BIBO, Iiiipulse Response arid El'fequency Kc>sponst: Curve 387 The slim itself is a known harmonic series, arid does riot oo~iverge, which tihows that the impulse response of the ideal l
Trang 116.1 BIBO, Iiiipulse Response arid El'fequency Kc>sponst: Curve 387
The slim itself is a known harmonic series, arid does riot oo~iverge, which tihows that the impulse response of the ideal low-pass cannot bc absolutely integrated The ided hW-J2aSS is therefore neithel c i ~ u s d nor stable
Q
Af'ter this rxample we have to ask whether it is worth examining such idralised systcms, when they arc innpossible to impleiiirnt, The answer is typical from tlic point of vicw of' systems theory:
o The ideal low-pass filter with an entiiely real rectaiigular frqiency plot i s
a very simple cority)t It allows many operations to be coiisideied in tire simplest form, for example, limiting spectra, and reconstructing contiriirour sigiials fruiii samplPs
0 The ideal lotv-pass rmriot be prrciscly rediwd lmt can bc apprtmimateil if miiie coritaehsions can be accepted A n cxarnple for this coiild be:
- Noncritical sampliiig
Oversampling allows the steepn
ure 11.13) 'rhe irripiilsc rqmrrse
can hc absolutely integrated and stable behaviour has beeii achieved
of thc edges to be rcduced (see Fig- eii drcays more quickly and therefore
- Permitting a time-delay
Ttic impulse resporise of' the ideal low-
well by i i causal system if it is shifted far eiiough to t h c righl
filtcr can be tipproximated