A preamplifier-shaper-stretcher integrated circuit system for use with germanium strip detectors

A 16-channel Integrated Circuit readout electronics chip is being developed for use with a germanium strip detector. Such a system will provide superior energy resolution with 2-dimensional imaging in a single instrument that can be used for X-ray imaging and nuclear line gamma-ray spectroscopy. As part of the total ASIC development, prototype ICs of a typical channel have been designed, fabricated and tested. These integrated circuits include a low-noise, variable gain, preamplifier circuit that can detect both positive and negative going input charges, a 4-pole pulse shaper with variable peaking times and stretcher circuit that can do a peak detect and hold for the different peaking times. The integrated circuits are fabricated in a 1.2 micron n-well CMOS process. The noise performance for this system was measured to be 185erms +14e/pF for a 2μs peaking time and gain at ∼200mV/fC. Linearity measurements in both inverting and non-inverting modes of operation were approximately +/-1%. Peaking times from 0.5 microseconds to 8 microseconds and gain adjustments to get up to 400mV/fC per channel were done through digital switching.