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A comparator in a low-power 65-nm complementary metal-oxide-semiconductor process (only standard transistors with threshold voltage Vt ap 0.4 V were used) is presented, where the circuit of a conventional latch-type comparator consisting of two cross-coupled inverters is modified for fast operation, even with 0.6 GHz at a low supply voltage of 0.65 V. The advantages of a high-impedance input, rail-to-rail output swing, robustness against the influence of mismatch, and no static power consumption are kept. To achieve a bit error rate of 10-9 at 1.2-V supply, an amplitude at the input of 16.5 mV at 4 GHz has to be applied. If the supply voltage is lowered, 12.1 mV at 0.6 GHz/0.65 V is necessary. The power consumption of the comparator is 2.88 mW at 5 GHz (1.2 V) and 128 muW at 0.6 GHz (0.65 V). Simulations show an offset standard deviation of about 6.1 mV at 0.65-V supply. With an on-chip measurement circuit, the delay time of the comparator of, e.g., 104 ps for 15-mV input amplitude at 1.2-V supply, is obtained.