Bode Plots

Gain Margin and Phase Margin

"GM/PM tells how much system can tolerate before going unstable!!!    "

•Phase Margin (PM):

–Phase margin is that amount of additional phase lag at the gain crossover frequency required to bring the system to the verge of instability (marginally stable)

  Φm=1800+Φ

  Where

  Φ=∠G(jωg)

  if   Φm>0 => +PM  (Stable System)

  if   Φm<0 => -PM  (Unstable System)

A Bode plot is a (semilog) plot of the transfer function magnitude and phase angle as a function of frequency. The gain magnitude is many times expressed in terms of decibels (dB)

A decade is defined as any 10-to-1 frequency range

     dB = 20 log10 A    where A is the amplitude or gain

Straight-line approximations of the Bode plot may be drawn quickly from knowing the poles and zeros

–response approaches a minimum near the zeros

–response approaches a maximum near the poles

The overall effect of constant, zero and pole terms

Term	Magnitude  Break	Asymptotic  Magnitude Slope	Asymptotic  Phase Shift
Constant (K)	N/A	0	0°
Zero	upward	+20 dB/decade	+ 90°
Pole	downward	–20 dB/decade	– 90°

Basic Plots  : Cases

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Note :  All the data shown in this page  is  taken from the reference books given in your syllabus. (Ref book: Manke/ J Nagrath , B C Kuo and from  google also)

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After reading this plz see this  video for more clarification

Viseo for how to draw Bode Plot

 https://www.youtube.com/watch?v=N9wxx6JPR_w