PM and AM noise in BJT amplifiers due to fluctuations of supply voltages

A theoretical analysis of output signal phase and amplitude sensitivities of the common emitter BJT amplifier to variations in supply (or biasing) voltages is presented. The dependence of collector junction capacitance on biasing voltage applied to this junction is taken into consideration. A separate influence of base biasing voltage noise and collector biasing voltage noise on PM and AM noise of the amplifier is investigated. An influence of internal 1/f noise sources of the BJT is also analyzed taking into consideration collector capacitance nonlinearity. The approach, developed in this paper, is applied to the CE amplifier with one source of supply voltage and balance circuit of the base biasing. Conditions of compression of the supply voltage contribution to total PM noise are analyzed and discussed. Results of this analysis can be used to set demands to biasing voltages fluctuations in low PM noise amplifiers.