CN112261324A - Method for eliminating frame transfer type EMCCD Smear effect - Google Patents
Method for eliminating frame transfer type EMCCD Smear effect Download PDFInfo
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- CN112261324A CN112261324A CN202011130273.XA CN202011130273A CN112261324A CN 112261324 A CN112261324 A CN 112261324A CN 202011130273 A CN202011130273 A CN 202011130273A CN 112261324 A CN112261324 A CN 112261324A
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- 238000012546 transfer Methods 0.000 title claims abstract description 44
- 238000000034 method Methods 0.000 title claims abstract description 31
- 230000000694 effects Effects 0.000 title claims abstract description 19
- 239000004973 liquid crystal related substance Substances 0.000 claims abstract description 87
- 230000003287 optical effect Effects 0.000 claims abstract description 49
- 238000006243 chemical reaction Methods 0.000 claims abstract description 7
- 210000002858 crystal cell Anatomy 0.000 claims description 11
- 239000000463 material Substances 0.000 claims description 5
- 239000003990 capacitor Substances 0.000 claims description 4
- 238000002834 transmittance Methods 0.000 claims description 3
- 238000003384 imaging method Methods 0.000 abstract description 7
- 238000010351 charge transfer process Methods 0.000 abstract description 5
- 230000010354 integration Effects 0.000 abstract description 3
- 238000010586 diagram Methods 0.000 description 5
- 230000005684 electric field Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000005286 illumination Methods 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 238000012805 post-processing Methods 0.000 description 1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
- H04N25/62—Detection or reduction of noise due to excess charges produced by the exposure, e.g. smear, blooming, ghost image, crosstalk or leakage between pixels
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/70—SSIS architectures; Circuits associated therewith
- H04N25/71—Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors
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Abstract
The invention discloses a method for eliminating a frame transfer type EMCCD Smear effect, which adopts the turn-off of a liquid crystal light switch to prevent light from entering a photosensitive area of an EMCCD device in the process of transferring charges in the EMCCD device from the photosensitive area to a storage area; in the process of horizontal transfer of charges in the EMCCD device, the liquid crystal optical switch is switched on to allow light rays to enter a photosensitive area of the EMCCD device, and photoelectric conversion is carried out through a photoelectric effect. The method realizes the functions of opening the optical channel during the exposure integration period of the frame transfer EMCCD and closing the optical channel during the charge transfer period by reasonably configuring the driving time sequence of the liquid crystal optical switch and the EMCCD device, so as to avoid the generation of redundant charges in the charge transfer process of the photosensitive area and eliminate the Smear phenomenon in the imaging process of the frame transfer EMCCD device.
Description
Technical Field
The invention relates to a method for eliminating the Smear effect of a frame transfer type EMCCD.
Background
The EMCCD with frame transfer structure is the most common device structure of CCD with electron multiplying function and includes photosensitive area, storage area, horizontal shift multiplying register and output amplifier module. However, the structural feature of frame transfer determines that the vertical CCD is also continuously performing photoelectric conversion during vertical transfer, and if the signal charge in the photosensitive region is not transferred to the storage region as soon as possible, the signal charge during transfer will add an excessive photoelectric conversion signal, especially the straight line through the strong light irradiation part will have a greater influence, and white line noise will be pulled out above and below the image, which is called light leakage, i.e., "Smear effect", and is reduced in inverse proportion to the frame transfer speed, but because the transfer speed is limited, the frame transfer mode cannot avoid the generation of such noise.
The technology for eliminating the Smear phenomenon in imaging detection is always the key research field at home and abroad at present. To eliminate the Smear effect generated during imaging of the frame transfer EMCCD device, there are generally three ways: the first way is to use a mechanical shutter to turn off the optical path during the charge transfer of the device, so as to avoid the generation of redundant charges; the second mode is to use an electronic shutter to ensure that the transfer time of the charge of the device from the photosensitive area to the storage area is as short as possible, thereby reducing the generation of redundant charge; the third mode is to use a Smear effect correction algorithm to carry out post-processing on the formed image so as to eliminate the Smear effect.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects of the prior art and provide a method for eliminating the Smear effect of a frame transfer type EMCCD, which eliminates the Smear phenomenon in the imaging process of the frame transfer type EMCCD device from the aspects of a hardware circuit and an optical structure.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a method for eliminating the Smear effect of frame transfer type EMCCD, in the transfer process of the internal charge of EMCCD device from the photosensitive area to the storage area, adopt the turn-off of the light switch of the liquid crystal, prevent the light from entering the photosensitive area of EMCCD device;
in the process of horizontal transfer of charges in the EMCCD device, the liquid crystal optical switch is switched on to allow light rays to enter a photosensitive area of the EMCCD device, and photoelectric conversion is carried out through a photoelectric effect.
Further, the liquid crystal optical switch is controlled to be turned off or turned on by a turn-off control signal provided by the driving circuit.
Further, the liquid crystal optical switch includes a liquid crystal cell; the driving circuit of the liquid crystal optical switch comprises a liquid crystal driving board which is arranged close to the rear surface of the liquid crystal box.
Furthermore, a shading material film is attached to the front surface of the liquid crystal box, an optical window is reserved in the central area of the shading material film, and the position and the size of the optical window are matched with the light-sensitive surface of the EMCCD device.
Furthermore, a window is reserved in the central area of the liquid crystal driving board, and the position and the size of the window are matched with the light-sensitive surface of the EMCCD device.
Further, the liquid crystal driving board is connected with the liquid crystal box through the driving electrode to provide external driving voltage for the liquid crystal box.
Further, the liquid crystal cell controls light transmittance by an external driving voltage, and switches the liquid crystal optical switch between on and off states by adjusting the magnitude of the driving voltage.
Furthermore, the driving circuit for switching on and off the light of the liquid crystal light comprises an exclusive-or gate, the two input ends of the exclusive-or gate respectively input the switching-on and switching-off control signal and a square wave pulse, the output end of the exclusive-or gate is connected with the back electrode of the equivalent capacitor of the liquid crystal box, and the front electrode of the equivalent capacitor of the liquid crystal box is connected with the square wave pulse.
Furthermore, the FPGA is adopted to respectively send time sequence signals of external driving voltage to the EMCCD device and the liquid crystal light switching driving circuit, and the states of the EMCCD device and the liquid crystal light switching are controlled.
The invention achieves the following beneficial effects:
the invention provides a method for eliminating the Smear phenomenon in the imaging process of a frame transfer type EMCCD device from the aspects of a hardware circuit and an optical structure by utilizing the electro-optical characteristic of a liquid crystal optical switch. By reasonably configuring the driving time sequence of the liquid crystal optical switch and the EMCCD device, the functions of opening the optical channel during the exposure integration period of the frame transfer EMCCD and closing the optical channel during the charge transfer period are realized, so that the generation of redundant charges in the charge transfer process of the photosensitive area is avoided.
Drawings
FIG. 1 is a schematic block diagram of an optical channel switch controlled by a liquid crystal optical switch;
FIG. 2 is a diagram of an EMCCD circuit structure using liquid crystal light switching;
FIG. 3 is a schematic diagram of a structure of a liquid crystal optical switch;
fig. 4a and 4b are schematic diagrams illustrating the operation principle of the liquid crystal optical switch;
FIG. 5 is a schematic diagram of a liquid crystal driving circuit;
FIG. 6 is an XOR gate truth table;
FIG. 7 shows a timing sequence for controlling the liquid crystal driving signals;
FIG. 8 utilizes the on-off timing of the liquid crystal optical switch to control the effective exposure time of the EMCCD device.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
The invention provides a method for eliminating the Smear phenomenon in the imaging process of a frame transfer type EMCCD device from the aspects of a hardware circuit and an optical structure by utilizing the electro-optical characteristic of a liquid crystal optical switch, which comprises the liquid crystal optical switch and a driving circuit thereof, and the frame transfer type EMCCD and the driving circuit thereof, and is shown in figure 1. And the FPGA respectively sends driving time sequence signals to the EMCCD device and the liquid crystal light switch driving circuit to control the working states of the EMCCD device and the liquid crystal light switch. By reasonably configuring the driving time sequence of the liquid crystal optical switch and the EMCCD device, the functions of opening the optical channel during the exposure integration period of the frame transfer EMCCD and closing the optical channel during the charge transfer period are realized, so that the generation of redundant charges in the charge transfer process of the photosensitive area is avoided. The structure of an EMCCD circuit using liquid crystal light switching is shown in fig. 2.
(1) The structure design of the liquid crystal optical switch is shown in fig. 3, a shading material film 2 is pasted on the front surface of a liquid crystal box 1, an optical window 21 is reserved in a central area, and the position and the size of the optical window 21 are matched with the light sensing surface of an EMCCD device; a liquid crystal driving board 3 is arranged close to the rear surface of the liquid crystal box 1 and connected with the liquid crystal box 1 through a driving electrode 4 to provide external driving voltage for the work of the liquid crystal box 1. Meanwhile, the central area of the liquid crystal driving board 3 needs to be hollowed, and the hollowed area is consistent with the position and the size of the reserved optical window 21, namely is matched with the light-sensitive surface of the EMCCD device.
(2) The liquid crystal box can control the light transmittance through external driving voltage, can switch between a completely opened state and a completely closed state by adjusting the voltage amplitude, has the working principle as shown in fig. 4a and 4b, and is based on the electro-optic effect and the optical waveguide effect of liquid crystal molecules, when the liquid crystal optical switch is applied with voltage, the liquid crystal molecules 6 are arranged in order, so that incident light 5 can penetrate through the polaroids 7 and 8; when no voltage is applied to the liquid crystal optical switch, the liquid crystal molecules 6 are disorderly arranged, and incident light cannot pass through the polarizing plates 7 and 8.
(3) Liquid crystal cell drive timing signal
The liquid crystal box is connected with the liquid crystal driving board through a pair of driving electrodes, and the working driving of the liquid crystal box is completed in a mode of continuously applying an electric field or not applying the electric field between the electrodes. The circuit schematic is shown in fig. 5, a pair of driving electrodes includes a switching control signal a and a square wave pulse B, a back electrode D is connected with the output end of the xor gate, and the relationship between the back electrode D, the switching control signal a and the square wave pulse B is shown in a truth table in fig. 6; the square wave pulse B is directly connected with the front electrode C of the liquid crystal cell, the on-off control signal a can be input with high and low levels for controlling the on and off of the liquid crystal, and the specific driving timing sequence is shown in fig. 7.
(4) Liquid crystal optical switch and EMCCD device combined drive
And in combination with the charge transfer driving time sequence of the EMCCD device, the applied voltage at two ends of the liquid crystal box is cut off in the charge transfer process of the EMCCD device, and the light path of the light signal incident to the photosensitive area of the device is cut off, so that redundant charges generated in the charge transfer process are avoided.
In fig. 8, IF1 and IF2 are the charge transfer timing of the photosensitive region of the EMCCD, controlling the vertical transfer of charge in the photosensitive region; SF1 and SF2 are EMCCD storage region charge transfer time sequences for controlling the vertical transfer of storage region charges; a is the on-off control signal of the liquid crystal optical switch, and controls the on-off (on at high level and off at low level) of the liquid crystal optical switch, so that the photosensitive area does not receive illumination and new photoelectric conversion signals are not added during the vertical transfer of the signal charges.
The imaging process of the EMCCD device is analyzed by combining the time sequences of FIG. 7 and FIG. 8: in the process of transferring the charge in the EMCCD device from the photosensitive area to the storage area (corresponding to the frame transfer time of FIG. 8), the on-off control signal A of the liquid crystal light switch is at a low level, the voltage difference between the front pole and the rear pole of the liquid crystal box is 0V, the liquid crystal light is turned on and off, and light is prevented from entering the photosensitive area of the EMCCD device; in the process of horizontal transfer of charges in the EMCCD device (corresponding to the horizontal charge transfer time in FIG. 8), the on-off control signal A of the liquid crystal optical switch lasts for a period of high level (corresponding to the effective exposure time in FIG. 8), at this time, a periodic pressure difference exists between the front pole and the rear pole of the liquid crystal box (see FIG. 7), the liquid crystal optical switch is switched on, light is allowed to enter a photosensitive area of the EMCCD device, and then photoelectric conversion is carried out through a photoelectric effect; and continuously completing the transfer of the charges from the photosensitive area to the storage area when the vertical driving time sequence of the next frame of the EMCCD device arrives.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (9)
1. A method for eliminating the Smear effect of frame transfer type EMCCD is characterized in that in the process of transferring the charge in the EMCCD from a photosensitive area to a storage area, a liquid crystal optical switch is turned off to prevent light from entering the photosensitive area of the EMCCD;
in the process of horizontal transfer of charges in the EMCCD device, the liquid crystal optical switch is switched on to allow light rays to enter a photosensitive area of the EMCCD device, and photoelectric conversion is carried out through a photoelectric effect.
2. The method of claim 1, wherein the liquid crystal optical switch is turned off or on by an on/off control signal provided by a driving circuit.
3. The method for eliminating the frame transfer type EMCCD Smear effect as claimed in claim 1, wherein said liquid crystal optical switch comprises a liquid crystal cell; the driving circuit of the liquid crystal optical switch comprises a liquid crystal driving board which is arranged close to the rear surface of the liquid crystal box.
4. The method as claimed in claim 3, wherein the liquid crystal cell has a light-shielding material film attached to its front surface, and an optical window is reserved in the central region of the light-shielding material film, and the position and size of the optical window are matched with the photosensitive surface of the EMCCD device.
5. The method as claimed in claim 3, wherein a window is reserved in the central area of the liquid crystal driving board, and the position and size of the window are matched with the light-sensing surface of the EMCCD device.
6. The method for eliminating the frame transfer type EMCCD Smear effect as claimed in claim 3, wherein said liquid crystal driving boards are connected to the liquid crystal cell through driving electrodes for supplying an external driving voltage to the liquid crystal cell.
7. The method of claim 6, wherein the liquid crystal cell controls transmittance by an external driving voltage, and the liquid crystal optical switch is switched between on and off states by adjusting the magnitude of the driving voltage.
8. The method according to claim 2, wherein the driving circuit for turning on/off the liquid crystal light comprises an xor gate, two input terminals of the xor gate respectively input the turn-on/off control signal and a square wave pulse, an output terminal of the xor gate is connected to the back electrode of the equivalent capacitor of the liquid crystal cell, and a front electrode of the equivalent capacitor of the liquid crystal cell is connected to the square wave pulse.
9. The method as claimed in claim 2, wherein the FPGA is used to send external driving voltage timing signals to the EMCCD device and the liquid crystal light switch driving circuit to control the states of the EMCCD device and the liquid crystal light switch.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202011130273.XA CN112261324A (en) | 2020-10-21 | 2020-10-21 | Method for eliminating frame transfer type EMCCD Smear effect |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202011130273.XA CN112261324A (en) | 2020-10-21 | 2020-10-21 | Method for eliminating frame transfer type EMCCD Smear effect |
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6888570B1 (en) * | 1999-11-17 | 2005-05-03 | Olympus Corporation | Image pickup device and exposure control method in the image pickup device |
| CN104159043A (en) * | 2014-08-07 | 2014-11-19 | 西北核技术研究所 | Superspeed dual-frame image acquisition method |
| CN108600658A (en) * | 2018-04-28 | 2018-09-28 | 中国科学院长春光学精密机械与物理研究所 | Matched time for exposure adjusting method is moved for earth observation frame transfer area array CCD picture |
| CN109031765A (en) * | 2018-09-06 | 2018-12-18 | 北京航空航天大学 | A kind of photoswitch based on the double-deck nematic liquid crystal |
-
2020
- 2020-10-21 CN CN202011130273.XA patent/CN112261324A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6888570B1 (en) * | 1999-11-17 | 2005-05-03 | Olympus Corporation | Image pickup device and exposure control method in the image pickup device |
| CN104159043A (en) * | 2014-08-07 | 2014-11-19 | 西北核技术研究所 | Superspeed dual-frame image acquisition method |
| CN108600658A (en) * | 2018-04-28 | 2018-09-28 | 中国科学院长春光学精密机械与物理研究所 | Matched time for exposure adjusting method is moved for earth observation frame transfer area array CCD picture |
| CN109031765A (en) * | 2018-09-06 | 2018-12-18 | 北京航空航天大学 | A kind of photoswitch based on the double-deck nematic liquid crystal |
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Application publication date: 20210122 |
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