EECCO – Energy Efficient Current-Mode Techniques for Free-Space Optical Front-End Receivers
Key words: Energy Efficiency, Optical Communications, Current-Mode, Wireless Communications
Environmental policies are an important item in the political program of governments all over the globe. Ozone layer preservation and climate changes are major concerns for future generations. Environmental policies are deeply concerned with the regulation of gas emissions and waste disposal. Electronic industry and equipment play an important role in this scenario. Electronic equipment generates a lot of waste during its life cycle, and besides is made of aggressive and, in many cases, non-recyclable materials. Energy consumption is another issue linked to electronic equipment environmental impact. Electronic systems employing power aware mechanisms able to switch between power consumption modes, according to operating requirements are presently of mainstream usage. On a worldwide scale, this kind of energy savings has an enormous impact on both energy consumption and gas emissions. These strategies are commonly known as Green Electronics. Green Electronic equipment obeys to a wide range of environmental directives. These directives include certification procedures for: efficient use of energy (like the Energy Star, the 80 Plus and the Alternative Energy certifications), clean materials assemblage (like the RoHS compliancy certificate), and directives for re-cycling and optimization.
The application of green electronics concepts at the industrial level brought dramatic changes to the production processes. These directives are now showing their benefits, but there is still room for improvement. For instance, circuit designers often rely on circuit optimization procedures that disregard power consumption (low power design is of course an exception to this rule). Thus, the exploitation of circuit optimization techniques able to cope with system requirements and at the same time with power optimization directives would be a potential possibility to implement green concepts at a circuit design level. The present proposal follows exactly this line of reasoning.
Project EECCO (Energy EffiCient Current-mode techniques for free-space Optical receivers), aims at introducing green electronic concepts into the design and optimization of free-space optical front-end amplifiers. The main goal is to present and validate a model able to predict the necessary power to achieve a specified BER for a targeted transmission rate. The outcome of this optimization procedure is an energy efficient front-end able to operate with the minimum power-per-bit requirements.
Project EECCO will address two areas of circuit design: optical signal amplification and current-mode design strategies. These two choices come as a natural consequence of the expertise gathered by the team members of this project over the past ten years (as evidenced by the list of prior publications). At a conceptual level, these choices also have other fundamental justifications. Free-space optical front-end amplifiers offer a suitable framework for the deployment of green concepts. This kind of circuits often poses several design challenges, namely, gain-bandwidth optimization, noise reduction and dynamic range adaptation, just to name a few. The mutual interaction of these optimization procedures often results in several demanded trade-offs, usually with added power penalties. Thus, the exploitation of methods to cope these procedures with power optimization requirements will pose challenging opportunities for the deployment of general design guidelines. Current-mode design appears as suitable technique for the design of these amplifiers. In the past, current-mode circuits were used to circumvent the gain-bandwidth duality often found in these amplifiers. Moreover, current-mode circuits are a natural choice for circuits demanding the usage of high performance CMOS integrated circuit processes. Their adequacy for low-voltage operation is an attractive feature for these environments. Current-mode circuits are also very immune to biasing conditions, meaning that their biasing conditions can be easily modified without drastically impairing the circuit’s operation — this is often difficult to attain using the traditional voltage-mode design approach. Biasing immunity is a useful property that can be explored for the integration of power control mechanisms.
Additionally free-space optical systems constitute an active research area, where applications using both infrared and visible light spectrums are currently being investigated. One of the team members on this proposal is the PI (Principal Investigator) on another active FCT project (PTDC/EEA-TEL/75217/2006). This project is investigating the potential usage of traffic light control systems as a means of transmitting traffic information to the circulating cars. The exploitation of green concepts on this project could represent good opportunities to establish research synergies.