Systematic Design of Companding Systems by Component Substitution

A design method for externally linear, internally nonlinear systems is presented which allows them to be derived from externally equivalent systems in a systematic way and with a minimum synthesis effort, just performing a simple component-to-component substitution. As a particular case, the synthesis of the most popular versions of voltage companding systems from externally equivalent Gm-C systems is addressed. The practical design of companding systems based on the MOS square law (Square-Root Domain systems) is fully illustrated along the complete design flow, from the Gm-C prototype to silicon. These systems, feasible in CMOS technologies and formerly difficult to obtain due to the inherent complexity of existing synthesis methods, particularly benefit from the simplicity of the proposed approach. Experimental results for two versions of tunable Square-Root Domain biquadratic filters and oscillators thus obtained and fabricated in a 2.4-μm CMOS process are presented, featuring favorable tunability and low THD.