RF2459
Application Schematic
V
CC
Preliminary
L2
L1
C2
IF Filter
IF OUT
C1
R
C1
4.7 nH
LO IN
1.5 pF
V
CC
1
2
3
4
8
7
6
5
1.5 pF
RF IN
2.2 nH
100 nF
22 pF
8
FRONT-ENDS
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:
f
IF
=
1
L1
2π
(C1 + C
EQ
)
2
where R
OUT
is the desired output impedance and R
P
is
the parasitic equivalent parallel resistance of L1.
C1 should be chosen as high as possible, while main-
taining an R
P
of L1 that allows for the desired R
OUT
.
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 cho-
sen to be large (suggested 8.2nH) and C2 is chosen to
be large (suggested 22nF) if a DC path to ground is
present in the IF filter, or omitted if the filter is DC
blocked.
Where C
EQ
is the equivalent stray capacitance and
capacitance looking into pins 7 and 8. An average
value to use for C
EQ
is 2.5pF.
R can then be used to set the output impedance
according to the following equation:
R=
1
(
4 R
-
1
OUT
R
P
)
-1
8-100
Rev A2 010717
RFMD [ RF MICRO DEVICES ]
