LMX2320 National Semiconductor, LMX2320 Datasheet - Page 17

• Manufacturer Part Number: LMX2320
• Description: Frequency Synthesizer for RF Personal Communications
• Manufacturer: National Semiconductor

Application Information
Consider the following application examples
Example
K
K
RF
F
N
ATTEN
if we choose R3
Converting to standard component values gives the follow-
ing filter values which are shown in Figure 4
Note 1 See related equation for K in Charge Pump Current Specification
VCO
ref
p
p
C1
R2
C2
R3
C3
e
opt
e
e
e
e
RF
e
e
e
e
e
45
e
2
e
5 mA (Note 1)
Definitions For this example V
be approximated using the curves in the Typical Peformance Char-
acteristics for Charge Pump Current vs D
K
case you must convert K
200 kHz
T1
T3
T2
C1
C2
R2
opt
e
1000 pF
3 3 k
10 nF
22 k
100 pF
20 MHz V
900 MHz
c
are in mA You may also use K
20 dB
e
e
e
e
e
e
e
e
e
20 kHz
1
f
ref
sec
(7 045e4)
7 045e4
3 549e
1 085 nF
1 085 nF
3 55e
10 6e
(3 29e
3 29e
e
(2
10
e
4500
(20 20)
p
e
1
b
b
b
22k then C3
b
b
b
a
1 256e5
p
5
9
200e3)
6
5
6
tan
2
e
(3 29e
(7 045e4)
a
b
(5e
(3 29e
3 35 k
3 55e
3 29e
VCO
(3 29e
p
2 387e
1
2
b
e
b
to (rad V) multiplying by 2
P
e
1
3) 20e6
b
b
3 29e
e
6
b
e
b
2 387e
2
a
5
6
b
5 0V The value of K can then
6
6
b
(3 29e
2 34e
e
6)
a
2 387e
4500
b
a
22e3
2
(5 mA 2
1
2 387e
6
(Continued)
o
a
b
2 387e
Voltage The units for
b
e
b
6
3 29e
b
6
6
10 6 nF
6)
e
b
a
1
rad) but in this
b
2
6)
b
a
106 pF
2 387e
6)
a
6 2 387e
e
(7 045e4)
3 29e
3 549e
b
b
6)
6 2 387e
b
2
b
2
17
1
5
6
a
(3 29e
(7 045e4)
b
b
6
6)
2
b
2
1
1
FIGURE 4 E 20 kHz Loop Filter
(3 549e
a
(7 045e4)
b
5)
2
2
(2 387e
b
6)
2
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