Bassem Fahs

A 12-m 2.5-Gb/s Lighting Compatible Integrated Receiver for OOK Visible Light Communication Links

This paper presents a visible light communication (VLC) system for indoor applications. The system employs a high-sensitivity integrated circuit (IC) receiver with detection levels in the microwatts range. The proposed link is a lighting compatible VLC system enabled by the low noise floor of the IC receiver and capable of establishing a VLC link in the gigabit-per-second range with only 250 lux illuminance or 600-μW transmitted optical power from a high-speed 680-nm laser diode source. Dedicated optics is used for light steering and for focusing the transmitted power toward the receiver to maximize the collected optical power. The receiver is implemented in AMS 0.35 μm CMOS technology with integrated photodiodes. An error-free VLC link with a bit error rate (BER) <;10-9 is measured up to 1.8 Gb/s and a VLC-compliant BER below 10-3 is measured up to 2.5 Gb/s with on-off-keying modulation over 12 m link distance. To our knowledge, this is the first reported IC receiver-based VLC link in the Gb/s range.

A 1.8 Gb/s fully integrated optical receiver for OOK visible light communication in 0.35 μm CMOS

This paper presents a fully integrated optical receiver for On-Off-Keying (OOK) visible-light communication (VLC) links. The circuit is implemented in AMS 0.35μm technology, with the OPTO process option allowing for high-quality photo-detectors integration. The implemented receiver exhibits a low input referred noise density of 5 pA/VHz to meet the sensitivity requirements of free-space optical wireless links in the visible spectrum. The receiver is tested as a part of an optical setup at 46 cm distance from a 680-nm laser-diode source. A measured 1.8 Gb/s data-rate with a bit-error-rate of 5×10−5 is achieved through the use of high bandwidth circuit design techniques and a programmable integrated equalizer function. The receiver draws 65 mA from a 3.3 V DC voltage supply. The die size is 1 mm × 0.8 mm.

A 6-m OOK VLC Link Using CMOS-Compatible p-n Photodiode and Red LED

This letter presents an ON-OFF-keying visiblelight-communication (VLC) link realized over 6-m distance. The transmitter is implemented with a commercially available red LED source at 650 nm. While most of the reported high-performance VLC links are using p-insulator-n photodetectors, this receiver employs a simple CMOS-compatible p-n photo-detector. A 150-Mb/s optical wireless transmission is measured with a bit-error rate of 1.3 × 10-6, which falls below the forward error correction limit of 3.8 × 10-3. The secondorder L-C-R equalization is used in both the transmitter and the receiver circuits to achieve maximum bandwidth extension. The VLC link is realized with a low illuminance of 250 lux. This power is below the common indoor illumination levels which enables advanced lighting-compatible VLC applications. The receiver and the source circuits consume around 240 and 105 mW, respectively, which represents to our knowledge a record energy-per-bit level of 2.3 nJ/b.

A novel blue-enhanced photodetector using honeycomb structure

In this paper, we present a honeycomb structure to maximize the edge-length in the detector and therefore enhance the detector responsivity in the blue region of the spectrum. A layout of a prototype honeycomb detector was designed and fabricated on a silicon wafer using a standard CMOS process. Based on our measured spectral response, the honeycomb structure improves the photocurrent in blue by about 60%. Moreover, the honeycomb detector demonstrates 20% less dark current than in conventional detector. Simulation results using MEDICI confirm the measured data.

A digitally tunable stabilization technique for transimpedance amplifiers in optical wireless and visible light communication links

A digitally controllable stabilization technique for bandwidth-enhanced shunt-feedback (SFB) transimpedance amplifiers (TIA) with active Gm-feedback is proposed. The Gm-feedback programmability uses a switchable tail current network to digitally control the global TIA phase margin and correct for any instability resulting from device modeling imperfections, unconsidered layout parasitics or PVT variations. The proposed technique is demonstrated using a dual-stage TIA implemented in 0.35 μm CMOS technology. The TIA consumes 10.9 mA from a 3.3 V DC voltage supply, with 600 μA additional current from the phase margin correcting circuits, to achieve around 25 degrees phase margin control range. The TIA was tested as a part of a fully integrated optical receiver in a 2.7-m link visible light communication (VLC) setup. The phase margin control bits allowed bit-error-rate (BER) improvement by three orders of magnitude (<; 10-10) at 1.8 Gb/s.

A meter-scale 600-Mb/s 2×2 imaging MIMO OOK VLC link using commercial LEDs and Si p-n photodiode array

This paper presents a free-space 4-channels imaging multiple-input multiple-output (MIMO) system for On-Off-Keying (OOK) Visible-Light-Communication (VLC) links. An aggregate data-rate of 600 Mb/s is measured over 6 meters link distance with a bit-error-rate (BER) below 10−3 with the 4-channels simultaneously modulated. While the majority of published VLC works to date use components-off-the-shelf (COTS) PIN or Avalanche PDs that require both non-standard and/or higher cost fabrication processes as well as high reverse bias potential, the presented receiver in this paper employs a 2×2 on-chip Nwell/Psub photodiodes (PD) array fabricated in a low cost CMOS-compatible process. To extract high data rate performance out of the proposed CMOS low speed PD array, a 2nd-order LCR equalization is used to compensate for the stringent bandwidth limitation of the PD, measured around 20 MHz and push the speed up to 150 Mbps/channel. With a red light-emitting-diode (LED) array at 650 nm, the 4-channels MIMO setup DC power consumption is 1.38 W, which represents to our knowledge an energy-per-bit record performance for OOK VLC systems of 2.3 nJ/bit.

A robust 2×2 CMOS receiver array for meter-scale point-to-point OOK VLC links

This paper presents a fully integrated 2×2 optical receiver array for Point-to-Point (P2P) On-Off-Keying (OOK) visible-light communication (VLC) links. The 2×2 PD-array design constraints and cross-talk issues are discussed. Each receiver exhibits a low input referred noise density of 5 pA/VHz to meet the sensitivity requirements of free-space optical wireless links in the visible spectrum. The VLC receiver is tested as a part of an optical setup at 2.7 m and 6.7 m distances from a 680-nm laser-diode source. A measured 2.3 Gb/s per-channel data-rate with a VLC-compliant bit-error-rate is achieved through the use of high bandwidth circuit design techniques and a programmable integrated equalizer function. The receiver is implemented in AMS 0.35 μm technology. Each single receiver draws 65 mA from a 3.3 V DC voltage supply. The complete array size is 2.0 mm × 1.6 mm.

Blue-enhanced and bandwidth-extended photodiode in standard 0.35-pm CMOS

In this paper, a photodiode structure based on N×N junctions is presented to enhance responsivity in the blue region and provide optical-bandwidth extension. The use of subsections or multiple junctions increases the number of generated blue photo-carriers as well as the collection speed of photo-carriers at the depletion regions edges. An NWell/Psub photodiode formed of 5×5 subsections is designed and fabricated in standard AMS 0.35 pm CMOS technology with the OPTO process option. The photodiode is compared to a solid structure with a single section having the same optical window area of 100 pm × 100 pm. A responsivity improvement of around 10% ∼ 15% is measured between 400 nm to 550 nm wavelength. The normalized AC-responsivity shows a 2× increase in bandwidth and at least 2 dB improvement around the cut-off frequency of the reference PD at 1 V reverse bias voltage.

A dual-Gm start-up boost technique for wide-band BiCMOS LC-VCOs

This paper presents a start-up boost technique dedicated to BiCMOS LC-oscillators. The proposed technique is applied to wide-band LC-VCOs which generally suffer from increased tank losses and require high bias current to ensure start-up and sustainable oscillation. To overcome these limitations, we propose to connect a bipolar transconductance to intermediate levels of the oscillators tank in order to enhance the global transconductance and boost the start-up while relaxing the total power consumption. The constraints of the auxiliary transconductance use as well as the achieved improvements relative to power saving are discussed in this paper. In addition, an LC-VCO design using the proposed technique in 0.25-μm BiCMOS technology is described. The oscillator covers the frequency range from 4.82 GHz to 9.86 GHz with 68.7% tuningrange. The achieved phase noise at 1-MHz offset varies from -121 dBc/Hz to -116 dBc/Hz, at 5.24 GHz and 8.8 GHz, respectively, with a maximum power consumption of 18.6 mW from 1.2-V DC supply voltage.