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Save Stability Considerations For Later Power sup plied to the ampli
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3.3, STABILITY CONSIDERATIONS /
3.3.1. Introduction
An amplifier circuit must be stable over the entire frequency range.
The RF circuits (amplifier) tend to oscillate depending on operating frequency
and termination.
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ie] > fe then the magnitude oF the retum voltage’ w
positive feedback, which causes instability (oscillator, rave increases
ip P| < the etum voltage wave is totally avoided ¢
as negative feedback. (amplifier), ty,
qiwo ~ port network amplifier is characterized by its S-par
s S-parameters
‘The amplifier is stable, when the magnitudes of reflect
ion coefficients
are i,
o
eal,
than unity
Iel 1, the origin (the point 7, =0) part isin unstable region
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Stable
Fig. 4.5. Output Stability Circle denoting the stable regions when |S, >1
+ Input Stability Circle:
Input stability circle equation is given by
(f-cl} + t¢-ca}
Circe radius al
a8 a)
(sul “fF
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Fig.3.6. Input stability Circle [=I in the complex I plane
“Two stability domains of ip stability cirees are:
(When |Sy| <1, the center (T, =0) must be stable
Catia |
sible
Fete
Circle denoting the stable regions when |S] < I
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becomes unstable.
| >E the center (I's
| 71 the COREE
oul? 1
Unstable
Wsl=4
Fig. 3.8. Input Stability Circ
rability Circle denoting the stable regions when [Sal ad
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