Static Phase Offset Reduction Technique for Delay Locked Loops

A new static phase offset reduction technique suitable for low bandwidth delay locked loops is proposed. Chopping, which is a well-known technique for offset reduction, can be easily applied to the phase detector. Applying it to the charge pump is non-trivial and requires complex circuitry. The proposed technique reduces the offset due to both PFD and the charge pump, without actually chopping the latter. Analysis of the proposed method shows an offset reduction at least by a factor of 2. A conventional DLL, a DLL with a chopped PFD, and the proposed DLL were designed in a 130 nm CMOS process to verify the proposed technique. Monte Carlo simulations with random process and mismatch variations show that the offset improves from 19.9 ps in the conventional technique to 1.7 ps in the proposed technique.