Researchers at Chalmers University in Sweden have demonstrated a sub-harmonic graphene FET mixer at microwave frequencies.
"Future applications at THz frequencies such as radar systems for security and safety, radio astronomy, process monitoring and environmental monitoring will require large arrays of mixers for high-resolution imaging and high-speed data acquisition," said the University. "Such mixer arrays or multi-pixel receivers need new types of device that are not only sensitive but also power-efficient and compact."
The field effect in graphene allows it to switch between hole or electron carrier transport, according to the Chalmers, opening a unique niche in RF ICs.
Using the symmetrical electrical characteristic, allowed the researchers to make a one-transistor sub-harmonic resistive mixer.
"No extra feeding circuits are required, which makes the mixer circuit more compact than conventional mixers," said the University. "As a consequence, it requires less wafer area when constructed and can open up for advanced sensor arrays, for example for imaging at millimetre waves and even sub-mm waves as G-FET [graphene FET] technology progress."
Sub-harmonic graphene-FET mixer. The LO and RF signals are fed to the gate and drain terminals, respectively, and the IF signal is extracted from the drain terminal.
Improvements are expected from optimising the circuit and making FETs with higher on-off current ratios.
THz operation is predicted from graphene's high carrier velocity and the fact that a sub-harmonic mixer only requires half the local oscillator (LO) frequency compared to a fundamental mixer.
"It is attractive especially at THz where there is a lack of sources providing sufficient LO power," said Chalmers. "Moreover, the G-FET is CMOS-compatible and among other things it can be used in CMOS electronics for back-end processing on a single chip."
More about graphene research at Chalmers.