Many Signals, One Chip

The human ear is a marvel of efficient engineering–using very little energy, it can detect a stunningly broad range of frequencies. Inspired by that prowess, MIT engineers have built a fast, ultrabroadband, low-power radio chip that could be used in wireless devices capable of receiving many different kinds of signals.

Rahul Sarpeshkar ‘90, associate professor of electrical engineering and computer science, and his graduate student Soumyajit Mandal, SM ‘04, designed the chip to mimic the inner ear, or cochlea. The chip separates radio signals into their individual frequencies faster than any other human-designed spectrum analyzer and operates at much lower power. Traditional radio chips that could do this would consume too much power to be practical.

“The cochlea quickly gets the big picture of what’s going on in the sound spectrum,” says Sarpeshkar. “The more I started to look at the ear, the more I realized it’s like a super radio with 3,500 parallel channels.”

The researchers describe their new chip, which they have dubbed the “radio frequency (RF) cochlea,” in a paper published in the June issue of the IEEE Journal of Solid-State Circuits. They have also filed for a patent for a universal radio architecture that uses the RF cochlea to process a broad spectrum of signals, including those transmitted in most commercial wireless applications.

In the biological cochlea, sound waves are converted to mechanical waves that travel along the cochlear membrane and the fluid of the inner ear, activating hair cells, which send electrical signals to the brain. In the RF cochlea, which is embedded on a silicon chip measuring 1.5 by 3 millimeters, electromagnetic waves travel through electronic inductors and capacitors that imitate the biological fluid and membrane, and electronic transistors play the role of the hair cells. But while the human ear can perceive frequencies from 100 to 10,000 hertz, the RF cochlea’s range extends from 600 megahertz to 8 gigahertz, encompassing cell-phone, Internet, radio, and television signals.

Trained as an engineer but also a student of biology, Sarpeshkar–with his group in MIT’s Research Laboratory of Electronics–often draws on the natural world for inspiration in designing electronic devices. He says engineers can learn a great deal from studying biological systems that have evolved over hundreds of millions of years to perform sensory and motor tasks very efficiently in environments noisy with competing signals.

Though we have a long way to go before our inventions will successfully compete with those in nature, Sarpeshkar says, “we can mine the intellectual resources of nature to create devices useful to humans.