Harmonic ring oscillator time-to-digital converter

A simple yet high performance time-to-digital converter (TDC) architecture is proposed in this paper. Its key advantage is its ability to sample-and-hold a time interval and thereafter oversample the stored quantity to provide sub-gate delay resolution and high linearity. The converter is fully digital, synthesizable from standard logic cells, and owes its properties to the time storage mechanism which relies on injecting more than one signal edge into a ring oscillator and tracking their relative angle. Results from a prototype on FPGA reveal excellent noise suppression by achieving a single-shot precision of 0.05 times the unit inverting logic cell delay in the ring oscillator by using an oversampling ratio of 64.