Analog peak detector and derandomizer for high-rate spectroscopy

A compact and accurate readout system has been developed for high-rate spectroscopy with multi-element detectors. The fully self-triggered system multiplexes the signals from 32 detectors into a novel peak detector, which also serves as a derandomizer. The captured pulse heights are stored as analog samples before being presented to the ADC along with the corresponding channel addresses. The peak detector incorporates a new two-phase configuration that cancels offsets and other errors found in conventional designs. Offset cancellation gives the peak detector rail-to-rail sensing and driving capability and permits two or more peak detectors to be operated in parallel to serve as a data-driven analog memory. First experimental results on the new peak detector and derandomizer (PDD) circuit, fabricated in 0.35 μm CMOS technology, include a 0.2% absolute accuracy for pulses with 500-ns peaking time, 2.7-V linear-input range, 3.5-mW power dissipation, 250-mV/s droop rate, and negligible dead time. We have tested the system with 32 CZT detectors and a ²⁴¹Am source. The spectra collected from the 32-channel system show that the noise performance of the preamp/shaper is not degraded by the multiplexing, peak detecting, and derandomizing operations.