Abstract
A low voltage start-up energy harvesting medium frequency (MF) receiver is presented, for use as the power and synchronisation part of a remote sensor node in a wide area industrial or agricultural application. Low operational duty cycle is possible with an embedded low speed data channel, leading to low start-up and operating voltage taking priority over power efficiency. The receiver consists of a rectifier, a power management unit and a phase-shift keying (PSK) demodulator. The proposed rectifier can cold start from 250mV antenna input and deliver 900mV DC output with 24% power conversion efficiency. The measurements demonstrate the QPSK demodulator consuming 1.27μW with a supply voltage of 630mV at a data rate of 1.6kbps with 1MHz carrier frequency. The rectifier is implemented in a standard threshold 0.18μm CMOS technology, occupies 0.54mm2 and can deliver 10.3μW at 3V to an external battery or capacitor.
Highlights
Remote sensor networks are becoming well established with the availability of very low power IC technology
The design is a conventional latched charge pump (CP) type [20], where the clock is derived from the quaternary phase-shift keying (QPSK) demodulator circuit
To be able to retain lock while the phase is changing with the data content, the voltage-controlled oscillator (VCO) runs at four times the input signal frequency so that there are edges available for the phase comparison process that are always in phase with the input for all states of the QPSK input signal
Summary
Remote sensor networks are becoming well established with the availability of very low power IC technology. A receiver could receive an activate or sleep command from the transmitter by means of the slow data modulated onto the power source magnetic field This approach provides the opportunity to deploy a number of sensor nodes operating at very low duty cycle ratios without the associated continuous power drain of internal timing or wake-up circuits [13,14,15,16]. We consider the requirements of end use applications where more conventional methods of power delivery are not practical, or line of sight RF propagation is not possible, excluding UHF and microwave solutions Such restrictions can exist in industrial and agricultural locations, but the site may well be suited to the use of a dedicated RF source.
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