Preliminary
8-43
RF2489
Rev A10 011017
8
Application Schematic
1
3
6
4
5
2
9
14
10
13
11
12
32
27
31
28
30
29
24
22
19
21
20
23
26
25
7
8
15
16
18
17
/2
/2 SELECT
33 nF
1pF
68
Ω
2nH
2nH
VCC
TX BUFF ENABLE
BUF ENABLE
1nH
DNI
47 nH
33 nF
DNI
IN
OUT
F1
2
5
LNA GAIN
MIX GAIN
7.5 nH
15 nH
VCC
33 nF
1.5 nH
47 nH
33 nF
8.7 nH
VCC
DNI
F2
1
4
3
6
GND
GND
GND
GND
20 k
Ω
5.1 k
Ω
47 nH
33 nF
DNI
IF SEL
IP SET
BAND SEL
33 nF
VCC
R
L1
C1
L2
0
Ω
C2
DNI
VCC
C1
R
L1
C1
C1
L2
VCC
0
Ω
C2
DNI
CDMA
IF OUT
FM IF OUT
LO IN
HB LO OUT
LB LO OUT
LNA H IN
LNA L IN
0
Ω
7.5 nH
0.5 pF
Output Interface Network
L1, C1, and R form a current combiner which per-
forms a differential to single-ended conversion at the
IF frequency and sets the output impedance. In most
cases, the resonance frequency is independent of R
and can be set according to the following equation:
Where CEQ is the equivalent stray capacitance and
capacitance looking into pins 1 and 2. An average
value to use for CEQ is 2.5pF to 3pF.
R can then be used to set the output impedance
according to the following equation:
where ROUT is the desired output impedance and RP
is the parasitic equivalent parallel resistance of L1.
C1 should be chosen as high as possible (not greater
than 22pF), while maintaining an RP of L1 that allows
for the desired ROUT.
L2 and C2 serve dual purposes. L2 serves as an out-
put bias choke, and C2 serves as a series DC block.
In addition, L2 and C2 may be chosen to form an
impedance matching network if the input impedance
of the IF filter is not equal to ROUT. Otherwise, L2 is
chosen to be large, and C2 is chosen to be large if a
DC path to ground is present in the IF filter, or omitted
if the filter is DC blocked.
1
2
π
L1
2
(C1+C
EQ)
f
IF =
R=
1
4R
OUT
- 1
R
P
()
-1
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