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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."
Twice in three days? How soon before phones are actually generating net power?
...and filed a patent for the implementation or call it execution....otherwise some clever company, that is better known for suing others in the industry,; that's had one of its famous patents invalidated recently, will file...and sue.
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.
One way to do high efficiency is to do separate phase and amplitude modulation, the so called A-theta modulator. you get your amplitude control by adjusting the PA voltage _continuosly_ and do your phase modulation with an IQ modulator.
For wide bandwidth modulation formats this is a bit of a pain since you need a very wideband, high current, power supply. so they are doing an A/theta modulator but trying to simplify the bias control on the PA to avoid that.
What I'm not clear on is why they are doing this when they have a predistortion loop anyway. a pure predistortion loop should be able to achieve very similar results without any need for the PA bias adjust. you can also do it with 1 PA instead of two.
maybe it simplifies the PD loop substantially, I can't tell yet from the paper, but it trades this off against needing two PAs and PA bias control. And that PA bias control is a bit of a headache two, because you can't just stick a switch in there. The selectable bias levels have to come from a switching power supply which switches between different output voltages. doing this is also non-trivial.
I don't know, looks like somebody's thesis to me. Doesn't look like it's particular practical.
Also, first rule of looking at schemes like this. How much of that power they saved is being used in the more complicated digital circuitry. That's the reason you don't see PD loops in cell phones. It's a wash, you spend so much power analyzing the signal to do PD that you burn up the savings . Now if you have a 10W transmitter, PD makes lots of sense.
Absolute statements are never true
Lots of novel stuff with state of the art DSP techniques. But every once in a while I spot the ghosts of tubes lurking around.
Have gnu, will travel.
How can there even be an "age old efficiency problem related to the power amplifier in smartphones"? Sounds like an oxymoron to be. Or maybe it's just me getting age old.
Editors: Please mark all links to PDFs (and any other content that is not easily digested by browsers)
coding is life
Yeah... I doubt that engineering professors at MIT have enough experience to know how to deal with IP issues even in cases where they understand the significance of their discovery.
50% is a lot of power. Even if they can only achieve half of that in a real world implementation, it's still a significant leap forward. The latest smartphones, such as the Nexus 4, are boasting 10 hours talk time right now. 12-14 hours would be phenomenal.
it's = "it is"; its = possessive. E.g., it's flapping its wings.
Because under FCC Part 97 rules, you have to use the minimum amount of power to convey your message. If they knew that rule we wouldn't have to deal with craptastic performance.
One does not send voltage, one uses voltage to send amperage.
I see even classic Slashdot is now pretty much unusable on dial up anymore.
When I was in support, they tried to get us to use these cheaper headsets that used less battery. Aside from the fact that the earphones hurt after an hour, they also had the insidious power saver tha ut out all the ti.
I would get there early to scoop up on of the Plantronics that was supposed to be phased out. The company-issued "savings" device? I never used it. I just carried it as a backup in case I couldn't get there early enough to score a Plantronics. They could have saved themselves a lot of money buy not trying to save the batteries. I imagine that those stupid white headsets contributed a lot of stress to a job that's already stressful.
You've invented the triac preregulator, as seen in Carver amplifiers from the 1980s and probably earlier!