Determining the multiplication of EMCCD sensor
View Patent ↗A method and device having a CCD in which charge multiplication is obtained by applying drive voltages to clocking elements and is arranged to derive the gain provided by the multiplication elements from at least first and second output signals. The CCD is operated at a first voltage or temperature setting, and then a second voltage or temperature setting and the output signals derived with the CCD imaging a substantially constant scene. The gain at a given voltage or temperature setting can then be derived as a function of the different operational voltage of temperature setting. The method and device can also derive the gain as a function of the rate of change of output signal with an operational parameter such as voltage or temperature.
1. A device incorporating a CCD of the type for providing charge gain by impact ionization, the CCD including a multiplication register for producing charge gain on application of a drive voltage, the device having an output arranged to provide an output signal from the CCD and a processor arranged to receive the output signal, the processor being arranged to produce at least first and second signals from the output signal when different respective drive voltage levels are applied to the multiplication register, the drive voltages being set so that greater than unity gain is provided, and to derive the gain of the multiplication register at one of the respective drive voltages from the at least first and second signals and from the different respective drive voltages.
2. A device incorporating a CCD of the type for providing charge gain by impact ionization, the CCD including a multiplication register for producing charge gain on application of a drive voltage, the device having an output arranged to provide an output signal from the CCD and a processor arranged to receive the output signal, the processor being arranged to produce at least first and second signals from the output signal when the multiplication register is at different respective temperatures and to derive the gain of the multiplication register at one of the respective temperatures from the at least first and second signals and from the different respective temperatures.
3. A device according to claim 1 , wherein the at least first and second signals are signals representing the average signal level for pixels within the CCD.
4. A device according to claim 3 , wherein the first and second signals represent the average signal level for pixels within a frame.
5. A device according to claim 2 , wherein the at least first and second signals are signals representing the average signal level for pixels within the CCD.
6. A device according to claim 5 , wherein the first and second signals represent the average signal level for pixels within a frame.
7. A device according to claim 1 , wherein the first and second signals are derived from the sum of the signal levels of pixels within a frame.
8. A device according to claim 2 , wherein the first and second signals are derived from the sum of the signal levels of pixels within a frame.
9. A device according to claim 1 , wherein the processor is operable to control the drive voltage level or the temperature of the multiplication register.
10. A device according to claim 1 , wherein the processor is a DSP or FPGA.
11. A device according to claim 1 , wherein the processor is arranged to derive the rate of change of output signal with voltage.
12. A device according to claim 1 , wherein the processor is arranged to derive the rate of charge of output signal with temperature.
13. A method of deriving the gain of a CCD of the type for providing charge gain by impact ionization, the CCD including a multiplication register for producing charge gain on application of a drive voltage, comprising deriving at least first and second signals from the output signal when different respective drive voltage levels are applied to the multiplication register, the drive voltages being set so that greater than unity gain is provided, and determining the gain of the multiplication register at one of the respective drive voltages from the at least first and second signals and from the different respective drive voltages.
14. A method of deriving the gain of a CCD of the type for providing charge gain by impact ionization, the CCD including a multiplication register for producing charge gain on application of a drive voltage, comprising deriving at least first and second signals from the output signal when the multiplication register is at different respective temperatures and determining the gain of the multiplication register at one of the respective temperatures from the at least first and second signals and from the different respective temperatures.
15. A method according to claim 13 , wherein the at least first and second signals are signals representing the average signal level for pixels within the CCD.
16. A method according to claim 14 , wherein the at least first and second signals are signals representing the average signal level for pixels within the CCD.
17. A method according to claim 15 , wherein the first and second signals represent the average signal level for pixels within a frame.
18. A method according to claim 16 , wherein the first and second signals represent the average signal level for pixels within a frame.
19. A method according to claim 13 , wherein the first and second signals are derived from the sum of the signal levels of pixels within a frame.
20. A method according to claim 14 , wherein the first and second signals are derived from the sum of the signal levels of pixels within a frame.
21. A method according to claim 14 , in which the method comprises measuring the output signal as the CCD is cooled to an operating temperature.