| Wireless body area networks(WBAN)is widely used in wireless medical treatment,physical detection,mobile control and somatosensory games,which brings a lot of conveniences for the live and the production.The development of the WBAN demands higher performance for the portable devices,the wearable devices and the implantable devices,therefore,the researches of the WBAN focus on the continuity of monitoring,the rate of communication and the security of devices.Based on the requirements of the WBAN,the portable devices also demands higher performance for power management unit(PMU).The PMU should achieve low power consumption,high efficiency and small size,which are also the emphasis of the proposed design.This paper introduces the SC DC-DC converter as the PMU because of its easy integration.Considering the uneasy integration and the electromagnetic interfence(EMI)in inductive DC-DC converters,this paper proposes a SC DC-DC converter as the PMU for the portable power devices.After a long term study of the SC DC-DC converter,this paper gives the optimization of the voltage ripple,the transient response and the power efficiency and proposes a high performance of a SC DC-DC converter for m W portable devices.This paper proposes a step-down SC DC-DC converter with PFM and burst mode.This design proposes dual mode control strategy to achieve high performance over the entire load range.PFM is adopted at heavy load to achieve small output voltage ripple while burst mode is adopted at light load to improve transient response and power efficiency.In addition,a detailed system stability analysis is introduced at PFM operation.To further improve the power efficiency,adaptive switch width modulation(ASWM)is proposed to reduce switching losses.This design is fabricated in 180 nm CMOS process,four conversion ratios(2/3,3/5,1/2,2/5)are realized for a 2.0-3.6V input voltage range,the measured results show that the converter operates from 0 to 2m A at a fixed 1.2V output voltage.PFM achieves 30 m V average ripple with 5n F output capacitance at heavy load.Compared with PFM at light load,burst mode achieves an 11% maximum improvement of power efficiency,improvements of 6% for average power efficiency is achieved with ASWM.The peak power efficiency is 84.2% from a 2.7V input voltage supply at a load current of 2m A.To reduce the output voltage ripple of the SC DC-DC converter,this design proposes an analog assistant digital low dropout regulator(LDO)with three step control strategy.The three step control strategy is utilized to improve the accuracy of the output voltage,the analog assistant LDO is implemented to eliminate the voltage ripple.The simulation results show that the load current range of the LDO is 0-10 m A,the input voltage is higher than 1.2V and the output voltage is fixed at 1V.The undershoot and overshoot is smaller than 100 m V for a 5m A load transition.The simulation results also show that the overall system operates normally. |
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