ABSTRACT
This chapter aims to introduce the reader to the field of ultra-low-noise amplification, the cryogenic noise performance of select semiconductor devices, and the design techniques employed to realize amplifiers with state-of-the-art noise performance. It focuses on the technology behind and the design of microwave and millimeter wave amplifiers for radio astronomy, as the application has driven most of the developments in ultra-low-noise amplification. The history of the technological development of ultra-low-noise amplifiers dates back to the mid-1950s and includes stories of masers, parametric amplifiers, tunnel diodes, and transistor amplifiers. Prior to the adoption of cooled semiconductor front ends, radio telescopes and other ultrasensitive instruments relied upon expensive low-noise amplifiers such as ruby masers and parametric amplifiers. For the amplifier to work at both room temperature and at 15 K, it is necessary to include provisions to reduce the bias current in each of the transistors by a factor of approximately 3 when it is operated cryogenically.
