A highly digital MDLL-based clock multiplier that leverages a self-scrambling time-to-digital converter to achieve subpicosecond jitter performance

This paper presents a mostly digital multiplying delay-locked loop (MDLL) architecture that leverages a new time-to-digital converter (TDC) and a correlated double-sampling technique to achieve subpicosecond jitter performance. The key benefit of the proposed structure is that it provides a highly digital technique to reduce deterministic jitter in the MDLL output with low sensitivity to mismatch and offset in the associated tuning circuits. The TDC structure, which is based on a gated ring oscillator (GRO), is expected to benefit other PLL/DLL applications as well due to the fact that it scrambles and first-order noise shapes its associated quantization noise. Measured results are presented of a custom MDLL prototype that multiplies a 50 MHz reference frequency to 1.6 GHz with 928 fs rms jitter performance. The prototype consists of two 0.13 mu m integrated circuits, which have a combined active area of 0.06 mm(2) and a combined core power of 5.1 mW, in addition to an FPGA board, a discrete DAC, and a simple RC filter.