Sunday, January 27, 2013

Energy Efficient Electronics

For the past few years in my professional life at ST I've been interested in areas of computing where energy efficiency and power efficiency are very important. An obvious example is small battery powered devices such as phones. However there is increasing interest in efficiency across a wide range of areas, driven by the rising cost of energy, the use of energy scavenging, the desire to create very dense computing systems, and the general green agenda.

One obvious way to decrease the power consumption of an electronic system is to reduce the voltage at which the circuitry works. It is common knowledge that the performance (speed) of electronics has increased over successive generations of electronic technologies, but it is less known that the operating voltage has decreased over those same generations. Although with a fixed technology, reducing voltage decreases speed, in each technology generation the fundamental speed increase has outweighed the voltage reduction, allowing both increased performance and better efficiency. 

However, recently the operating voltage hasn't been falling, which has created new challenges for electronic engineers. To meet these challenges recent electronic systems, such as found in smart phones, turn off circuitry when is not needed (your phone's screen is off when it is in your pocket), and modify the operating voltage according to required performance. This "dynamic voltage frequency scaling" (DVFS) exploits the fact that a system does not have to run flat-out at all times. For example, when playing "Grand Theft Auto: Vice City" on your phone you need a lot of performance, so DVFS runs the computer at high voltage; when composing a text message you need relatively little performance and so DVFS runs the computer at low voltage gaining better power efficiency.

Energy efficiency solved? Unfortunately not. With current technology we cannot reduce operating voltage (and hence increase efficiency) as much as we would like. The problem is the performance drops too quickly as we reduce the voltage; our efficient computers are too slow to be useful. However, one development (FDSOI) that ST has been responsible for, offers a great improvement in this area, allowing high performance to be achieved at much lower voltages. There are a couple of videos below which talk about this development and its application to smart phones. The bottom line is that compared to standard (bulk) technology, FDSOI can improve power efficiency nearly three-fold. 

[For those familiar with simple electronics - the same performance (1 GHz operation of an ARM A9) is achieved on FDSOI at 0.65v as on bulk silicon at 1.1v, so the (dynamic) power efficiency improvement is (1.1/0.65)^2 = 2.9 - see Video 2 at 1:50]

[Probably for scientists, engineers and geeks only]. The first video explains FDSOI technology:


and the second demonstrates a phone made with FDSOI and compares it one using bulk silicon:




2 comments:

Ray McConnell said...

Is there any issue with the bulk 'mirrors' interfering with neighbouring devices?

The analogue porting issue would seem to have been somewhat dismissed as being a small % of die area..

However I bet the process would provide substantial benefit to fast analogue, particularly RF interfaces.

Ray

Ray McConnell said...

Is there any issue with the bulk 'mirrors' interfering with neighbouring devices?

The analogue porting issue would seem to have been somewhat dismissed as being a small % of die area..

However I bet the process would provide substantial benefit to fast analogue, particularly RF interfaces.

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