SP8861NAHP Ver la hoja de datos (PDF) - Mitel Networks
Número de pieza
componentes Descripción
Fabricante
SP8861NAHP Datasheet PDF : 13 Pages
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FROM
CHARGE
PUMP
C2
C1
R2
R1
−
+
TO VCO
FROM
CHARGE
PUMP
Cx
C1
R2
R1
−
+
SP8861
R3
TO VCO
C3
Fig. 11 Standard form of third order loop filter
Fig. 12 Modified form of third order loop filter
where Ku, K0, N and vn are as defined for the second order
loop and F0 is the phase margin, normally set to 45°. These
values can now be substituted in equation (3) to obtain a value
for C1 and in equations (4) and (5) to determine values for C2
and R2.
Example
Calculate values for a third order loop with parameters as
for the second order loop and F0 = 45°.
From
equation
(5):
t3
=
2tan 45°1cos145°
500Hz32p
= 0·4142
3161·6
∴t3 = 131·8µs
From equation (4):
t2 =
1
(500323p)231·31831024
∴t2 = 768·7µs
Using these values in equation (3):
t1 =
7·963102332p310MHz/V
1
3[A]2
80003(50032p)2
where
A
=
11vn2
11vn2
t22
t32


= 11(50032p)23(7·68731024)2
11(50032p)23(1·31831024)2
1
t1
=
500141·6  6·832
7·896110101·1714


2
= 6·3343102632·415
∴t1 = 15·3µs
Now, since t1 = C1R1 and R1 =1kΩ, C1 1=·5313013 025
∴C1 = 0·0153µF
For Fig. 11,
t2 = R2 (C11C2)
For Fig. 12,
t3 = C2R2
Substituting for C2:
t2
=
R2 C11Rt32


=
R2
C11t3
or, R2=
t22t3
C1
=
7·6873102421·31831024
0·015331026
∴R2 = 41·627kΩ
t3
=
C2R2
= t3
R2
= 1·31831024
41627
∴C2 = 3·17nF
For Fig. 12,
t1 = C1R1
or,
C1
=
1·5331025
103
∴C1 = 0·0153nF
t2 = C1R2
or,
R2
=
7·68731024
1·5331028
∴R2 = 50·242kΩ
t3 = C2R3
Since the values of C2 and R3 are independent of the other
components, either can be chosen and the other determined.
Assuming that R3 = 1kΩ, then
C2
=
1·31831024
103
∴C2 = 0·01318µF
11
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