EECS240 – Spring 2008Lecture 19: ComparatorsElad AlonDept. of EECSEECS240 Lecture 19 2Comparator• Specs and issues:• Clock rate fs• Offset• Resolution• Hysteresis• Input cap• Power dissipation• CM rejection• Kickback noise• …EECS240 Lecture 19 3Flash Converter• Fast: one clock cycle per conversion• High complexity: 2B-1 comparators• High input capacitanceR/2RRRR/2REncoderDigitalOutputVINVREFEECS240 Lecture 19 4Comparator Gain-BandwidthExample:• 4Gb/s link• Minimum ∆V: 1mV• Vdd = 1VÆ Av> 1V / 1mV = 1000 in < 250ps!EECS240 Lecture 19 5Operational Amplifier?3213T23T10001.33THz3 250psudBvo bitvoubitffAAf−=====×EECS240 Lecture 19 6Open-Loop Amplifier CascadeEECS240 Lecture 19 7Cascaded Amplifier• Simplified bandwidth analysis:• Open-circuit time constants• (Not most accurate, but leads to nearly the right answer for design optimization) EECS240 Lecture 19 8Bandwidth/Gain OptimizationEECS240 Lecture 19 9Bandwidth/Gain OptimizationEECS240 Lecture 19 10Power ConsumptionEECS240 Lecture 19 11Regenerative LatchEECS240 Lecture 19 12CML Comparator (Latch)EECS240 Lecture 19 13StrongArm LatchEECS240 Lecture 19 14Another CMOS ComparatorEECS240 Lecture 19 15HysteresisEECS240 Lecture 19 16KickbackEECS240 Lecture 19 17Kickback cont’dEECS240 Lecture 19 18Kickback
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