Time-varying radio-frequency circuits for low-noise and broadband front-ends

Ming, Shuxin

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https://hdl.handle.net/2142/122138 Copy

Description

Title

Time-varying radio-frequency circuits for low-noise and broadband front-ends

Author(s)

Ming, Shuxin

Issue Date

2023-11-28

Director of Research (if dissertation) or Advisor (if thesis)

Zhou, Jin

Doctoral Committee Chair(s)

Zhou, Jin

Committee Member(s)

• Rosenbaum, Elyse
• Schutt-Aine, Jose
• Hanumolu, Pavan

Department of Study

Electrical & Computer Eng

Discipline

Electrical & Computer Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

RFIC, VCO, RF delay, LPTV, time-varying

Abstract

To overcome the stringent requirements on circuits in high frequency operation, this work presents time-varying radio-frequency (RF) circuits for lownoise and broadband front-ends. Specifically, it includes a K-band quad-core class-F VCO with tail-filtering to achieve ultra-low phase noise at high RF frequencies, and a commutated-inductor-capacitor (Commutated-LC) circuit that acts as a tunable delay line with nanosecond scale delay at RF frequencies. The introduction of class-F operation to a circular-geometry multi-core oscillator lowers phase noise but results in new mode ambiguity. We propose to add cross-coupled thin metal traces at the class-F transformer secondary winding to suppress the new spurious modes. Also, we extend the circular geometry design to the VCO tail LC filters, saving the chip area. A proofof-concept prototype is fabricated in a standard 65 nm CMOS technology. In measurement, the VCO operates from 17.7 to 20.7 GHz. At 18 GHz, the VCO achieves a phase noise of −113 dBc/Hz at 1 MHz offset with a figure of merit (FoM) of 186.4 dB. The VCO core has an area of 0.13 mm2 and consumes a dc power of 16 mW from a 0.75-V supply. Thanks to the linear-periodically-time-varying (LPTV) operation and fully passive implementation of our commutated-LC delay circuit, it concurrently achieves long maximum delays, fine delay tuning steps, and wide instantaneous bandwidths while being low loss and highly linear. Unlike existing LPTV switched-capacitor broadband delays, the introduction of inductors in the proposed commutated-LC delay circuit provides a new degree of freedom, allowing it to operate at a much higher RF with a wider instantaneous bandwidth. A proof-of-concept prototype in a 65-nm CMOS process demonstrates a measured 1.3-GHz 3-dB bandwidth around a 4.3-GHz RF, i.e. a 30% fractional bandwidth, when clocked at 250 MHz. The measured maximum delay is 1.4 ns with 23 dB loss and noise figure; this loss or noise iiis orders-of-magnitude lower compared to fully-passive linear-time-invariant RF delay lines operating at a similar frequency with the same delay. The measured IIP3 is +16 dBm. Then, we present a comprehensive study on the one-port and two-port linear time-invariant (LTI) models of the commutated-LC broadband delay circuit, aiming to provide a more intuitive understanding of its functioning. In addition, we have summarized the crucial design considerations and tradeoffs associated with each parameter, namely the number of paths (N), damping factor (α), switch-on time (TC), and the ratio between switch-on time and time constant (Γ). To address the on-chip inductor loss, we have introduced negative conductance into the commutated-LC delay circuit, transforming it into a commutated-LC-negative-R (commutated-LC-nR) broadband delay circuit. In order to shed light on the reasons behind the improvement in both insertion loss (IL) and noise figure (NF) with increased negative conductance, we have conducted a comprehensive noise analysis of the commutated-LCnR circuit. The results reveal that the enhancement in NF is attributed to the high efficiency of compensating the transfer function loss in the delay region, while the total output noise remains relatively constant. A proof-ofconcept delay line has been demonstrated in 65-nm CMOS, achieving 1.5-ns delay, 1.4-GHz instantaneous bandwidth, and 6-dB loss at C-band.

Graduation Semester

2023-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Shuxin Ming

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