Multiplierless analog LMS adaptive FIR filters

Two adaptive FIR filter configurations are proposed which implement the LMS algorithm with no analog delay elements or multipliers. The first configuration uses a linear feedback shift register (LFSR) to genenrate pseudo-random binary sequences for applications where white noise has been traditionally used. The binary signals are delayed by a shift register and multiplied by on-and-off switching so that the resulting structure is free of the analog delay line and multipliers. For applications where colored inputs must be used, the second adaptive filter configuration uses a Σ-Δ modulator as a front-end for converting the filter's reference input into a binary sequence. It is shown that the filter tends to adapt itself into a lowpass shape to remove the high frequency noise generated by the modulator. Computer simulations show very good performance for such hardware efficient configurations.