It has been calculated that data centres use around 200 terawatt hours of electricity annually, equating to about 1 % of global electricity demand. Some forecasts predict this demand will grow to around 7 % in little over a decade. To overcome current data centre energy inefficiencies, supported by the EU’s SME instrument fund, the MERCURY project prototyped and demonstrated a pioneering Integrated Circuit (IC) chipset. MERCURY used, for the first time, industry-standard CMOS technology on 12 inch wafers to drive 25 Gigabits per second (Gbps) Optical Transceiver Modules (OTM) in a 4 x 25 Gb format. Bridging the optical and electrical domains At data rates of 25 Gb or more, typical of recent high-bandwidth communications, if the distance signals must travel on an electrical printed circuit board is longer than a few inches, they are attenuated and soon completely lost in noise. ICs with optical transceivers avoid this limitation by using low-loss optical fibres to send and receive signals. These chips often start out using bipolar transistors made from Silicon-Germanium (BiCMOS SiGe). While offering high-speed processing, this arrangement compromises power efficiency, with SiGe transistors operating at higher voltages than CMOS transistors. MERCURY’s innovation lay in the conversion from optical to electrical signals, and back again, using CMOS. For MERCURY, on the transmission side, incoming digital data was re-timed, with advanced analogue drive signals created to operate the laser component. On the reception side, a photodiode converted the incoming light to a low-level photocurrent which is amplified through several stages up to full digital levels, with the clock (coordinating digital timing) and the data signals both extracted. “By way of example, a recent data centre built in Dublin was fitted with 1 million optical transceivers. Using our technology, each OTM would use half to 1 watt less power. Once the inefficiencies of air-conditioning are included, that easily equates to 5 MW of total saved power – equivalent to over 1 600 kettles operating continuously, at just one site!” says project coordinator, Mr Gary Steele. At 12 inches, MERCURY’s CMOS wafers offer greater economies of scale than the 8-inch wafers of SiGe. As well as reducing cost, by using less than half the power of these competitors, without performance or functionality loss, MERCURY technology looks capable of displacing BiCMOS – as has already happened at lower data rates. The growing demand for energy-efficient data centres Investment in European data centres is growing and, by 2020, Europe’s data centres will be using over 100 billion kWh of energy every year. The EC’s Code of Conduct for Energy Efficiency in Data Centres was designed to help counter this unsustainable situation, without jeopardising the speed and memory capacity of data centres. Replacing BiCMOS with CMOS MERCURY reduces power consumption and waste heat from data centre equipment and so contributes to this effort. Additionally, as Mr Steele says: “25 Gbps is also the mainstream solution for the 5G cellular roll-out. With much higher consumer data rates than 3G and 4G phones, along with many more base stations, MERCURY’s power savings apply here too. We calculate that production volumes could reach up to 50 million units a year, with total installation easily reaching 250 million worldwide.” After demonstrating full functionality, then making subsequent performance improvements (included in a further prototyping run), the team are now lab testing engineering samples in anticipation of full mass-production.
MERCURY, 5G, integrated circuits, optical transceivers, CMOS, BiCMOS, data centres, data rates, bipolar transistors, energy efficiency, green, sustainable