In one aspect, a digital PLL (DPLL) operates based on fractional portions of input and output phases. The DPLL accumulates at least one input signal to obtain an input phase. The DPLL determines a fractional portion of an output phase based on a phase difference between an oscillator signal from an oscillator and a reference signal, e.g., using a time-to-digital converter (TDC). The DPLL determines a phase error based on the fractional portion of the input phase and the fractional portion of the output phase. The DPLL then generates a control signal for the oscillator based on the phase error. In another aspect, a DPLL includes a synthesized accumulator that determines a coarse output phase by keeping track of the number of oscillator signal cycles based on the reference signal.