A real-time implementation of half-band filters to obtain 18-20 bit resolution from the DSP56ADC16 sigma-delta A/D converter

A method of obtaining 18-20-bit resolution from a commercially available 16-bit Sigma - Delta A/D converter, the Motorola DSP56ADC16, is presented, and Sigma - Delta technology in general is discussed. A series of half-band filters was implemented on the Motorola DSP56001 (24-bit digital signal processor) to take advantage of the third-order noise-shaping methodology and oversampling employed by the DSP56ADC16. Based on this multistage filter implementation and using the 12-bit comb-filter output of the DSP56AC16, a signal-to-noise ratio (SNR) of greater than 3 dB/octave is anticipated. The kernel of the DSP 56001 assembly code for the main macro routine and the parameters for designing the half-band filters are included.<>