A 3.68 aF<sub>rms</sub> Resolution Continuous-Time Bandpass Δ Σ Capacitance-to-Digital Converter for Full-CMOS Sensors in 0.18 μm CMOS
Sujin Park, Hyungil Chae, SeongHwan Cho
Abstract
This article describes a fourth-order continuous-time (CT) bandpass (BP)- <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> capacitance-to-digital converter (CDC) for full-CMOS sensors having ultrahigh-resolution and high-energy efficiency. To improve the resolution of <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> CDC, a CT instead of a discrete-time (DT) operation is employed to overcome a thermal noise limitation. Moreover, a BP- <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> modulator is used to save power consumption compared to lowpass (LP) or highpass (HP)- <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. In addition, a charge-domain digital-to-analog converter (DAC) at the input stage of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \Sigma M$ </tex-math></inline-formula> is proposed for low thermal noise and simplicity. An inverter-based amplifier is used for low power consumption and gain boosting circuit is added to increase dc gain of the amplifier. Implemented in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.18~\mu \text{m}$ </tex-math></inline-formula> CMOS, the proposed CDC achieves a ultrahigh-resolution of 3.68 aFrms and the highest Schreier figure-of-merit (FoMS) of 183 dB which is 3.3 dB improvement over the recent state-of-the-art CDCs.