Cascomp BJT Amplifier vs. traditional configurations

Abstract

All transistor circuits introduce distortion. In Radio Frequency (RF) circuits, the third-order distortion components are the most important. The quest for more linear circuits has become more important with complex-modulation as used in modern cellular phone systems. Quinn’s Cascomp Amplifier, first reported in the 1970s, promises ideal linearity and can deliver close to that promise. We review the theory and address the question of why the Cascomp has not replaced other configurations in amplifiers where low distortion is important. Calculations are supported by measurements. A new, alternative variant of the Cascomp topology is introduced and compared with the existing configura-tion. We assert that the improved linearity comes at such a price in gain that it does not make sense to use the configuration in broadband RF circuits.