EE290C – Spring 2011Lecture 8: Equalization: FIR II and DFEElad AlonDept. of EECSEE290C Lecture 8 2VM TX + Equalization• First implementation (K.-L. J. Wong, JSSC 2004):EE290C Lecture 8 3Constant Current VM TX Design• D. Dettloff, ISSCC 2010EE290C Lecture 8 4RX FIR Equalizers• Currently not very popular – why?EE290C Lecture 8 5Coefficient Shuffling Architecture• Lee, Razavi, CICC 2001EE290C Lecture 8 6Shuffling Implementation• Can shuffle digital tap coefficients or analog inputsEE290C Lecture 8 7Interleaving• Often combined with tap shuffling• Ex: J. Jaussi, ISSCC 2004EE290C Lecture 8 8DFE: ImplementationRX_in• Design driven by feedback latency constraint• New summer output needs to settle (at comparator input) within one bit timeEE290C Lecture 8 9DFE Summer Design• Key constraint:tdig_fb+ tana_settle= Tbit• Need some Nτof settling:τsum= (Tbit–tdig_fb)/Nτ• Typically want ~4τ for ~98% settlingEE290C Lecture 8 10A ReminderEE290C Lecture 8 11Self-Loading 0 0.2 0.4 0.6 0.8 100.10.20.30.40.50.6GBW/(ωT/γ)GmCL = 20fFCL = 40fFCL = 80fF• Creates bandwidth limit• No matter how much power you spend• DFE has increased “self-loading” due to taps…EE290C Lecture 8 12DFE Summer DesignEE290C Lecture 8 13Maximum Cancelled ISI0 2 4 6 8 1000.010.020.030.040.05MDFEGm!0Gb/s DFEtdig = 30pstdig = 40pstdig = 50ps• There is a maximum MDFEyou can achieve• Don’t forget that every tap has to handle worst-case possible ISI• Implies max. number of taps (in given tech.)EE290C Lecture 8 14TX FIR RX DFE Duality• Can use same techniques we talked about in TX for RX DFE• But still need to watch out for digital power…d0clkVin0 – Imax/20 – Imax/20 – Imax/4z-1z-1d1d2d1d0d2d1d2EE290C Lecture 8 15Closing the First TapEE290C Lecture 8 16Split Summation• B. Leibowitz, ISSCC 2007EE290C Lecture 8 17All CML Design• H. Wang, VLSI 2009• Over 20Gb/s in 65nm CMOSEE290C Lecture 8 18Loop Unrolling• K. Parhi, ISCAS 1990+1+α-1+α+α+1-α-1-α-αDQ1−nddClk1|1=−nndd0|1=−nndddClknx+α-αEE290C Lecture 8 19Extended Loop UnrollingEE290C Lecture 8 20LE + DFEEE290C Lecture 8 21Practical DFE Design IssuesEE290C Lecture 8 22Practical DFE Design IssuesEE290C Lecture 8 23Practical DFE Design
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