The invention provides a fractional frequency all-digital phase-locked loop and a control method thereof. The method comprises the following steps: S1, a fractional frequency controller generates a
delay control word, a frequency division ratio control word, an integer frequency control word and a fractional frequency control word according to an external fractional frequency control word; s2, theclock generation and
control circuit generates a
clock signal ckr according to the reference
clock and the frequency control word; s3, the digital time converter generates a low-frequency
clock signal according to the ckr and the
delay control word; s4, the feedback
signal generation circuit outputs a feedback signal fb according to the frequency division ratio control word and a high-frequency
clock signal ckv generated by the
numerical control oscillator; s5, the phase
discriminator generates
phase error digital signals phe of ckr and fb; s6, the auxiliary frequency locking loop outputs a
control signal ft1 according to the integer frequency control word, the fractional frequency control word and the low-frequency
clock signal, and the
numerical control oscillator updates ckv accordingto the sum of ft1 and phe.