Preliminary
8-39
RF2460
Rev A7 010912
8
Output Interface Network of the Mixer
L1, C1, C2, 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 7 and 9. An average
value to use for CEQ is 2.5pF.
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.
C2 should first be set to 0 and C1 should be chosen as
high as possible (suggested less than 20pF), while
maintaining an RP of L1 that allows for the desired
ROUT. If the self-resonant frequencies of the selected
C1 produce unsatisfactory linearity performance, their
values may be reduced and compensated for by
including C2 capacitor with a value chosen to maintain
the desired FIF frequency.
L2 and C3 serve dual purposes. L2 serves as an out-
put bias choke, and C3 serves as a series DC block.
In addition, L2 and C3 may be chosen to form an
impedance matching network if the input impedance of
the IF filter is not equal to ROUT.Otherwise,L2ischo-
sen to be large (suggested 120nH) and C3 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.
f
IF
1
L1
2
------ C
1
2C
2
C
EQ
++
()
2
π
-----------------------------------------------------------
=
R
1
4 R
OUT
⋅
---------------------
1
R
P
------
–
èø
æö 1
–
=
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