The DuAmp - An Alternative Input Configuration For Detector Preamplifiers

An alternative type of detector-preamplifier configuration (DuAmp) has been assembled and tested* . The circuit employs two identical charge sensitive preamplifiers with the detector connected between the two preamplifier inputs. One of the preamplifiers is powered by voltage supplies referenced to ground potential, while the second one is powered by isolated supplies referenced to the bias voltage of the detector. The detector is biased by the voltage difference between the inputs of the two preamplifiers. The output of one of the preamplifiers is inverted and added to the output signal of the other preamplifier. The resultant signal is processed by pulse shaping electronics. For our application, the circuit has been shown to exhibit an overall noise level that is lower than that obtained using an equivalent single preamplifier in a conventional manner. A preliminary analysis of the circuit shows that the improvements are to be expected only in circumstances in which the ratio of detector to preamplifier capacitance is small.