| Recently,with the development of sensor technology and wireless communication technology,wireless sensor network(WSN)has become a research hotspot in academia and industry.The realization of low-power integrated nodes is one of the main development trends of WSN at present.Since the power consumption used for communication on the existing WSN node accounts for a large proportion of the total power consumption,an effective method to realize a low-power WSN node is to reduce the communication power consumption on the node.A low-power communication scheme for WSN nodes that is currently widely studied is to use wake-up receivers for sleep/wake-up communication.In this scheme,the main transceiver is in sleep-state when there is no data communication,and the wake-up receiver(Wu Rx)is responsible for activating it before data communication starts.Since the Wu Rx has to work all the time to monitor data communication request signals from other nodes,how to implement a Wu Rx with ultra-low power consumption is the key to highlight the advantages of this scheme.Based on the study of the above-mentioned sleep/wake-up communication scheme,this paper proposes an integrated wake-up receiver that uses an envelope detector as the first stage of the RF front-end and uses an oversampling voltage comparator in the baseband circuit to recover the data signal.The wake-up receiver has the advantages of ultra-low power consumption,high sensitivity,and small implementation area.To suppress the influence of power supply noise and common mode noise on signal processing,a differential baseband receiving path is adopted in the proposed wake-up receiver.For the specific circuit implementation,firstly,to improve the sensitivity of the wake-up receiver,a single-ended-to-differential passive envelope detector is designed in this paper.Compared with the traditional single-ended passive envelope detector,it can not only get a differential envelope signal at the output,but also can obtain twice the conversion gain and output signal-to-noise ratio(SNR)without increasing the rise time of the output signal.Secondly,this paper proposes a differential-input voltage comparator based on voltage domain-time domain(V-T)conversion,which can add low-pass filtering characteristics in the conversion process while completing voltage comparison.Compared with the passive RC low-pass filter cascaded voltage comparator in the traditional structure,it greatly reduces the area of chip implementation.Besides,to eliminate the offset between the positive and negative signal paths of the differential baseband receiving path,this paper proposes a DC offset calibration loop based on discrete-time phase-locked loop(PLL)according to the characteristics of V-T conversion,which can equivalently eliminate the offset after multiple sampling periods,thereby improving the robustness of the wake-up receiver against process mismatch.Finally,to solve the problem that the traditional reference current source cannot use the cascode structure to improve the power regulation rate under low power supply,an improved reference current source based on voltage clamping is designed in this paper,which can achieve a reference current with high power supply rejection(PSR)under low power supply.Based on the TSMC 65nm LP CMOS process,the circuit schematic design and layout implementation of the proposed ultra-low-power Wu Rx are completed in this paper.The designed OOK-Modulated Wu Rx is compatible with the 434-MHz Industrial,Scientific,and Medical(ISM)band,and the data transmission rate used is 250bps.The simulation results show that the designed Wu Rx functions normally,and achieves an RF sensitivity of-72d Bm at the level of false alarm rate(FAR)less than 1/h and missed detection rate(MDR)less than10-3,and consumes 17.9n W from 0.6V power supply.The layout implementation results show that the area of the Wu Rx chip is 0.9mm×0.6mm,of which the core area is0.6mm×0.3mm. |
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