RF2460PCBA Просмотр технического описания (PDF) - RF Micro Devices
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RF2460PCBA Datasheet PDF : 20 Pages
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Preliminary
RF2460
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:
fIF
=
-----------------------------1------------------------------
2π
-L---1--
2
(
C1
+
2C2
+ CEQ)
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:
R
=
æ
è
----------1----------
4 ⋅ ROUT
– R--1--P--øö –1
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, L2 is cho-
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.
8
Rev A7 010912
8-39
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