The “switch off” baseline restorer for the 120 channel silicon detector system for EXAFS at NSLS

Abstract

A new circuit for high precision baseline restoration in multichannel nuclear pulse spectrometers is proposed. It has been designed for the 120 channel silicon detector system for EXAFS research at NSLS (National Synchrotron Light Source), Brookhaven National Laboratory, USA [L.R. Furenlid et al., Nucl. Instr. and Meth. A 319 (1992) 408], and is based on a current “switch off” mechanism self-triggered on the input signal pulses. No auxiliary gate signals are required, and, consequently, the network is particularly compact. As opposed to Robinson restorers, this restorer is not affected by undershoot, and it does not involve the significant complexity of gated solutions. The restorer has been tested with a 7 pole quasi-Gaussian filter permitting very high resolution X-ray spectroscopy (160 eV FWHM on pulser peak). The signal-to-noise degradation due to the restorer is about 7%. The BLR response to 18 μs large trapezoidal input pulses shows an undershoot which is about 0.3%. Baseline is correctly recovered for repetition rates of up to 5 × 104 trapezoidal signals/s, which corresponds to a duty cycle of 60%. The BLR has been layed out in SMT on a 0.8 in. × 0.8 in. area, which is suitable for multichannel applications where the circuit has to be largely used as the last stage of each individual unipolar shaping filter.