A 0.0022 mm², 2 GS/s Resettable VCO-Based ADC With-out Quantization Noise Shaping

With the rapid advancement of sensing and communications, there is an increasing demand for medium-resolution (6–8 b), high-speed (> 1 GS/s) ADCs. Flash and time-interleaved ADCs typically obtain high sampling rates, albeit at the cost of large power [1], [2], [3]. Taking advantage of the significant advances in digital performance in CMOS, time-domain based converters enable ever faster conversion speeds [4], [5], [6], [7]. Highly digital low-power VCO-based ADCs have particularly benefited from this trend. Although VCO-based ADCs features inherently first-order noise shaping of quantization noise, they are widely used in low-speed, high-precision applications thanks to oversampling [14], [8], [9], [10], [11], [12], [13]. However, with the continual increase in VCO frequency in newer process nodes, Nyquist VCO-based ADCs can achieve progressively better accuracy at high sample rates, thus making them attractive for high-speed applications [16], [17]. Additionally, since a Nyquist VCO-based ADC can achieve an extra bit of resolution by halving the sample rate [15], this feature enables easy adaption to various communication standards and frequency bands, thus enhancing versatility. In this paper, we propose a Nyquist VCO-based ADC with a single channel of 2 GS/s. The key innovations include: 1) a resettable ring VCO (R-RVCO), 2) switched buffers (sw-buf), and 3) a compact fine-quantizer with phase folding, all aimed at substantially improve SNDR and FOM.