CN102508142A - Method for measuring quantum efficiency and responsivity parameter of charge coupled device (CCD) chip - Google Patents

Abstract

The invention discloses a method for measuring quantum efficiency and a responsivity parameter of a charge coupled device (CCD) chip, and mainly solves the problem of low measurement precision in the prior art. The method comprises the following steps of: selecting a series of wavelengths at equal intervals, setting a tunable wavelength monochromatic uniform light source system by using the wavelength values respectively, generating monochromatic light with the corresponding wavelengths, shooting image information according to requirements, uploading to a computer, selecting needed images by using matched computer software, calculating the mean gray value mu and the image variance sigma<2> of the images, calculating a gain K of a control circuit respectively according to the calculated values, and calculating the quantum efficiency eta and the responsivity R according to the mean gray value mu, the image variance sigma<2> and the gain K. The method for measuring the quantum efficiency and the responsivity parameter of the CCD chip has the advantages of high precision and high stability in parameter measurement and is suitable for the precise measurement of the quantum efficiency and the responsivity parameter of the CCD chip.

Description

Measure the method for CCD chip quantum efficiency and responsiveness parameter

Technical field

The invention belongs to field of measuring technique, be specifically related to measurement, be used for development, assessment and the screening of CCD chip CCD chip quantum efficiency and responsiveness parameter.

Background technology

In the middle of the development and application of CCD chip; Because the restriction of processing and measuring technique; Cause actual quantum efficiency and the responsiveness parameter of CCD chip and measured value that manufacturer provides to have certain difference, and, need quantitatively to understand the actual performance parameter of CCD chip in some key application fields; Thereby, obtain data better more accurately to collecting to such an extent that data are reasonably proofreaied and correct.Therefore, be necessary to propose quantum efficiency and the responsiveness parameter that a kind of method effectively measures the CCD chip,, the CCD output data handled the data that more geared to actual circumstances through these performance parameters.

Traditional CCD chip quantum efficiency and responsiveness measurement method of parameters generally adopt laser instrument as the monochromatic light light source; Yet; Owing to also can't adopt laser instrument to realize the continuous variation of wavelength at present, cause to produce the monochromatic light of some wavelength coverage, thereby make the quantum efficiency of these wavelength coverages can only use the quantum efficiency of other wavelength to derive; Cause the quantum efficiency and the actual value of measurement that the bigger gap that gets is arranged, can't reflect quantum efficiency and responsiveness parameter that the CCD chip is actual.

Summary of the invention

The objective of the invention is to deficiency to above-mentioned prior art; A kind of method of measuring CCD chip quantum efficiency and responsiveness parameter is proposed; With the quantum efficiency that reduces to measure and the gap of actual value, improve the quantum efficiency of reality and the measuring accuracy of responsiveness parameter.

For realizing above-mentioned purpose, the present invention includes following steps:

1) CCD chip to be measured is placed in the middle of the Dewar flask that has entrance window, the CCD chip is linked to each other with the control circuit corresponding interface, this control circuit is used to control the imaging of CCD chip;

2) near the CCD chip, place the good detector of demarcation, be used for the nominal light source power, for measurement provides the luminous power reference value;

3) placing the monochromatic uniform source of light of wavelength-tunable system apart from CCD chip 80cm place, the monochromatic light that this light-source system sends shines directly into CCD and demarcates above the good detector;

4) electronic shutter that carries through shutter device or CCD chip is adjusted the integral time of CCD chip, the exposure of control CCD chip;

5) choose monochromatic wavelength width Δ λ, scanning wavelength scope [λ according to application demand _s, λ _e], scanning wavelength λ at interval _Int, it is λ that initial wavelength is set _s, cutoff wavelength is λ _e, from initial wavelength X _sBeginning, the scanning wavelength that superposes successively is λ at interval _Int, reach cutoff wavelength λ up to wavelength _eTill, obtain a series of wavelength value, as parameter, the control light-source system produces the monochromatic light of respective wavelength with these wavelength value;

6) every monochromatic wavelength that is provided with a time is taken two picture group pictures with the CCD chip, and every group of image number of taking is greater than 5; Wherein take first picture group as the time integral time of choosing need make the CCD chip reach 50% exposure or more than; The gained image is called bright image, take second picture group as the time, use with shooting first picture group as identical integral time; But need close shutter this moment, and the gained image is called dark image;

7) two bright images and two dark images in the middle of each extracts from the first picture group picture and the second picture group picture;

8) utilize the image calculation CCD chip of extraction and total gain K of control circuit thereof, be called system-gain:

8a) from two dark images and two bright images, respectively choose one, calculate the bright image choose and the average gray value μ of dark image respectively _Y1And μ _Y2:

${\mathrm{\&mu;}}_{y1}=\frac{1}{\mathrm{MN}}\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{y}_1\left[m\right]\left[n\right],$ ${\mathrm{\&mu;}}_{y2}=\frac{1}{\mathrm{MN}}\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{y}_2\left[m\right]\left[n\right]$

Wherein, y ₁, y ₂Represent the bright image and dark image chosen respectively, M, N are respectively the capable pixel count and the row pixel count of photographic images;

8b) use the bright image variance of two bright image calculation that extracts

${\mathrm{\&sigma;}}_{y1}^2=\frac{1}{2\mathrm{NM}}\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{\left(y^A\right[m\left]\right[n]-y^B[m\left]\right[n\left]\right)}^2$

Y wherein ^A, y ^BRepresent first and second in the bright image respectively;

8c) use the dark image variance of two dark image calculation

that extracts

${\mathrm{\&sigma;}}_{y2}^2=\frac{1}{2\mathrm{NM}}\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{\left(y^C\right[m\left]\right[n]-y^D[m\left]\right[n\left]\right)}^2$

Wherein, y ^C, y ^DRepresent first and second in the dark image respectively;

The calculation of parameter system-gain K that 8d) obtains more than the basis:

$K=\frac{{\mathrm{\&sigma;}}_{y1}^2-{\mathrm{\&sigma;}}_{y2}^2}{{\mathrm{\&mu;}}_{y1}-{\mathrm{\&mu;}}_{y2}};$

9) utilize the responsiveness R of four image calculation CCD chips that extract in the step 7):

$R=\frac{{\mathrm{\&mu;}}_{y1}-{\mathrm{\&mu;}}_{y2}}{{\mathrm{\&mu;}}_p}$

Wherein

Be the average photon number of the single pixel of CCD chip, A is the area of the single pixel of CCD chip, and E is the monochromatic light power that shines on the CCD chip, t _ExpUsed integral time when take extracting bright image, λ shines the monochromatic wavelength on the CCD chip when extracting bright image for taking, and h is a Planck's constant, and c is the light velocity;

10) try to achieve the quantum efficiency of CCD chip by system-gain K and responsiveness R:

$\mathrm{\&eta;}\left(\mathrm{\&lambda;}\right)=\frac{R}{K}.$

The present invention has following advantage:

1) The data chosen of the present invention is taken many, chooses the method for center section image, has well got rid of the error of imaging system, has improved the precision of measurement parameter.

2) the present invention gets many images for the calculating employing of space variance and asks average mode, has got rid of the influence of time domain variance basically, makes the space heterogeneity of measurement more accurate.

3) the present invention can calculate the absolute value of quantum efficiency and responsiveness owing to use the detector of demarcating that incident monochromatic light light intensity is demarcated, and with respect to relative quantum efficient and relative response degree, the user is more had reference value.

4) owing to adopt the monochromatic uniform source of light of wavelength-tunable system, can produce the monochromatic light of each wavelength, thereby can measure the quantum efficiency and the responsiveness parameter of each wavelength.

Description of drawings

Fig. 1 is the used hardware acquisition system of a present invention block diagram;

Fig. 2 is the process flow diagram that the present invention measures CCD chip quantum efficiency η and responsiveness parameter K.

Embodiment

The CCD chip is a kind of widely used image device; Be widely used in many fields such as uranology, Aero-Space, biology and medical research, molecular dynamics, spectroscopy, underwater photography, X ray detection, it is vital assessing for this performance parameter to the CCD chip.At present, the CCD chip assessed mainly contained following these parameters:

1. quantum efficiency η: CCD is at wavelength X the irradiation photoelectron number of generation and the ratio of incident light subnumber down, this parameter characterization the CCD chip to the monochromatic responding ability of specific wavelength.

2. responsiveness parameters R: CCD is under the setted wavelength monochromation illumination, the ratio of signal voltage and exposure.This parameter has been described CCD quantum efficiency and system-gain on the whole.

3. saturation degree μ _P.sat: the photon number that can receive when CCD reaches capacity.

4. system-gain K: the electron number that system's pixel produces and the ratio of gray-scale value.

5. dark noise

the noise summation relevant with CCD chip sensing circuit.

6. signal to noise ratio snr: signal that photon produces and the ratio between the noise signal.

7. absolute sensitivity threshold value μ _P.min: signal to noise ratio (S/N ratio) equals 1 o'clock required average photon number.

8. dynamic range DR: saturation degree is in the ratio of absolute sensitivity threshold value.

9. the error that departs from linear concerns between the output signal of nonlinearity error LE:CCD chip and the incident optical signal.

10. the ratio of the standard deviation of dark signal heterogeneity DSNU:CCD chip each pixel output gray level value under unglazed photograph and its average.

photo response heterogeneity PRNU:CCD chip under 50% saturated conditions of exposure, the standard deviation of each pixel output gray level value and the ratio of average.

Dark current μ _I: the CCD chip unglazed according under the situation the output current size.

Double thermal constant T _d: unglazed according under the situation, corresponding temperature when dark current is increased to reference temperature and goes out a times of dark current value.

Below will combine accompanying drawing, clear, intactly describe among the present invention to the 1. 2. perfect measurement flow process of responsiveness parameters R of quantum efficiency η and parameter of parameter.

With reference to Fig. 1, the used hardware acquisition system of the present invention block diagram, total system comprises the monochromatic uniform source of light of wavelength-tunable system, Dewar flask temperature controlled compartment, CCD chip, standard detector, control circuit and computing machine.CCD chip and standard detector are placed in the Dewar flask temperature controlled compartment; Its working temperature can be controlled by the Dewar flask temperature controlled compartment; Regulate the monochromatic uniform source of light of wavelength-tunable system and export even monochromatic light, be radiated on CCD chip and the standard detector, the CCD chip is driven into picture by control circuit; And the output information of CCD chip uploaded on the computing machine, computing machine calculates the performance parameter of CCD chip to be measured according to image information.For different measurement parameters, through regulating wavelength-tunable monochromatic source system, integral time and CCD chip operation temperature, gather corresponding image and intensity signal, basis calculates measurement parameter with the specific step of parameter correlation again.

With reference to Fig. 2, the present invention measures the method for CCD chip quantum efficiency η and responsiveness parameters R, comprises the steps:

Step 1, CCD chip to be measured is placed in the Dewar flask temperature controlled compartment of test macro; This Dewar flask temperature controlled compartment has entrance window; The transmitance of entrance window requires the transmitance of incident light is reached more than 98%; The CCD chip is linked to each other with the control circuit corresponding interface, and this control circuit is used to control the temperature of imaging of CCD chip and adjusting Dewar flask temperature controlled compartment, and the temperature of Dewar flask temperature controlled compartment is the working temperature of CCD chip.

Step 2, near the CCD chip, place standard detector, this detector is demarcated, and is used for measurement light source power, for thereafter calculating provides the luminous power reference value.

Step 3, placing the monochromatic uniform source of light of wavelength-tunable system apart from CCD chip 80cm place; The monochromatic uniform source of light of this wavelength-tunable system is made up of broad spectrum light source, monochromator, integrating sphere; Its wavelength regulation area requirement covers the response wave length scope of CCD chip; The monochromatic wavelength width requirement that produces is less than 50nm, and the monochromatic light that the monochromatic uniform source of light of this wavelength-tunable system sends shines directly into CCD and above the standard detector.

The integral time of step 4, the electronic shutter adjustment CCD chip that carries through the CCD chip; The exposure of control CCD chip; If the electronic shutter of CCD chip does not satisfy application demand; Then need add shutter device in the middle of the input path, generally be added on before the entrance window or before the monochromatic uniform source of light of the wavelength-tunable system, use this shutter device to regulate the exposure of CCD chip.

Step 5, choose wavelength width Δ λ, scanning wavelength scope [λ according to the response wave length scope of application demand and CCD chip _s, λ _e], scanning wavelength λ at interval _Int, wherein wavelength width Δ λ need be less than 50nm, and in the scanning wavelength scope will be included in the wavelength response range of CCD chip, scanning wavelength is λ at interval _IntBe less than the wavelength width of twice, it is λ that initial wavelength is set _s, cutoff wavelength is λ _e, beginning from initial wavelength, the scanning wavelength that superposes successively is λ at interval _Int, reach λ up to wavelength _eTill, obtain a series of wavelength value, as parameter, the control light-source system produces the monochromatic light of respective wavelength with these wavelength value.

Step 6, every monochromatic wavelength that is provided with a time are taken two picture group pictures with the CCD chip, and every group of image number of taking is greater than 5; Wherein take first picture group as the time integral time of choosing need make the CCD chip reach 50% exposure or more than; The gained image is called bright image, take second picture group as the time, use with shooting first picture group as identical integral time; But need close shutter this moment; The gained image is called dark image, and the image of all shootings all uploads in the middle of the computing machine through control circuit, next uses supporting computer software that these data are handled and obtains measurement parameter.

Step 7, two bright images and two dark images from the first picture group picture and the second picture group picture in the middle of the extraction, these four images will be used for follow-up calculating, and remaining image abandons need not.

Image calculation CCD chip and the total gain K of control circuit thereof that step 8, utilization are extracted are called system-gain:

8a) from two dark images and two bright images, respectively choose one, calculate the bright image choose and the average gray value μ of dark image respectively _Y1And μ _Y2:

${\mathrm{\&mu;}}_{y1}=\frac{1}{\mathrm{MN}}\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{y}_1\left[m\right]\left[n\right],$ ${\mathrm{\&mu;}}_{y2}=\frac{1}{\mathrm{MN}}\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{y}_2\left[m\right]\left[n\right]$

Wherein, y ₁, y ₂Represent the bright image and dark image chosen respectively, M, N are respectively the capable pixel count and the row pixel count of photographic images, and these two sizes can obtain from the product manual of CCD chip or from image information, come out;

8b) use the bright image variance of two bright image calculation

that extracts

${\mathrm{\&sigma;}}_{y1}^2=\frac{1}{2\mathrm{NM}}\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{\left(y^A\right[m\left]\right[n]-y^B[m\left]\right[n\left]\right)}^2$

Y wherein ^A, y ^BRepresent first and second in the bright image respectively;

8c) use the dark image variance of two dark image calculation

that extracts

${\mathrm{\&sigma;}}_{y2}^2=\frac{1}{2\mathrm{NM}}\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{\left(y^C\right[m\left]\right[n]-y^D[m\left]\right[n\left]\right)}^2$

Wherein, y ^C, y ^DRepresent first and second in the dark image respectively;

The calculation of parameter system-gain K that 8d) obtains more than the basis:

$K=\frac{{\mathrm{\&sigma;}}_{y1}^2-{\mathrm{\&sigma;}}_{y2}^2}{{\mathrm{\&mu;}}_{y1}-{\mathrm{\&mu;}}_{y2}}.$

Step 9, utilize resulting average gray parameter μ in the step 8 _Y1And μ _Y2Calculate the responsiveness R of CCD chip:

$R=\frac{{\mathrm{\&mu;}}_{y1}-{\mathrm{\&mu;}}_{y2}}{{\mathrm{\&mu;}}_p}$

Wherein

Be the average photon number of the single pixel of CCD chip, A is the area of the single pixel of CCD chip, and E is the monochromatic light power that shines on the CCD chip, t _ExpUsed integral time when take extracting bright image, λ shines the monochromatic wavelength on the CCD chip when extracting bright image for taking, and h is a Planck's constant, and c is the light velocity.

Step 10, try to achieve the quantum efficiency of CCD chip by system-gain K and responsiveness R:

$\mathrm{\&eta;}\left(\mathrm{\&lambda;}\right)=\frac{R}{K}.$

More than describing only is an instantiation of the present invention; Do not constitute any restriction of the present invention; Obviously to those skilled in the art, after having understood content of the present invention and principle, all maybe be under the situation that does not deviate from the principle of the invention, structure; Carry out various corrections and change on form and the details, but these are based on the correction of inventive concept with change still within claim protection domain of the present invention.

Claims (2)

1. a method of measuring CCD chip quantum efficiency and responsiveness parameter comprises the steps:

1) CCD chip to be measured is placed in the middle of the Dewar flask temperature controlled compartment that has entrance window, the CCD chip is linked to each other with the control circuit corresponding interface, this control circuit is used to control the imaging of CCD chip;

2) near the CCD chip, place the good detector of demarcation, be used for the nominal light source power, for measurement provides the luminous power reference value;

3) placing the monochromatic uniform source of light of wavelength-tunable system apart from CCD chip 80cm place, the monochromatic light that this light-source system sends shines directly into CCD and demarcates above the good detector;

4) electronic shutter that carries through shutter device or CCD chip is adjusted the integral time of CCD chip, the exposure of control CCD chip;

5) choose monochromatic wavelength width Δ λ, scanning wavelength scope [λ according to application demand _s, λ _e], scanning wavelength λ at interval _Int, it is λ that initial wavelength is set _s, cutoff wavelength is λ _e, from initial wavelength X _sBeginning, the scanning wavelength that superposes successively is λ at interval _Int, reach cutoff wavelength λ up to wavelength _eTill, obtain a series of wavelength value, as parameter, the control light-source system produces the monochromatic light of respective wavelength with these wavelength value;

6) every monochromatic wavelength that is provided with a time is taken two picture group pictures with the CCD chip, and every group of image number of taking is greater than 5; Wherein take first picture group as the time integral time of choosing need make the CCD chip reach 50% exposure or more than; The gained image is called bright image, take second picture group as the time, use with shooting first picture group as identical integral time; But need close shutter this moment, and the gained image is called dark image;

7) two bright images and two dark images in the middle of each extracts from the first picture group picture and the second picture group picture;

8) utilize the image calculation CCD chip of extraction and total gain K of control circuit thereof, be called system-gain:

8a) from two dark images and two bright images, respectively choose one, calculate the bright image choose and the average gray value μ of dark image respectively _Y1And μ _Y2:

${\mathrm{\&mu;}}_{y1}=\frac{1}{\mathrm{MN}}\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{y}_1\left[m\right]\left[n\right],$ ${\mathrm{\&mu;}}_{y2}=\frac{1}{\mathrm{MN}}\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{y}_2\left[m\right]\left[n\right]$

Wherein, y ₁, y ₂Represent the bright image and dark image chosen respectively, M, N are respectively the capable pixel count and the row pixel count of photographic images;

8b) use the bright image variance of two bright image calculation

that extracts

${\mathrm{\&sigma;}}_{y1}^2=\frac{1}{2\mathrm{NM}}\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{\left(y^A\right[m\left]\right[n]-y^B[m\left]\right[n\left]\right)}^2$

Y wherein ^A, y ^BRepresent first and second in the bright image respectively;

8c) use the dark image variance of two dark image calculation

that extracts

${\mathrm{\&sigma;}}_{y2}^2=\frac{1}{2\mathrm{NM}}\underset{m=0}{\overset{M-1}{\mathrm{\&Sigma;}}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{\left(y^C\right[m\left]\right[n]-y^D[m\left]\right[n\left]\right)}^2$

Wherein, y ^C, y ^DRepresent first and second in the dark image respectively;

The calculation of parameter system-gain K that 8d) obtains more than the basis:

$K=\frac{{\mathrm{\&sigma;}}_{y1}^2-{\mathrm{\&sigma;}}_{y2}^2}{{\mathrm{\&mu;}}_{y1}-{\mathrm{\&mu;}}_{y2}};$

9) utilize the responsiveness R of four image calculation CCD chips that extract in the step 7):

$R=\frac{{\mathrm{\&mu;}}_{y1}-{\mathrm{\&mu;}}_{y2}}{{\mathrm{\&mu;}}_p}$

Wherein

Be the average photon number of the single pixel of CCD chip, A is the area of the single pixel of CCD chip, and E is the monochromatic light power that shines on the CCD chip, t _ExpUsed integral time when take extracting bright image, λ shines the monochromatic wavelength on the CCD chip when extracting bright image for taking, and h is a Planck's constant, and c is the light velocity;

10) try to achieve the quantum efficiency of CCD chip by system-gain K and responsiveness R:

$\mathrm{\&eta;}\left(\mathrm{\&lambda;}\right)=\frac{R}{K}.$

2. measuring method according to claim 1, wherein the described control light-source system of step 5) produces the monochromatic light of respective wavelength, carries out as follows:

2a) choose monochromatic wavelength width: Δ λ＜50nm;

2b) choose scanning wavelength [λ _s, λ _e], this wavelength need cover the wavelength response range of CCD chip;

2c) choosing sweep spacing is: λ _Int＜2* Δ λ;

2d) from initial wavelength X _sBeginning, the scanning wavelength that superposes successively is λ at interval _Int, reach cutoff wavelength λ up to wavelength _eTill, obtain a series of wavelength value;

The a series of wavelength value that 2f) obtain more than the basis are provided with light-source system and produce corresponding monochromatic light.

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