2022 Theses Doctoral

Architectures and Integrated Circuits Leveraging Multi-phase Clocking of Passive Mixers for Applications in RF/MM-wave and Electro-optical Systems

Ahasan, Sohail

Over the last decade, the demand for wireless networks with faster data rates has grown significantly. According to the 2021 Ericsson mobility report, the total global mobile data traffic is projected to grow by more than five times in the next five years. Wireless paradigms such as massive-MIMO and channel bonding have become increasingly popular in sub-6GHz systems to meet these demands. However, the future wireless growth demands us to look beyond these congested frequency bands toward the large unlicensed bandwidths available mm-wave and THz spectrum. In this dissertation, we exploit paradigms such as multi-user MIMO and channel bonding at the 60GHz IEEE 802.11ad/ay frequency band to build multi-Gbps transmitters.The other need for future wireless systems is high-resolution imaging, which has applications in autonomous systems, machine vision, medical diagnostics, and 3-D imaging. Particularly, Light-detection and Ranging systems, namely LIDARs, have attracted considerable attention owing to their higher spatial resolution over radars. Here, we show multiple prototypes of such electro-optical systems and demonstrate their capabilities through imaging with mm- to micro- meter-scale resolution.

The key insight of this dissertation is that we use signal processing capabilities within a passive mixer driven by multi-phase LO to implement such wireless systems. These systems are demonstrated to provide significant improvement in power efficiency and scalability. The first chapter of the thesis presents compact, low-loss electro-optical phase-locked loops(EOPLL) with wide loop bandwidth, where we use harmonic- and image- reject capabilities of a multi-phase mixer to cancel the spurious tones generated by the phase detector. This EO-PLL, integrated with CMOS technology, suppresses the spurs at beat note by >25dB, enabling us to detect an object at a maximum range of >3.3m, with a precision of .558 mm at a 2m distance.

The later part of the thesis focuses on building multi-Gbps mm-wave transmitters(TX) leveraging wireless paradigms such as multi-user MIMO and channel bonding. The thesis presents a MIMO 4-element transmitter(TX) array architecture where a single-wire IF interface connects the front-end with a baseband modem to increase the scalability of such systems. We use the harmonic-rejection mixing (HRM) feature of a single passive mixer to de-multiplex the four modulated signals simultaneously from the single-wire interface. A 60GHz, 4-element TX prototype is presented, which can support an 8GHz of total IF bandwidth at the single-wire interface and is capable of transmitting 64-QAM modulated signals.

Later on, we realized that the same harmonic- and image- rejection feature can readily be applied to channel bonding TX systems with high aggregate bandwidth. The benefit of this architecture is that it alleviates the need for high-speed, power-hungry ADCs/DACs at the baseband and thereby significantly improving the system cost and efficiency. This thesis presents a 59-67GHz channel bonding transmitter with a channel bonded bandwidth of more than 8GHz while using DACs with a sampling rate of only 2GS/sec, providing 4 times improvement from traditional architectures.

Looking into the future, we envision that the concepts and prototypes presented in this dissertation can be deployed in THz systems. In conclusion, we look beyond CMOS technology and provide pathways to enable THz transmitters with high transmit power, leveraging the heterogeneous integration capabilities of III-V semiconductors.