cic_analysis

This function computes and shows the frequency response of a CIC filter and then analyse the aliasing that occurs after decimation.

Namespace: dsp::filter

Prototype

CICAnalyse cic_analysis(const CICConfig &config, float Fin, float Fint=0)

Parameters

config	Main parameters of the CIC filter (see CICConfig)
Fin	Input sample frequency
Fint	Fréquence où mesurer l'atténuation

Returns

A tuple with :

Theorical transfert function (not taking into account the decimation),
Number of additionnal bits needed to implement the CIC filter

Description

This functions draws two plots:

The first plot shows the frequency response before decimation (both the global one, and one centered on the passband).
The second plot shows the effect of the decimation (aliasing in the baseband).

Also, this function computes the number of additionnal bits needed to implement the filter in fixed point / integer arithmetic. This is computed as (see http://www.tsdconseil.fr/log/scriptscilab/cic/cic-en.pdf): \[n_{bits} = N\cdot\log_2(R) - 1\]

Example

// 10 MHz input sample frequency
Fin = 10e6;
// Decimation ratio = 16, 5 CIC stages
// (sample rate at output of CIC is 10 MHz / 16 = 625 KHz)
R = 16, N = 5, M = 1;
cic_analysis(R, N, M, Fin);