A 120-MHz BW, 122-dBFS SFDR CTΔΣ ADC With a Multi-Path Multi-Frequency Chopping Scheme

Abstract

Advances in CMOS technologies and circuit techniques have led to the development of continuous-time delta–sigma modulators (CT <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \Sigma $ </tex-math></inline-formula> Ms) that sample at gigahertz (GHz) frequencies and achieve high linearity [−100 dBc and >120 dBFS spurious-free dynamic ranges (SFDRs)] in wide bandwidths (>100 MHz). However, at low frequencies ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\leq $ </tex-math></inline-formula> 10 MHz), their performance is limited by the 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}$ </tex-math></inline-formula> noise generated by the near-minimum size devices used in their wide-bandwidth input stages. This, in turn, limits their use in radio receivers intended to cover both the AM and FM bands. In this work, a multi-path multi-frequency chopping scheme is proposed to suppress 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}$ </tex-math></inline-formula> noise, while preserving interferer robustness, thermal noise levels, and linearity. Implemented in a CT <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \Sigma $ </tex-math></inline-formula> analog-to-digital converter (ADC) sampling at 6 GHz, it achieves a 22 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> reduction in 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}$ </tex-math></inline-formula> noise, as well as 122-dBFS SFDR and −98.3-dBc THD in a 120-MHz BW.