A 7-GHz Fast-Lock Two-Step Time-to-Digital Converter-Based All-Digital DLL

Abstract

This paper presents a new fast-lock all-digital delay-locked loop (DLL) for next-generation memory devices such as DDR5 SDRAMs. The proposed DLL utilizes a new two-step time-to-digital converter (TDC)-based phase detecting and tracking scheme that results in a fast lock time of less than seven clock cycles. Unlike previous TDC-based DLLs, there is an advantage of having a fast lock time regardless of the long-replica clock buffer delay in the DRAM DLL. Implemented in a 65 nm CMOS process, the proposed digital DLL has a wide operating frequency range of 1.65–7.0 GHz and occupies an area of only 0.021 mm2. The DLL dissipates only 7.1 mW from a 1.0 V supply at 7 GHz, and the effective peak-to-peak (p–p) jitter of the output clock is about 4.55 ps at 7 GHz.