Optical Power Delivery and Data Transmission in a Wireless and Batteryless Microsystem Using a Single Light Emitting Diode

In this paper, a light emitting diode (LED) is used both to harvest energy and to transmit data in a wireless and batteryless microsystem. The microsystem consists of an LED die (350 μm × 350 μm), an application specific integrated circuit (230 μm × 210 μm) and a storage capacitor (0.5 mm × 1 mm) forming a small footprint. A modular optical energy management and data transmission framework is presented. A proof of concept design that transmits a 16-bit identification number serially at a data rate depending on the amount of received optical power is described. The LED has a power efficiency of 22%; better than silicon photodiodes under monochromatic light of 680-nm wavelength. The higher voltage supplied by the LED compared with a silicon photodiode allows circuitry to be powered directly from it without requiring the elevation of the photovoltaic potential, as in the case of using on-chip silicon photodiodes. Data transmission task of the LED requires a charge pump circuit to elevate the photovoltaic voltage. The 0.8 V generated by the LED under a 680-nm laser beam of 4-mW/mm
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optical power density is elevated to 1.4 V for optical transmission at a rate of 4 kbit/s. Under 70-mW/mm
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optical power density, 1.3 V is elevated to 2.4 V, achieving a data rate of 26 kbit/s.