CN106324470A - Method for measuring CCD charge conversion factor - Google Patents

Abstract

The invention discloses a method for measuring a CCD charge conversion factor. The method includes the steps that a CCD optical integration region is kept at optical integration, a charge channel of a CCD continues to be kept in an on state, and control pulses are periodically applied to an output control grating and a resetting grating of the CCD so that a horizontal transferring region can output signals outwards periodically; the output signals of the CCD are processed to measure the charge conversion factor. The method has the advantages that there is no need to design a driving schedule for the CCD, in this way, generality is high, and operation is easy and convenient.

Description

The method measuring CCD charge conversion factor

Technical field

The present invention relates to a kind of CCD measuring technology, particularly relate to a kind of method measuring CCD charge conversion factor.

Background technology

In numerous performance parameters of CCD, charge conversion factor (CVF) is to weigh an important finger of CCD device performance Mark, it can characterize CCD and the electric charge collected is converted to the ability of voltage, with the saturation voltage of CCD, responsiveness, dark current The performance parameters such as density are closely related.

Gordon R.Hopkinson et al. introduced the method for a series of measurement charge conversion factor in its works (A Guide to the Use and Calibration of Detector Array Equipment, Gordon R.Hopkinson, Teresa M.Goodman, Stuart R.Prince, SPIE Press, 2004), these methods are domestic The documents and materials such as outer paper are quoted, including: 1. reset Leakage Method: according to the definition of charge conversion factor, by measuring CCD's Reset leakage current, amplitude output signal, the time of integration and effectively pixel number calculate；2. x-ray method: pass through at a certain temperature The x-ray bombardment CCD device of external radiation source, produces a number of freedom-hole-electron pair, then to working in integrating state Under output node voltage measure, obtain CVF value；3. Mean-Variance method: by the statistics of output signal institute band noise Rule calculates.

There are problems in preceding method in practical operation: 2. method all exists bigger mistake with method test result 3. Difference；2. method needs the test device of complexity and harsher test environment；Method 3. process is loaded down with trivial details, and test job amount is big；And Maximum of which deficiency is that three kinds of methods the most do not possess versatility: 1. such as method requires the shape that CCD is operated in normal imaging State, the time of integration therein must determine according to sequential during normal imaging, but the work schedule of every kind of CCD is different from, When testing different types of CCD, must be every kind of the most individually designed drive circuit of CCD, workload be big, takes time and effort, And poor universality；The physical characteristic parameter of method 2. and the most then heavy dependence CCD self, the most not only adds workload, with Time also add test period of device parameters, consume substantial amounts of manpower and materials.

Summary of the invention

For the problem in background technology, the present invention proposes a kind of method measuring CCD charge conversion factor, described CCD includes anti-blooming grid, light integrated area, the first transfer control gate, vertical transitions district, the second transfer control gate, horizontal transfer district, defeated Go out control gate and resetting gate；Described first transfer control gate is used for controlling electric charge and is transferred to vertical transitions district from light integrated area；Institute State the second transfer control gate and be transferred to horizontal transfer district for controlling electric charge from vertical transitions district；Described output control gate and reset Grid are used for controlling electric charge and outwards export from horizontal transfer district, and its innovation is: enter the charge conversion factor of CCD as follows Row is measured:

1) CCD is placed in photoenvironment, controls anti-blooming grid and make light integrated area be continuously maintained in light integrating state, meanwhile, Controlling the first transfer control gate makes the charge pathway between light integrated area and vertical transitions district be continuously maintained in conducting state, with Time, control the second transfer control gate and make the charge pathway between vertical transitions district and horizontal transfer district be continuously maintained in conducting shape State；

2) periodically apply to control pulse to output control gate and resetting gate, make horizontal transfer district the most defeated Go out signal；

3) under the first light-intensity conditions, when the outside output signal in horizontal transfer district, at horizontal transfer district output node Electric current and output signal sample；Under the second light-intensity conditions, when the outside output signal in horizontal transfer district, level is turned Move the electric current at district's output node and output signal is sampled；The light intensity of the first light-intensity conditions and the second light-intensity conditions is different；

4) according to the charge conversion factor of following formula calculating CCD:

$CVF=\frac{{\mathrm{\ΔV}}_o\×{10}^3}{{\mathrm{\ΔI}}_{RD}\×{10}^{-9}}\×q\×f$

Wherein, Δ V_o=V_o1-V_o2, Δ I_RD=I_RD1-I_RD2, Δ V_oUnit be mV, Δ I_RDUnit be nA, V_o1For right Answer the signal amplitude of the output signal of the first light-intensity conditions, V_o2For the signal amplitude of the output signal of corresponding second light-intensity conditions, I_RD1For the electric current of corresponding first light-intensity conditions, I_RD2Electric current for corresponding second light-intensity conditions；Q is the quantity of electric charge of Single Electron, q Take 1.6 × 10^-19Coulomb；F is the output frequency in horizontal transfer district；CVF is charge conversion factor, and unit is μ V/e^-。

When specifically applying, CCD is placed in photoenvironment, controls anti-blooming grid and make light integrated area be continuously maintained in light integration shape State (will anti-blooming grid be persistently placed in low level state), is in the CCD under light integrating state, under continuous light, sustainable not Produce electric charge, to provide the signal source that can be used for test disconnectedly；Meanwhile, controlling the first transfer control gate makes light integrated area with vertical Charge pathway between transition range be continuously maintained in conducting state (will first transfer control gate persistently be placed in high level state, This allows for the internal sustainable existence of CCD can store the potential well of electric charge, and these potential wells are interconnected, and define thus Steady electric field within through CCD, light integration the electric charge produced can be evenly distributed in the inside of CCD, if illumination bar Part does not changes, and CCD output within the unit interval will keep stable), meanwhile, control the second transfer control gate and make vertically Charge pathway between transition range and horizontal transfer district is continuously maintained in conducting state and (will persistently be placed in by the second transfer control gate High level state, electric charge just can be transferred to horizontal transfer district from vertical transitions district continuously)；Subject to the foregoing, to Output control gate and resetting gate periodically apply to control pulse, and the horizontal transfer district of CCD just can be made the most outwards to export Signal, at this moment, so that it may carry out step 3 sampling operation), sampling operation terminates, by step 4) in formula to data at Reason just can obtain the charge conversion factor data of this CCD；

The principle of the present invention is:

The definition of charge conversion factor is relatively simple, i.e. output voltage and being stored between the electron number at output node Ratio, single from the point of view of definition, if the output voltage of CCD can be got and is stored in the electron number at output node, with regard to energy Calculate the charge conversion factor of this CCD easily；But in practical situation, under prior art conditions, it is impossible to defeated to being stored in Electron number at egress is directly measured, and this results in and cannot directly utilize the definition of charge conversion factor and carry out calculated charge Conversion factor；

The versatility problem of measurement problem and measurement means in order to solve charge conversion factor, inventor is to the most of the same race The CCD of class conducts in-depth research, and in research process, inventor finds, existing CCD, regardless of its kind, Ta Mendou There are following two common ground: 1) workflow of existing CCD the most all follows and " accepts illumination-light integration and produce charge-charge Transfer-output " step, 2) for same CCD, in its response range, under the conditions of different illumination intensity, its output is Different；

For the 2nd) common ground, it will be apparent to those skilled in the art that under normal circumstances, the output of CCD and intensity of illumination There is linear relationship in size, i.e. intensity of illumination is the biggest, and in the unit interval, the electricity of CCD output is the most, and electricity can be converted into Electron number, then just can according under the conditions of different illumination intensity CCD output electricity difference indirectly reflect electric charge conversion because of Electron number in sub-definite, and then try to achieve charge conversion factor, along this thinking, inventor has made following derivation:

If the signal amplitude of ccd output signal is V under the conditions of intensity of illumination 1_o1, the corresponding output node quantity of electric charge is Q₁, Under the conditions of intensity of illumination 2, the signal amplitude of ccd output signal is V_o2, the corresponding output node quantity of electric charge is Q₂；Represent single with q The quantity of electric charge (1.6 × 10 of electronics^-19Coulomb), Δ V_o=V_o2-V_o1, Δ Q=Q₂-Q₁, then by the definition of charge conversion factor, its Value can be expressed as:

$CVF=\frac{{\mathrm{\ΔV}}_o}{\mathrm{\Δ}Q/q}$

If the output cycle of single pixel is t, then according to current capacity formula Q/t=I, Δ Q=Δ I_RD× t, Δ I_RD=I_RD1-I_RD2, then above formula can be deformed into following formula:

$CVF=\frac{{\mathrm{\ΔV}}_o}{{\mathrm{\ΔI}}_{RD}\×t/q}$

From existing theory, the inverse in the output cycle of single pixel is exactly the output frequency of pixel, if representing picture with f The output frequency of unit, then have f=1/t, and then above formula is rewritable is:

$CVF=\frac{{\mathrm{\ΔV}}_o}{{\mathrm{\ΔI}}_{RD}}\×q\×f$

After parameters in above formula is analyzed, we it finds that, the numerical value of f depend on control CCD output Time sequential pulse, it is known quantity, as long as being obtained in that Δ V_oWith Δ I_RDWe just can calculate CVF exactly, and is used for calculating ΔV_oWith Δ I_RDParameter all can by existing means carry out quantify detection, illustrate that preceding method is feasible；Specify that measurement side After method, we are referring again to the versatility seeing the method:

Another common ground of previously described existing CCD is, their workflow the most all follow " accept illumination- Light integration produce charge-charge transfer-output " step, based on existing CCD control theory understand, " connecing in workflow Being produced charge-charge by illumination-light integration to shift " step all realizes driving by impulse level, and in aforesaid formula, institute Need is only the CCD output signal that can provide the unit interval, and then, the present invention uses step 1) in operation to make at CCD In a kind of abnormal operating state (for normal operating conditions), then by output control gate and resetting gate last week Phase property ground applies to control pulse, just can get the parameter needed for aforementioned formula calculates, and so far, those skilled in the art should be bright Bai Liao, the present invention need not to design complete work schedule to drive CCD normally to work, only need to control in CCD light integration with The control gate of electric charge transfer provides fixed level, and the control gate controlling output in CCD provides and simply controls pulse, with regard to energy Obtaining the parameter needed for formula calculates, compared with the CCD driver' s timing complete with design, the present invention only needs to design and exports phase with CCD The control pulse closed, workload and running cost will significantly reduce, and only relevant to output control pulse is very simple, only Wanting to make CCD periodically output signal signal, as long as the particular type of CCD determines, those skilled in the art are with regard to energy Implement.

For different types of CCD, the quantity of its control gate possible there are differences, it is also possible to it is only that some CCD possesses some Some additional functions, but, no matter which kind of CCD, when they work, the main body principle of institute's foundation is but identical；Applying this Bright time different types of CCD is tested, only need to be placed on the present invention according to the control gate quantity of CCD and additional function Step 1) set by condition, then to control pulse carry out simple modification, just can meet the testing requirement of variety classes CCD； Such as, CCD output uses three-phase or four phases drive, and only need to increase the way of output drive signal, and and for example CCD gathers around There are vertical merged grid etc., only need to be set to high level；

With the method in background technology 1. compared with, 1. method needs for the most individually designed driver' s timing of different types of CCD, And after using the present invention, it is no longer necessary to carry out complicated loaded down with trivial details design of driving timing sequence work, only need to according to the quantity of control gate or Drive circuit is made some and trickle is adjusted by additional function；With method 2. and 3. compared with, the measurement operation of the present invention need not Understanding the physical parameter of device, test process is the most efficient；

What deserves to be explained is: owing to, in Practical Project, the conventional unit of charge conversion factor is μ V/e^-, and by inspection Electric current and the measurement unit of signal amplitude that survey means get are not mated, for mutual of the unit making parameters Joining, then aforementioned formula has been made again following deformation by inventor:

$CVF=\frac{{\mathrm{\ΔV}}_o\×{10}^3}{{\mathrm{\ΔI}}_{RD}\×{10}^{-9}}\×q\×f$

Preferably, the electric current at described output node is sampled by ammeter.

Preferably, under same illumination condition, electric current is carried out multiple repairing weld, I_RD1And I_RD2Take the most corresponding illumination respectively Under the conditions of the meansigma methods of multiple sampled signals.

Preferably, under same illumination condition, output signal is carried out multiple repairing weld, V_o1And V_o2Take respective correspondence respectively The signal amplitude meansigma methods of the multiple sampled signals under illumination condition.

Preferably, when described output signal is sampled, under same light-intensity conditions, carry out multiple repairing weld, correspondence is same Multiple sampled signals of one light-intensity conditions are converted to digital picture, then calculate the pixel of single pixel in digital picture average Value, is then scaled corresponding V by pixel average_o1And V_o2.In prior art, some image processing software is the most It is integrated with the function extracting pixel average, directly utilizes this kind of image processing software, the processing routine of the present invention can be made to obtain To suitable simplification.

The method have the benefit that: providing a kind of method measuring CCD charge conversion factor, the method is not required to CCD design driven sequential to be, highly versatile, easy and simple to handle.

Accompanying drawing explanation

Fig. 1, a kind of test sequence figure of employing the present invention program；In figure, AG is that anti-blooming grid, TG amass from light for controlling electric charge Subregion is transferred to the TG transfer gate (namely first transfer control gate) in vertical transitions district, V1 and V2 for controlling electric charge from vertical transitions district Be transferred to the TG transfer gate (namely second transfer control gate) in horizontal transfer district, H1 and H2 turns in horizontal transfer district for controlling electric charge The TG transfer gate (namely output control gate), the RG that move are resetting gate.

Detailed description of the invention

A kind of method measuring CCD charge conversion factor, described CCD includes that anti-blooming grid, light integrated area, the first transfer control Grid, vertical transitions district, the second transfer control gate, horizontal transfer district, output control gate and resetting gate；Described first transfer control gate It is transferred to vertical transitions district from light integrated area for controlling electric charge；Described second transfer control gate is used for controlling electric charge and turns from vertical Move district and be transferred to horizontal transfer district；Described output control gate and resetting gate are used for controlling electric charge and outwards export from horizontal transfer district, Its innovation is: measure the charge conversion factor of CCD as follows:

1) CCD is placed in photoenvironment, controls anti-blooming grid and make light integrated area be continuously maintained in light integrating state, meanwhile, Controlling the first transfer control gate makes the charge pathway between light integrated area and vertical transitions district be continuously maintained in conducting state, with Time, control the second transfer control gate and make the charge pathway between vertical transitions district and horizontal transfer district be continuously maintained in conducting shape State；

2) periodically apply to control pulse to output control gate and resetting gate, make horizontal transfer district the most defeated Go out signal；

3) under the first light-intensity conditions, when the outside output signal in horizontal transfer district, at horizontal transfer district output node Electric current and output signal sample；Under the second light-intensity conditions, when the outside output signal in horizontal transfer district, level is turned Move the electric current at district's output node and output signal is sampled；The light intensity of the first light-intensity conditions and the second light-intensity conditions is different；

4) according to the charge conversion factor of following formula calculating CCD:

$CVF=\frac{{\mathrm{\ΔV}}_o\×{10}^3}{{\mathrm{\ΔI}}_{RD}\×{10}^{-9}}\×q\×f$

Wherein, Δ V_o=V_o1-V_o2, Δ I_RD=I_RD1-I_RD2, Δ V_oUnit be mV, Δ I_RDUnit be nA, V_o1For right Answer the signal amplitude of the output signal of the first light-intensity conditions, V_o2For the signal amplitude of the output signal of corresponding second light-intensity conditions, I_RD1For the electric current of corresponding first light-intensity conditions, I_RD2Electric current for corresponding second light-intensity conditions；Q is the quantity of electric charge of Single Electron, q Take 1.6 × 10^-19Coulomb；F is the output frequency in horizontal transfer district；CVF is charge conversion factor, and unit is μ V/e^-。

Further, the electric current at described output node is sampled by ammeter.

Further, under same illumination condition, electric current is carried out multiple repairing weld, I_RD1And I_RD2Take the most corresponding light respectively The meansigma methods of the multiple sampled signals under the conditions of according to.

Further, under same illumination condition, output signal is carried out multiple repairing weld, V_o1And V_o2It is the most right to take respectively Answer the signal amplitude meansigma methods of multiple sampled signals under illumination condition.

Further, when described output signal is sampled, carry out multiple repairing weld under same light-intensity conditions, by correspondence Multiple sampled signals of same light-intensity conditions are converted to digital picture, then calculate the pixel of single pixel in digital picture and put down Average, is then scaled corresponding V by pixel average_o1And V_o2。

Claims (5)

1. the method measuring CCD charge conversion factor, described CCD includes that anti-blooming grid, light integrated area, the first transfer control Grid, vertical transitions district, the second transfer control gate, horizontal transfer district, output control gate and resetting gate；Described first transfer control gate It is transferred to vertical transitions district from light integrated area for controlling electric charge；Described second transfer control gate is used for controlling electric charge and turns from vertical Move district and be transferred to horizontal transfer district；Described output control gate and resetting gate are used for controlling electric charge and outwards export from horizontal transfer district, It is characterized in that: as follows the charge conversion factor of CCD is measured:

1) CCD is placed in photoenvironment, controls anti-blooming grid and make light integrated area be continuously maintained in light integrating state, control meanwhile First transfer control gate makes the charge pathway between light integrated area and vertical transitions district be continuously maintained in conducting state, meanwhile, and control System the second transfer control gate makes the charge pathway between vertical transitions district and horizontal transfer district be continuously maintained in conducting state；

2) periodically apply to control pulse to output control gate and resetting gate, make horizontal transfer district the most outwards export letter Number；

3) under the first light-intensity conditions, when the outside output signal in horizontal transfer district, to the electricity at horizontal transfer district output node Stream and output signal are sampled；Under the second light-intensity conditions, when the outside output signal in horizontal transfer district, to horizontal transfer district Electric current and output signal at output node are sampled；The light intensity of the first light-intensity conditions and the second light-intensity conditions is different；

4) according to the charge conversion factor of following formula calculating CCD:

$CVF=\frac{{\mathrm{\ΔV}}_o\×{10}^3}{{\mathrm{\ΔI}}_{RD}\×{10}^{-9}}\×q\×f$

Wherein, Δ V_o=V_o1-V_o2, Δ I_RD=I_RD1-I_RD2, Δ V_oUnit be mV, Δ I_RDUnit be nA, V_o1For corresponding the The signal amplitude of the output signal of one light-intensity conditions, V_o2For the signal amplitude of the output signal of corresponding second light-intensity conditions, I_RD1For The electric current of corresponding first light-intensity conditions, I_RD2Electric current for corresponding second light-intensity conditions；Q is the quantity of electric charge of Single Electron, and q takes 1.6 ×10^-19Coulomb；F is the output frequency in horizontal transfer district；CVF is charge conversion factor, and unit is μ V/e^-。

The method of measurement CCD charge conversion factor the most according to claim 1, it is characterised in that: at described output node Electric current sampled by ammeter.

The method of measurement CCD charge conversion factor the most according to claim 1 and 2, it is characterised in that: at same illumination bar Under part, electric current is carried out multiple repairing weld, I_RD1And I_RD2Take the average of multiple sampled signals under respective corresponding illumination condition respectively Value.

The method of measurement CCD charge conversion factor the most according to claim 1, it is characterised in that: at same illumination condition Under, output signal is carried out multiple repairing weld, V_o1And V_o2Take the signal of multiple sampled signals under respective corresponding illumination condition respectively Amplitude average value.

The method of measurement CCD charge conversion factor the most according to claim 1, it is characterised in that: to described output letter When number sampling, under same light-intensity conditions, carry out multiple repairing weld, multiple sampled signals of corresponding same light-intensity conditions are changed For digital picture, then calculate the pixel average of single pixel in digital picture, then pixel average is scaled phase The V answered_o1And V_o2。