CXA3106Q
Here, ωn and ζ are as follows.
ωn characteristic angular frequency:
The oscillatory angular frequency when PLL oscillation is assumed to have been maintained by the loop filter
and individual loop gains is called the characteristic angular frequency: ωn.
ζ damping factor:
This is the PLL transient response characteristic, and serves as a measure of the PLL stability. It is
determined by the loop gain and the loop filter.
A capacitor C2 is added to the actual loop filter.
This added capacitor C2 is used to reduce the R noise, and a value of about 1/10 to 1/1000 of C1 should be
selected as necessary.
Current input type active filter with added capacitor C2
C2
C1
R
ii
Vo
–A
–1
–Vo
The filter transmittance is as follows.
The Bode diagram for formula (7) is as follows.
1 + C1 · R · S
F (S) =
S ((C1 + C2) + C1 · C2 · R · S)
1
1
1 + τ1 · S
S (C1 + C2) (1 + τ2 · S)
..................
=
(7)
τ1
τ2
log w
τ1 = C1 · R
C1 · C2 · R
τ2 =
C1 + C2
log w
0
–45deg
Here, assuming C2 = C1/100, then:
C1 · C1/100 · R
τ2 =
–90
C1 + C1/100
1
101
=
=
C1 · R
1
101
τ1
– 28 –
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