Noise and Low-Frequency Amplifiers

摘要

This paper is a study of low-noise amplification in the near direct current frequency range. The paper is a survey of the problem and no 'ultimate amplifier' is presented in conclusion. The purpose of this paper is to analyze the problem and to present conclusions as to best class of amplifiers to use in this frequency range. Two classes of amplifiers are considered. The 'chopper' amplifier and the semiconductor diode parametric amplifier. It is concluded that the semiconductor diode parametric amplifier is inherently the lower noise device of the two. There are no intrinsic noise sources in this amplifier and noise arises mainly from parasitic effects which theoretically can be made arbitrarily small. The use of this type of amplifier at low frequencies marks a new and successful application of a device usually associated with microwave frequencies. The first section of the paper is a critique of the various figures of merit used in specifying noise performance. The significance and proper use of the noise figure is discussed. The section on the 'chopper' amplifier includes analysis involving both the junction transistor and the field effect transistor. The conclusions are that the best overall performance of the chopper amplifier results when the junction transistor is used with a low impedance source. (Author)