Preliminary
RF2449
Application Schematic
VCC
100 pF
1 nF
L1
L2
LO IN
56 Ω
C2
Filter
ENABLE
IP SET
IF2+
IF2-
C1
C1
L
1
2
24
23
22
21
20
19
18
17
16
15
14
IF SEL
R
LNA GAIN
MIX GAIN
3
4
5
30 nH
RF IN
VCC
33 nF
6
6.8 nH
100 pF
7
1 nF
6.8 nH
510 Ω
100 pF
8
*
9
10
11
12
R
3.0 pF
C1
L
C2
Filter
L1
8
22 kΩ
33 kΩ
IF+
IF-
13
C1
1.5 nH 33 nF
L2
VCC
RF SAW Filter
1 nF
22 nH
*NOTE:
Microstrip Inductor, ZO = 50 Ω, L = 100 mils
Suggested component values for 85.38 MHz IF and
ROUT = 1 kΩ:
L1 = 470 nH
C1 = 10 pF
R = 7.5 kΩ
Output Interface Network
L1, C1 and R form a current combiner which performs
a differential to single-ended conversion at the IF fre-
quency and sets the output impedance. In most cases,
the resonance frequency is independent of R and can
be set according to the following equation:
–1
1
1
-------------------- ------
R =
–
4 ROUT RP
where ROUT is the desired output impedance and RP is
the parasitic equivalent parallel resistance of L1.
1
-----------------------------------------------
fIF
=
C1 should be chosen as high as possible, while main-
L1
taining an RP of L1 that allows for the desired ROUT
.
------
2π
(C1 + CEQ)
2
L2 and C2 serve dual purposes. L2 serves as an out-
put bias choke, and C2 serves as a series DC block.
Where CEQ is the equivalent stray capacitance and
capacitance looking into pins 16 and 17. An average
value to use for CEQ is 2.5pF.
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 cho-
sen 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.
R may then be used to set the output impedance
according to the following equation:
8-80
Rev A4 001016
RFMD [ RF MICRO DEVICES ]
