A quasi-cusp digital filter for gamma-ray spectroscopy

In this research project, a quasi-cusp digital filter for use with high-purity germanium detectors was developed to provide optimal resolution at long and short pulse width settings while eliminating errors due to ballistic deficit. The implementation allows the filter to operate in real-time with 32 programmable pulse width settings and throughput rates as high as 70,000 counts per second. A cusp factor adjustment allows the pulse shape to be optimized to match the characteristics of the particular detector which is connected to the spectrometer. Furthermore, a digital gated baseline restorer is included in the filter to eliminate peak shifts due to changing DC levels in the detector and the electronics. A digital peak detecting circuit which uses a pattern matching algorithm applied to the slope of the filtered pulse selects the peak of the digital pulses to histogram.