Continuing with the occasional note about interesting ISSCC presentations, there was an interesting talk about a self-healing radio-on-a-chip – in fact, probably the best actual presentation I’ve ever seen at ISSCC. The topic seems aligned with a budding tendency of radio systems to correct themselves dynamically while in use.
In this case, a number of “knobs” were built into the radio circuitry, and the device was instrumented with the ability to create various test tones, sensors to detect the response to those tones as well as other parameters like power level and temperature, and then a “cautious” control mechanism. The term “cautious” was never clearly defined, but I’m assuming it means that adjustments are made conservatively rather than rocketing the settings around with every little blip.
They used a fundamentally different optimization strategy. Simplistically put, if you vary parameters in a circuit and measure resulting performance, you can take the design in one of two different directions. Getting the best performance generally means you have a very high peak right at the sweet spot of the parameter, but performance drops off precipitously on either side – it looks like a cusp. For a static design, this isn’t practical, since the chance of remaining atop that peak is nil. To quote the speaker, “Everything is sensitive to everything.”
Instead, designers compromise on peak performance, but design in a way that is more tolerant of drift, more like an upside-down parabola or something. This is how design is typically done.
For this paper, however, the concept was to use the optimal approach and then dynamically measure and adjust in real time to keep performance balanced atop that peak. Kind of like designing a Seque to remain upright, it’s least-likely position.
Specifically, the healable parameters they chose were transmitter 3rd-order distortion, transmitter IQ mismatch, receiver noise figure, and PLL automatic locking. They included a self-healing controller ASIC on the same chip. Where possible, they re-used existing circuits, like the DAC, to minimize the area impact of the self-healing circuits.
You can find more in paper 18.5 of the ISSCC proceedings.