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A high-speed high-accuracy on-chip current sensor for current-mode switching dc-dc converters is presented in this paper. By employing local shunt feedback, the non-dominant pole in the current sensor is pushed to high frequency. Both speed and accuracy of the current sensor can then be improved simultaneously by consuming low quiescent current. The proposed current sensor for the buck converter is designed using a standard 0.35Â¿m CMOS process. Results show that the proposed sensor achieves at least 95% sensing accuracy and ≪50ns settling time by consuming the quiescent current of 35Â¿A. The sensor allows the current-mode buck converter to operate at switching frequencies up to 2MHz with a duty cycle down to 0.2.