Towards Battery-Free Wide Area Network With Ultra-Low Voltage Chirp Spread Spectrum Modulation

Next generation of wireless sensors networks is poised to operate at zero-power. To reach this goal while operating over long range, there is a need for ultra-efficient RF transmitter and associated modulation techniques. The spread spectrum modulation for digital communication features best in class advantages, with its robustness to narrow band interference or its ability of the receiver and demodulate signals with extra low SNR. The objective of this paper is to propose a charge-to-chirp circuit capable of producing this modulation. Unlike competing architectures, this ultra-low voltage transmitter is capable of generating a spread waveform of the CSS type. It implements a tunnel-diode-based voltage-controlled-oscillator driven by ramp generator cells. Chirp of spreading factors SF=6 are demonstrated with the circuit. The VCO is driven by 300 mV capacitor micro-discharges (power consumption of 280 mu W) and produces has an output power of - 12dBm. This characteristic allows to consider the deployment of a long range wide area network transmitter operating without battery.