A Multistep Multistage Fifth-Order Incremental Delta Sigma Analog-to-Digital Converter for Sensor Interfaces

Abstract

Incremental analog-to-digital converters (IADCs), by adding a simultaneous reset in analog modulators and digital filters, are Nyquist-rate ADCs which use noise-shaping to convert a finite number of analog samples into a single digital word. They retain most advantages of the delta sigma ( <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> ) ADCs, and are much easier to be multiplexed with shorter latency and simpler digital filters. Integrated sensor fusion system-on-chips (SoCs) require a high-accuracy low-latency analog-to-digital converter (ADC) to interface a wide input range signal and multiplex among multiple sensor channels. To fulfill these demands at the same time, a multistage multistep incremental ADC is proposed. A third-order multistage IADC, implemented by cascading a second-order IADC (IADC2) and a first-order IADC (IADC1), performs the coarse quantization in the first step. When the coarse quantization is finished, the residue is also accumulated at the last integrator’s output and is ready for fine quantization. The circuit is reused and reconfigured as a second IADC in the second step. Prototyped in 180 nm technology and power supplied at 1.8 V, the proposed work can achieve 20 kHz signal bandwidth with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$358.4 \mu \text{W}$ </tex-math></inline-formula> power dissipation. The measured performance of the prototype is 91 dB dynamic range (DR), 89.1 dB signal-to-noise-and-distortion (SNDR), and 107.5 dB spurious-free DR (SFDR). The measured SNDR/DR achieves Schreier figure-of-merit (FoM) of 166.6/168.5 dB.