- Digital Iage Processig ad Copressio D DSP Basics: Systes Stability D Saplig
Stability ty Syste is stable if a bouded iput always results i a bouded output BIBO For LSI syste a sufficiet coditio for stability: h S < D FIR filters always stable Stability test is difficult for IIR filters Z-trasfor is used to study stability
D Z rasfor x akes sese whe < { valuesof ad for which < } ROC fiite su coverges N D d fiite su
D Z rasfor Note: oly if uit circle ROS a s o ω ω ω ω e e j j y stable syste rasfer fuctio: { } b a Y H h Z Liear costat-coefficiets differece equatio to ipleet IIR syste: x a y b
D Z rasfor Aalogous to D -trasfor pole-ero plot is the Root Map i D: H : hold cost. o the Uit e.g. ad fid the roots i e.g. H 0 repeat for all o the Uit Circle Repeat the sae thig with o Uit Circle ad fid roots i We get a pair of plots: Root Map cosists of two parts I{ } I{ } Re{ } Re{ } Stable if root aps stay i Uit Circle
Saplig Saplig i oe doai Periodicity i other Replicas ay overlap ad we loose sigal Aliasig If o overlap we ca recover sigal by keepig oe replica -D Saplig: A badliited sigal i oe doai ca be periodically sapled with o loss of iforatio provided d it is sapled ofte eough Miiu saplig rate Nyquist rate is proportioal to the sigal badwidth
Saplig D sigals sg as here are ay ways to saple D sigals Aalog Iage Saplig exaple Saplig exaple
Saplig D sigals sg as he siplest ad ost coo of this is rectagular saplig Saple t ad t x a t t x a x Cotiuous-doai D sigal discrete tie at regular itervals idices of saples : Horiotal saplig iterval F.. replicated with period / i horiotal directio : Vertical saplig iterval F.. replicated with period / i vertical directio
Saplig D sigals sg as he siplest ad ost coo of this is rectagular saplig t x a t t 0 t
Saplig D sigals sg as he Bed of Nails t p t t δ t t 0 t
Saplig D sigals sg as We ca saple x a t t as follows: x s a t t x t t δ t t a x x a t t δ t t δ t t
Saplig D sigals Sa p g sg as the Fourier trasfor is 4 ** 4 a s δ ** 4 a δ a
Saplig D sigals sg as Aliasig occurs if we saple below the Nyquist rate critical saplig rate Nyquist rate o aliasig oversaplig rate > Nyquist rate o aliasig usually oversaple saple sice oideal atialiasig filter does ot have to have sharp cutoff replicas ore spaced out udersaplig rate < Nyquist rate Aliasig caot recover sigal
Saplig D sigals Sa p g sg as I the frequecy doai DF saple r r t t x a a ω ω 64748 r r ω ω b a
Saplig D sigals sg as I the frequecy doai ω / - ω ω / - ω -
Saplig D sigals sg as Udersaplig gives aliasig: / b / -/ -/ -/ / b -/ / Aliasig
Saplig D sigals sg as I the frequecy doai f s f b s b b b
Saplig D sigals sg as Hexagoal saplig y 0 x
Note about polar frequecy doai Agular frequecy Radial frequecy Relatio to rectagular frequecies
Note about polar frequecy doai f cosω 0 f θ cosω +ω ω +ω cst θ he cut of fuctio alog horiotal will be of period he vertical cat will be of period
Note about polar frequecy doai cosθ cosθ ω ω0 cosθ cosθ si θ si θ ω ω0 si θ siθ ω + +ω ω 0 horiotal frequecy vertical frequecy radial frequecy Note: Fuctio rotated by agle θ F.. rotated by agle θ
Note about polar frequecy doai Relatio betwee cosω 0 old ad cosω ew + ω ew : rotatio by agle θ For a poit rotate back by agle θ to get value of fuctio at that poit old old old ew cosθ + ew siθ cos cos θ si θ siθ cosθ or to express old i ters of ew ew ew ω cos ω cosθ + siθ cos ω + ω 0 old 0 ew ew ew ew ew ew cosθ siθ siθ cosθ old old