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This paper represents an innovative solution to
reduce phase noise present on the GMSK modulated spectrum in
an all-digital RF transmitter employing a discrete-time oscillator.
The root cause of this issue is the improper timing of oscillator
tuning word update with respect to the digitally-controlled
oscillator (DCO) capacitor state. Using the built-in self test (BIST)
circuit in the all-digital PLL (ADPLL), the DCO tuning word
update timing is calibrated such that the impact on the phase
noise is compensated and desired modulated spectrum margin
from the specification is achieved.