Overload Recovery Circuit for Charge Amplifiers

In this paper the operation of low noise charge preamplifiers under high instantaneous pulse rates - "bursts" - is considered. An overload recovery circuit employing a field-effect transistor as the switch for the recovery current is described. The overload charge generated in the detector by the radiation burst in a time short compared to the small signal resolving time of the spectrometer may be 105 or more times larger than the charge due to a single particle to be measured between the bursts. The recovery time of the charge amplifier with the recovery circuit is less than 10 μsec. With a conventional amplifier-filter, the recovery time of the system to within the noise level is 50 to 100 μsec. The increase in noise due to the recovery circuit corresponds to an increase in the input capacitance of the charge amplifier of 2 pF.