A 3.2-GHz 405 fs rms Jitter –237.2 dB FoM JIT Ring-Based Fractional-N Synthesizer

A ring-oscillator (RO)-based low-jitter digital fractional-N frequency synthesizer is presented. It employs a frequency doubler (FD) that doubles the reference clock frequency, a 2-bit time-to-digital converter (TDC) with optimized thresholds to minimize the quantization error, and a high-resolution digital-to-time converter (DTC) to cancel the quantization error of the delta-sigma fractional divi...