CN102143332A - Standard complementary metal oxide semiconductor (CMOS) process-based color image sensor - Google Patents

Abstract

A color image sensor based on a standard CMOS process, comprising: a color pixel unit array; an analog input end of a noise removal module is connected to an output end of the color pixel unit array; an input end of a buffer is connected to an output of the noise removal module terminal connection, used for buffering and parallel-serial conversion of the output signal of the noise removal module; the first output terminal of a digital controller and a digital processor is connected with the input terminal of the color pixel unit array, and the second output terminal of the digital controller It is connected with the digital input terminal of the noise removal module, and the digital control terminal of the digital processor is connected with the fourth output terminal of the digital controller for processing the digital image signal output by the analog-to-digital converter and converting the signal into image information output ; The analog input end of an analog-to-digital converter is connected to the output end of the buffer, its digital input end is connected to the third output end of the digital controller, and the output end of the analog-to-digital converter is connected to the analog input end of the digital processor, The analog signal for the output of the buffer is converted to a digital signal.

Description

Color image sensor based on standard CMOS process

technical field

The invention relates to the technical field of semiconductor CMOS image sensors, in particular to the technical field of a metal grating color image sensor based on a standard CMOS process.

Background technique

Semiconductor color image sensors have been developing toward high integration and low cost, and have a huge market demand. At present, the most widely used semiconductor color image sensors include color filter array (CFA-Color Filter Array) image sensor, thin film technology (TFA-Thin film on ASIC) image sensor and filterless color CMOS image sensor under Foveon X3 technology ( FCS-Filterless Color Sensor).

The color filter image sensor and the thin-film technology image sensor add a Bayer filter to the photosensitive unit. Color filter optics used to select the desired radiation band fall into two categories: color filters and thin-film filters. Color filters are sheets of flat glass or gelatin of various colors. Thin-film filters are divided into two types: thin-film absorption filters and thin-film interference filters. The former is on a specific material substrate, using chemical etching to make the absorption line just at the required wavelength. The latter is to alternately form a metal-dielectric-metal film with a certain thickness with a high or low refractive index, or an all-dielectric film, on a certain substrate by vacuum coating. Foveon X3 technology is a CMOS image sensor technology that provides three primary colors with a single pixel. The photosensitive unit of X3 technology is similar to silver salt color film. It consists of three layers of photosensitive elements stacked vertically, and different layers absorb different wavelengths of color incident light. However, these color image sensors need to add other processes on the basis of standard CMOS processes or non-standard CMOS processes that require adjustment of process parameters. The main disadvantages of these complicated process flow limit the development of high integration and low cost of semiconductor color image sensor.

Contents of the invention

The main purpose of the present invention is to provide a color image sensor based on a standard CMOS process, which has stronger process compatibility, higher integration, excellent system compatibility, and lower cost. It is especially suitable for integration in image processing vision chips, and is used in real-time tracking of high-speed moving targets, robot vision systems, image recognition, intelligent transportation, automatic product quality inspection of production lines, and various intelligent toys and other fields.

The invention provides a color image sensor based on a standard CMOS process, comprising:

A color pixel unit array, used to collect the original information of the incident light, and convert the collected color image light signal into an electrical signal;

A noise removal module, the analog input end of the noise removal module is connected to the output end of the color pixel unit array, which is used to eliminate the fixed pattern noise generated when the color pixel unit array collects color images;

A buffer, the input end of the buffer is connected to the output end of the noise removal module, and is used for output signal buffering and parallel-to-serial conversion of the noise removal module;

A digital controller and a digital processor, the first output of the digital controller is connected to the input of the color pixel unit array, the second output of the digital controller is connected to the digital input of the noise removal module, the digital processing The digital control terminal of the processor is connected with the fourth output terminal of the digital controller, and the output terminal of the digital processor outputs the processed image information, which is used to process the digital image signal output by the analog-to-digital converter and convert the signal into an image information output;

An analog-to-digital converter, the analog input of the analog-to-digital converter is connected to the output of the buffer, the digital input of the analog-to-digital converter is connected to the third output of the digital controller, and the output of the analog-to-digital converter The terminal is connected with the analog input terminal of the digital processor, and is used for converting the analog signal output by the buffer into a digital signal.

The color pixel unit array described therein is arranged in a Bayer mosaic pattern, and each color pixel unit includes four metal grating photodiode units, one red, two green, and one blue metal grating filter unit.

The metal grating photodiode unit is composed of a CMOS process photodiode layer and a two-dimensional metal grating layer.

The metal grating photodiode unit is directly formed on the photodiode layer by a two-dimensional metal grating layer. The two-dimensional metal grating layer is composed of the first metal layer of the standard process used. The metal grating period value is determined by the grating interval value and the metal grating The two-dimensional metal grating period of different period values realizes the filtering of different color wavelengths, and the two-dimensional metal grating layers of three different colors of red, green and blue period values are used as the red, green and blue of the color image sensor respectively. Blue metallic grating structure.

The analog-to-digital converter described therein is composed of a sample-and-hold device, a sampling amplifier, an error-correcting code, a gating clock, and a power-off part. Redundancy and error-correcting coding techniques are used to improve the accuracy requirements of the analog-to-digital converter. , the digital signal output by the digital controller respectively controls the gate control clock and the power off, realizes the clock distribution of each module when the analog-to-digital converter is working normally and cuts off the power when it is not working, thereby reducing the power consumption of the analog-to-digital converter.

The digital processor is composed of an arithmetic logic unit, a line processor and a memory, and the digital processor completes color image algorithm processing, and is suitable for expanding the requirements of visual chip color image processing.

As can be seen from the foregoing technical solutions, the present invention has the following beneficial effects:

1. The color image sensor provided by the present invention can be manufactured by using a wide range of standard CMOS processes, and the circuits can be implemented in a chip. The system structure is simple and easy to expand, with high integration and low cost.

2. In the color image sensor provided by the present invention, the metal grating photodiode unit is composed of a photodiode layer and a two-dimensional metal grating layer. The structure of the device is simple, the use of complex process layers is reduced, and the projection rate and absorption rate of incident light are improved.

3. In the color image sensor provided by the present invention, the noise removal module is composed of a noise removal circuit and a gain amplifier. The fixed mode noise elimination and signal dynamic range adjustment of the color image sampling signal can be realized, and the color image quality can be improved.

4. In the color image sensor provided by the present invention, since the analog-to-digital converter adopts redundancy and error correction coding technology, the accuracy of the analog-to-digital converter is improved, thereby improving the quality requirements of the color image. The gate control clock and power supply of the analog-to-digital converter are turned off to realize the clock distribution of each module when the analog-to-digital converter is in normal operation and the power supply is cut off when the analog-to-digital converter is not working, thereby reducing the power consumption of the analog-to-digital converter.

5. In the color image sensor provided by the present invention, the digital processor is composed of an arithmetic logic unit, a line processor and a memory. It is beneficial to complete the basic algorithm processing of color images, and is suitable for expanding the complex algorithm requirements of color image processing of visual chips.

6. The color image sensor based on the standard CMOS process provided by the present invention is particularly suitable for being integrated in an image processing vision chip, and is applied to real-time tracking of high-speed moving targets, robot vision systems, image recognition, intelligent transportation, automatic product quality detection of production lines and various Intelligent toys and other fields.

Description of drawings

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings, wherein:

Fig. 1 is a system block diagram of a color image sensor based on a standard process provided by the present invention;

Fig. 2 is a system structure diagram (based on Fig. 1) of a color image sensor based on a standard process provided by the present invention;

FIG. 3 is a schematic diagram of a metal grating photodiode unit 221 provided by the present invention (based on FIG. 2 );

FIG. 4 is the characteristic curve of the metal grating photodiode unit 221 provided by the present invention: FIG. 4(a) is the photodiode correlation quantum efficiency, and FIG. 4(b) is the transmittance after linear conversion (based on FIG. 2 ).

Detailed ways

Please refer to shown in Fig. 1, the present invention provides a kind of color image sensor based on standard CMOS process, comprising:

A color pixel unit array 10 is used to collect the original information of the incident light, and convert the collected color image optical signal into an electrical signal; the color pixel unit array 10 is arranged in a Bayer mosaic pattern, and each color pixel unit 21 It includes four metal grating photodiode units 221, which are one red, two green, and one blue metal grating filter unit. The metal grating photodiode unit 221 consists of a CMOS process photodiode layer 223 and a two-dimensional metal grating layer 224 Composed, the metal grating photodiode unit 221 is directly formed on the photodiode layer 223 by a two-dimensional metal grating layer 224, the two-dimensional metal grating layer 224 is composed of the first metal layer of the standard process used, and the period value of the metal grating is given by The grating interval value and the metal layer width value are composed. Two-dimensional metal grating periods with different period values can filter different color wavelengths. Two-dimensional metal grating layers 224 with three different colors of red, green and blue period values are respectively used as color images. The red, green and blue metal grating structure of the sensor; based on the system block diagram of the color image sensor based on the standard process described in FIG. 1, FIG. 2 shows the system structure diagram of the color image sensor based on the standard process provided by the present invention. Wherein N represents the size of the color pixel unit array 10, and 2×2 pixels form a color pixel unit 21, including one red, two green and a blue metal grating photodiode unit 221, then the size of the color pixel unit array is (N /2)×(N/2). Based on the structural diagram of the color image sensor system based on the standard process described in FIG. 2 , FIG. 3 shows a schematic diagram of the metal grating photodiode unit 221 provided by the present invention. It mainly includes two parts from bottom to top: photodiode layer 223 and two-dimensional metal grating layer 224 . On top is the passivation protection layer of the standard CMOS process. The 2D metal grating layer 224 is formed from the first metal layer using standard processes. The metal grating period value (W _p ) is composed of the grating interval value (W _g ) and the metal layer width value. Two-dimensional metal grating layers 223 (W _p , W _g ) of three different colors of red, green and blue periodic values serve as red, green and blue metal grating filter units of the color image sensor respectively. Based on the structural diagram of the color image sensor system based on the standard process described in FIG. 2 , FIG. 4 shows the characteristic curve of the two-dimensional metal grating photodiode 221 provided by the present invention. Figure 4(a) shows the photodiode-related quantum efficiency. Figure 4(b) shows the transmittance curve after linear transformation by 3×3 matrix. It can be seen that the two-dimensional metal grating color pixel unit 21 provided by the present invention can realize red, green and blue metal grating filtering;

A noise removal module 11, the analog input end of the noise removal module 11 is connected to the output end of the color pixel unit array 10, and is used to eliminate fixed pattern noise and signal dynamic range adjustment generated when the color pixel unit array 10 collects a color image;

A buffer 12, the input end of the buffer 12 is connected to the output end of the noise removal module 11, and is used for buffering and parallel-to-serial conversion of the output signal of the noise removal module 11;

A digital controller 13 and a digital processor 15, the first output of the digital controller 13 is connected to the input of the color pixel unit array 10, the second output of the digital controller 13 is connected to the digital input of the noise removal module 11 The digital control terminal of the digital processor 15 is connected with the fourth output terminal of the digital controller 13. The digital controller 13 is used to provide digital control instructions to the color pixel unit array 10 , the noise removal module 11 , the analog-to-digital converter 14 and the digital processor 15 . The output terminal of the digital processor 15 outputs processed image information, which is used to process the digital image signal output by the analog-to-digital converter 14, and convert the signal into image information output; the digital processor 15 is composed of an arithmetic logic unit , row processor and memory form, digital processor 15 completes color image algorithm processing, and is suitable for expanding the requirement of visual chip color image processing;

An analog-to-digital converter 14, the analog input of the analog-to-digital converter 14 is connected to the output of the buffer 12, the digital input of the analog-to-digital converter 14 is connected to the third output of the digital controller 13, the analog The output end of the digital converter 14 is connected with the analog input end of the digital processor 15, and the analog signal used for buffer 12 output is converted into a digital signal; Code, gated clock and power off parts, using redundancy and error correction coding technology to improve the precision requirements of the analog-to-digital converter 14, the digital signal output by the digital controller 13 respectively controls the gated clock and power off cut off, realize the clock distribution of each module when the analog-to-digital converter 14 works normally and cut off the power supply when it is not working, thereby reducing the power consumption of the analog-to-digital converter 14;

The working principle of the color image sensor based on the standard technology is as follows: the incident light is transmitted to the color pixel unit array 10 and an analog voltage signal is collected. The N×N image signals are sequentially read into the noise removal module 11 and the buffer 12 in a row-parallel mode through the column decoder according to the instructions of the digital controller 13 to perform noise removal processing, signal dynamic range adjustment and parallel serialization. convert. Finally, the digital signal read into the digital-to-analog converter 14 for digital-to-analog conversion is serially output to the digital processor 15 to complete color image algorithm processing. The sampling, conversion and processing of the incident light color image signal are coordinated and completed by the instructions of the digital controller 13 .

The system block diagram and implementation circuit diagram described above have further described the purpose of the present invention, technical solutions and beneficial effects in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (6)

1. A color image sensor based on a standard CMOS process, comprising: A color pixel unit array, used to collect the original information of the incident light, and convert the collected color image light signal into an electrical signal; A noise removal module, the analog input end of the noise removal module is connected to the output end of the color pixel unit array, which is used to eliminate the fixed pattern noise generated when the color pixel unit array collects color images; A buffer, the input end of the buffer is connected to the output end of the noise removal module, and is used for output signal buffering and parallel-to-serial conversion of the noise removal module; A digital controller and a digital processor, the first output of the digital controller is connected to the input of the color pixel unit array, the second output of the digital controller is connected to the digital input of the noise removal module, the digital processing The digital control terminal of the processor is connected with the fourth output terminal of the digital controller, and the output terminal of the digital processor outputs the processed image information, which is used to process the digital image signal output by the analog-to-digital converter and convert the signal into an image information output; An analog-to-digital converter, the analog input of the analog-to-digital converter is connected to the output of the buffer, the digital input of the analog-to-digital converter is connected to the third output of the digital controller, and the output of the analog-to-digital converter The terminal is connected with the analog input terminal of the digital processor, and is used for converting the analog signal output by the buffer into a digital signal. 2. The color image sensor based on standard CMOS technology according to claim 1, wherein said color pixel unit array adopts Bayer mosaic pattern arrangement to form, and each color pixel unit comprises 4 metal grating photodiode units, respectively one Red, two green, one blue metal grating filter unit. 3. The color image sensor based on a standard CMOS process according to claim 2, wherein the metal grating photodiode unit is composed of a CMOS process photodiode layer and a two-dimensional metal grating layer. 4. The color image sensor based on standard CMOS technology according to claim 2, wherein said metal grating photodiode unit is directly formed on the photodiode layer by a two-dimensional metal grating layer, and the two-dimensional metal grating layer is formed by the standard process used The metal grating period value is composed of the grating interval value and the metal layer width value. The two-dimensional metal grating period with different period values can filter different color wavelengths. Three different colors of red, green and blue The two-dimensional metal grating layers with periodic values serve as the red, green and blue metal grating structures of the color image sensor respectively. 5. The color image sensor based on standard CMOS technology according to claim 1, wherein said analog-to-digital converter is made up of sample holder, sampling amplifier, error correction code, gating clock and power supply shut-off part, adopts Redundancy and error correction coding technology improve the accuracy requirements of the analog-to-digital converter. The digital signal output by the digital controller controls the gate control clock and power off respectively, and realizes the clock distribution of each module and the normal operation of the analog-to-digital converter. The power supply is cut off during non-operation, thereby reducing the power consumption of the analog-to-digital converter. 6. The color image sensor based on standard CMOS technology according to claim 1, wherein said digital processor is composed of arithmetic logic unit, line processor and memory, and digital processor completes color image algorithm processing, and is suitable for extending vision Chip color image processing requirements.

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