BYU students are working with Dr. Wood Chiang, an Assistant Professor of Electrical and Computer Engineering, to create a low-power circuit. The device acts as an Analog-to-Digital Converter (ADC) and can be operated for several years without needing to be replaced due to its low power consumption.
They are creating sensors requiring little power to operate due to the limited access to power sources like batteries or energy harvesters. “We designed a circuit that has a power consumption of only 22 nanowatts. It’s about a billion times less than that of a light bulb,” Chiang said.
The project started about 2.5 years ago with the financial support of NASA and ON Semiconductor. The team proposed the idea of developing a low-power ADC for a space-based sensor network. The satellites and spacecraft used by NASA have limited power available, making the chips a natural fit for these applications.
Alexander Petrie, a recent MS in Electrical and Computer Engineering graduate, started on the project as an undergraduate student. When he began his master’s degree, he and Chiang brainstormed the idea of developing the low-power consumption circuit into his thesis.
Although there are a couple other co-authors on the paper, Petrie is the main student involved with the project. He said the ADC he designed uses a supply voltage of 0.2 volts in comparison to a supply voltage of 1.8 volts normally used for this technology. This is the lowest supply voltage demonstrated in an ADC and the key to achieving the low-power consumption.
According to Petrie, low-power ADC’s are crucial in their many applications, including wireless sensor networks and implantable medical devices. A surgery is required to implant them into the human body, making the long-lasting power capability a crucial aspect of their performance.
“In this application, the ADC needs to be able to operate with very low power consumption and at a very low supply voltage,” Petrie said. “The need for low-power ADC’s is ever-increasing, especially as Internet-of-Things technology becomes more and more ubiquitous.”
Other applications for the project include instances where wireless sensors need to be deployed in remote locations, such as borders, war zones, or anywhere else threats and intruders need to be monitored. “It would be very difficult to go out and replace batteries, so you want these things to last months, maybe years at a time,” Chiang said.
Creating a chip with those capabilities is no small task. The design and fabrication phase can take up to two years, with testing adding an additional six months to a year. The process is very precise to ensure no mistakes are made.
“The ADC is only about 0.1 mm 2. It is so small that if a mistake goes into the chip, you cannot fix it. You have to redesign it and refabricate the chip. The turnaround can be up to a year. It’s high-risk, high profile research that has very little tolerance to errors. Alex got it right the first time,” Chiang said.
The process for circuit design is very defined, starting with computer simulations to predict the circuit performance. The design is refined and laid out in a computer tool before it is sent to a foundry to be manufactured. Afterwards, a test bench is built to verify the performance.
When a circuit consumes such a small amount of power, there is a lot of variability in its performance. To fix this problem, the team designed a specialized circuit block in the chip to monitor the performance and make adjustments automatically on-the-fly to improve the yield.
The group has completed the project’s design and verification and will continue to utilize the techniques they have developed for other projects. “We have more ambitious chips now being worked on in this lab utilizing the techniques that we designed, and we will try to reduce the power consumption even further,” Chiang said.
During the project’s duration, status updates were sent regularly to NASA and ON Semiconductor. Now that the project is completed, they can decide whether they want to use the chips in their systems.
“What we do here is very practical; it’s all the same kind of work that a student would expect to do once they graduate and go into the industry,” Chiang said. “By going through the whole research process to build a chip, test it, and publish it, we are training students to go into the world and do great work based on their experience here.”
The low-power circuit will be presented at the Custom Integrated Circuits Conference from March 22-25 in Boston, MA.