RF2489
Application Schematic with Dual-Band TX LO Buffer Output
VCC
BAND SEL
IP SET
33 nF
DNI
F2
33 nF
6
3
4
1
GND GND
GND GND
47 nH
VCC
IF SEL
VCC
L2
C1
20 kΩ
5.1 kΩ
DNI
8.7 nH
FM IF OUT
32
31
30
29
28
27
26
25
0 Ω
C2
DNI
L1
R
1
2
3
4
5
6
7
8
24
23
22
21
20
19
18
17
C1
47 nH
33 nF
1 pF
C1
1.5 nH
33 nF
VCC
L2
L1
R
LNA L IN
LNA H IN
CDMA
IF OUT
0 Ω
C2
/2
33 nF
C1
DNI
/2 SELECT
LO IN
7.5 nH
VCC
7.5 nH
15 nH
68 Ω
0.5 pF
0 Ω
9
10
11
12
13
14
15
16
1 nH
HB/LB LO OUT
VCC
2 nH
DNI
LNA GAIN
MIX GAIN
TX BUFF ENABLE
BUF ENABLE
F1
47 nH
33 nF
DNI
5
2
IN
OUT
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 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
.
1
fIF =
L1
2
2π
(C1 + C )
EQ
L2 and C2 serve dual purposes. L2 serves as an output
bias choke, and C2 serves as a series DC block.
Where CEQ is the equivalent stray capacitance and
In addition, L2 and C2 may be chosen to form an imped-
ance 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.
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:
1
4 R
1
RP
-1
R =
-
(
)
OUT
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
Rev A21 DS070308
13 of 30
RFMD [ RF MICRO DEVICES ]
