Bipolar active inductor realizability limits, distortion, and bias considerations

Active inductors for MMICs offer an interesting alternative to passive implementations when the rf currents are below the threshold levels needed to maintain low distortion. This paper examines the limits of realizability for a MMIC inductor circuit that utilizes two bipolar junction transistors in a common collector-common emitter configuration to gyrate the base-emitter capacitance of the common emitter stage to form a synthetic inductor. The inductance range, Q-factor, distortion, dc bias points, and dc power consumption for the circuit are considered. Governing equations and graphs describing circuit performance are presented. The results show that the goals of higher Q, lower distortion, and good DC power utilization are not conflicting in terms of the biasing of the transistors.