An Energy-Efficient Asynchronous Hybrid-Searching Algorithm for Auto Frequency Calibration in IEEE 802.11ax Applications

Modern totally on-chip systems now demand that phase-locked loops are designed with auto frequency calibration (AFC) circuits for multi-band voltage controlled oscillators (VCO). This paper proposes an energy-efficient asynchronous hybrid searching algorithm for high-speed integrated AFC. Asynchronous architecture breaks the minimum limit of searching time. Hybrid method overcomes non-monotonic variation of frequency errors in binary search. A true-single-phase-clock(TSPC)-based high-speed digital counter accelerates AFC further by directly quantizing frequency from VCO. Designed in a 55nm CMOS technology, the proposed AFC achieves a calibration time of $1.5-3.5\mu\mathrm{s}$ across required tuning range by IEEE-802.11ax standard, with a Figure-of-Merit(FoM) of 0.8.