THEORY AND PERFORMANCE OF PARABOLIC TRUE LOGARITHMIC AMPLIFIER

A novel design technique for the true logarithmic amplifier scheme is presented. The methodology is based on a parabolic approximation of th e ideal logarithmic characteristic yielding a major reduction of the l ogarithmic error. The basic theory is developed and presented in this paper. A sample design in GaAs 0.5 mu m MESFET monolithic low-noise te chnology has been performed. The realised amplifier features ultrabroa dband performance from 0.3 GHz to 5 GHz, together with a good input-ou tput match throughout the operating bandwidth. The complete amplifier has been assembled utilising a modular strategy, allowing the fulfilme nt of design goals with a simple increase in the number of stages. The design steps and the measured results both for the single stage and f or the cascade of three stages are presented in the following.