Direct Count of VCO Clock n E=Ncntr-Ndec Counter Comparison VCO Clock Tvco p/fret L Ndec=p*(N.Fdec) ÷p Decoded by Band shiftVCO Ref.Clock division ratio AFC: Tref 贝.四， MUX rst hold Ncntr<0> Ncntr<1> Nontr<12> Counter-Ncntr Nentr[2:0](TSPC) Ncntr[12:31(Digital) High-speed asynchronous divide-by-2 counters are used to count the VCO clock directly 2009 IEEE International Solid-State Circuits Conference 2009 IEEE 11© 2009 IEEE International Solid-State Circuits Conference © 2009 IEEE 11 Direct Count of VCO Clock • High-speed asynchronous divide-by-2 counters are used to count the VCO clock directly Ncntr cntr dec ref AFC cntr cntr cntr cntr cntr cntr vco vco ref Counter Ncntr dec dec