Making power converters for the IoT efficient

February 21, 2017 // By Jean-Pierre Joosting
At the recent International Solid-State Circuits Conference, researchers from MIT's Microsystems Technologies Laboratories (MTL) presented a new power converter that maintains its efficiency at currents ranging from 500 picoamps to 1 milliamp, a span that encompasses a 200,000-fold increase in current levels.

IoT sensors have to operate at very low powers, in order to extend battery life for months or make do with energy harvested from the environment. But that means that they'll need to draw a wide range of electrical currents. Generally, power converters, which take an input voltage and convert it to a steady output voltage, are efficient only within a narrow range of currents.

A sensor might, for instance, wake up every so often, take a measurement, and perform a small calculation to see whether that measurement crosses some threshold. Those operations require relatively little current, but occasionally, the sensor might need to transmit an alert to a distant radio receiver. That requires much larger currents.

"Typically, converters have a quiescent power, which is the power that they consume even when they're not providing any current to the load," says Arun Paidimarri, who was a postdoc at MTL when the work was done and is now at IBM Research. "So, for example, if the quiescent power is a microamp, then even if the load pulls only a nanoamp, it's still going to consume a microamp of current. My converter is something that can maintain efficiency over a wide range of currents."

Paidimarri, who also earned doctoral and master's degrees from MIT, is first author on the conference paper and is joined by his thesis advisor, Anantha Chandrakasan, the Vannevar Bush Professor of Electrical Engineering and Computer Science at MIT.