A LOW-NOISE DIFFERENTIAL PREAMPLIFIER

The differential method of reading the signal from an ionizing radiation detector allows the signal-to-noise ratio to be improved if the detector interelectrode capacitance is less than the preamplifier input capacitance. The maximum possible degree of improvement is by a factor of square-root 2. Another advantage of the differential scheme is the suppression of in-phase electrical interference. This paper is concerned with a differential preamplifier for detecting short (50 nsec) current pulses from an ionization chamber. The preamplifier transmission coefficient is 540 kOMEGA with the chamber inserted symmetrically. The mean-square value of the preamplifier noise charge, which is normalized to the signal, is 3100 electrons (8000 electrons including the detector connected to the preamplifier by two 20-m-long matched cables).