Design and Characterization of Active Matrix LED Microdisplays With Embedded Visible Light Communication Transmitter

Abstract

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 × 240 blue micro-LED (μLED) pixels fabricated on a single gallium nitride (GaN) substrate. The size of each μLED pixel is 30 × 30 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . 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 μLED 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-μm 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> up to 25-cm distance without a lens. When using optical lenses, the VLC distance is extended to >500 cm.