Hello,
I am currently working on a design for a system that will convert analog currents from a photomultiplier tube to digital voltages that will be processed in an FPGA. The signals I want to detect are Terrestrial Gamma-ray Flashes (TGFs). What I have done in order to convert analog currents to digital voltages is to use a transimpedance amplifier to convert the currents to voltages. It is also at the transimpedance amplifier I placed all the gain in order to have the least noise, and it is easy to change the gain if necessary. After making the signals to voltages, I have placed a 4th order Butterworth filter; A 2nd order KRC filter followed by a 2nd order MFB filter that is placed externally on the ADC driver (ADC driver is used as a single-ended to differential converter). After the 4th order filter, the signals are sent to the ADC.
The components that I have used are the ADS5404 (500MSPS ADC), OPA855 (for the transimpedance amplifier), THS4303 (for the KRC filter) and THS4505 (for the ADC driver).
What I am having problems with is that I don't know the signal strength from the PMTs. It says on the OPA855 that it can withstand up to +-10mA of continuous currents, should I have a current limiter in front so that it does not go above this maximum? In that case, what can I use? I also require a voltage limiter so that the differential output signal on the ADC driver does not go above 1-1.25 Vpp. Any suggestions as to what I can do here? I am thinking of using a diode clamp to limit the signal to +-0.6V at the single-ended input of the ADC driver.
If there is anything that you think should be changed otherwise, do not hesitate to say! I am a Bachelor student in electronics, so I am quite inexperienced, but I want to learn as much as possible!
Hope you can help,
Best regards,
Sindre
I am currently working on a design for a system that will convert analog currents from a photomultiplier tube to digital voltages that will be processed in an FPGA. The signals I want to detect are Terrestrial Gamma-ray Flashes (TGFs). What I have done in order to convert analog currents to digital voltages is to use a transimpedance amplifier to convert the currents to voltages. It is also at the transimpedance amplifier I placed all the gain in order to have the least noise, and it is easy to change the gain if necessary. After making the signals to voltages, I have placed a 4th order Butterworth filter; A 2nd order KRC filter followed by a 2nd order MFB filter that is placed externally on the ADC driver (ADC driver is used as a single-ended to differential converter). After the 4th order filter, the signals are sent to the ADC.
The components that I have used are the ADS5404 (500MSPS ADC), OPA855 (for the transimpedance amplifier), THS4303 (for the KRC filter) and THS4505 (for the ADC driver).
What I am having problems with is that I don't know the signal strength from the PMTs. It says on the OPA855 that it can withstand up to +-10mA of continuous currents, should I have a current limiter in front so that it does not go above this maximum? In that case, what can I use? I also require a voltage limiter so that the differential output signal on the ADC driver does not go above 1-1.25 Vpp. Any suggestions as to what I can do here? I am thinking of using a diode clamp to limit the signal to +-0.6V at the single-ended input of the ADC driver.
If there is anything that you think should be changed otherwise, do not hesitate to say! I am a Bachelor student in electronics, so I am quite inexperienced, but I want to learn as much as possible!
Hope you can help,
Best regards,
Sindre