EV9900 Datasheet, PDF (18/27 Pages) CML Microcircuits – Evaluation Kit

Evaluation Kit for CMX990
In the mixer bypass mode the 400MHz main VCO should be used (U17).
The following changes should be made:
EV9900
• Remove R152, R200, C97.
• Fit R164 with 120Ω.
• Fit R153 with 0Ω.
• Fit R184 with 0Ω.
For 400MHz operation of the transmitter the Tx VCO needs to be changed to a 400MHz part for
example the V560MC03 from Z-Communications.
NOTE: Problems may be encountered with the transmitter in mixer bypass mode and with
the main local oscillator on the EV9900, as no shielding is provided between the power
amplifier and the local oscillator.
To achieve optimum performance from the diode ring mixer (U15) all ports should see a good
50Ω match. The IF port is particularly critical and a matching arrangement is provided into a
buffer amplifier. Using negative feedback in such buffer amplifiers is often beneficial but in this
case can be problematic, as it is essential to ensure that the buffer provides good isolation so as
to prevent the crystal filter impedance from disturbing the match to the mixer. The buffer is
configurable to allow the user to determine the best configuration for particular design
requirements.
© 2005 CML Microsystems Plc
18
UM9900/1