Restriction lift date: 2030-06-12
CMOS techniques for direct digitisation of current signals
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Date
2024
Authors
Wall, Anthony
Journal Title
Journal ISSN
Volume Title
Publisher
University College Cork
Published Version
Abstract
This thesis presents a series of techniques and circuits to further the art of CMOS current-to-digital conversion using digitally-assisted techniques, particularly suited to highly-scaled technology nodes. A new model of the Current-Controlled Ring Oscillator (CCRO) is presented which describes its non-linearity with a single parameter, the Active-to-Dead Time Ratio (TADR). An improved squaring CCRO topology is presented, based on the TADR model which improves upon the linearity of inverter-based CCROs by 9.75 dB. The power-linearity trade-off is greatly improved by the introduction of the Ping-Pong CCO (PP-CCO), a new Current Controlled Oscillator (CCO) architecture. It demonstrates power consumption 19× lower than the improved squaring CCRO, and 2.75× lower than the state of the art. Based on the TADR model, a novel time-based, digitally-assisted linearity correction method is designed. This method uses a Time Quantiser (TQ) to quantise the period of the CCO, and its dead time is simply subtracted in the digital domain. The TQ is designed using a novel injection-locked Cyclic-Coupled Ring Oscillator (Cyc-CRO), which enables the oscillator’s use in TQs. Using the PP-CCO and the time-based linearity correction backend, the second harmonic, usually dominant in single-ended CCRO architectures, drops below the noise floor and >25 dB of correction is seen without the need for calibration or lookup tables.
Description
Keywords
Analogue to digital converter , ADC , Current controlled ring oscillator , CCRO , Time domain ADC , Current to digital converter , CDC , Time quantiser , TQ , Digitally assisted , Linearity correction
Citation
Wall, A. 2024. CMOS techniques for direct digitisation of current signals. PhD Thesis, University College Cork.