An InSb charge amplifier for use in a spectrometer array

An eight-channel, low-noise charge amplifier system developed for an InSb photodiode array is described. The InSb charge amplifier is composed of: eight FET-input integrating preamplifiers inside the cold Dewar, a set of correlated double samples, and a sequence controller. The functions of the components are discussed and block and circuit diagrams of the system are presented. The amplifier's rest switch for resetting the integrating capacitor, which consists of two reverse biased gate-channel JFET junctions illuminated by an LED, is examined. The parallel resistance and shot noise of the input currents, and the shot and thermal noises of the JFET are analyzed. The performance of the amplifier system is evaluated. A single-channel version of the InSb photometer is applied to the TIRGO telescope of the Arcetic Observatory. A measured noise level of about 210 electrons in 1-s integration time which corresponds to a noise equivalent power of 2.8 x 10 to the -17th W/sq rt Hz is obtained for the amplifier.