Journal
JOURNAL OF LIGHTWAVE TECHNOLOGY
Volume 34, Issue 14, Pages 3449-3457Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/JLT.2016.2562667
Keywords
Active matrix; flip-chip; internet of things (IoT); microdisplay; micro-LED (mu LED); on-off keying (OOK); pulse-width modulation (PWM); system-on-a-chip (SoC); transmitter; visible light communication (VLC)
Funding
- Research Grants Council of the Hong Kong Special Administrative Region Government under the Theme-Based Research Scheme [T23-612/12-R]
- HKUST-Qualcomm Joint Innovation and Research Laboratory
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This paper presents the design and characterization of the first active matrix light-emitting diode (AMLED) microdisplay with an embedded visible light communication (VLC) transmitter, enabling LED digital signage for location-based applications such as information broadcasters and indoor positioning beacons. The driver system-on-a-chip (SoC) integrates four identical macro-cells, each containing a pixel driver array, a row driver, a column driver, and a first-in first-out memory, to drive a wide quarter-VGA (WQVGA) display featuring 400 x 240 blue micro-LED (mu LED) pixels fabricated on a single gallium nitride (GaN) substrate. The size of each mu LED pixel is 30 x 30 mu m(2). At the system level, pulse-width modulation (PWM) superimposed with ON-OFF keying modulation is proposed to accomplish grayscale control for display and simultaneously transmit VLC signal by modulating the mu LED array. At the circuit level, a pixel driver cell composed of three transistors and one capacitor (3T1C) with a novel VLC function is employed to implement the control scheme. Flip-Chip bonding is adopted to establish connections between the WQVGA microdisplay and the AMLED driver SoC. Implemented in a 0.5-mu m 2P3M CMOS process, the driver SoC enables a high-resolution microdisplay module to achieve 4-bit grayscale at a 100-Hz frame rate, while supporting 1.25-Mb/s VLC for a bit error rate <10(-5) up to 25-cm distance without a lens. When using optical lenses, the VLC distance is extended to >500 cm.
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