Self-powered light sensor for simultaneous intensity-And-direction sensing and maximum-energy harvesting with shared photodiodes

Tai Haur Kuo, Kuan Yu Chen, Hsiao Ping Lin, Shang Jung Liu

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Self-powered light sensors are ubiquitous in internet-of-Things applications for sustained operation without battery replacement. Figure 1 right shows an example, in which a museum needs thousands of light sensors to sense light intensity and direction for lighting control. Photodiodes (PDs) are inherently suited to both light sensing (LS) and light energy harvesting (LEH). Figure 1 top-left shows a PD's P-V curve. A PD must be forward-biased for simultaneous LS and LEH, and be biased at its maximum powerpoint (MPP) voltage VMP for maximum LEH. Recent PD-based light sensors can sense light intensity [1]-[4] and/or direction [4] and harvest light energy [1], [3]. However, [1] performs LS and LEH with separated PDs. The PDs for LS in [1]-2, [4] are zero/reverse-biased and thus cannot perform LEH. Although the PD in [3] is forward-biased, the PD harvests little energy since it operates near the open-circuit voltage VoC and consumes all for proper LS function. Light direction sensors [4] commonly use masks on PDs to increase light-direction sensitivity, but the incident light at some angles is largely blocked. Thus, the incorporation of LEH into these light sensors [1]-[4] is inefficient. This paper proposes a self-powered light sensor for simultaneous LS and maximum-LEH with the same PDs, as shown in Fig. 1 bottom-left. Instead of minimizing the power consumption of the sensor operating under high dynamic range, the proposed sensor can harvest more energy while detecting higher light intensity. This sensor includes a light-To-frequency converter (LFC) and a frequency-To-digital converter (FDC). The LFC uses a dc-dc converter with input (output) connected to a PD (an energy storage unit, ESU) to regulate the PD's voltage VP around VMP with pulse-skipping modulation (PSM). Thus, the average frequency fILo of the inductor current ILo charge packet is linear to the light intensity, while the packets deliver energy from a PD to an ESU. The dc-dc converter is extended to multiple inputs (dual outputs) to sense light direction (provide a regulated voltage VL for the FDC and RF TX). The FDC simply uses a counter and a look-up table for readouts. Combining LEH and LS alleviates the need for reducing FDC power in high light intensity. In addition, a low-cost plastic Fresnel lens is adopted to concentrate incident light to increase light-direction sensitivity [5], which can be further increased by placing the PDs on different surfaces of a polyhedron [6].

Original languageEnglish
Title of host publicationProceedings - A-SSCC 2021
Subtitle of host publicationIEEE Asian Solid-State Circuits Conference
PublisherInstitute of Electrical and Electronics Engineers Inc.
ISBN (Electronic)9781665443500
Publication statusPublished - 2021
Event2021 IEEE Asian Solid-State Circuits Conference, A-SSCC 2021 - Busan, Korea, Republic of
Duration: 2021 Nov 72021 Nov 10

Publication series

NameProceedings - A-SSCC 2021: IEEE Asian Solid-State Circuits Conference


Conference2021 IEEE Asian Solid-State Circuits Conference, A-SSCC 2021
Country/TerritoryKorea, Republic of

All Science Journal Classification (ASJC) codes

  • Hardware and Architecture
  • Signal Processing
  • Electrical and Electronic Engineering


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