The Design of the CIC-HB Digital Decimation Filter for the Sigma-Delta Modulator

In this study the structure of a decimating digital low-pass filter is proposed using a four-stage structure containing three CIC filters of different orders and decimation coefficients and one Halfband filter. The achieved structure has a variable decimation coefficient in the range from 64 to 8192 and has the possibility of filtering in the frequency range up to the frequencies of the rise region of the quantization noise level. The frequency response of the filter has a sharp transition region in the stopband and a low value of passband droop due to the use of a Halfband type filter. The signal level in the stopband is about $\mathbf{1 2 0} \mathrm{dB}$. The designed decimating filter does not bring significant distortions in the filtered signal according to the results of computer modeling and allows the achievement of a signal-to-noise ratio of more than 70 dB in all modeled frequency bands of the signal at corresponding decimation coefficients.