Theses Doctoral

Advances in Linear Periodically Time Variant Circuits: From High Performance Filters to Magnetic-Free Inductorless Nonreciprocal Components

Khorshidian, Mohammad

Commutated N-path networks have seen a resurgence in the past decade in the context of modern integrated circuits. N-path circuits have been used to implement high-quality tunable band-pass and notch filters with just switches and capacitors. Recently, nonreciprocal circuits such as circulators and isolators have also been reported as other applications of Linear Periodically-Time-Varying (LPTV) networks.

In this dissertation, high performance filters and inductorless nonreciprocal components based on novel LPTV networks are introduced. We proposed a concept called Negative Transresistance (NTR) in phase-shifted N-path structures. The rejection of the conventional N-path notch filters is limited to the number of paths used; however, by using our proposed NTR concept, we were able to achieve more than 50dB rejection regardless of the number of paths. Using the same concept, we introduced the first prototype of N-path Low-Pass Filter (LPF). The resulting components can find application in blocker-tolerant systems, to select closely-spaced frequency channels, and also in the analog Baseband (BB).

Nonreciprocal components such as circulators and isolators have traditionally relied on ferrites that offer nonreciprocal behavior based on Faraday Effect (by applying an external magnetic field). Recent efforts to eliminate the need for magnetic materials, despite being a huge success involve the usage of transmission lines (and/or inductors). In this dissertation, a novel concept called Nonreciprocal Transresistance (NRTR) is introduced. This led to the first ever inductorless RF isolator. Furthermore, we expanded the idea to the first inductorless circulator consisting of only switches and capacitors. The resulting isolator can find application in base stations to prevent back reflections (e.g. to protect the Power Amplifier (PA)). Also, in superconducting quantum systems, an isolator is necessary to separate the noise and reflections at the interface of different blocks. The introduced circulator can find applications in wireless communication systems as an antenna interface connecting the Transmitter (TX) and the Receiver (RX) to a shared antenna. This is crucial, especially for Full-Duplex (FD) applications where high isolation between RX and TX is necessary as they are operating at the same frequency.

Finally, we enhanced the performance of the conventional N-path Band-Pass Filter (BPF). We first introduced a second-order N-path BPF with passive gain called impedance-transforming N-path filter. We then proposed a concept called rotary-clock-path in N-path filters which enables passive frequency shifting of N-path filters of any kind without the need for a separate clock frequency or active circuitries. Then by combining the impedance-transforming BPF and rotary-clock-path ideas, we implemented the first ever inductorless passive higher-order N-path BPF with voltage gain. The resulting BPFs can find applications in matching networks and also in a Surface Acoustic Wave (SAW)-less mixer-first receivers.


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More About This Work

Academic Units
Electrical Engineering
Thesis Advisors
Krishnaswamy, Harish
Ph.D., Columbia University
Published Here
April 13, 2022