Method for dynamic correction for pixels of thermal image array

Abstract

To provide a method for dynamic correction for pixels of a thermal image array that solves the problem of pixel resistance non-uniformity, improves production yield, and expands a dynamic range of a read chip.SOLUTION: According to the present invention, a method for dynamic correction for pixels of a thermal image array, which is applied to correction of a bolometer at shipment from a factory, includes: an individual resistance calculation step of, at a reference temperature, sequentially providing a reference current to thermistors of all pixels in an image sensing array to measure corresponding resistance array values and recording the measured values into a memory; an individual current parameter calculation step of, on the basis of the resistance array values and a prescribed voltage value, respectively calculating current array values, and recording the calculated values into the memory; and a prescribed voltage value confirmation step of, at the reference temperature, when reading the individual pixel voltage value of the image sensing array, providing the individual current parameter corresponding to each pixel on the basis of the current array value, and confirming coincidence of the current parameter with the prescribed voltage value.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a compensation technique for thermal imaging array pixels, and more particularly to a dynamic correction method for thermal imaging array pixels. [Background technology]

[0002] Currently, when a bolometer is applied to an infrared thermal imaging device, it adopts a microarray structure as the infrared sensing architecture. In the fabrication of the chip, a bolometer focal plane array (Bolometer FPA) is fabricated above a read-out IC (Read-out IC - ROIC), and a multi-layered microelectromechanical system (MEMS) structure is created during the semiconductor manufacturing process. Each pixel on the image array is a single thermistor, and the basic principle of taking a thermal image is to use a compound film thermistor included in the MEMS structure to pass a constant current through it. When the temperature of the object to be measured changes, the resistance of the thermistor changes accordingly, so the output voltage also changes. By using an appropriate gain amplifier to output these voltage change values ​​(ΔV), the temperature change value (ΔT) can be inversely estimated, and by calculating the temperature change values ​​of all thermistors on the image array, the temperature distribution of the object to be measured can be obtained, and finally, the thermal image of the object to be measured can be combined through image processing.

[0003] Among them, the compound film materials that constitute the thermistor of the bolometer array generally include amorphous silicon, vanadium oxide (VOx), indium arsenide (InAsx), zinc oxide (ZnOx), etc. Due to their sensitivity, the most widely used material among them is vanadium oxide, followed by amorphous silicon, and other materials are rarely found in commercialized bolometers.

[0004] Since the thermistor in each pixel is formed of a compound material film, the film composition of each pixel cannot be made completely the same in the semiconductor coating process of film formation, and the error depends on the stability of the process. Taking vanadium oxide material as an example, x (the ratio of V and O) in VOx is controlled in the sputtering or evaporation process. Even if each pixel is controlled to have the same (almost the same) x as much as possible in the coating process and is considered to have the same material properties, the film thickness and area at each pixel position cannot be completely matched. As a result, due to physical and electrical properties, the voltage values ​​displayed by each pixel after a constant current is passed through them are significantly different. Currently, this non-uniformity is often reduced by using a compensation process. In the compensation process, the temperature range of the bolometer is often limited because the differences in characteristics between individual pixels are too large, and the differences in characteristics between pixels are too large, so it is often seen that the product yield cannot be effectively improved significantly. Therefore, commercially available bolometer array chips are often shipped with different sensing temperature ranges, and the selling price remains high.

[0005] The imaging principle of the bolometer array chip is basically to use a thermistor array to measure the temperature distribution of the environment or object and perform imaging. However, the characteristics of the thermistor change with different temperatures. Ideally, the thermistor characteristics in each pixel are completely identical, and the resistance of each thermistor is measured at several specific temperatures before the bolometer array chip is shipped, so that good imaging and temperature measurement can be realized in practice. However, in reality, there are still manufacturing process deviations in any precise semiconductor manufacturing process. Therefore, the thermistor distribution of the bolometer array chip is as shown in FIG. 1A. The bolometer array 10 has M×N pixels. When each pixel is fabricated, it has a specific resistance; for example, pixel 11-0-0, pixel 11-0-2, pixel 11-0-M, pixel 11-N-2, pixel 11-NM, etc. may have different corresponding resistances R(0,0), R(0,2), R(0,M), R(N,2), and R(N,M).

[0006] In the pixel array, the thermistor of each pixel has a different resistance value. Therefore, in the known art, based on the distribution map of the pixel array resistance value at the reference temperature, the resistance value with the largest distribution (the largest number) is taken as the reference resistance, and the reference resistance is used to calculate the appropriate current value (fixed current value) that the current source should provide. According to the formula V=IR (voltage=current×resistance), the fixed current value is used to calculate the output voltage of each P pixel, and then the temperature change is calculated based on the comparison of the voltage change amount at different temperatures and the reference temperature, and the subsequent imaging is performed. In this manner known in the art, after the constant current is outputted, the bolometer array chip will have an output voltage of the pixel array at a certain temperature, as shown in FIG. 1B, in the M×N pixels of the bolometer array 10, pixel 11-0-0, pixel 11-0-2, pixel 11-0-M, pixel 11-N-2, pixel 11-NM, etc., may have different corresponding resistances, so that the corresponding voltages V(0,0), voltage V(0,2), voltage V(0,M), voltage V(N,2), and voltage V(N,M) may be different after providing the constant current.

[0007] As can be seen from FIG. 1B, the problem with this known technique is that a pixel having a resistance value that is too different from the reference resistance will result in the following: A pixel with an output voltage that is too high will be oversaturated and become a so-called bright spot when the gain of the power amplifier is even slightly high. Conversely, a pixel with a voltage output that is too low will not receive a sufficient temperature change signal and will be a so-called dark spot when the gain is even slightly low. This significantly impairs the yield and sensitivity expression of the bolometer since the gain range that can be set is very narrow. These pixels that are easily oversaturated or have too low an output are sometimes called dead pixels, weak pixels, or blind pixels.

[0008] Many known techniques are used to compensate blind pixels after reading them out, so that the blind pixels are no longer blind. For example, patent CNA-101980283A discloses a dynamic blind pixel compensation method, which uses the values ​​of pixels adjacent to the blind pixel to compensate the blind pixel. Most of these compensation techniques only compensate for bright or dark spots, and cannot solve the problem of pixel resistance non-uniformity caused by the above manufacturing process.

[0009] Therefore, in the current huge market demand, the development of a solution to the problem of non-uniform pixel resistance caused by the manufacturing process of the bolometer array chip, as well as a solution that can expand the dynamic range of the readout chip (Read out IC, ROIC) and improve the production yield (to increase the number of usable chips) has become a technical goal that each manufacturer wants to achieve. Summary of the Invention [Problem to be solved by the invention]

[0010] In view of this, the present invention proposes a dynamic compensation method for thermal imaging array pixels. At the reference temperature, different currents are provided for different resistance values ​​of individual pixels, and the voltages output by each pixel are made the same, thus achieving the purpose of single pixel compensation. This can achieve several special technical effects, such as solving the problem of pixel resistance non-uniformity in the matrix caused by the manufacturing process, and achieving a sufficient yield improvement and a widening of the dynamic range of the readout chip. [Means for solving the problem]

[0011] The present invention further provides a method for dynamic correction of thermal imaging array pixels, which is applied to factory correction of bolometers, comprising the steps of: At a reference temperature, a reference current is sequentially applied to the thermistors in all pixels in the image sensing array, and the corresponding resistance array values ​​are measured and recorded in memory, calculating the individual resistances. A step of calculating individual current parameters, respectively calculating current array values ​​based on the resistor array values ​​and predetermined voltage values ​​and recording them in the memory. a step of verifying a predetermined voltage value, when reading out individual pixel voltage values ​​of the image sensing array at the reference temperature, providing individual current parameters corresponding to each pixel based on the current array values, and verifying consistency with the predetermined voltage value;

[0012] The present invention further provides a method for dynamic correction of thermal imaging array pixels applied to post-shipment temperature measurement of a bolometer, comprising the steps of: A sensing step of controlling the image sensing array to sense the temperature of an object within a predetermined time period. a readout process of reading out the current array values ​​stored in the memory by a readout chip, sequentially outputting individual currents according to individual current parameters corresponding to the pixels of the image sensing array, and reading out the measured voltage values ​​of the corresponding pixels to obtain a measured voltage array; A temperature calculation step of sequentially calculating temperatures detected at the pixels based on differences between the measured voltage values ​​and the predetermined voltage values ​​to obtain a measured temperature array.

[0013] The present invention further provides a method for dynamic correction of a pixel of a thermal imaging array, which is applied to a bolometer having a lens valve, comprising the steps of: The process of starting up. Measuring the environmental temperature, controlling the lens valve to close, measuring the environmental temperature value and recording it in memory. A step of controlling the lens valve to close, sequentially providing reference currents to thermistors in pixels in an image sensing array, and measuring and recording corresponding resistance array values ​​in the memory, calculating individual resistances. A step of calculating individual current parameters, respectively calculating current array values ​​based on the resistor array values ​​and predetermined voltage values ​​and recording them in the memory. A process of confirming a predetermined voltage value, which includes controlling the lens valve to close, taking the environmental temperature as a reference temperature, reading out individual pixel voltage values ​​of the image sensing array, providing individual current parameters corresponding to each pixel based on the current array values, and confirming the consistency with the predetermined voltage value. a sensing step of opening the lens valve and sensing the temperature of an object within a predetermined time by controlling the image sensing array; a readout process, in which a readout chip reads out the current array values ​​stored in the memory, sequentially outputs individual currents according to individual current parameters corresponding to the pixels of the image sensing array, and reads out the measured voltage values ​​of the corresponding pixels to obtain a measured voltage array; A temperature calculation step of sequentially calculating temperatures detected at the pixels based on differences between the measured voltage values ​​and the predetermined voltage values ​​to obtain a measured temperature array.

[0014] The detailed inventive features and advantages of the present invention are described in detail in the following embodiments, and the contents are sufficient for those skilled in the art to understand the technical aspects of the present invention and to implement the present invention. Furthermore, based on the contents, claims and drawings disclosed in this specification, those skilled in the art can easily understand the objectives and advantages of the present invention. [Brief description of the drawings]

[0015] [Figure 1A] FIG. 2 is a schematic diagram of resistance and voltage measured by a bolometer array according to a known technique. [Figure 1B] FIG. 2 is a schematic diagram of resistance and voltage measured by a bolometer array according to a known technique. [Diagram 2] FIG. 2 is a schematic diagram of each pixel current of the dynamic current compensation method according to the dynamic correction method of the thermal imaging array pixel of the present invention; [Figure 3A] 1 is a detailed embodiment of the thermal imaging array pixel dynamic compensation method of the present invention, the compensation flow chart and the operation flow chart applied to a shutterless thermal imaging device product; [Figure 3B] 1 is a detailed embodiment of the thermal imaging array pixel dynamic compensation method of the present invention, the compensation flow chart and the operation flow chart applied to a shutterless thermal imaging device product; [Figure 4] 1 is a detailed embodiment of a thermal imaging array pixel dynamic correction method according to the present invention, the correction flow chart and the operation flow chart applied to a thermal imaging device product with a shutter; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The dynamic compensation method for thermal imaging array pixels of the present invention provides different currents to different resistance values ​​of individual pixels at the reference temperature, so that the voltage output by each pixel is the same, thereby achieving the purpose of single pixel compensation, solving the problem of pixel resistance non-uniformity in the matrix caused by the manufacturing process, and achieving several special technical effects, such as fully improving the yield and widening the dynamic range of the readout chip.

[0017] Please refer to FIG. 2. FIG. 2 is a schematic diagram of the dynamic compensation method of the thermal imaging array pixel of the present invention applied to the pixel matrix of FIG. 1A and FIG. 1B, and the dynamic compensation method of the thermal imaging array pixel of the present invention may be abbreviated as dynamic current compensation method. The dynamic current compensation method of the present invention calculates the I(y,x) value from the R(y,x) distribution of FIG. 1A by the following formula: Vconst=I(y,x)×R(y,x), and during the operation of the readout chip (not shown), the current source provides different current values ​​to each pixel (y,x) according to the I(y,x) value. As shown in FIG. 2, the output current of the readout chip to the pixel array is provided by pixel 11-0-0, pixel 11-0-2, pixel 11-0-M, pixel 11-N-2, pixel 11-NM, etc., among the M×N pixels of the bolometer array 10, because the corresponding resistances may be different, and the corresponding voltages are all equal to Vconst. That is, current I(0,0) = Vconst / resistance R(0,0), current I(0,2) = Vconst / resistance R(0,2), current I(0,M) = Vconst / resistance R(0,M), current I(N,2) = Vconst / resistance R(N,2), current I(N,M) = Vconst / resistance R(N,M).

[0018] Wherein, Vconst is the constant voltage output, and the current I(y,x) is the individual current value distribution of each pixel calculated based on the resistance R(y,x) distribution in Figure 1A. At a specific compensation temperature, the voltage output by each pixel will not be different from each other as shown in Figure 1B, but rather, the voltage output of each pixel will be Vconst.

[0019] At a particular temperature, the voltage output by each pixel is the same constant value, so the dynamic range of gain is greatly expanded, thereby improving chip yield and sensitivity expression.

[0020] Next, reference is made to Fig. 3A, which shows a correction flow of the dynamic correction method of the thermal image array pixel of the present invention, which is a flow of correction at the time of shipment.

[0021] Step S101: Calculation of individual resistance: At a reference temperature, sequentially provide a reference current to thermistors in all pixels in the image sensing array, and measure the corresponding resistance array values ​​and record them in memory, i.e., the flow of FIG. 1A, where the memory can be a SPI Flash memory or a non-volatile memory built into the microcontroller.

[0022] Step S102: Calculation step of individual current parameters: Calculate current array values ​​according to the resistor array values ​​and the predetermined voltage values, and record them in the memory. That is, apply the above Vconst=I(y,x)×R(y,x), and Vconst becomes the predetermined voltage value. This predetermined voltage value is adjustable, and is dynamically adjusted according to factors such as the properties of the compound material of the thermistor in the bolometer, the manufacturing process, the sensitivity demand of the product, and the temperature measurement range of the product.

[0023] Step S103: Confirmation of the predetermined voltage value: when reading out the voltage value of each pixel of the image sensing array at the reference temperature, provide the individual current parameters corresponding to each pixel according to the current array value, and confirm whether they are consistent with the predetermined voltage value. If it is confirmed by actual measurement that all of them are consistent with the predetermined voltage value, it means that the bolometer array chip has been calibrated and can be shipped.

[0024] Next, please refer to Fig. 3B, which shows the correction flow of the dynamic correction method of the thermal image array pixel of the present invention, which is the flow of temperature measurement after shipment.

[0025] Step S201: Sensing step: within a certain time, the image sensing array is controlled to sense the temperature of the object. Generally, after starting up and going through a basic control check procedure, the microcontroller controlling the bolometer array chip can start preparing for temperature measurement. Once a temperature measurement command is received, the complete sensing process can start. In the above description, the microcontroller control flow is simplified, and only the sensing process after receiving a temperature measurement command is described. The sensing process is part of the well-known technology, and no further description is provided in the present invention.

[0026] Step S202: Reading step: read the current array value stored in the memory by the readout chip, sequentially output individual currents according to the individual current parameters corresponding to the pixels of the image sensing array, and read the measured voltage values ​​of the corresponding pixels to obtain a measured voltage array. This step is a part of the main inventive feature of the present invention. As described in the prior art, the known technology measures the pixel voltage in the bolometer array using a constant current method. Meanwhile, the present invention uses a microcontroller (MCU) to control the readout chip (ROIC) to read the individual current parameters (which may be collectively referred to as an individual current parameter table) of each pixel pre-stored in the memory, and then provides each pixel with an individually determined current value (variable current), and then reads out the voltage value.

[0027] Step S203: Temperature calculation step: Sequentially, the temperature detected by the pixel is calculated based on the difference between the measured voltage value and the predetermined voltage value to obtain a measured temperature array. The difference between the measured voltage value and the predetermined voltage value is the temperature difference detected by each pixel. Since the current of each pixel is not all the same, which also represents the temperature measurement characteristics of each pixel are different, an individual and relatively accurate temperature difference change can be derived. Therefore, the method of the present invention can improve the sensitivity and accuracy of the bolometer.

[0028] Next, refer to FIG. 4. FIG. 4 is a correction flow of the dynamic correction method of the thermal imaging array pixel of the present invention, which is the flow of the adaptive dynamic current compensation method after shipment. In some embodiments of the present invention, the terminal thermal imaging device has a shutter structure, and the microcontroller can control the opening and closing of the shutter to control the entry and exit of the external light source. Such product control can be regarded as the adaptive dynamic current compensation method of the present invention, that is, each time it is started, the current compensation correction is performed once again. The steps include the following:

[0029] Step S301: Start-up. Every time the device is restarted, the current compensation correction is performed once again.

[0030] Step S302: Measuring the environmental temperature: The lens valve is controlled to close, and the environmental temperature value is measured and recorded in the memory. The current environmental temperature may change depending on the environment and time, so the current environmental temperature can be used as the reference temperature. The current environmental temperature is measured with the lens valve (shutter) closed, and at this time, the shutter is closed and no external light source is inserted, and the measured temperature is the current temperature of the thermal imaging device. Since the dynamic current compensation temperature correction of the present invention is performed before shipping, this can be used as the reference for temperature measurement.

[0031] Step S303: Calculation of individual resistance: Control the lens valve to close, sequentially provide reference current to thermistor in the pixel in the image sensing array, measure the corresponding resistance array value, and record it in the memory. Different from step S101 of Fig. 3A, this step uses the temperature in the shutter closed state as the reference temperature, while step S101 measures with a reference temperature fixture (a heat sink that radiates a uniform temperature).

[0032] Step S304: Calculation step of individual current parameters: Calculate current array values ​​based on the resistor array values ​​and the predetermined voltage values, respectively, and record them in the memory. This is the same as step S102, and further description is omitted.

[0033] Step S305: confirming the predetermined voltage value: control the lens valve to close, take the environmental temperature as a reference temperature, read out the individual pixel voltage value of the image sensing array, provide the individual current parameter corresponding to each pixel according to the current array value, and confirm the consistency with the predetermined voltage value. This is the same as step S103, and further description is omitted.

[0034] Step S306: Sensing step: The lens valve is opened, and the image sensing array is controlled within a predetermined time to sense the temperature of the object. There are many substeps before this step, but they are omitted. The sensing step starts after the user outputs a control command for temperature measurement. However, in this embodiment, the sensing step starts after receiving a control command after the adaptive correction steps of steps S301 to S305.

[0035] Step S307: reading step: read the current array value stored in the memory by a reading chip, and sequentially output individual currents according to individual current parameters corresponding to the pixels of the image sensing array, and read the measured voltage values ​​of the corresponding pixels to obtain a measured voltage array, which is the same as step S202, and will not be described further.

[0036] Step S308: temperature calculation step: sequentially calculate the temperature detected by the pixel according to the difference between the measured voltage value and the predetermined voltage value to obtain a measured temperature array, which is the same as step S202, and will not be described further.

[0037] In the above embodiment, the dynamic current compensation method of the present invention can be applied to thermal imaging products without shutters or thermal imaging products with shutters, the thermal imaging products without shutters can adopt the factory-set dynamic current compensation method, and the thermal imaging products with shutters can adopt the adaptive dynamic current compensation method.

[0038] The dynamic current compensation method of the present invention can solve the problem of pixel-to-pixel resistance mismatch caused by the bolometer array chip, and achieve special technical effects such as improving production yield, improving readout temperature sensitivity, and increasing dynamic range.

[0039] The technical matters of the present invention have been disclosed by the preferred embodiments as described above, but the present invention is not limited thereto. All slight changes and modifications made by those skilled in the art without departing from the spirit of the present invention are included in the scope of the present invention, and the technical scope of the present invention is equivalent to that defined by the claims. [Explanation of symbols]

[0040] 10: Bolometer array 11-0-0, 11-0-2, 11-0-M, 11-N-2, 11-NM: pixels

Claims

1. 1. A method for dynamic calibration of thermal imaging array pixels as applied to factory calibration of a bolometer, comprising: a step of calculating individual resistances by sequentially providing a reference current to thermistors in all pixels in the image sensing array at a reference temperature and measuring and recording in memory the corresponding resistance array values; a step of calculating individual current parameters, respectively calculating current array values ​​based on the resistor array values ​​and predetermined voltage values, and recording the current array values ​​in the memory; a step of verifying a predetermined voltage value, when reading out individual pixel voltage values ​​of the image sensing array at the reference temperature, providing individual current parameters corresponding to each pixel according to the current array value, and verifying whether the individual current parameters correspond to the predetermined voltage value; A method for dynamic compensation of thermal imaging array pixels, comprising:

2. 2. The method of claim 1, wherein the memory is selected from a flash memory or a non-volatile memory embedded in a microcontroller.

3. 1. A method for dynamic correction of thermal imaging array pixels applied to post-shipment temperature measurements of a bolometer, comprising: a sensing step of controlling the image sensing array to sense the temperature of the object within a predetermined time; a read step of reading the current array values ​​stored in the memory by a read chip, sequentially outputting individual currents according to individual current parameters corresponding to the pixels of the image sensing array, and reading the measured voltage values ​​of the corresponding pixels to obtain a measured voltage array; a temperature calculation step of calculating temperatures detected at the pixels based on differences between the measured voltage values ​​and a predetermined voltage value to obtain a measured temperature array; A method for dynamic compensation of thermal imaging array pixels, comprising:

4. 4. The method of claim 3, wherein the memory is selected from a flash memory or a non-volatile memory embedded in a microcontroller.

5. 1. A method for dynamic correction of thermal imaging array pixels as applied to a bolometer having a lens valve, comprising: Startup and Measuring an environmental temperature by controlling the lens valve to close and measuring and recording an environmental temperature value in a memory; controlling said lens valve to close, sequentially providing reference currents to thermistors in pixels in an image sensing array, and measuring and recording corresponding resistance array values ​​in said memory; and calculating individual resistances. a step of calculating individual current parameters, respectively calculating current array values ​​based on the resistor array values ​​and predetermined voltage values, and recording the current array values ​​in the memory; a predetermined voltage value verification step, which includes controlling the lens valve to close, taking the environmental temperature as a reference temperature, reading out individual pixel voltage values ​​of the image sensing array, providing individual current parameters corresponding to each pixel according to the current array values, and verifying whether the voltage values ​​are consistent with the predetermined voltage value; a sensing step of opening the lens valve and sensing the temperature of an object by controlling the image sensing array within a predetermined time; a readout process, reading out the current array values ​​stored in the memory by a readout chip, sequentially outputting individual currents according to individual current parameters corresponding to the pixels of the image sensing array, and reading out the measured voltage values ​​of the corresponding pixels to obtain a measured voltage array; a temperature calculation step of calculating temperatures detected at the pixels based on differences between the measured voltage values ​​and the predetermined voltage values ​​to obtain a measured temperature array; A method for dynamic compensation of thermal imaging array pixels, comprising:

6. 6. The method of claim 5, wherein the memory is selected from a flash memory or a non-volatile memory embedded in a microcontroller.

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