Single chip 25GHz mmWave circulator works without magnets

Columbia mmWave circulator

It uses a non-reciprocal structure – one whose physical characteristics differ depending on the direction of flow.

In this case, seen as the straight section in the double ring circulator in the diagram, it is  a pair of transmission lines that are either directly-connected or cross-connected by switches at the ends.

Columbia mmWave circulator operationIf the length of the section is just right, and the switches at one end are 90° out of phase with the other, then signals can travel in one direction, but mutually cancel in the other direction.

“The method enables loss-free, compact, and extremely broadband non-reciprocal behaviour, theoretically from DC to daylight, that can be used to build a wide range of non-reciprocal components such as isolators, gyrators, and circulators,” said the University.

Columbia mmWave gyratorResearchers propose it as a three-port circulator (see diagram) to connect transmit and receive amplifiers to the same aerial, perhaps in 5G systems.

The circuit (see top photo) is built on a 45nm SOI CMOS process.


“The key advance of this new approach is that it enables circulators to be built in conventional semiconductor chips and operate at millimeter-wave frequencies, enabling full-duplex or two-way wireless,” said Columbia. “Virtually all electronic devices currently operate in half-duplex mode below 6GHz, and consequently, we are rapidly running out of bandwidth. Full-duplex communications, in which a transmitter and a receiver of a transceiver operate simultaneously on the same frequency channel, enables doubling of data capacity within existing bandwidth. Going to the higher mm-wave frequencies, 30GHz and above, opens up new bandwidth that is not currently in use.”

The work is published as ‘Synchronized conductivity modulation to realize broadband lossless magnetic-free non-reciprocity‘ in Nature Communications.

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