Evaluation Kit for CMX990
EV9900A
6.7
Troubleshooting
The CMX990 is a complex RF and Baseband system. If incorrectly programmed or modified,
results will be at variance from datasheet performance. Please study the datasheet, this manual
and the associated schematics and layout drawings carefully when troubleshooting.
This section provides some suggestions to help users resolve application issues they might
encounter.
6.7.1 Receiver Operation
Error Observed
Possible Cause
Remedy
No packets are received, ‘INV’ bit incorrectly set.
however synthesisers are locked
Invert current setting of ‘INV’ bit.
and the receiver otherwise Incorrect baud rate set.
Select correct clock control
register value.
appears
to
be
operating
correctly.
Receiver sensitivity is 30dB less ‘Sign’ bit is incorrectly set. Invert current setting on ‘Sign’
than anticipated.
bit
Degraded receiver performance. Incorrect
correction.
DC
offset Ensure DC offset correction
sequence has been executed.
Degraded receiver sensitivity There is
a
frequency To check if a frequency error
and/or imbalance in adjacent offset between EV9900A exists measure the frequency of
channel power in the transmitter reference oscillator and the main local oscillator either
(i.e. ACP high is much better the test equipment.
than ACP low or vice versa)
using the measuring equipment
in question or compare results
(Note: EV9900A requires from EV9900A with those from
an approximate AFC the measurement equipment.
value to be programmed
into the DAC1. A value of To overcome a frequency error
0x95 in register 0x0B is a either:
good starting point.)
a) Use a external reference for
the EV9900A
b) Tune to control voltage on
the AFC output (DAC1).
Poor
channels
sensitivity
on
some The main Tx VCO is not In a normal modem design the
powered down and can Tx VCO (U18) would be
drift into the Rx band.
powered down during Rx mode.
This is not implemented on
EV9900A.
or
BER results variable.
To overcome the problem the
Tx VCO should be disabled
during Rx BER testing. This can
be done by removing R67.
© 2007 CML Microsystems Plc
22
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