Origin of 1/f PM and AM noise in bipolar junction transistoramplifiers

摘要

In this paper we report the results of extensive research on phasenmodulation (PM) and amplitude modulation (AM) noise in linear bipolarnjunction transistor (BJT) amplifiers. BJT amplifiers exhibit 1/f PM andnAM noise about a carrier signal that is much larger than the amplifiersnthermal noise at those frequencies in the absence of the carrier signal.nOur work shows that the 1/f PM noise of a BJT based amplifier isnaccompanied by 1/f AM noise which can be higher, lower, or nearly equal,ndepending on the circuit implementation. The 1/f AM and PM noise in BJTsnis primarily the result of 1/f fluctuations in transistor current,ntransistor capacitance, circuit supply voltages, circuit impedances, andncircuit configuration. We discuss the theory and present experimentalndata in reference to common emitter amplifiers, but the analysis can benapplied to other configurations as well. This study provides thenfunctional dependence of 1/f AM and PM noise on transistor parameters,ncircuit parameters, and signal frequency, thereby laying the groundworknfor a comprehensive theory of 1/f AM and PM noise in BJT amplifiers. Wenshow that in many cases the 1/f PM and AM noise can be reduced below thenthermal noise of the amplifier