MIT Research Tweaks Smartphone Amplifier Voltage To Gain Battery Life

hypnosec writes "Two MIT electrical engineering professors, Joel Dawson and David Perreault, have claimed that they have cracked the age old efficiency problem related to the power amplifier in smartphones by designing a new amplifier that consumes just half the power as compared to their current counterparts. Current transistor-based power amplifiers consume power in two modes – standby and output signal mode. The only way to reduce power consumption and increase battery life is to use the least possible power when in standby mode. The problem here is that if the power is kept very low when in standby mode, because of sudden jumps from low-power standby mode to high-power output mode, signals get distorted. This is why current technologies waste a lot of electricity as standby power levels are kept at a relatively higher level to avoid distortion. The new technology, dubbed asymmetric multilevel outphasing, is basically a blazingly fast electronic gearbox that would select the best possible voltage to send across to the transistors that would minimize power consumption."

Comments

Duplicate story from Oct 31

[MattskEE]

This is a duplicate story posted on Slashdot on Oct 31: http://hardware.slashdot.org/story/12/11/01/0021213/breakthrough-promises-smartphones-that-use-half-the-power

Luckily this time the summary includes a link to an actual technical paper. The summary and the news article make it sound like this is an Envelope Tracking amplifier, but if you read the paper this is actually something different, it is more complicated and more interesting.

They are starting from an outphasing amplifier which divides a variable envelope signal into two constant amplitude but variable phase signals which can be amplified more efficiently since the amplifier doesn't need to output both large and small signals. But combining the signals is inefficient because the combiner must absorb some of the power when the two halves of the signal are very out of phase with each other. What the MIT researchers are doing is extending the outphasing technique to allow multiple discrete amplitudes on each amplifier to minimize the combiner inefficiency. It's more efficient than plain outphasing, I'm not sure how it compares to envelope tracking since the authors did not compare it to this in their paper.

Re:Duplicate story from Oct 31

[Andy Dodd]

Zero crossings and low output amplitudes with outphasing techniques are a bitch. If you use a hybrid combiner, nearly all of the energy goes into a dummy load on the difference port. If you use a "lossless" combiner such as a matching network, the VSWR seen by the amp elements skyrockets and - best case, efficiency is crap. Worst case, you fry the output stages of the amp.

Around a decade ago I worked on an outphasing system - I fried a LOT of hardware by accidentally feeding the system a low or zero amplitude, which effectively caused two amps to fight each other 180 degrees out of phase. http://www.google.com/patents/US6930547

What they seem to be doing here is reducing the voltage provided to the amp elements, reducing the power output, which allows them to reduce total output power efficiently while keeping the two amp elements relatively in-phase, and also allowing them to "fight" each other without frying themselves like they would if running at full power.

E.g. it's probably something like outphasing for 70-100% envelope levels, and power supply modulation below that. Likely not a "hard" threshold - they probably transition from one approach to the other somewhere in the 30-70% operating region.

http://slashdot.org/comments.pl?sid=3222705&cid=41842229 for some more details.

Re:Age old?

[__aaltlg1547]

It's clumsily worded. It's an age-old problem in power amplifiers that are used in situations where power varies, such as radio receivers and transmitters that need to work at multiple power levels. But I don't understand why they identify smartphones as a place where this has a great potential to improve battery life. It's really more applicable to non-smart cellphones where the audio amp and transmitter PA are bigger proportions of the total battery draw.

Cellphone power is often dominated by processor and display power.