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A low-cost, high-efficiency, compact archilecture of a PWM (pulse-width-modulationr drive fan controller is designed for use in an embedded multicomputer system with an integrated hierarchicai thermal management schema. This pure digital design yields lower cost and higher efficiency than conventional linear drive fan controllers while providing the functionality and advantages of PWM drive fan controllers. The implementation and system integration of this circuit is also described in this paper.

A continuous-time common-mode feedback circuit (CMFB) is presented. A two-stage high-gain architecture is used to minimize the offset of the common-mode voltage. A special compensation scheme enables this circuit to be used in high-impedance current-mode systems without a stability problem. Simulation and testing results show the superior performance of this circuit. It is proven to be an ideal common-mode feedback circuit for systems which require an accurate and stable commonmode voltage. This circuit has been implemented in a continuous-time switched-current modulator with a 2m CMOS process. With a 50MHz clock, the modulator has achieved a 60dB dynamic range in a 1MHz bandwidth.

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