Digitized Preamplifiers: A Circuit Structure for Sliding-Scale Optimization of the ADC Range

This work deals with the digitization of charge-preamplifier waveforms obtained from X-ray and$gamma$-ray sensors. We suggest that the well-known “sliding-scale correction” structure can be inserted into a negative-feedback control loop to cancel the signal walks brought about by event pileup, low-frequency disturbances, microphonism, and hum. Cancellation of the walks permits to use the full analog-to-digital converter (ADC) range for the signals, even in high event rate conditions. The signal distortion caused by such cancellation is then eliminated numerically by the sliding-scale mechanism. As a result an extended dynamic range is obtained. Using a 12-bit ADC we got two extra bits to accomodate the baseline walks and 1.14 to 1.43 extra bits on individual signals with 0.1 to 1 micro s. rise time.