AN OVERLOAD CANCELLATION CIRCUIT FOR A CHARGE-SENSITIVE PREAMPLIFIER

An active circuit which prevents saturation due to overloads in a charge-sensitive preamplifier is presented. Cosmic rays often produce relatively bright scintillations in a detector, especially if the crystal is large. The resulting overload may saturate the preamplifier, significantly increasing the dead time of the system. To reduce this undesirable effect, an active stage containing a field-effect transistor is inserted in parallel with the normal feedback network of the charge-sensitive preamplifier. This stage prevents an excessive charge from being deposited on the feedback capacitor and thereby prevents blocking in the preamplifier and permits a prompt return to linear operation. A description of the operation of the circuit and results of tests are included. © 1969.