L M X 2 5 3 1 L Q 2 8 2 0 E E V A L U A T I O N B O A R D O P E R A T I N G I N S T R U C T I O N S
Free-Running VCO Phase Noise (Internal Divide by 2 Enabled)
Fout = ~1355 MHz (~2710 MHz/2)
The plots to the left show the true phase
noise capability of the VCO. In order to
take these plots, the E5052 phase nose
analyzer was used. The method was to
lock the PLL to the proper frequency, then
disable the EN_PLL, EN_PLLLDO1,
EN_PLLLDO2, EN_DIGLDO, and
EN_OSC bits. The equipment needs to be
able to track the VCO phase noise to
measure in this way, and one can not let
the VCO drift too far off in frequency. If this
kind of equipment is not available, the
VCO phase noise can also be measured
by making a very narrow loop bandwidth
filter.
When divide by 2 is enabled, the phase
noise at lower offsets is about 6 dB better;
but at high offsets, the phase noise
improvement may be less because the
divider is noise floor is adding to the phase
noise.
Fout = ~1410 MHz (~2820 MHz/2)
Fout = ~1460 MHz (~2920 MHz/2)
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