CMX991 Datasheet, PDF (12/56 Pages) CML Microcircuits – Two-mode demodulator

RF Quadrature Transceiver / RF Quadrature Receiver
CMX991/CMX992
4.2.2 Rx 1^st IF Filtering
The output of the CMX991/CMX992 first receive mixer can be switched between MIXOUT1 and MIXOUT2
to support two different external 1^st IF filters for different receiver operating modes. The IF output should
be in the range 10MHz to 150MHz. The integrated IF amplifier that follows external 1^st IF filters has two
switchable inputs. It is recommended that an IF filter (e.g. crystal or SAW type) be placed between the
mixer output and IF amplifier input stages to protect the IF amplifier and subsequent stages from off-
channel signals. Matching arrangements will vary with the particular filter used, however an example of a
typical configuration for a 45MHz IF is given in Figure 7. The configuration shown only utilises one possible
combination of the two 1^st Mixer outputs and two IF amplifier inputs; the other input and output (IFIP2 and
MIXOUT2 respectively) could be configured to use a SAW filter or operate with a different IF frequency or
bandwidth, for example. The MIXEROUT1 and MIXEROUT2 pins should have a dc blocking capacitor, as
should the IF amplifier inputs IFIP1 and IFIP2. IFINN should be ac coupled to the IF filter ground.
For additional information see sections 5.2.2 and 7.6.
MIXINN
MIXINP
CMX991
CMX992
C8
C1
R2
L1
MIXOUT1
MIXOUT2
F1
IFIP1
IFIP2
C5
IFINN
C7
R1
C2
C3a C3b
C4 ^L2
Figure 7 Example External Components – Receive 1^st IF Section
 2015 CML Microsystems Plc
12
D/991_992/20