The problem of on-chip automatic tuning in continuous-time integrated filters

A discussion is presented of the most important and difficult aspect of the design of fully integrated continuous-time filters: continuous, real-time, on-chip tuning of filter parameters against errors caused by such factors as fabrication tolerances, changes in operating conditions, parasitic effects, and aging. The origins of the errors in filter parameters are pointed out, and the generally adopted methods for automatic error correction are discussed. These methods are a phased-locking loop for tuning of frequency parameters and a magnitude-locking loop for maintaining the transfer characteristic´s shape. Guidelines are given to aid the designer in avoiding the most prevalent pitfalls, and an illustrative example is presented which incorporates the ideas and concepts discussed