editor's blog
Subscribe Now

Optimizing at the Cellphone Antenna

So you run across an announcement from Imec that they’ve presented a circuit at ISSCC that involves tuning to match changing antenna impedances in cell phones. And if you’ve been hanging out in the same places I have, you might have the following reaction: “Hey, this is what some MEMS guys are doing as well! Fight! Fight! Fight!”

Turns out it’s not quite that simple. I’d feel like it was just another day of me discovering yet another knowledge gap, but I wasn’t the only one conflating two concepts. Conversations with Cavendish Kinetics and WiSpry helped me pry the two issues apart.

You may recall coverage we’ve done of both WiSpry and Cavendish Kinetics on the MEMS side and Peregrine on the SoS side. They make capacitor arrays that can be configured as variable capacitors. The first two guys use MEMS switches; Peregrine uses electrical.

What problems do they solve? They help tune the antenna as conditions drift on the phone (grip changes etc.). In fact, even this conflates two things, as we covered before: both matching changing antenna impedances and recentering the resonance of the antenna to ensure that the strongest possible signals enter the phone.

Critically, that frequency centering can’t be done too tightly: full duplex on your cellphone is achieved by placing receive and transmit on two slightly different frequencies so that they don’t interfere with each other. So the antenna response has to be wide enough to provide good performance at both frequencies.

Meanwhile, Imec is actually working on something different. The duplexer in the phone separates out the receive and transmit signal paths. Filters are typically implemented using relatively bulky surface acoustic wave (SAW) or thin-film bulk acoustic resonator ((T)FBAR) devices. Imec wanted to try instead to use an electrical-balancing (EB) technique, with the initial goal of simplifying the circuit.Imec_ISSCC_image.png 

The high-level concept they’re exploring was actually used in the original telephone: taking a combined full duplex signal, consisting of mixed receive and transmit, and subtracting out the transmit signal (which you know because you’re at its origin) to get the pure receive signal. While that was a simple thing on old phones at voice frequency, it’s apparently not so easy up in the many-megahertz range with changing conditions. The three challenges in particular are isolation between receive and transmit, linearity, and insertion loss – and managing these in the face of changing antenna impedance.

In this particular project, Imec tackled the linearity and insertion loss as a step towards a commercially-viable EB duplexer. This is distinct from optimizing the antenna; they’re complementary solutions.

That’s all well and good, but there’s more promise if this all works out. If you can effectively isolate receive and transmit through subtraction, then you no longer need to place the signals on different frequencies. In fact, there was a paper presented at ISSCC by Columbia University that claims to have done just that: run receive and transmit at the same frequency. (Unfortunately I missed ISSCC this year due to illness and didn’t see the presentation; I received no response to a request for more information from Columbia).

And here’s the big payoff: if we can combine signals at one frequency, then instead of receive on one and transmit on the other, we can have both on both – we’ve doubled our capacity just like that.

So a relatively obscure-sounding topic (believe me, reading the Imec paper got me lost pretty quickly) may turn out to have rather astonishing consequences. We might eventually return to the old telephone approach that used to work so well.

The Imec paper can be found here (behind a paywall).

 

(Image courtesty Imec)

Leave a Reply

featured blogs
Apr 11, 2021
https://youtu.be/D29rGqkkf80 Made in "Hawaii" (camera Ziyue Zhang) Monday: Dynamic Duo 2: The Sequel Tuesday: Gall's Law and Big Ball of Mud Wednesday: Benedict Evans on Tech in 2021... [[ Click on the title to access the full blog on the Cadence Community sit...
Apr 8, 2021
We all know the widespread havoc that Covid-19 wreaked in 2020. While the electronics industry in general, and connectors in particular, took an initial hit, the industry rebounded in the second half of 2020 and is rolling into 2021. Travel came to an almost stand-still in 20...
Apr 7, 2021
We explore how EDA tools enable hyper-convergent IC designs, supporting the PPA and yield targets required by advanced 3DICs and SoCs used in AI and HPC. The post Why Hyper-Convergent Chip Designs Call for a New Approach to Circuit Simulation appeared first on From Silicon T...
Apr 5, 2021
Back in November 2019, just a few short months before we all began an enforced… The post Collaboration and innovation thrive on diversity appeared first on Design with Calibre....

featured video

Learn the basics of Hall Effect sensors

Sponsored by Texas Instruments

This video introduces Hall Effect, permanent magnets and various magnetic properties. It'll walk through the benefits of Hall Effect sensors, how Hall ICs compare to discrete Hall elements and the different types of Hall Effect sensors.

Click here for more information

featured paper

Understanding Functional Safety FIT Base Failure Rate Estimates per IEC 62380 and SN 29500

Sponsored by Texas Instruments

Functional safety standards such as IEC 61508 and ISO 26262 require semiconductor device manufacturers to address both systematic and random hardware failures. Base failure rates (BFR) quantify the intrinsic reliability of the semiconductor component while operating under normal environmental conditions. Download our white paper which focuses on two widely accepted techniques to estimate the BFR for semiconductor components; estimates per IEC Technical Report 62380 and SN 29500 respectively.

Click here to download the whitepaper

Featured Chalk Talk

Innovative Hybrid Crowbar Protection for AC Power Lines

Sponsored by Mouser Electronics and Littelfuse

Providing robust AC line protection is a tough engineering challenge. Lightning and other unexpected events can wreak havoc with even the best-engineered power supplies. In this episode of Chalk Talk, Amelia Dalton chats with Pete Pytlik of Littelfuse about innovative SIDACtor semiconductor hybrid crowbar protection for AC power lines, that combine the best of TVS and MOV technologies to deliver superior low clamping voltage for power lines.

More information about Littelfuse SIDACtor + MOV AC Line Protection