Low-Noise Discrete Preamplifiers For InSb IR Detectors

Abstract

For many applications, for example, in ground-based astronomy, detector systems using small arrays or small numbers of discrete IR. detectors are very useful. In particular, systems using indium antimonide (InSb) detectors are approaching background-limited performance throughout most of their useful wavelength band of 1 to 5 μm. The general requirements of preamplifiers for background-limited performance of InSb IR detector systems are presented. These amplifiers require a cryogenic Field-effect transistor (FET) first stage to achieve this level of performance. The electrical and thermal design tradeoffs of such amplifiers are presented. The noise performance of transimpedance amplifiers (TIAs) is estimated from a noise model. Measurements of noise voltage and noise current versus temperature are presented for a sample of commercially available junction FETs (JFETs). It is concluded that if JFETs with reasonably low values of noise voltage are selected, then the IR TIA system noise will be dominated by an input noise current from the JFET, typically 5 x 1047 A/.117z at 10-Hz frequency. Most significantly, this source appears to be correlated over temperature with the input noise voltage. This suggests that the voltage and current noise sources are caused by the same mechanism. A JFET selection procedure is proposed that includes a minimum of low-temperature testing.