Gas spectroscopy system at 245 and 500 GHz using transmitters and receivers in SiGe BiCMOS

A compact gas spectroscopy system is demonstrated, which contains a transmitter (TX) and a receiver (RX) in SiGe BiCMOS, as well as a gas absorption cell. The sensitivity of this spectroscopy system is demonstrated by measuring the high-resolution 2f absorption spectrum (second harmonic detection) of gaseous methanol (CH3OH) at 238-252 GHz, and at 495-497 GHz. The 245 GHz TX consists of a 120 GHz local oscillator (LO) and a frequency doubler, and the 245 GHz RX includes a low noise amplifier (LNA), a LO, and an active subharmonic mixer. A 245 GHz TX-array increases significantly the sensitivity of the sensor system. The 500 GHz system includes a TX-array, and a subharmonic RX with a transconductance mixer. The 500 GHz TX contains a frequency quadrupler, and the RX uses a frequency doubler for the LO. The LOs of the RX and the TX are controlled by two external phase-locked loops (PLLs).