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A clock generator for high-speed chip-to-chip link receivers was implemented in a 45-nm CMOS SOI technology. A low sensitivity to supply voltage noise was achieved by means of a low dropout voltage regulator using a replica feedback in the regulation loop, where the replica resistance is regulated by a second loop. We show that by adjusting the replica load the necessary matching of the gm/gds ratio of the current sources can be achieved. A power supply rejection of > 22 dB was measured up to 1 GHz for a circuit operating from a 1 V supply with 80 pF decoupling capacitance and a load current of 18.5 mA. The maximum supply sensitivity of the clock generation circuit (DLL plus phase rotators) was 4.5 ps/100 mV supply noise over the entire noise frequency range at clock frequencies from 1.25-5 GHz. The phase rotator achieves a wide range of operating frequencies by providing programmable rise/fall times in its selection stage. In addition, low voltage operation of the circuit was demonstrated at supply voltages down to 0.7 V and a clock frequency of 1.6 GHz.
Date of Publication: Nov. 2009