De-oscillating preamplifier signals through digital filtering techniques

We present a time-domain digital filtering technique able to eliminate the ringing of preamplifier signals. The preamplifier signal is sampled by an ADC and then processed by a digital filter, whose aim is to eliminate the ringing while minimizing the loss of high-frequency information. We developed such a filtering technique for the case of a charge-sensitive preamplifier for gamma-ray spectroscopy installed far away from the detector/FET cryogenic assembly. With such a setup a damped oscillation is caused by the long connection cable acting as a delay line along the feedback loop. We could completely eliminate the ringing in the output signals and maintain, at the same time, a large bandwidth and a high loop gain. Experimental results are shown.