I have a charge sensitive preamplifier (CSP) that can be used with a photomultiplier tube (PMT) detector. (http://www.cremat.com/CR-Z-PMT.pdf) I am trying to figure out CSP's working. I don't have a PMT. So I want to use some circuitry to generate some charge pulses and can be given as a test input to the CSP. I am totally new in this area. Is there any device or function generator that can be used as a charge generator? Any comments?