Upload
duongduong
View
225
Download
2
Embed Size (px)
Citation preview
1
Introduction
• Physical systems incorporate some form of feedback
• Theory of negative feedback developed by Electrical Engineers.
• Feedback theory used in modeling of systems.
• Negative or Positive Feedback
3
Sampling & MixingHere, we look at feedback ckts
voltage-sampling series-mixing (series-shunt) topology
β
β
AA
xxA
xxAxx
sf
f
i
+==
==
10
0
0
8
Measuring the output resistance of the voltage-sampling
series-mixing (series-shunt) topology
feedback amplifier of Rof ≡ Vt/I.
9
Derivation of the A circuit and β circuit for the series-shunt feedback amplifier.
(a) Block diagram of a practical series-shunt feedback amplifier.
(b) The circuit in (a) with the feedback network represented by its hparameters.
(c) The circuit in (b) after neglecting h21.
Amplifier instability
20
)()(1)()(
180180
180180 ωβω
ωωjjA
jAjAf +=
999.0)()( 180180 −=ωβω jjA
A(jώ180) =999β(jώ180) = -0.001
)sin(1.0)( 180ttxi ω= )sin(100)( 180ttxo ω=
)sin(1.0)( 180ttx f ω−=