A high-precision time-to-digital converter using a two-level conversion scheme

This paper describes a design of time-to-digital converter (TDC) using a two-level conversion scheme. The first level is accomplished by a multi-phase sampling technique with the aid of delay-locked loop (DLL). Then the input signal and its adjacent sampling clock are manipulated and sent into a vernier delay line (VDL) sampling circuit at the second level. The proposed TDC can provide high resolution with less hardware compared to one level VDL sampling circuit with the same dynamic range. A new architecture of dual DLL circuit is also implemented to stabilize delay control against process and ambient variations. A test chip is designed and fabricated in 0.35-μm logic technology. With an input reference clock within 130 to 160 MHz, the TDC achieves 24 to 30 ps resolution. The DNL is less than ±0.55 LSB and INL is within +1 to -1.5 LSB.