design_cic_comp

Design of a compensation FIR filter for a CIC filter.

Namespace: dsp::filter

Prototype

CICComp design_cic_comp(const CICConfig &config, float Fin, int R2, float fc, int ncoefs)

Parameters

configParamètres principaux (voir CICConfig)
Fininput frequency
R2compensation filter decimation ratio
fccutoff frequency for the compensation FIR filter
ncoefsnumber of taps of the FIR filter

Returns

compensation FIR filter coefficients

Description

This function will try to design a compensation filter for the specified CIC filter. The global decimation chain will be composed of two stages:

  • The first stage is the CIC filter, and decimate by the ratio \(R\).
  • The second stage is the compensation filter, and decimate by the ratio \(R_2\).

So, the global decimation ratio will be \(R\cdot R_2\).

The compensation filter is generated through the frequency sampling technique. This function will do the FIR compensation design, plot the frequency responses, and output (output parameter cfir) the compensation filter coefficients. 

// Input signal frequency: Fin = 6.4 KHz
// CIC decimation factor: R = 1/16 (freq at output of CIC: 400 Hz)
// Compensation FIR decimation factor: R2 = 1/2
// Output signal frequency: 6400/(R*R2) = 200 Hz
// Cut-off frequency for FIR filter: 80 Hz
int R = 16, N = 4, M = 1;
float fin = 6400, fcut=80;
int ntaps = 61, R2 = 2;
lets h = design_cic_comp(R,N,M,fin,R2,fcut,ntaps);
// h is the array of coefficents of the FIR compensation filter.