Charge-based CMOS FIR adaptive filter

A low-power, high-density CMOS design for an LMS adaptive FIR filter is presented. A combination of charge-based and subthreshold MOS circuits is used for filtering and adaptation. Accurate analog linear filtering is achieved through pulse-width modulation of input signal. A wide dynamic range is obtained by biasing the MOS switched current sources in the subthreshold regime, with the filter coefficients stored on the gates and adapted through a pilot version of the LMS rule. Simulation results with SpectreS verify the linearity and simplicity of the approach.