Dark current testing method of infrared detector

Abstract

The invention relates to a dark current testing method of an infrared detector, and belongs to the technical field of infrared imaging. According to the relation between the output of the infrared imaging system and the integral time and the black body temperature, the output signal of the infrared imaging system is acquired by changing the integral time and the black body temperature so as to obtain the dark current value. The problem that the dark current is difficult to test is solved from the engineering perspective, the test conditions are easy to realize, the test process is easy to operate, and the measurement process error is small.

Description

Technical Field

[0001] The invention belongs to the technical field of infrared imaging, and in particular relates to a dark current testing method of an infrared detector. Background Art

[0002] Dark current refers to the current flowing through the PN junction in the absence of light. It is a key factor in determining the performance of cooled infrared detectors, affecting the detector's detection rate and thus affecting the target recognition distance of the infrared imaging system. Therefore, testing and evaluating the detector's dark current is of great significance for analyzing the characteristics of the dark current, optimizing the detector process, and improving the performance of the infrared imaging system.

[0003] At present, since the photocurrent signals generated by infrared detectors are converted into voltage signals through readout circuits, it is relatively complicated to directly measure the dark current of each detection element of the device. In foreign countries, the dark current output voltage of the focal plane detector is generally obtained by testing it under zero field of view (0FOV, i.e. blind cold screen) conditions, but this test method is still subject to certain limitations, that is, the structure of the component must be changed, and the normal cold screen must be replaced with a blind cold screen to obtain it. For components that are generally packaged and want to know the size of their dark current, this method is impossible to achieve.

[0004] The article "Calculation of Dark Current of Infrared Focal Plane Detector" (Infrared Technology, Vol38(3), 2016) introduces a quick test method, which is to select two different black body temperature points within the linear response range of the detector, and calculate the dark current based on the detector output voltage V(T1) and V(T2). Although the test process of this method is simple, it does not consider the error of the background voltage of the peripheral circuit on the test result. The method introduced in the article "Research on Dark Current Test Method of Infrared Detector" (Infrared Technology, Vol 34(4), 2012) is not very effective in calculating the total radiation illuminance of the black body. This will introduce calculation errors and increase the error in the dark current test results. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] The technical problem to be solved by the present invention is to design a method for testing the dark current of a refrigerated infrared detector at the infrared imaging system level.

[0007] (II) Technical solution

[0008] In order to solve the above technical problems, the present invention provides a dark current testing method for an infrared detector, wherein an infrared imaging system is placed in front of a black body, and based on the relationship between the output of the infrared imaging system and the integration time and the black body temperature, the output signal of the infrared imaging system is collected by changing the integration time and the black body temperature of the infrared imaging system to obtain the dark current value.

[0009] Preferably, the method specifically comprises the following steps:

[0010] Assume that when the infrared imaging system receives black body radiation, the system output charge is V out , then:

[0011] V out =V dark +V signal +V o (1)

[0012] Where: V dark : refers to dark current; V signal : refers to the amount of charge converted from the received radiation energy; V o : Refers to the background signal of the system circuit;

[0013] Among them, V dark and V signal They are all linearly related to the integration time t;

[0014] V dark =I dark ×t (2)

[0015] To calculate V signal First, we need to calculate the radiation energy received by the infrared imaging system; assuming that the radiation in the field of view is spatially uniform, the infrared imaging system receives the total blackbody spectral radiation power P λ for:

[0016]

[0017] Where: a: length of the pixel; b: width of the pixel; f: focal length of the optical system in the infrared imaging system; τ: transmittance of the optical system; D0: aperture of the optical system; M λ : the energy radiated from a unit area of ​​a black body to the hemispherical space; c1: the first radiation constant; c2: the second radiation constant; λ: wavelength; T: black body temperature;

[0018] In the infrared imaging system spectral response range λ1~λ2, the total radiant illumination P is:

[0019]

[0020] Among them, F refers to the F number, which is the ratio of the focal length to the aperture of the optical system;

[0021] The amount of charge N obtained by converting the radiation energy received by the infrared imaging system per unit time into the infrared detector e :

[0022]

[0023] Vsignal =N e ×t (7)

[0024] Where η is the quantum efficiency, h is Planck's constant, and c is the speed of light;

[0025] From equations (1) to (7), we can get V out :

[0026] V out =(I dark +N e )×t+V0 (8)

[0027] At the same blackbody temperature, the integration time of the infrared imaging system is adjusted to t1 and t2, and V0 is obtained according to equations (9) and (10):

[0028] V out1 =(I dark +N e )×t1+V0 (9)

[0029] V out2 =(I dark +N e )×t2+V0 (10)

[0030] Then substitute V0 into formula (8), we have:

[0031] V out -V0=(I dark +N e )×t (11)

[0032]

[0033] Adjust the blackbody temperature and obtain the (I dark +N e ) value, and then fit the blackbody temperature and (I dark +N e ) value, fitting the blackbody temperature and (I dark +N e ) value, the intercept of the fitting curve equation obtained is the dark current.

[0034] (III) Beneficial effects

[0035] The invention collects the output signal of the infrared imaging system by changing the integration time and the black body temperature based on the relationship between the output of the infrared imaging system and the integration time and the black body temperature to obtain the dark current value. The invention solves the problem of the difficulty in testing the dark current from an engineering perspective, the test conditions are easy to achieve, the test process is easy to operate, and the measurement process error is small. DETAILED DESCRIPTION

[0036] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below in conjunction with embodiments.

[0037] The purpose of the present invention is to provide a dark current test method based on an infrared imaging system, which is a method for testing the dark current of a refrigerated infrared detector at the infrared imaging system level. The main idea is to obtain the dark current based on the relationship between the output of the infrared imaging system and the integration time and the black body temperature. The specific steps are as follows:

[0038] Assume that when the infrared imaging system receives black body radiation, the system output charge is V out ,

[0039] V out =V dark +V signal +V o (1)

[0040] Where: V dark : refers to dark current; V signal : refers to the amount of charge converted from the received radiation energy; V o : Refers to the background signal of the system circuit.

[0041] Among them, V dark and V signal They are all linearly related to the integration time t;

[0042] V dark =I dark ×t (2)

[0043] To calculate V signal First, we need to calculate the radiation energy received by the infrared imaging system. Assuming that the radiation in the field of view is spatially uniform, that is, the blackbody radiation fills the entire field of view, the total blackbody spectral radiation power P received by the infrared imaging system is λ for:

[0044]

[0045] Where: a: pixel size (length); b: pixel size (width); f: focal length of the optical system in the infrared imaging system; τ: transmittance of the optical system; D0: aperture of the optical system;

[0046] M λ : The energy radiated into the hemispherical space per unit area of ​​the black body; c1: the first radiation constant; c2: the second radiation constant; λ: wavelength; T: black body temperature.

[0047] Within the spectral response range of the infrared imaging system (λ1~λ2), the total radiant illumination P is:

[0048]

[0049] Among them, F refers to the F number, which is the ratio of the focal length to the aperture of the optical system;

[0050] The amount of charge N obtained by converting the radiation energy received by the infrared imaging system per unit time into the infrared detector e :

[0051]

[0052] V signal =N e ×t (7)

[0053] Where η is the quantum efficiency, h is Planck's constant, and c is the speed of light;

[0054] From equations (1) to (7), we can get V out :

[0055] V out =(I dark +N e )×t+V0 (8)

[0056] At the same blackbody temperature, the integration time of the infrared imaging system is adjusted to t1 and t2. According to equations (9) and (10), V0 can be obtained:

[0057] V out1 =(I dark +N e )×t1+V0 (9)

[0058] V out2 =(I dark +N e )×t2+V0 (10)

[0059] Then substitute V0 into equation (8),

[0060] V out -V0=(I dark +N e )×t (11)

[0061]

[0062] Adjust the blackbody temperature and obtain the (I dark +N e ) value, and then fit the blackbody temperature and (I dark +N e ) value, fitting the blackbody temperature and (I dark +N e ) value, the intercept of the fitting curve equation obtained is the dark current.

[0063] The specific steps of the embodiment of the present invention are given below:

[0064] 1) Place the infrared imaging system in front of a black body, set the black body temperature to 40°C, adjust the integration time of the imaging system, set the integration time to 1ms and 2ms respectively, according to formula (9):

[0065] And (10) to get V0;

[0066] 2) Then set the integration time to 1.5ms, change the black body temperature from 20°C to 80°C, and collect the output signals of the imaging system at different black body temperatures at intervals of 10°C;

[0067] 3) Based on the test results of step 2), the following equation (11) is used to obtain the (I dark +N e )value;

[0068] 4) Fitting blackbody temperature and (I dark +N e ) value, and its intercept is the dark current.

[0069] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A dark current test method for an infrared detector, characterized in that: The infrared imaging system is placed in front of a black body. Based on the relationship between the output of the infrared imaging system and the integration time and the black body temperature, the output signal of the infrared imaging system is collected by changing the integration time and the black body temperature to obtain the dark current value.

2. The method according to claim 1, characterized in that This method specifically The following steps are involved: Assume that when the infrared imaging system receives black body radiation, the system output charge is V out , then: V out =V dark +V signal +V o (1) Where: V dark : refers to dark current; V signal : refers to the amount of charge converted from the received radiation energy; V o : Refers to the background signal of the system circuit; Among them, V dark and V signal They are all linearly related to the integration time t; V dark =I dark ×t(2) To calculate V signal First, we need to calculate the radiation energy received by the infrared imaging system; assuming that the radiation in the field of view is spatially uniform, the infrared imaging system receives the total blackbody spectral radiation power P λ for: Where: a: length of the pixel; b: width of the pixel; f: focal length of the optical system in the infrared imaging system; τ: transmittance of the optical system; D0: aperture of the optical system; M λ : the energy radiated from a unit area of ​​a black body to the hemispherical space; c1: the first radiation constant; c2: the second radiation constant; λ: wavelength; T: black body temperature; In the infrared imaging system spectral response range λ1~λ2, the total radiant illumination P is: Among them, F refers to the F number, which is the ratio of the focal length to the aperture of the optical system; The amount of charge N obtained by converting the radiation energy received by the infrared imaging system per unit time into the infrared detector e : V signal =N e ×t(7) Where η is the quantum efficiency, h is Planck's constant, and c is the speed of light; From equations (1) to (7), we can get V out : V out =(I dark +N e )×t+V0 (8) At the same blackbody temperature, the integration time of the infrared imaging system is adjusted to t1 and t2, and V0 is obtained according to equations (9) and (10): V out1 =(I dark +N e )×t1+V0 (9) V out2 =(I dark +N e )×t2+V0 (10) Then substitute V0 into formula (8), we have: V out -V0=(I dark +N e )×t (11) Adjust the blackbody temperature and obtain the (I dark +N e ) value, and then fit the blackbody temperature and (I dark +N e ) value, fitting the blackbody temperature and (I dark +N e ) value, the intercept of the fitting curve equation obtained is the dark current.

3. The method according to claim 2, characterized in that When the radiation in the field of view is spatially uniform, the blackbody radiation fills the entire field of view.

4. The method according to claim 1, characterized in that The dark current is the current flowing through the PN junction in the absence of light.

5. The method according to claim 1, characterized in that The infrared detector is a refrigeration type infrared detector.

6. A system for implementing the method according to any one of claims 1 to 3.

7. A dark current characteristic analysis method based on the method according to any one of claims 1 to 3.

8. An infrared detector optimization process implemented based on the method according to any one of claims 1 to 3.

9. An infrared imaging system designed and implemented based on the method as claimed in any one of claims 1 to 3.

10. A process for preparing the system according to claim 9.

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