A mixed-mode PLL is disclosed. The mixed-mode PLL comprises a digital sigma-delta modulator, a low pass filter, and a digital controlled oscillator. The digital sigma-delta modulator receives a fractional bit signal. The low pass filter is coupled to the digital sigma-delta modulator. The low pass filter receives an output signal of the digital sigma-delta modulator and converts the output signal to an analog control signal. The digital controlled oscillator comprises a varactor dynamically coupled to the low pass filter and receiving the analog control signal.