TAILIEUCHUNG - 03 Finite Wordlength Effects

Practical digital filters must be implemented with finite precision numbers and arithmetic. As a result, both the filter coefficients and the filter input and output signals are in discrete form. | Bomar . Finite Wordlength Effects Digital Signal Processing Handbook Ed. Vijay K. Madisetti and Douglas B. Williams Boca Raton CRC Press LLC 1999 1999 by CRC Press LLC Finite Wordlength Effects Bruce W. Bomar University of Tennessee Space Institute Introduction Number Representation Fixed-Point Quantization Errors Floating-Point Quantization Errors Roundoff Noise Roundoff Noise in FIR Filters Roundoff Noise in Fixed-Point IIR Filters Roundoff Noise in Floating-Point IIR Filters Limit Cycles Overflow Oscillations Coefficient Quantization Error Realization Considerations References Introduction Practical digital filters must be implemented with finite precision numbers and arithmetic. As a result both the filter coefficients and the filter input and output signals are in discrete form. This leads to four types of finite wordlength effects. Discretization quantization of the filter coefficients has the effect of perturbing the location of the filter poles and zeroes. As a result the actual filter response differs slightly from the ideal response. This deterministic frequency response error is referred to as coefficient quantization error. The use of finite precision arithmetic makes it necessary to quantize filter calculations by rounding or truncation. Roundoff noise is that error in the filter output that results from rounding or truncating calculations within the filter. As the name implies this error looks like low-level noise at the filter output. Quantization of the filter calculations also renders the filter slightly nonlinear. For large signals this nonlinearity is negligible and roundoff noise is the major concern. However for recursive filters with a zero or constant input this nonlinearity can cause spurious oscillations called limit cycles. With fixed-point arithmetic it is possible for filter calculations to overflow. The term overflow oscillation sometimes also called adder overflow limit cycle refers to a .

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