EV9900 Datasheet, PDF (16/27 Pages) CML Microcircuits – Evaluation Kit

Evaluation Kit for CMX990
EV9900
Transmitter
The transmitter provides at least +30dBm in the default configuration (819-825MHz). Two power
amplifier footprints are provided on the PCB, however only the 800MHz (U6) device is fitted to the
EV9900. The other PA (U20) can be fitted for 400MHz operation. The 400MHz PA is tuneable
(by component changes) over the range 380 to 512MHz. The transmit VCO (U18) also has very
broad tuning range typically from below 800MHz to above 900MHz with a 3.3V charge pump.
The CMX990 RAM DAC output (DAC 0) is be connected to the PA control line with a buffer (U7)
which is used to scale the gain and transistor (TR7) to provide sufficient current to the PA control
pin. The buffer is required as the PA control lines can sink several mA of current, which is more
than the CMX990 DAC output can provide.
Local Oscillators
VCO’s are provided for the main and aux synthesizers. The aim is to cover the frequency bands
of 864-870MHz (Rx) and 819-825MHz (Tx).
This requires the following local oscillator frequencies, based on the following frequency plan:
Rx Band / MHz
864 – 870
Tx Band / MHz
819-825MHz
Tx IF / MHz
90.0
Rx IF / MHz
45.0
LO Range / MHz
1818 - 1830
1818 - 1830
Table 6 – Local Oscillator Frequencies
If the mixer bypass mode is to be used the main LO should be operated at the desired local
oscillator frequency, rather than twice the LO frequency (as required by the CMX990 image reject
mixer). The CMX990 has a control register bit to switch into this mode. The VCO for the main
PLL now requires an operating band at around 800MHz.
The VCOs are packaged parts from Z-communications, who provide a range of VCO’s in the
same package outline, so that the user can evaluate other frequency bands if required. These
VCOs have some performance limitations and so fail to meet EN 300 113 adjacent channel
requirements for transmitter and receiver.
The aux VCO is a discrete design operating at 180MHz and covering the range 160-180MHz.
This may be re-tuned by component changes if required by the user.
© 2005 CML Microsystems Plc
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UM9900/1