Methods, systems, and apparatuses are described for compensating for an undesired fractional spur due to a PLL in a communication system. The communication system includes a time-to-digital converter (TDC) that is configured to execute in parallel to the PLL. The TDC is configured to determine a phase difference between a reference frequency and an output oscillation signal provided by the PLL. The phase difference is received by a processor to estimate particular characteristics of the undesired fractional spur, and the estimate of the characteristics is used to construct an estimate of the undesired fractional spur.