Wideband Time-Based Data Converters

Rapid development of integrated circuit (IC) technologies has enabled the emergence of powerful and energy-efficient electronic systems such as smart phones. Nowadays, such devices can process immense amounts of data, which places stringent requirements on wireless data transmission and reception. The new fifth generation (5G) standard supports wide bandwidths and high data rates, which necessitates high-speed analog-to-digital converters (ADCs). The ongoing CMOS process scaling continues to improve the performance of digital circuits, while posing additional challenges for the circuit structures used for the necessary analog functions. Hence, digital-intensive ADC solutions are needed to realize high-performance ADCs in modern CMOS processes. One such design approach is time-based ADCs, where analog information is mapped to the time intervals of a digital signal, and is processed by mostly digital circuit structures. This work explores techniques related to time-based and digital-intensive analog-to-digital (A/D) conversion in terms of voltage-to-time (V/T) and time-to-digital (T/D) conversion. One of the central outcomes of the research is the use of a cyclic-coupled ring oscillator (CCRO) to achievesub-gate-delay time resolution in a time-to-digital converter (TDC). Two prototype ICs are implemented in a 28-nm CMOS process to demonstrate the circuit concepts developed in this work. The first prototype IC demonstrates a 100--750-MS/s CCRO-TDC, which achieves a peak linear resolution of 9.29 bits and a sub-gate-delay time resolution of 4.4 ps. The results verify the robust delay interpolation provided by the CCRO, and highlight the potential of CCROs in time-domain converter applications. The second prototype IC demonstrates the application of time-interleaving (TI) to the time-based converter. The IC contains a time-based TI-ADC with 2-GS/s sample rate and 40-dB SNDR, as well as a 1.5-GS/s TI-TDC with a 10.1-bit linear resolution at 2.3-ps time resolution. The implemented designs demonstrate the effectiveness of the developed time-based circuit concepts in the context of wideband time-based ADCs.