Preventing Inductive Output Impedance of High-Frequency Emitter Follower Stages

Abstract

Large output inductance is one of major issues of high-frequency emitter follower design. The most often suggested technique to reduce its value is the decreasing of AC transconductance which offers small output inductance at the expense of loosing low output resistance. The paper presents a different approach; it is shown that output inductance can be completely cancelled while keeping very low output resistance by introducing a pole at the input node which may be more suitable in many types of design. Complete analytical evaluation based on the full hybrid-n model of the bipolar transistor device is given.