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VLSI Digital Signal Processing Systems: Design and Implementation by Keshab K. Parhi

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11.9    PROBLEMS

  1. Consider the SFG in Fig. 11.25 which corresponds to the all-pole transfer function

    image

    where − 1 < a < 1 for stability.

    (a)  Calculate the output roundoff noise. Show that the noise variance image gets amplified through the feedback section, i.e., even though e(n) may be small, its effect on y(n) can be large.

    (b)  Compute roundoff noise for (i) a = 0.1, (ii) a = 0.5, and (iii) a = 0.998. Comment on the relation between roundoff noise and pole locations.

    image

    Fig. 11.25    Signal flow graph of an all-pole IIR filter.

    image

    Fig. 11.26    Signal flow graph of a scaled all-pole IIR filter.

    (c)  For narrowband filters, |a| is typically very close to 1. For example, a = 0.998 is not uncommon. For such filters, the noise variance image gets amplified enormously. (In that case, low-noise/sensitivity filter structures such as lattice filters and wave digital filters need to be considered.) Explain conceptually why poles are located very close to the unit circle for narrowband filters.

  2. Assume that the ...

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