iTfe thus calcuiak the riiagnituutlr for this point from H s.. As the rrunher o f poles is by one grratcr than the nunlher of zeros, the magnitude frequency response lar >> 2 fah at 20
Trang 1252 IQ Bode Plots
plot W P recognise that at, U = 2 there i h a resoilant point iTfe thus calcuiak the riiagnituutlr for this point from H ( s ) As the rrunher o f poles is by one grratcr than the nunlher of zeros, the magnitude frequency response lar >> 2 fah at
20 dU/clrcnde To confirni this w~ determincl the rringnitudc at d = 10 In order
to apyroximatc tlw path more accurateiy we ~ a l c i i l a l ~ the tdur fm L 7 1 8s
wrll The cli-;lmces in equation (10 3 ) are calciilatcd from the pole-zero plot
As is evident in Figure 10.9, the lollowirrg apprtrxiniatte v;zhies are yielded, if the
c
- 1,2
4
*t
9
(I
w = 0 w - 1 u l = 2 w = L0
Fipirr 10 9: Estimating the lengths €or various w
distances of the zeros are multiplicd and divided by thc distmce of t h c p o l ~ s :
(10.5)
For the pliase plot wc need the phase at J = 0 and recognise from the pole-zero diagram that diie to the pole s = -4 + 2 j the phrtsc changes sharply around w -= 2 I/'lirtlncxr, the phase of H ( s ) for w >> 2 t,akes a value of -90" Considering this,
we c m est,irrtat,e the phase a t the following points with the pole-zero diagram, as shown in Figure 10.10 We obtain
t7(.?0) = 0
p(j2)
~('1) M 2 x 60" - 30" + 90' - 90" == 90"
2 x 80" - 50" - 0" 90" = 2 0 "