the information into a current or voltage corresponding to the information. The current or voltage corresponding to the above information is later converted into digital data.

When a new CMOS photon array sensor was developed, the sensor's capabilities depended on a number of factors (microlens, color filter, photodiode, fill factor, circuit, sensor pixel size, sensor technology, manufacturing procedure). Many of these factors are the main sources of noise in CMOS photon array sensors.

2 is a conceptual diagram of a CMOS photon array sensor according to an embodiment of the present invention.

Referring to Figure 2, the CMOS photon array sensor visualizes the image with photon, sensor, ISP, OS and CPU / GPU flows.

Noise depends on various factors, such as micro lenses, color filters, photodiodes, fill factors, circuits, sensor pixel size, sensor technology and manufacturing.

The image quality (including noise reduction) after image signal processing depends on the performance of the ISP block or pipeline depending on the ISP provider or ISP provider.

Noise from CMOS photon sensor

Spatial noise: spatial variation in pixel output, resulting from unpredictable position and time

1) Fixed Pattern Noise (FPN): Static change in the offset of a dark signal between pixels from pixel to pixel. Change in offset and gain, constant deviation between read channel offset and amplification

2) Photo-Response Nonuniformity: Non-uniformity of spatial variation of pixel values for a specific lighting level (e.g. 50% saturation level)

3) Shading: Static change of the incident angle according to the change of the main ray angle and the carrying capacity value

Temporal noise: Random fluctuations in a signal that fluctuate over time. Occurrence is location-based due to the underlying structure. Given the entire pipeline from photons to final image data, transient noise can be largely eliminated by the system's image signal processor.

1) Dark Current Shot Noise: Dark current shot noise is the result of a thermal randomly generated electron-hole pair in the dark.

2) Photon Shot Noise: Photon shot noise is due to the statistical difference between electron-hole pairs generated and excited due to the random arrival of photons colliding under lighting, and follows Poisson statistic statistics.

3) Read Noise: This is the result of various noise sources such as ADC noise, transient row noise and other noise sources.

4) Reset Noise: Noise sampled from the floating diffusion capacitor due to charge redistribution and capacitor uncertainty when the reset switch is turned on or off. However, reset noise is eliminated in modern CMOS image sensors using CDS technology.

3 is a conceptual diagram of a measurement system of a CMOS photon array sensor according to an embodiment of the present invention.

Referring to FIG. 3, the measurement system of the CMOS photon array sensor is composed of a parallel light system composed of a dark box including a light source and a jig, and a PC connected to the parallel light system.

3 shows the noise characteristic test conditions of a lensless CMOS photon array sensor and module.

Since noise does not change significantly with color temperature, noise can be measured and analyzed in one of the representative lights in the parallel light system of FIG. 3.

4 is a flowchart of a method for evaluating noise characteristics of a CMOS photon array sensor according to an embodiment of the present invention.

Referring to FIG. 4, a method for evaluating noise characteristics of a CMOS photon array sensor includes setting an exposure time and an analog amplification factor according to test items and evaluation methods, checking the uniformity and maximum illuminance of the measurement system, and measuring the sensor board of the measurement system. Step about 1.5M away from the light source, correcting exposure time and analog gain according to test items and evaluation methods, capturing raw images according to evaluation methods and test items, test data according to evaluation methods and test items It includes steps to measure and test reports.

5 is a test item embodiment of a measurement system of a CMOS photon array sensor according to an embodiment of the present invention.

Referring to FIG. 5, a test item of a measurement system of a CMOS photon array sensor includes fixed pattern noise (FPN), photo-response nonuniformity, and shading.

Referring to FIG. 5, fixed pattern noise (FPN), photo-response nonuniformity, and shading test images, light conditions, and detailed description are shown.

6 is an example of an evaluation method of a measurement system of a CMOS photon array sensor according to an embodiment of the present invention.

1) Step of separating the sensor board at a distance of about 1.5M from the light source with the maximum light source power (e.g. 70 u ux)

2) capturing the number of images (e.g. 10, 20) in a dark environment

3) Turn on the light source and maintain thermal stability for 10 minutes

4) capturing the light environment (50% of saturation level) and number of images for the saturation environment (e.g. 10, 20)

5) Calculating the average of all captured images for dark environment, light environment and saturation environment respectively

6) Result image for all three conditions.

FPN is the static variation of the offset of the dark signal from pixel to pixel.

7) PRNU is a spatial change in pixel values.

Glossary note

Dark (DARK): Average image of all images taken in dark environment, resulting image

LIGHT: Image of average of all images taken in a bright environment

Saturation: The resulting image by taking the average of all images taken in the saturation environment

STDEV: standard deviation

7 is an example of a test report of a measurement system of a CMOS photon array sensor according to an embodiment of the present invention.

Referring to FIG. 7, a test report of a measurement system of a CMOS photon array sensor includes test equipment and environmental specifications, a CMOS photon sensor specification, and a test report.

The steps of a method or algorithm described in connection with an embodiment of the present invention may be implemented directly in hardware, a software module executed by hardware, or a combination thereof. The software modules may include random access memory (RAM), read only memory (ROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), flash memory, hard disk, removable disk, CD-ROM, or It may reside on any type of computer readable recording medium well known in the art.

The embodiments of the present invention have been described above with reference to the accompanying drawings, but a person skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing its technical spirit or essential features. You will understand. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and not restrictive.

Claims (1)

Setting an exposure time and an analog amplification factor according to test items and evaluation methods;
Checking the uniformity and maximum roughness of the measurement system;
Placing the sensor board at a distance of about 1.5M from the light source of the measurement system;
Modifying exposure time and analog gain according to test items and evaluation methods;
Capturing the raw image according to the evaluation method and test items;
Measuring test data according to the evaluation method and test items; and
Test report included
Method for evaluating noise characteristics of a lens-free CMOS photon array sensor.

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