CN106199370B - The test device that basic data is provided can be calculated for CCD charge conversion factors - Google Patents

Abstract

The invention discloses a test device for detecting the charge conversion factor of a CCD. The test device is composed of a light source, an ammeter, a driving circuit board and a processing module; A test device for charge conversion factor, the test device is simple in structure and easy to operate, and only needs to make slight changes to the driving circuit board in the device to meet the test requirements of various CCDs.

Description

A test device that can provide basic data for the calculation of CCD charge conversion factor

technical field

The invention relates to a CCD charge conversion factor detection technology, in particular to a testing device capable of providing basic data for the calculation of the CCD charge conversion factor.

Background technique

Among the many performance parameters of CCD, charge conversion factor (CVF) is an important index to measure the performance of CCD device. Performance parameters such as current density are closely related.

Gordon R.Hopkinson et al have introduced a series of methods for measuring the charge conversion factor in their works (A Guide to the Use and Calibration of Detector Array Equipment, GordonR.Hopkinson, Teresa M.Goodman, Stuart R.Prince, SPIEPress, 2004), these methods are cited by domestic and foreign papers and other documents, including: ①Reset leakage current method: According to the definition of charge conversion factor, it is calculated by measuring the reset leakage current of CCD, output signal amplitude, integration time and effective pixel number ;②X-ray method: irradiate the CCD device with X-rays from an external radiation source at a specific temperature to generate a certain number of free-hole electron pairs, and then measure the output node voltage working in the integral state to obtain the CVF value; ③Mean-variance method: Calculated by the statistical law of the noise in the output signal. There are many problems in the actual operation of the aforementioned methods: the test results of method ② and method ③ all have large errors; method ② requires complex testing devices and a harsh test environment; method ③ is cumbersome and the test workload is large; The biggest shortcoming is that the three methods are not universal: For example, method ① requires the CCD to work in the normal imaging state, and the integration time must be determined according to the timing of normal imaging. However, the working timing of each CCD is different. When testing different types of CCDs, it is necessary to design a drive circuit for each type of CCD separately, which is labor-intensive, time-consuming, and labor-intensive, and has poor versatility; methods ② and ③ are heavily dependent on the physical characteristic parameters of the CCD itself. The workload is increased, and the test cycle of device parameters is also increased, which consumes a lot of manpower and material resources.

Contents of the invention

For the problems in the background technology, the present invention proposes a test device that can provide basic data for the calculation of the CCD charge conversion factor, and its innovation is that the test device is composed of a light source, an ammeter, a drive circuit board and a processing module; The light intensity of the light source can be adjusted; the drive circuit board is provided with a plurality of drive sockets and output sockets, the drive pins of the CCD are plugged into the drive sockets, and the output pins of the CCD are plugged into the output sockets;

The light source is arranged on the top of the driving circuit board, and the area for setting the CCD on the driving circuit board is located in the irradiation range of the light source, and the light-receiving surface of the CCD is opposite to the light source; the ammeter is respectively connected to the output socket and the processing module; the processing module Connect to the output socket;

Described driving circuit board can keep the light integrating region of CCD continuously in the light integrating state (that is to say, the pin corresponding to the anti-halation grid on the CCD is continuously placed in low level state by driving the socket, under this condition, if the CCD is illuminated, The light integration area will continuously generate charges), and at the same time, the drive circuit board can keep the charge channel between the light integration area and the vertical transfer area of the CCD continuously in the conduction state through the drive socket (that is, the corresponding first transfer on the CCD The pin of the control gate is continuously placed in a high level state, and the first transfer control gate defined in the present invention is used to control the transfer of charges from the light integration area of the CCD to the vertical transfer area, which makes the continuous existence of the charge storage in the CCD. Potential wells, and these potential wells are connected to each other, so that a constant electric field is formed through the inside of the CCD, and the charges generated by light integration can be evenly distributed inside the CCD. The output will remain stable), and at the same time, the drive circuit board can keep the charge channel between the vertical transfer area and the horizontal transfer area of the CCD in the conduction state continuously through the drive socket (that is, the pin corresponding to the second transfer control gate on the CCD Continuously placed in a high level state, the second transfer control gate defined herein is used to control the transfer of charges from the vertical transfer region of the CCD to the horizontal transfer region. In this state, the charge can be continuously transferred from the vertical transfer region to the horizontal transfer region. At the same time, the drive circuit board can periodically apply control pulses to the output control gate and reset gate of the CCD through the drive socket (the output control gate and the reset gate are used to control the output of the charge from the horizontal transfer area), so that The CCD periodically outputs signals to the outside, and at the same time, the drive circuit board can output the output signals of the CCD through the output socket; state to be tested;

The ammeter can detect the current at the output socket, and output the detection result to the processing module;

The processing module can sample the output signal of the CCD, and convert the sampled signal into a digital image. After obtaining the digital image, the processing module extracts the pixel average value of the digital image, and then converts the pixel average value into a corresponding CCD signal amplitude.

Principle of the present invention is:

The definition of the charge conversion factor is relatively simple, that is, the ratio between the output voltage and the number of electrons stored at the output node. From the definition alone, if the output voltage of the CCD and the number of electrons stored at the output node can be obtained, then The charge conversion factor of the CCD can be easily calculated; but in actual conditions, under the existing technical conditions, the number of electrons stored at the output node cannot be directly measured, which leads to the inability to directly use the definition of the charge conversion factor to Calculate the charge conversion factor;

In order to solve the measurement problem of the charge conversion factor and the universality of the measurement means, the inventor has carried out in-depth research on different types of CCDs. The following two things are in common: 1) The workflow of existing CCDs generally follows the steps of "accepting illumination-light integration to generate charge-charge transfer-output", 2) for the same CCD, within its response range, different illumination Under the intensity condition, its output is different;

For the 2) common point, those skilled in the art should be clear that under normal circumstances, there is a linear relationship between the output of the CCD and the light intensity, that is, the greater the light intensity, the greater the power output by the CCD per unit time, and the power can be converted Then the number of electrons in the definition of the charge conversion factor can be indirectly reflected according to the difference in the output power of the CCD under different light intensities, and then the charge conversion factor can be obtained. Following this line of thinking, the inventor made the following derivation:

Let the signal amplitude of the CCD output signal under the condition of light intensity 1 be V _o1 , the corresponding output node charge is Q ₁ , and the signal amplitude of the CCD output signal under the condition of light intensity 2 is V _o2 , and the corresponding output node charge is Q ₂ ; use q to represent the charge of a single electron (1.6×10 ^-19 Coulomb), ΔV _o =V _o2 -V _o1 , ΔQ = Q ₂ -Q ₁ , then according to the definition of charge conversion factor, its value can be expressed as:

Assuming that the output period of a single pixel is t, then according to the current quantity formula Q/t=I, ΔQ=ΔI _RD ×t, ΔI _RD =I _RD1 -I _RD2 , then the above formula can be transformed into the following formula:

It can be seen from the existing theory that the reciprocal of the output cycle of a single pixel is the output frequency of the pixel. If f is used to represent the output frequency of the pixel, then f=1/t, so the above formula can be rewritten as:

After analyzing the parameters in the above formula, we will find that the value of f depends on the timing pulse that controls the output of the CCD, which is a known quantity. As long as ΔV _o and ΔI _RD can be obtained, we can accurately calculate the CVF , and the parameters used to calculate ΔV _o and ΔI _RD can be quantitatively detected by existing means;

Another common point of the existing CCDs mentioned above is that their work processes generally follow the steps of "accepting light-light integration to generate charge-charge transfer-output", based on the existing CCD control theory, it is different from "accepting Operations related to the step of "light-light integration to generate charge-charge transfer" are all driven by pulse level. From the aforementioned derivation process, it can be seen that the acquisition of each parameter in the formula does not require the CCD to be in a normal working state, but only requires the CCD to be able to The output signal per unit time is provided, so in the present invention, the CCD is in the aforementioned state to be tested by driving the socket. Compared with the normal working state of the CCD, the aforementioned state to be tested only needs to apply a fixed level and can be realized, which is Avoiding the problem of designing the drive sequence for the CCD, so far, those skilled in the art should understand that, compared with designing a complete CCD drive sequence, the aforementioned method only needs to design the control pulses related to the CCD output, and the test workload and hardware consumption will be reduced. substantially reduced;

For different types of CCDs, there may be differences in the number of control grids, and some CCDs may have some special additional functions. However, no matter what kind of CCDs, the main principle they work on is the same; in the application of this When the invention tests different types of CCDs, it is only necessary to place the control gates used to control the internal charge transfer of the CCD in a corresponding fixed level state according to the number and functions of the control gates of the CCD, and to control the charge output of the CCD. Minor modification of the control pulse (as long as the type of CCD is determined, it is a basic skill for those skilled in the art to modify the control pulse so that the CCD periodically outputs signals, and the workload of modifying the control pulse is far less than Design a complete driving sequence for CCD) to meet the test requirements of different types of CCD; Merge gate, etc., just set it to high level;

Compared with the method ① in the background technology, the method ① needs to separately design the drive timing for different types of CCDs, but after the present invention is adopted, it is no longer necessary to carry out complicated and tedious design of the drive sequence, and only needs to be based on the number of control gates or The additional functions only need to make some minor adjustments to the driving circuit; compared with methods ② and ③, the measurement operation of the present invention does not need to understand the physical parameters of the device, and the testing process is simple and efficient;

During the specific test, the state of the CCD is first adjusted to the state to be tested by the drive circuit board, and then the light intensity of the light source is adjusted to the first light intensity condition. At this time, the current I _RD1 at the output socket (the current at the output socket is equivalent to the current at the CCD output node) and the output signal for sampling, after the output signal is processed, the signal amplitude V _o1 can be obtained, and then the light intensity of the light source is adjusted to the second light intensity condition (the second light intensity condition is the same as the first light intensity condition The light intensity of the first light intensity condition is different), and then the CCD output signal is sampled to obtain the current I _RD2 and the amplitude V _o2 , q and f are known, and the charge conversion factor of the CCD can be calculated according to the aforementioned formula.

In order to meet the test requirements of different types of CCDs, the circuit structure related to the drive socket and output socket on the drive circuit board can be modularized. When the test object is changed, only the corresponding drive socket and output socket need to be replaced, and the control pulses Minor modification, so there is the following preferred solution: the drive circuit board is composed of a transfer circuit and a control module; the drive socket and the output socket are arranged on the transfer circuit, and the control module can drive the output signal of the socket to control .

Preferably, the control module is realized by FPGA.

Preferably, the test device is provided with a casing, the casing wraps the light source and the driving circuit board, and the casing is made of light-blocking material. The shell made of light-blocking material can prevent external light from shining on the CCD and prevent interference to the test results.

The beneficial technical effects of the present invention are: provide a test device that can provide basic data for the calculation of CCD charge conversion factor, the test device is simple in structure, easy to operate, only need to make slight changes to the drive circuit board in the device to adapt to Various CCD testing requirements.

Description of drawings

Fig. 1, structural representation of the present invention;

The names corresponding to each mark in the figure are: light source 1, ammeter 2, drive circuit board 3, processing module 4, and CCD 5.

Detailed ways

A test device that can provide basic data for the calculation of CCD charge conversion factor, its innovation is that: the test device is composed of a light source 1, an ammeter 2, a driving circuit board 3 and a processing module 4; the light intensity of the light source 1 can be adjusted ; The driving circuit board 3 is provided with a plurality of driving sockets and output sockets, the driving pins of the CCD are plugged in the driving sockets, and the output pins of the CCD are plugged in the output sockets;

The light source 1 is arranged on the top of the driving circuit board 3, and the area for setting the CCD on the driving circuit board 3 is located in the irradiation range of the light source 1, and the light receiving surface of the CCD is opposite to the light source 1; the ammeter 2 is connected to the output socket and the light source respectively. The processing module 4 is connected; the processing module 4 is connected to the output socket;

The drive circuit board 3 can keep the optical integration area of the CCD in the light integration state continuously through the drive socket; at the same time, the drive circuit board 3 can continuously maintain the charge channel between the light integration area and the vertical transfer area of the CCD through the drive socket In conduction state; Simultaneously, drive circuit board 3 can make the charge channel between the vertical transfer area of CCD and the horizontal transfer area continue to be kept in conduction state by drive socket; The output control gate and the reset gate periodically apply control pulses, and when the CCD is illuminated, the CCD can periodically output signals to the outside; at the same time, the drive circuit board 3 can output the output signal of the CCD to the outside through the output socket ;

The ammeter 2 can detect the current at the output socket, and output the detection result to the processing module 4;

The processing module 4 can sample the output signal of the CCD, and convert the sampled signal into a digital image. After obtaining the digital image, the processing module 4 extracts the pixel average value in the digital image, and then converts the pixel average value For the corresponding CCD signal amplitude.

Further, the drive circuit board 3 is composed of a switch circuit and a control module; the drive socket and the output socket are arranged on the switch circuit, and the control module can drive the output signal of the socket for control.

Further, the control module is realized by FPGA.

Further, the test device is provided with a casing, the casing wraps the light source 1 and the driving circuit board 3, and the casing is made of a light-blocking material.

Claims (4)

1. a kind of can calculate the test device for providing basic data for CCD charge conversion factors, it is characterised in that：The test dress It sets and is made of light source (1), ammeter (2), drive circuit board (3) and processing module (4)；The intensity of illumination energy of the light source (1) It is enough to adjust；Multiple drive sockets and output socket are provided on the drive circuit board (3), the driving pin of CCD is plugged on drive In dynamic socket, the output pin of CCD is plugged in output socket；

The light source (1) is arranged on the top of drive circuit board (3), drive circuit board (3) to be located at for the region of CCD to be arranged In the range of exposures of light source (1), the light-receiving surface of CCD is opposite with light source (1)；The ammeter (2) respectively with output socket and place Module (4) is managed to connect；Processing module (4) is connect with output socket；

The drive circuit board (3) can make the light integrated area of CCD be continuously maintained in light integrating state by drive socket, i.e., will The pin that anti-blooming grid are corresponded on CCD is persistently placed in low level state；Meanwhile drive circuit board (3) can make CCD by drive socket Light integrated area and vertical transition range between charge pathway be continuously maintained in conducting state, i.e., will corresponding first transfer on CCD The pin of control gate is persistently placed in high level state, and the first transfer control gate is for controlling light integrated area of the charge from CCD It is transferred to vertical transition range；Meanwhile drive circuit board (3) can make vertical transition range and the horizontal transfer of CCD by drive socket Charge pathway between area is continuously maintained in conducting state, i.e., is persistently placed in the pin of corresponding second transfer control gate on CCD High level state, the second transfer control gate are transferred to horizontal transfer area for controlling charge from the vertical transition range of CCD；Together When, drive circuit board (3) can periodically apply control pulse by output control gate from drive socket to CCD and resetting gate, When CCD is by illumination, CCD can periodically outside output signal；Meanwhile the drive circuit board (3) can pass through output Socket exports the output signal of CCD outward；

The ammeter (2) can be detected the electric current at output socket, and testing result is exported to processing module (4)；

The processing module (4) can sample the output signal of CCD, and the signal sampled is converted to digital picture, After obtaining digital picture, processing module (4) extracts the pixel average of digital picture, then converts pixel average For corresponding ccd signal amplitude.

2. according to claim 1 can calculate the test device for providing basic data, feature for CCD charge conversion factors It is：The drive circuit board (3) is made of built-up circuit and control module；The drive socket and output socket setting are turning It connects on circuit, the control module can control the output signal of drive socket.

3. according to claim 2 can calculate the test device for providing basic data, feature for CCD charge conversion factors It is：The control module is realized using FPGA.

4. according to claim 1 can calculate the test device for providing basic data, feature for CCD charge conversion factors It is：It is provided with shell in the test device, in light source (1) and drive circuit board (3) are wrapped in by the shell, shell is adopted It is made of light blocking material.