MC145152-2 Freescale Semiconductor, Inc, MC145152-2 Datasheet - Page 18

• Manufacturer Part Number: MC145152-2
• Description: Parallel-input Pll Frequency Synthesizer
• Manufacturer: Freescale Semiconductor, Inc

Design Considerations
4
4.1
18
NOTE: Sometimes R
Definitions:
N = Total Division Ratio in feedback loop
K
K
Damping Factor:
for a typical design w
φ
φ
K
(Phase Detector Gain) = V
(Phase Detector Gain) = V
VCO
A)
filter φ
The φ
op amp used in the combiner/loop filter.
Design Considerations
C)
B)
(VCO Gain) =
Phase-Locked Loop — Low-Pass Filter Design
R
V
PD
PD
PD
and φ
and φ
φ
φ
φ
φ
out
out
out
R
V
R
V
φ
φ
R
-
-
-
-
V
-
ζ ≅
V
1
R
. The value of C
outputs swing rail-to-rail. Therefore, the user should be careful not to exceed the common mode input range of the
is split into two series resistors, each R
n
1
(Natural Frequency)
2π∆f
∆V
Figure 12. Phase-Locked Loop — Low-Pass Filter Design
VCO
R
R
VCO
R
DD
DD
R
1
1
1
1
/4
/2
π
π
R
C
MC145151-2 and MC145152-2 Technical Data, Rev. 5
C
C
for PD
for φ
2
should be such that the corner frequency of this network does not significantly affect ω
R
C
V
2
and φ
out
R
_
+ A
≈
VCO
VCO
2
R
2πfr
10
C
(at phase detector input).
VCO
1
÷
2. A capacitor C
C
F(s) =
F(s) =
is then placed from the midpoint to ground to further
Assuming gain A is very large, then:
F(s) =
ω
ζ =
n
ω
ω
ζ =
=
n
ζ =
n
=
=
0.5 ω
R
ω
2K
R
(R
2
n
R
1
Nω
sC + 1
NC(R
K
R
φ
n
sC + 1
1
2
K
1
R
K
+ R
φ
2
NR
(
NCR
sC
1
φ
K
2
K
C
VCO
K
n
sC + 1
φ
R
VCO
VCO
2
K
1
1
2
)sC + 1
C
VCO
C +
1
+ R
2
K
)
φ
K
N
VCO
Freescale Semiconductor
)
n
.