A system includes a ring oscillator including an odd number of inverters arranged in a ring. The system also includes a time to digital converter including an odd number of flops, where each of the flops is coupled to an output of a different inverter. The system includes a level shifter coupled to the inverters and to the flops. The system also includes a Gray counter coupled to at least one of the flops. The system includes a decoder coupled to the time to digital converter. The system also includes a phase frequency detector coupled to the decoder.