Student Invention May Significantly Extend Mobile Device Battery Life 160
imamac writes with this excerpt from news out of Carleton University:
"Atif Shamim, an electronics PhD student at Carleton University, has built a prototype that extends the battery life of portable gadgets such as the iPhone and BlackBerry, by getting rid of all the wires used to connect the electronic circuits with the antenna. ... The invention involves a packaging technique to connect the antenna with the circuits via a wireless connection between a micro-antenna embedded within the circuits on the chip. 'This has not been tried before — that the circuits are connected to the antenna wirelessly. They've been connected through wires and a bunch of other components. That's where the power gets lost,' Mr. Shamim said."
The story's headline claims the breakthrough can extend battery life by up to 12 times, but that seems to be a misinterpretation of Shamim's claim that his method reduces the power required to operate the antenna by a factor of about 12; 3.3 mW down from 38 mW. The research paper (PDF) is available at the Microwave Journal. imamac adds, "Unlike many of the breakthroughs we read about here and elsewhere, this seems like it has a very high probability of market acceptance and actual implementation."
Re:Counter-intuitive! (Score:5, Informative)
Wires radiate RF like mad unless they're heavily shielded, which is something you really can't do effectively in tight spaces. Of course, testing was done at 5.2GHz, so it will be interesting to see how it works at cellphone frequencies - packaging size might become a factor at lower frequencies.
Re:Counter-intuitive! (Score:1, Informative)
From the article:
"The strategy is useful as it eliminates the need of isolating buffers, bond pads, bond wires, matching elements, baluns and transmission lines. It not only reduces the number of components and simplifies SiP design but also
consumes lower power."
Less compenents = Less power?
Less range by 3x; less power by 12x (Score:2, Informative)
Last line of the pdf:
The conventional LTCC package provides 3 times more range than the proposed design but consumes 12 times more power.
Re:What? (Score:2, Informative)
Definitely bad journalism. The culprit isn't wire resistance, it's reactance. The impedance mismatch at the junctions from amplifier to circuit board to connector to cable to antenna all create reflections and thus standing waves [wikipedia.org]. The power that goes into those standing waves is reflected back into the amplifier, where it is dissipated as heat. The result is that you need (in his example) a 38mW amplifier in order to get 3.3mW of radiated power out of the antenna.
What his invention does is create a near-field transmission to the antenna directly from the amplifier output, without all that intervening cable and PCB trace and such. Near-field antennas can be efficient at *much* smaller sizes, so you can put one on the chip. It's counterintuitive to me that you could get lower losses that way, but that's what he's claiming. Multi-GHz radio waves (microwaves) behave in weird ways, and I'm not an RF engineer...
Re:Counter-intuitive! (Score:2, Informative)
So you save power versus the conventional design, but you lose range.
Impedance Matching technique (Score:3, Informative)
"This configuration isn't uncommon and many microwave systems employ this technique. (Attaching the amplifier nearly directly to the antenna.)"
I agree, it sounds very much like some kind of Impedance Matching technique where the Inductive coupling is direct to the antenna. I'm not so sure that's as patentable as this University is drumming it up to sound. (I guess they hope to earn a lot of money from it, mainly from from phone companies). But Impedance Matching using windings to effectively wireless couple to the antenna (where the antenna acts like part of the winding) isn't something new. If anything its something very old.
Re:I don't get it. (Score:5, Informative)
He's using a waveguide coupling to launch the wave to an external hunk of waveguide, rather than running it through pins, wires, PC board traces, etc. The latter are very lossy at cellphone frequencies.
(I'm working on something similar right now and lose virtually all my signal going through about 6" of PC board wiring. B-( )
Re:Counter-intuitive! (Score:4, Informative)
Powered speakers are popular because it gives monitor manufacturers a way to make line level crossovers, power amps and speaker drivers work together.
Having control over the specifications of all those components means better fidelity. It is tidier too.
I don't think RF or IR is ever used with studio monitors. They would cause phase alignment problems and a loss of fidelity. Simpler is better, so people use wires. Anyway, aren't we trying to avoid RF transmitters here?
Speaker cables can be shielded too, but people don't bother as any interference would be imperceptible.
Power loss in speaker cables is pretty tiny too. Powered speakers really are all about convenience and potential better fidelity.
Re:Counter-intuitive! (Score:4, Informative)
Re: wired vs wireless audio signals (Score:5, Informative)
Not true.
Wired mics sound better because they lack the companders involved in transmitting the audio signal. Performers like wireless because it's convenient, not because it sounds better. Those concerned with sound quality stick to wired.
Balance signals use common mode rejection to eliminate induced noise. This has been standard practice for years. Recording studios used either balanced wiring, or digital in the form of AES or optical ADAT.
Re:What? (Score:5, Informative)
Oh my god. Please not another "informative" post. I really wish you people would stop commenting on these articles when you clearly have no clue what you are talking about. The reflected power (if it happens to exist in this case...which it doesn't because these transmitters are designed quite well and usually include a circulator or isolator at the output of the amplifier to ensure an excellent match) does not go back into the amplifier, because if it did the amplifier would not work as it was designed and would either oscillate or produce extremely poor waveform quality at the output.
Now, if you can bypass the circulator/isolator I mentioned above (which is what I gather they are trying to do in this article) then that is one less place power can be lost on the way to the antenna.
Re:I am no chip designer..... (Score:1, Informative)
You can see this with a HDTV set and an antenna. Too low of a signal and you get no picture at all.
With an analog signal, you would have seen a very noisy picture as received signal to noise is reduced. Digital digs it out of the noise until it is unrecoverable, all the while, presenting a perfectly clear picture.
The actual signal in both cases is an analog signal. The difference is in the information conveyed. Where digital transmission methods do require more transmit power is where the bandwidth is increased over its analog counterpart. HDTV conveys more information than an NTSC signal while occupying the same bandwidth. Therefore, it is more efficient. In the absence of multi-path, the digitally modulated signal should have increased usable range over the analog modulated signal transmitting the same power.
Re:What? (Score:4, Informative)
The article is crap. The paper, however, makes sense. Read it.
Re:Counter-intuitive! (Score:3, Informative)
The summary is misleading.
The paper describes a method of simply and efficiently coupling energy from the transmitter VCO chip to the main antenna, making good use of the R.F. energy that chip provides. It seems that most of the power savings is from avoiding (power used by) an external buffer amplifier by eliminating the amplifier.
That's great if the chip can provide sufficient output power, and if the spectral purity is good enough to comply with F.C.C. or other requirements. I'd expect that most cell phones need more transmit power than provided by the example in the paper, but perhaps the same methods are viable with higher power modules.
Note that the power savings only occurs in transmit mode, and the savings is only in the circuit providing signal to the antenna. Something like an iPhone has a bunch of other electronics and a display using considerable power, none of which is affected by the changes proposed in the paper.
What's presented is innovative but in reality isn't likely to do much for the overall power consumption of a complex product like an iPhone. The savings would be more likely to amount to something in smaller and and much simpler devices, more along the lines of battery powered WiFi or BlueTooth products.
Re:How about that inverse-square law? (Score:5, Informative)
You are assuming an isotropic emitter, where field strength falls off as 1/r^2. That behavior is invalid for other antennas; for example a dipole's field strength falls off as 1/r (in the far-field approximation). The paper is complicated by the fact that the radiation patterns of the antennas used in this paper are directional and different. The "conventional" chip used a folded dipole with a "boresight radiation pattern", and the "proposed" chip used a custom design with a front-to-back ratio of 10dB.
Table 1 has the numbers:
Module Type / Power Consumption / Gain / Range
Standalone
TX chip / 3.3 mW / -34 dBi / 1 m
TX chip in
conventional
LTCC package / 38 mW / -1 dBi / 75 m
TX chip in
proposed LTCC
package / 3.3 mW / -2.3 dBi / 24 m
Let's do some reckless hand-wavy extrapolation. The difference in power is 38/3.3 = 11.5 = 10.6 dB; if we assume perfect scaling of the new package to 38mW, we'd expect 10.6-2.3=8.3 dBi. This is an improvement of 9.3 dB over the conventional method -- it's almost 10 times as efficient.
This analysis ignores, among other things, the relative directionalities of the antennas. I wonder why they didn't choose a more directional antenna for the "conventional" chip, or used the same sort of antenna in order to do a level comparison.
The other point of comparison is between the "standalone" chip and the "proposed" chip. A 32 dB improvement with no power increase is nothing to sneeze at!
Re:Counter-intuitive! (Score:4, Informative)
Except that omnidirectional range is proportional to the cube of the output.
If, as the GP says, you use 1/12 the power of a conventional device with this design, but have 1/3 the range, you need to bump the power to 3^3/12 of a conventional device to get the same range, or 27/12, or more than double.
That doesn't seem like a win to me.
You can't violate the first law of physics:: You don't get sumtin for nuttin.
Re:What? (Score:2, Informative)
Oh please, another software engineer? Amplifiers are by their very nature non linear devices as a whole (they just happen to have a linear region which we can make use of). The amplifiers in question are operated within their linear region as much as possible where possible, but certain requirements like efficiency force the designers to drive the transistor partly into its non-linear region (closer to P1dB). Some non-linearity is tolerated and is dictated by the FCC, ETSI or CRTC in the form of emissions masks or by the wireless standard in the form of modulation quality. The only way to ensure the amplifier is always inside the linear region under all conditions would be to back off from P1dB by so much that your efficiency tanks. But that is entirely not feasible for cellular design...consumers like long battery life and carriers like low operating costs.
Now, getting back to your comments. "As long as the mismatch is within spec, the only problem will be reduced efficiency". Amplifiers (or to be more specific, the transistors used in amplifiers) do not have real imput and output impedances. The real (resistive) component will generally not have the desired characteristic impedance (usually 50 ohms) and can be quite small (sometimes a few ohms or even tenths of an ohm). The imaginary (reactive) component will also be non-zero (which is undesirable, but a fact of life) which will tell whether the output (or input) is capacitive or inductive (depending on the sign of the reactive element). Real "high power" amplifiers (I say "high power" to describe the condition where the amplifier is operated towards the upper bounds of the linear region) are not simply matched for maximum power transfer and your done (the input is often matched this way since you would like to ensure any power available to the transistor will actually be taken into the device to be amplified...this is different for low noise amplifiers). This is called conjugate matching (where you set the real parts equal, and negate the reactive part).
On the output a different set of techniques is used. Loadpull is one technique which allows you to design your output matching network not only for linearity, but also efficiency or any other characteristic you can measure. The output matching network that produces the best efficiency (which is what we are talking about here) is most likely not the same as the one that produces the best P1dB or linearity. Also note that conjugate matching or other types of matching do not mean zero reflection (or VSWR=1). By the nature of the networks, the resulting VSWR (albeit low VSWR) is actually part of the desired characteristics of certain matching networks. Put another way, having the best VSWR response (i.e. zero reflection) will not get you the best efficiency (this is the aspect of your post that I take issue with). Reactive components do not dissipate energy (well, if you cosider the small resistive component they do, but this is orders of magnitude smaller than the other resistive components).
All this being said, another way to look at it is that if the reflections occur as part of the matching network, these can be tolerated since they are an inherent part of the design. Reflections after you have reached 50 ohms (i.e. between the matching network and the antenna) can be devastating to an amplifier. This is why they place a circulator or isolator directly after the matching network in most cases...this allows the output of the matching network to see a 20 dB match at least (depending on the circulator) regardless of what happens after (the antenna breaks, cable breaks, etc.). This prevents potentially devastating power from returning to the amplifier.