2025 Theses Doctoral

Architectures Leveraging Switched Capacitor Circuits for Emerging Wireless Applications

Garikapati, Sasank

Switched capacitor circuits have become a ubiquitous building block in various analog and mixed signal circuit architectures. Recent advancements in time interleaved switched capacitor circuits have demonstrated their capability of realizing a variety of frequency responses. Particularly, a polyphase multipath switched capacitor circuit can realize the response of a narrowband bandpass filter (commonly referred to as an 𝑁-path filter) or a true time delay (referred to as a quasielectrostatic delay) based on ratio between the charging time constant of the capacitor and the modulation time period. In this dissertation, we explore these switched-capacitor circuit architectures to find applications in modern day wireless systems.

Full-duplex wireless is an emerging communication paradigm which enables simultaneous transmission and reception within the same frequency band. Enabling wideband full-duplex systems would require cancellation of the strong self-interference signal leaking from the transmitter to the receiver within the same node. This requires self-interference cancelers which emulate the self-interference channel across the desired bandwidth. 𝑁-path based true time delay circuits present an attractive method to realize the self-interference canceler by utilizing multiple of these delay elements in parallel, creating a configurable FIR filter to adapt to the self-interference channel.We utilize this FIR filter to realize a time-domain RF canceler demonstrating wideband self-interference cancellation.

𝑁-path filters can be utilized to create compact, tunable, high-quality on-chip bandpass filters which offer an attractive alternative to bulky SAW filters in RF frontends. Typically, 𝑁-path filters remain restricted to sub-6 GHz operation and low frequency selectivity. To circumvent this issue, we present high order 𝑁-path filters operating up to 12 GHz frequencies by utilizing higher order intermediary baseband loads with overlapping clock signals to enable higher frequencies of operation.

Further, a transmission line periodically loaded with a switched capacitor can be utilized to realize time-interfaces in electromagnetic signals, which are the temporal analogue of spatial interfaces.We use CMOS switches to demonstrate an electromagnetic time interface operating inthe GHz-frequency range which can be utilized towards building time metameterials and photonic time crystals, opening a wide range of opportunities in the rising field of time-varying photonic media.