1 research outputs found
Power and spectrally efficient integrated high-speed LED drivers for visible light communication
Recent trends in mobile broadband indicates that the available radio frequency (RF) spectrum
will not be enough to support the data requirements of the immediate future. Visible
light communication, which uses visible spectrum to transmit wirelessly could be a potential
solution to the RF ’Spectrum Crunch’. Thus there is growing interest all over the
world in this domain with support from both academia and industry. Visible light communication(
VLC) systems make use of light emitting diodes (LEDs), which are semiconductor
light sources to transmit information. A number of demonstrators at different data
capacity and link distances has been reported in this area. One of the key problems holding
this technology from taking off is the unavailability of power efficient, miniature LED
drive schemes. Reported demonstrators, mostly using either off the shelf components or
arbitrary waveform generators (AWGs) to drive the LEDs have only started to address this
problem by adopting integrated drivers designed for driving lighting installations for communications.
The voltage regulator based drive schemes provide high power efficiency (> 90 %) but it is difficult to realise the fast switching required to achieve the Mbps or Gbps
data rates needed for modern wireless communication devices. In this work, we are exploiting
CMOS technology to realise an integrated LED driver for VLC. Instead of using
conventional drive schemes (digital to analogue converter (DAC) + power amplifier or
voltage regulators), we realised a current steering DAC based LED driver operating at
high currents and sampling rates whilst maintaining power efficiency. Compared to a
commercial AWG or discrete LED driver, circuit realised utilisng complementary metal
oxide semiconductor (CMOS) technology has resulted in area reduction (29mm2).
We realised for the first time a multi-channel CMOS LED driver capable of operating
up to a 500 MHz sample rate at an output current of 255 mA per channel and >70%
power efficiency. We were able to demonstrate the flexibility of the driver by employing
it to realise VLC links using micro LEDs and commercial LEDs. Data rates up to 1 Gbps
were achieved using this system employing a multiple input, multiple output (MIMO)
scheme. We also demonstrated the wavelength division multiplexing ability of the driver
using a red/green/blue commercial LED. The first integrated digital to light converter
(DLC), where depending on the input code, a proportional number of LEDs are turned
ON, realising a data converter in the optical domain, is also an output from this research.
In addition, we propose a differential optical drive scheme where two output branches of
a current DAC are used to drive two LEDs achieving higher link performance and power
efficiency compared to single LED drive