A Portable Digital DLL for HighSpeed CMOS Interface Circuits

A digital delay-locked loop (DLL) that achieves infinite phase range and 40-ps worst case phase resolution at 400 MHz was developed in a 3.3-V, 0.4-¿m standard CMOS process. The DLL uses dual delay lines with an end-or-cycle detector, phase blenders, and duty-cycle correcting multiplexers. This more easily process-portable DLL achieves jitter performance comparable to a more complex analog DLL when placed into identical high-speed interface circuits fabricated on the same test-chip die. At 400 MHz, the digital DLL provides >250 ps peak-to-peak long-term jitter at 3.3 V and operates down to 1.7 V, where it dissipates 60 mW. The DLL occupies 0.96 mm².