Evaluation Kit for CMX979 (engineering samples)
EV9790
2017 CML Microsystems Plc
23
UM9790/1
7.5
Troubleshooting
The EV9790 is a complex RF system. If incorrectly programmed or modified, results will be at variance from datasheet
performance. Please study the CMX979 datasheet, along with the User Manuals, associated schematics and layout
drawings for the EV9790 board when troubleshooting. This section provides suggestions to help users resolve application
issues that may be encountered.
7.5.1
RF PLL Operation
Error Observed
Possible Cause
Remedy
PLL output unstable /
noisy but on frequency
Unstable / low reference input
level
Check the input reference connections and
level. Check operation using the default on-
board reference.
Loop instability
The programmed PLL values may give a high
gain peak. Check the loop components fitted
and reprogram with a higher charge pump
current or comparison frequency.
VCO not close to
programmed frequency
Not calibrated.
Run auto calibration of the RFVCO and bias
using the VCO calibration tab.
Check continuity of the loop filter.
Incorrect programming
Check that the correct output division ratio
has been selected
Table 8 RF PLL – Possible Errors
7.5.2
IF PLL Operation
Error Observed
Possible Cause
Remedy
PLL output unstable / noisy
but on frequency
Loop instability
The programmed PLL values may give a high
gain peak. Check the pump current or
comparison frequency selected.
VCO not close to
programmed frequency
Not calibrated.
Run auto calibration of the
I
FVCO and bias
using the VCO calibration tab.
Incorrect programming
Check that the correct output division ratio
has been selected
Table 9 IF PLL – Possible Errors
