A digitally-controlled, bi-level CMOS LED driver circuit combining PWM dimming and data transmission for visible light networks

Recent breakthroughs in solid-state lighting technology has opened the door to a myriad of applications using light-emitting diodes for both illumination and optical wireless networking. Low-power CMOS technology enables realization of mixed-mode, system-on-chip driver circuits integrating multiple functions on a single substrate to control LED device performance, luminance, and data modulation for “intelligent” visible light networking. This paper presents a novel LED driver circuit architecture incorporating digitally-controlled analog circuit blocks to deliver concurrent illumination control and serial data transmission. To achieve this goal, a bi-level pulse-width modulation (PWM) driving scheme is applied to enable data transmission during the “OFF” period of the LED drive current. With 3-bit PWM dimming resolution, the driver circuit enables linear luminous intensity control from 5% to 100%. Pseudo-random binary sequences (PRBS) are generated to compare circuit performance for various data modulation formats. The LED driver circuit is simulated in a 0.5µm CMOS process and exhibits a worst-case power consumption of 100mW with 33mA peak PWM current.