Improved structures for programmable filters: application in aswitched-capacitor adaptive filter design

摘要

In designing switched-capacitor (SC) filters for high-frequencynoperation, there is a tradeoff to be made between the gain and the speednof the operational amplifiers (op amps). Taking into account this fact,nwe present in this paper new structures (an SC integrator and an SC gainnstage) which relax the constraint requirements on the op amp whilenachieving improved performance accuracy. These structures use thendouble-sampled technique, which increases by a factor of two the maximumnspeed of operation and correctly operate even with low dc-gain op amps.nIn order to effectively use all features (low sensitivity to op-ampnimperfections) of these SC building blocks in the implementation of annadaptive filter, we also describe an offset-cancelled tunable SC gainnstage based on four-quadrant analog multiplier cells. Numerical resultsnare reported to confirm the viability of the proposed design method, andntechniques to further improve the adaptive filter electricalncharacteristics are discussed