FPGA-Based Automatic Digital Pole-Zero Cancellation for Nuclear Pulse Spectroscopy Systems: Real-Time Decay Constant Estimation and Adaptive Tuning.

In modern radiation sensor systems, the analog output of charge-sensitive preamplifiers (CSA) often suffers from long exponential tails, which severely limit the performance of the sensor system at high counting rates. At high counting rates in nuclear spectroscopy, overlapping exponential pulse tails from charge-sensitive preamplifiers lead to baseline drift and degraded energy resolution. Effective pole-zero cancellation (PZC) is necessary to mitigate these effects; however, conventional PZC tuning is typically manual and repetitive. We present an FPGA-based automatic digital PZC algorithm for nuclear pulse spectroscopy systems that estimates the preamplifier decay time constant online and automatically adjusts the PZC filter in real time. The proposed system combines high-speed digital pulse acquisition with FPGA firmware to achieve robust baseline restoration, pulse deconvolution, and improved energy resolution. Experimental validation with a high-purity germanium (HPGe) detector and a 60Co gamma source demonstrates that the automatic PZC achieves near-optimal tail cancellation and recovers accurate pulse amplitudes. Compared to manual tuning, the adaptive approach yields superior baseline stability and approximately 6.8% better energy resolution for the 1332.5 keV peak, while reducing adjustment time from minutes to seconds.