A single stage decimator architecture for sigma-delta demodulators using Laguerre filters

Conventional Sigma-Delta (Σ-Δ) demodulator decimation techniques are based on multi-stage down-sampling via the use of long FIR filters. However, these methods are not optimal because of the aliasing of quantization noise. This paper proposes a novel, single stage decimation method that simplifies the implementation of the decimation process. The method makes use of an optimal Laguerre filter as the noise-shaping filter followed by another Laguerre filter that acts as a narrow-band filter. The optimal Laguerre FIR filter design methodology is based on optimizing a quadratic function subject to a linear and a quadratic constraint. The narrow-band Laguerre filter can be efficiently designed using a min-max criterion via a modified Parks-McClellan FIR filter design algorithm. These two filters are then combined to form an efficient single stage decimation architecture