Noise analysis in distributed amplifiers with feedback-active load

Abstract

This paper presents the noise analysis of amplifiers when the input line termination is implemented via an active load. The noise figure (NF) of distributed amplifiers is analysed to determine the effect of the gate and drain terminations. The noise of a transistor configured as a one-port device has been analysed and a lower noise temperature has been achieved as compared with a conventional resistor. In order to improve the noise performance of the overall amplifier, a parallel feedback has been added to the active load, and its effects are analysed in terms of noise. A distributed amplifier has been designed as a test vehicle of the analysis and characterised with a resistor as input line termination and with an active load to demonstrate the improvement in NF at frequencies below 2 GHz. The resulting amplifier exhibits 10.9 dB of small signal gain from 1 to 5 GHz, with a reduction of 0.6 dB in NF below 2 GHz when the input line termination is replaced by an active load.