1.

What is the causal inverse of the FIR system with impulse response h(n)=δ(n)-aδ(n-1)?(a) δ(n)-aδ(n-1)(b) δ(n)+aδ(n-1)(c) a^-n(d) a^nThe question was posed to me in a job interview.Origin of the question is Inverse Systems and Deconvolution topic in portion Frequency Analysis of Signals and Systems of Digital Signal Processing

Answer»

The CORRECT option is (d) a^n

To elaborate: Given h(n)= δ(n)-aδ(n-1)

Since h(0)=1, h(1)=-a and h(n)=0 for n≥a, we have

hI(0)=1/h(0)=1.

and

hI(n)=-AHI(n-1) for n≥1

Consequently, hI(1)=a, hI(2)=a^2,….hI(n)=a^n

Which corresponds to a CAUSAL IIR system as expected.



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