Near Millimeter Wave CMOS Receiver and Transmitter
Electromagnetic waves in the millimeter (mm) and sub-millimeter wave (sub-mm) frequency ranges have caught a lot of attention. The waves at these frequencies can interact with gas molecules possessing dipole moments and change their rotational states. This phenomenon can be utilized for fast scan rotational spectroscopy to detect gas molecules and measure their concentrations. Rotational spectrometers have a wide range of applications including indoor air quality monitoring, detection of harmful gas leaks, breath analyses for monitoring bodily conditions and many others. At the mm and sub-mm wave frequencies, a large bandwidth is available for extremely high data rate communication. Communication over a dielectric waveguide at these frequencies with a loss less than 10dB/m has been proposed to mitigate the complexity of communication over copper wires as well as the integration challenges for optical communication that are being developed to meet the ever-increasing bandwidth demand.
The advances of complementary metal-oxide-semiconductor (CMOS) technology have enabled the implementation of mm-wave and sub-mm wave frequency circuits with reduced cost and increased system integration and complexity. A receiver with a radio frequency front-end bandwidth of 95 GHz and noise figure of 13.9 -19 dB for a rotational spectrometer is demonstrated in 65-nm CMOS. In addition, a 300-GHz QPSK transmitter with a 30-Gbps data rate is demonstrated that consumes 180mW for dielectric waveguide communication.
The system level tradeoff of a receiver for rotational spectroscopy is first analyzed with a focus on the noise mechanism. A detailed signal-noise interaction derivation due to a 2nd order non-linearity is presented and signal to noise ratio degradation is shown for different modulation scenarios. A receiver front-end using a broadband antenna backed by a phase compensated artificial magnetic conductor reflector, a floating body antiparallel diode pair as the mixing device and a multi-mode isolated broadband hybrid is demonstrated. The receiver also includes an on-chip LO generator using frequency multipliers and capacitive neutralized power amplifiers, an IF cascode low noise amplifier and a baseband power detector. The receiver exhibits a responsivity of 400-1200 kV/W and noise equivalent power of 0.4 to 1.2 pW/√Hz at 225 to 280 GHz. Detection of Ethanol, Propionitrile (EtCN), Acetonitrile (CH3CN) and Acetone in a mixture is demonstrated using the receiver in a rotational spectroscopy setup. This is the first demonstration that a CMOS receiver can be used for rotational spectroscopy and that a CMOS integrated circuit can support an existing application at frequencies above 200 GHz.
A heterodyne transmitter with a current mode logic modulator, a multi-stage constant gain and group delay wideband data buffer using coupled resonators, a double balance passive up-conversion mixer using a Marchand balun which acts as built-in LO spur traps, and a quadrature oscillator with quadrature calibration are demonstrated. The transmitter generates the required RF power for the system of -6 dBm and supports a maximum data rate of 30Gbps while consuming 180mW of power resulting in an energy efficiency of 6 pJ/bit. The single channel data rate is almost 2X higher than that of the previously reported CMOS QPSK transmitter and the energy efficiency is among the highest of CMOS QPSK transmitters operating at the similar frequency range.