CN113340435A - Infrared thermal imaging method and infrared detector system - Google Patents

Abstract

The application discloses infrared thermal imaging method and infrared detector system, through adopting dislocation pixel mode of arranging, acquire the first pixel that receives the diffraction limit influence less, pass through the algorithm according to a plurality of first pixels and establish the second pixel, the influence of diffraction limit to the spatial resolution restraint among the infrared thermal imaging process has been avoidd, can improve imaging device spatial resolution under the condition of not reducing the pixel size, and simultaneously, the pixel need not to adopt the three-dimensional technology of high difficulty to realize, has high stability and yield, in addition, need not to adopt the high-cost lens design of high difficulty in the optics realization.

Description

Infrared thermal imaging method and infrared detector system

Technical Field

The present application relates to the field of image sensor technologies, and in particular, to an infrared thermal imaging method and an infrared detector system.

Background

With the continuous development of infrared thermal imaging technology, in order to improve the spatial resolution of an infrared camera, the size of pixels in a detector becomes smaller and smaller, so that the number of pixels in the detector is increased, and the distance between rows and columns in a pixel array is reduced. However, as the pitch of the pixels in the sensor becomes smaller and smaller, the problem of continuing to shrink due to the diffraction limit in the prior art has been faced. The diffraction limit is that when a beam of light is focused on a single pixel, it rapidly defocuses at the pixel surface due to diffraction, forming a cone of light in cross section, i.e., an airy disk. When the center of one airy disk falls on the first minima of the other airy disk, the two airy disks can be barely resolved, which is the theoretical resolution limit, the rayleigh criterion. According to Rayleigh criterion, the size of the pixel is calculated to be not less than the airy disk radius r =1.22 lambda F #.

Therefore, in the process of improving the spatial resolution of the infrared thermal imaging device by reducing the size of the pixels, the pixel array in the infrared detector faces the following problems: 1. when the pixel is reduced to a certain size, the signals of adjacent pixels can generate crosstalk due to the constraint action of the diffraction limit, and the effect of improving the spatial resolution cannot be achieved. 2. For the small-size pixels, a three-dimensional process is needed to increase the absorption area in process implementation, but the use of the three-dimensional process increases the process complexity and reduces the yield. 3. Under the condition that the infrared wavelength lambda is constant, if the size of a pixel is required to be reduced, in order to break through the influence limitation of the diffraction limit, the optical F number needs to be adjusted, and the manufacturing difficulty and the cost of an optical system are greatly improved.

Disclosure of Invention

In view of this, the present application provides an infrared thermal imaging method and an infrared detector system, which avoid the influence of the diffraction limit on the spatial resolution, and improve the spatial resolution of the imaging device.

In order to solve the technical problem, the following technical scheme is adopted in the application:

a first aspect of the present application provides a method of infrared thermal imaging, the method comprising:

s1, receiving infrared heat radiation by a pixel array to generate variable resistance, wherein the pixel array comprises a plurality of diamond-shaped pixels, each pixel is provided with a diagonal line parallel to the horizontal direction, the distance between every two adjacent pixels in the horizontal direction is the length of the diagonal line in the horizontal direction, each pixel is provided with a diagonal line parallel to the vertical direction, and the distance between every two adjacent pixels in the vertical direction is the length of the diagonal line in the vertical direction;

s2, reading out the pixel analog signals by a reading circuit according to the changed resistance, and sending the pixel analog signals to an analog-digital conversion circuit, wherein the pixels in the same column in the reading circuit are connected with the same output end;

s3, the analog-digital conversion circuit converts the pixel analog signal into a pixel digital signal and sends the pixel digital signal to the image signal processor;

and S4, the image signal processor processes the pixel digital signal to obtain a first pixel, and establishes a second pixel at the intersection point position of four adjacent pixels according to four first pixels corresponding to the four adjacent pixels.

Optionally, each column in the readout circuit comprises: bias voltage, a field effect transistor, an integrator, a sampling capacitor and a row selection switch.

Optionally, the reading out of the pixel analog signal by the reading out circuit according to the changed resistance specifically includes: and the row selection switches of the pixels in two adjacent rows are switched on each time, and the resistance changed by the pixels in two adjacent rows is read out in the form of analog signals.

A second aspect of the present application provides an infrared detector system, the system comprising:

the pixel array is used for receiving resistance which is changed by infrared heat radiation, and comprises a plurality of rhombic pixels, each pixel is provided with a diagonal line which is parallel to the horizontal direction, the distance between every two adjacent pixels in the horizontal direction is the length of the diagonal line in the horizontal direction, each pixel is provided with a diagonal line which is parallel to the vertical direction, and the distance between every two adjacent pixels in the vertical direction is the length of the diagonal line in the vertical direction;

the reading circuit is used for reading out the pixel analog signals according to the changed resistance and sending the pixel analog signals to the analog-digital conversion circuit, and pixels in the same column in the reading circuit are connected with the same output end;

the analog-digital conversion circuit is used for converting the pixel analog signal into a pixel digital signal and sending the pixel digital signal to an image signal processor;

and the image signal processor is used for processing the pixel digital signals to obtain first pixels and establishing second pixels at the intersection points of the four adjacent pixels according to the four first pixels corresponding to the four adjacent pixels.

Optionally, each column in the readout circuit comprises: bias voltage, a field effect transistor, an integrator, a sampling capacitor and a row selection switch.

Compared with the prior art, the method has the following beneficial effects:

based on the technical scheme, the infrared thermal imaging method and the infrared detector system provided by the application have the advantages that firstly, the first pixels less affected by the diffraction limit are obtained by adopting a unique staggered pixel arrangement mode, the second pixels are established according to a plurality of first pixels through an algorithm, the influence of the diffraction limit on the spatial resolution constraint in the infrared thermal imaging process is avoided, and the spatial resolution of the imaging equipment can be improved under the condition of not reducing the size of the pixels; secondly, the absorption area is not required to be improved by adopting a high-difficulty three-dimensional process because the size of the pixel is not required to be reduced, so that the effect of improving the yield is achieved, the stability of the infrared detector is ensured, and the cost can be reduced; thirdly, the pixel size does not need to be reduced, so that the F number in the optical design does not need to be adjusted, the difficulty and the cost of the optical design are reduced, and the effect of reducing the cost of an application system is finally achieved.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without creative efforts.

Fig. 1 is a schematic diagram of pixel array arrangement in an infrared detector in the prior art.

Fig. 2 is a schematic diagram of arrangement of a pixel array in an infrared detector provided in an embodiment of the present application.

Fig. 3 is a schematic diagram of a limit of a resolvable light spot of a pixel array in an infrared detector provided by an embodiment of the application.

Fig. 4 is a schematic structural diagram of a readout circuit according to an embodiment of the present application.

Fig. 5 is a schematic layout diagram of a reconstruction pixel provided in an embodiment of the present application.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.

As shown in fig. 1, fig. 1 is a layout of an infrared detector pixel array in the prior art, pixels are continuously arranged in a horizontal direction and a vertical direction, the distance between adjacent pixels in the horizontal direction and the vertical direction is equal to L, the limit of the pixel distance L in the detector is about 12 microns as long-wave infrared wavelength is 8-14 microns, and the calculation according to rayleigh criterion indicates that when the pixel distance is smaller than the value, signal crosstalk occurs between adjacent pixels due to the influence of diffraction limit constraint, which causes the spatial resolution of the camera equipment to be reduced.

Based on this, in order to solve the above technical problem, the present application provides an infrared thermal imaging method and an infrared detector system, and the method avoids the influence of the diffraction limit on the spatial resolution by changing the physical arrangement mode of the pixels without reducing the size of the pixels, and does not need to adopt a high-difficulty stereo process to improve the absorption area, thereby achieving the effect of improving the yield, ensuring the stability of the infrared detector, and reducing the cost, and without adjusting the F number in the optical design, thereby reducing the difficulty and the cost of the optical design, and finally achieving the effect of reducing the cost of the application system.

Specific embodiments of the infrared thermal imaging method and the infrared detector system provided in the present application are described in detail below with reference to the accompanying drawings.

In an embodiment of the present application, an infrared thermal imaging method is provided, which includes the specific steps of:

s1: the pixel array receives infrared heat radiation to generate variable resistance, the pixel array comprises a plurality of diamond-shaped pixels, each pixel is provided with a diagonal line parallel to the horizontal direction, the distance between every two adjacent pixels in the horizontal direction is the length of the diagonal line parallel to the horizontal direction, each pixel is provided with a diagonal line parallel to the vertical direction, and the distance between every two adjacent pixels in the vertical direction is the length of the diagonal line parallel to the vertical direction.

Specifically, the physical arrangement mode of the pixel array is as shown in fig. 2, and compared with the pixel arrangement mode in the prior art, the pixel array provided by the application realizes staggered arrangement by rotating the pixels by 45 degrees, and the pixel array realizing staggered arrangement causes changes in two aspects of pixel spacing and row-column spacing. On one hand, the row-column spacing of the pixel array after dislocation is reduced to 1.414L/2 from L, and the reduction of the row-column spacing is the basis for improving the resolution capability; on the other hand, the horizontal and vertical distances of the pixel are increased from L to 1.414L, and as the horizontal and vertical distances of the pixel are less affected by diffraction limit, the airy disk can be expanded to 1.414 times the size of the pixel after the horizontal and vertical distances of the pixel are increased, such as a dotted line light spot in FIG. 3, the light spot is not affected by diffraction limit in the horizontal and vertical directions, the horizontal and vertical directions are imaging sensitive directions, and the 45-degree direction is not imaging sensitive direction. Therefore, after the pixels are arranged in a staggered mode, the method has the following advantages: firstly, the single pixel is facilitated to collect more energy in the horizontal and vertical directions and wide spectrum energy, and the effective energy density is improved; secondly, the aperture of the optical system can be smaller, the design difficulty of the lens is reduced, and the cost is reduced; finally, the absorbable infrared limit wavelength is increased.

S2: and the reading circuit reads out the pixel analog signals according to the changed resistance and sends the pixel analog signals to the analog-digital conversion circuit, and pixels in the same column in the reading circuit are connected with the same output end.

Specifically, a schematic structural diagram of a readout circuit provided by the present application is shown in fig. 4, where the readout circuit is composed of multiple columns, each column of readout circuits is electrically connected to all pixels in the column, and each column of readout circuits includes: the circuit comprises a bias voltage Vsk, an auxiliary resistor Rd, bias voltages Veb and Vfrid, transistors PM and NM, an integrator, a sampling capacitor, a row selection switch and a pixel equivalent resistor Rs. After the pixels receive infrared waves radiated by an object, the resistance changes, the row selection switches of two adjacent rows of pixels are switched on each time, the resistance changed by the pixels of two adjacent rows is read out, and the read-out signals are in an analog signal format.

An analog-to-digital conversion circuit converts the pixel analog signal into a pixel digital signal, and sends the pixel digital signal to an image signal processor S3.

Specifically, after the readout circuit outputs the pixel analog signal, it is sent to an analog-to-digital conversion circuit, which converts the analog signal into a digital signal and outputs it to an image processor.

And S4, the image signal processor processes the pixel digital signal to obtain a first pixel, and establishes a second pixel at the intersection point position of four adjacent pixels according to four first pixels corresponding to the four adjacent pixels.

Specifically, after receiving the digital signal, the image processor executes a series of algorithms to process the digital signal, including but not limited to linear correction, noise removal, dead pixel removal, and other algorithm processes on the image. As shown in fig. 5, the image processor establishes a second pixel at the intersection of four adjacent pixels by running a pixel reconstruction algorithm based on four first pixels corresponding to the four adjacent pixels. Because the four pixels at the position are arranged in a staggered mode, the airy disk can be expanded to the size of 1.414 times of the pixel, the first pixels corresponding to the four pixels are information which is less affected by diffraction limit, and the second pixels established by proper algorithm have higher fidelity. After the second pixel is established, the pixel array is changed into a full pixel matrix with the row-column spacing of 1.414L/2, compared with the prior art, the pixel spacing is reduced from L to 1.414L/2 by adjusting the physical arrangement mode of the pixels under the condition of not changing the size of the pixels, the pixel spacing is reduced, the resolution capability is determined by the size of the pixel spacing, the number of the pixels is substantially reduced, but the effect of increasing the pixel density is achieved, and therefore the spatial resolution of the imaging system is improved.

The foregoing is only a preferred embodiment of the present invention, and although the present invention has been disclosed in the preferred embodiments, it is not intended to limit the present invention. Those skilled in the art can make numerous possible variations and modifications to the present teachings, or modify equivalent embodiments to equivalent variations, without departing from the scope of the present teachings, using the methods and techniques disclosed above. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.

Claims (5)

1. A method of infrared thermal imaging, the method comprising:

s1, receiving infrared heat radiation by a pixel array to generate variable resistance, wherein the pixel array comprises a plurality of diamond-shaped pixels, each pixel is provided with a diagonal line parallel to the horizontal direction, the distance between every two adjacent pixels in the horizontal direction is the length of the diagonal line in the horizontal direction, each pixel is provided with a diagonal line parallel to the vertical direction, and the distance between every two adjacent pixels in the vertical direction is the length of the diagonal line in the vertical direction;

s2, reading out the pixel analog signals by a reading circuit according to the changed resistance, and sending the pixel analog signals to an analog-digital conversion circuit, wherein the pixels in the same column in the reading circuit are connected with the same output end;

s3, the analog-digital conversion circuit converts the pixel analog signal into a pixel digital signal and sends the pixel digital signal to the image signal processor;

and S4, the image signal processor processes the pixel digital signal to obtain a first pixel, and establishes a second pixel at the intersection point position of four adjacent pixels according to four first pixels corresponding to the four adjacent pixels.

2. The method of claim 1, wherein each column in the readout circuit comprises: bias voltage, a field effect transistor, an integrator, a sampling capacitor and a row selection switch.

3. The method of claim 2, wherein said readout circuitry reads out pixel analog signals in accordance with said varying resistance, in particular: and the row selection switches of the pixels in two adjacent rows are switched on each time, and the resistance changed by the pixels in two adjacent rows is read out in the form of analog signals.

4. An infrared detector system, comprising:

the pixel array is used for receiving resistance which is changed by infrared heat radiation, and comprises a plurality of rhombic pixels, each pixel is provided with a diagonal line which is parallel to the horizontal direction, the distance between every two adjacent pixels in the horizontal direction is the length of the diagonal line in the horizontal direction, each pixel is provided with a diagonal line which is parallel to the vertical direction, and the distance between every two adjacent pixels in the vertical direction is the length of the diagonal line in the vertical direction;

the reading circuit is used for reading out the pixel analog signals according to the changed resistance and sending the pixel analog signals to the analog-digital conversion circuit, and pixels in the same column in the reading circuit are connected with the same output end;

the analog-digital conversion circuit is used for converting the pixel analog signal into a pixel digital signal and sending the pixel digital signal to an image signal processor;

and the image signal processor is used for processing the pixel digital signals to obtain first pixels and establishing second pixels at the intersection points of the four adjacent pixels according to the four first pixels corresponding to the four adjacent pixels.

5. The system of claim 4, wherein each column in the readout circuit comprises: bias voltage, a field effect transistor, an integrator, a sampling capacitor and a row selection switch.

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