85-to-127 GHz CMOS transmitter for rotational spectroscopy

A transmitter for rotational spectroscopy using a fractional-N PLL (FNPLL) that generates frequency shift keyed signals from 85 to 127 GHz (39% tuning range) with a fine frequency step of ∼570 Hz and settling time of ∼10 μS is demonstrated. Implemented in 65-nm CMOS, the FNPLL delivers greater than 5 μW of output power, and achieves measured phase noise of less than −70 dBc/Hz in-band and less than −102 dBc/Hz at 10-MHz offset over the output frequency range while consuming 80 mW. The transmitter output is radiated using a bond-wire antenna and successfully utilized in a spectrometer for detection of gas molecules.