Researchers demonstrate a circulator on a silicon chip at mm-wave frequencies

October 09, 2017 // By Jean-Pierre Joosting
Researchers from Columbia Engineering, led by Harish Krishnaswamy, associate professor of electrical engineering, in collaboration with Professor Andrea Alu's group from UT-Austin, claim to be the first to demonstrate a circulator on a silicon chip at mm-wave frequencies that enables nonreciprocal transmission of waves: device could enable two-way radios and transform 5G networks, self-driving cars, and virtual reality.

At the IEEE International Solid-State Circuits Conference in February, Krishnaswamy's group unveiled a new device: the first magnet-free non-reciprocal circulator on a silicon chip that operates at millimeter-wave frequencies (frequencies near and above 30GHz). Following up on this work, in a paper (DOI 10.1038/s41467-017-00798-9) published in Nature Communications, the team demonstrated the physical principles behind the new device.

Most devices are reciprocal – signals travel in the same manner in forward and reverse directions. Nonreciprocal devices, such as circulators, on the other hand, allow forward and reverse signals to traverse different paths and therefore be separated. Traditionally, nonreciprocal devices have been built from special magnetic materials that make them bulky, expensive, and not suitable for consumer wireless electronics.

A new way to enable nonreciprocal transmission of waves was developed by the the research team that uses carefully synchronized high-speed transistor switches that route forward and reverse waves differently. In effect, it is similar to two trains approaching each other at super-high speeds that are detoured at the last moment so that they do not collide.

This is a chip microphotograph of the 25 GHz fully-integrated non-reciprocal passive magnetic-free 45nm SOI CMOS circulator based on spatio-temporal conductivity modulation. Image courtesy of Tolga Dinc/Columbia Engineering.