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RF2861
Rev A3 DS050902
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
IF Output Interface Network
Single-End IF Matching
L1, C1, C2, and R form a current combiner which performs 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 fol-
lowing equation:
Where CEQ is the equivalent stray capacitance and capacitance looking into pins 9 and 10. 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 (not greater than 39pF), while maintaining an RP of L1
that allows for the desired ROUT. If the self-resonant frequencies of the selected C1 produce unsatisfactory linearity perfor-
mance, 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 output 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 chosen 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.
Differential IF Matching
IF-
IF+
C2
R
L1
L2
VCC
33 nF
C3
IF Saw
4
5
9
10
IF+
IF-
C1
C1
f
IF
1
L1
2
------ C
1
2C
2
C
EQ
++
()
2
π
-----------------------------------------------------------
=
R
1
4 R
OUT
⋅
---------------------
1
R
P
------
–
⎝⎠
⎛⎞ 1
–
=
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