245 GHz SiGe sensor system for gas spectroscopy

A 245 GHz sensor system for gas spectrosopy is presented, which includes a SiGe receiver (RX), a SiGe transmitter (TX), and a 0.6 m long gas absorption cell between the TX and RX. The integrated local oscillators of the RX and the TX are controlled by two external PLLs, whose reference frequencies are swept with constant frequency offset for a low IF of the RX. The RX consists of a differential LNA, an integrated 122 GHz local oscillator with 1/64 divider, a 90° differential hybrid, and active subharmonic mixer. The TX consists of an integrated 122 GHz local oscillator with 1/64 divider, and a frequency doubler. The RX and TX are fabricated in 0.13 μm SiGe BiCMOS with ft/fmax of 300GHz/500GHz. Using external dielectric lenses for the TX and RX, the absorption spectrum of methanol has been measured.