A Time-Domain Dual-Edge Asynchronous Pipelined SAR ADC Featuring Reset-Free Quantization at Multi-GS/s

Abstract

Time-domain ADCs are attractive for high-speed wireline receivers, as time resolution scales favorably with advanced CMOS technologies, enabling multi-GS/s single-channel sampling rates. However, conventional time-domain ADCs require explicit reset of voltage-to-time and time-domain signal paths between samples, introducing dead time that fundamentally limits resolution, speed, and energy efficiency. This paper introduces a dual-edge reset-free quantization concept for asynchronous pipelined SAR time-domain ADCs, in which both rising and falling signal edges are exploited to enable reset-free quantization within a single conversion period. By eliminating explicit reset phases, the proposed approach expands the effective conversion window and relaxes the resolution-speed tradeoff at high sampling rates. An 8-bit dual-edge asynchronous pipelined SAR time-domain ADC is implemented in 22-nm FD-SOI, incorporating a linearity-compensated dual-edge voltage-to-time converter and a dual-edge time-to-digital converter with independently tunable rising- and falling-edge delays. The prototype occupies a core area of 0.0089 mm^2 and achieves continuous single-channel operation at 3.5 GS/s, with architectural scalability demonstrated through intermittent operation at 10.5 GS/s and higher. At 3.5 GS/s, the ADC achieves 21.6 dB SNDR and 32.2 dB SFDR. The measured performance is primarily limited by identifiable implementation-level factors rather than by architectural constraints, demonstrating the feasibility of dual-edge reset-free quantization for high-speed time-domain ADCs.