CMOS (Complementary Metal Oxide Semiconductor) transmitter and receiver circuits for rotational spectroscopy are demonstrated. The IC’s implemented in 65-nm CMOS consist of a 208-252 GHz transmitter and a 225-280 GHz receiver. Use of CMOS electronics can reduce the cost of electronics for rotational spectrometer application from over $50k to less than $1k. The receiver (RX) includes an on-chip antenna for air-to-chip interface, a 2nd order sub-harmonic down-conversion mixer, a low noise IF amplifier and an amplitude detector. The transmitter (TX) includes an on-chip antenna for chip-to-air interface, Fractional-N synthesizer with a frequency step less than 1 kHz with a built-in frequency shift keying circuit as well as a frequency up-converter to generate the signal at the RF. The integrated circuits were assembled into a rotational spectrometer and utilized to detect numerous gases including Ethanol and Acetone in human breath. It is the first ever demonstration of spectroscopy on pure gases as well as breath using CMOS circuits, and this work paves the way toward a more compact, affordable and efficient rotational spectroscopy system.
Terahertz (THz) electronics using mainstream CMOS technologies can be a small, low-cost alternative to discretecomponent THz systems. Due to high yield and integration level, large-scale THz imaging systems can be affordably realized in a small form factor. In this paper, state-of-the-art CMOS circuits for THz imaging are reviewed. Incoherent detectors in CMOS process offer comparable noise equivalent power (NEP) to III-V counterparts at a fraction of the cost. An 820-GHz 8×8 array with minimum NEP of 12.6pW/√Hz is demonstrated using diode-connected MOSFET’s in 130- nm CMOS. Schottky-barrier diodes (SBD’s) fabricated using a 130-nm CMOS process demonstrate higher cutoff frequency than MOSFET’s. Using the SBD, detection at 9.7THz is demonstrated. The same SBD’s are also used to implement a 218-GHz 6×6 detector array for a THz camera module. Mixer-based coherent detectors show orders-ofmagnitude better sensitivity than that of incoherent detectors. Mixers require a local oscillator (LO) signal. The design challenge of including an LO can be relaxed by using a sub-harmonic mixing technique. A 410-GHz 4th order subharmonic mixer requires −1.6-dBm LO power at 102.5GHz and shows 44-dB better sensitivity than incoherent detectors operating near 400GHz. LO’s can be directly integrated with the mixing device to form a compact transceiver. A 260-GHz transceiver that integrates a VCO, antenna and mixer, occupies only 480×580μm2 and shows a 13.5-dB better sensitivity at 260 GHz than the incoherent detector with the lowest NEP. Since the area is less than λ/2×λ/2, it should be possible to build large-scale focal plane arrays with coherent detectors and transmitters.