THE SWITCH-OFF BASE-LINE RESTORER FOR THE 120 CHANNEL SILICON DETECTOR SYSTEM FOR EXAFS AT NSLS

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 (Nation al Synchrotron Light Source), Brookhaven National Laboratory, USA [L.R . Furenlid et al., Nucl. Instr. and Meth. A 319 (1992) 408], and is ba sed on a current ''switch off'' mechanism self-triggered on the input signal pulses. No auxiliary gate signals are required, and, consequent ly, the network is particularly compact. As opposed to Robinson restor ers, this restorer is not affected by undershoot, and it does not invo lve the significant complexity of gated solutions. The restorer has be en tested with a 7 pole quasi-Gaussian filter permitting very high res olution X-ray spectroscopy (160 eV FWHM on pulser peak). The signal-to -noise degradation due to the restorer is about 7%. The BLR response t o 18 mu s large trapezoidal input pulses shows an undershoot which is about 0.3%. Baseline is correctly recovered for repetition rates of up to 5 X 10(4) trapezoidal signals/s, which corresponds to a duty cycle of 60%. The BLR has been layed out in SMT on a 0.8 in. X 0.8 in. area , which is suitable for multichannel applications where the circuit ha s to be largely used as the last stage of each individual unipolar sha ping filter.