A Novel Energy-Efficient RF VCO-ADC with an Intrinsic Quasi-Sinc³Anti-Aliasing Filter

Voltage-controlled oscillator-based analog-to-digital converters (VCO-ADCs) inherently exhibit a sinc filtering response that serves as an intrinsic anti-aliasing filter (AAF) for attenuating out-of-band signals. However, the filter attenuation, even for a second-order <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(sinc^{2})$</tex> response in the state-of-the-art VCO-ADC, is inadequate to sufficiently suppress aliased signals below the noise floor in wideband <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\geq 100$</tex> MHz) RF receiver systems. This necessitates power and area-consuming dedicated analog AAFs, incongruous for low-power <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{IoT}$</tex> applications. In this paper, we propose a novel RF VCO-ADC architecture with an unprecedented intrinsic quasi-sinc<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>AAF. The ADC embodies a proposed opposite-phase sampling technique that emulates a finite-impulse-response filter, effectively enhancing the inherent sinc AAF by two orders, yet featuring low complexity. The proposed ADC is designed in a CMOS 65 nm process and simulated for comparison against state-of-the-art ADCs. On the basis of this comparison, the proposed ADC achieves a significant 20 dB improvement in maximum alias attenuation at the sampling frequency without requiring extra AAFs, outperforming the state-of-the-art with a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$6^{\text{th}}$</tex> -order analog AAF. It dissipates only 0.34 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{mW}, \sim 4\times$</tex> lower than the state-of-the-art, and features exceptional energy efficiency with a highly competitive Figure-of-Merit of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 34$</tex> fJ/conversion, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 2\times$</tex> more efficient than the state-of-the-art.