Design principles and limitations of integrated silicon bipolar transistor amplifiers for mobile communications

A numerical analysis of Class-C amplifiers on the basis of a simple model of the bipolar junction transistor is presented. The trade-off between collector efficiency, power added efficiency, gain, and input impedance of a 250-mW Class-C amplifier on one side and power supply voltage on the other is evaluated. Results are obtained using nonlinear time-domain simulation and optimization without recourse to graphical methods invoking the concept of conduction angle or to piecewise-linear approximations. It is found that, in contrast to other mobile terminal components, a reduction of the Class-C amplifier supply voltage causes lower gain and an increase of the required battery power at constant RF-output power.