ORIGIN OF 1 FPM AND AM NOISE IN BIPOLAR JUNCTION TRANSISTOR-AMPLIFIERS/

In this paper we report the results of extensive research on phase mod ulation (PM) and amplitude modulation (AM) noise in linear bipolar jun ction transistor (BJT) amplifiers. BJT amplifiers exhibit 1/f PM and A M noise about a carrier signal that is much larger than the amplifiers thermal noise at those frequencies in the absence of the carrier sign al. Our work shows that the 1/f PM noise of a BJT based amplifier is a ccompanied by 1/f AM noise which can be higher, lower, or nearly equal , depending on the circuit implementation. The 1/f AM and PM noise in BJTs is primarily the result of 1/f fluctuations in transistor current , transistor capacitance, circuit supply voltages, circuit impedances, and circuit configuration. We discuss the theory and present experime ntal data in reference to common emitter amplifiers, but the analysis can be applied to other configurations as well. This study provides th e functional dependence of 1/f AM and PM noise on transistor parameter s, circuit parameters, and signal frequency, thereby laying the ground work for a comprehensive theory of 1/f AM and PM noise in BJT amplifie rs. We show that in many cases the 1/f PM and AM noise can be reduced below the thermal noise of the amplifier.