Finite word length effect in IIR filters By M.NITHIYANANDHAM V.SHANKAR RAM
Finite word length effect in IIR filters
ByM.NITHIYANANDHAMV.SHANKAR RAM
INTRODUCTION
• The coefficients obtained from 2 stage FIR filter is of infinite length
• These degrade the performance of filter• These errors can be reduced by using more bits• The effects of finite word length on performance are
more difficult to analyze in IIR filters than in FIR filters because of feedback arrangement
ErrorsADC Quantization noise
Coefficient Quantization errors
Overflow errors
Product round off errors
ErrorsDegrade the performance of filter
Filter leads to instability
Filter Degradation Depends onWord length and type of arithmetic used to perform the
filtering operation
Method used to perform quantize filter coefficient and variable
Filter structure
Influence of filter effectsDirect form 1
Direct form 2
Direct form 1
Direct form 2
Cascade Realization
Parallel Realization
Coefficient Quantization error in IIR filters
Additional overflow errorsIt is due to addition of two large numbers of
similar sign.Because of recursive nature of iir filter , an
overflow at w(n) is fed back and used to compute the next output where it cause an further overflow.