A 155 /spl mu/W 88-dB DR Discrete-Time /spl Delta/ /spl Sigma/ Modulator for Digital Hearing Aids Exploiting a Summing SAR ADC Quantizer

Abstract

This paper presents a low-power switched-capacitor ∆Σ modulator for digital hearing-aid applications that features a novel summing successive approximation (SAR). The summing SAR performs multi-bit quantization together with the analog addition required in feed-forward (FF) ∆Σ modulator (∆ΣM) topologies, with no attenuation of the input signals and no need for amplifiers. The prototype is implemented in a 0.18- μ m CMOS technology and its measurements demonstrate a dynamic range of 88 dB in 10 kHz bandwidth while consuming 155 μW from a 1.8 V supply. The combined use of passive addition and SAR quantization reduces the complexity and power consumption of the modulator. The summing SAR ADC quantizer results in a calculated power saving of 40% when compared to a multi-bit FF ∆ΣM using active addition and flash quantization.

An NTF-enhanced incremental ΣΔ modulator using a SAR quantizer

“…4. This direct path owing to the use of a SAR ADC, eliminates the requirement of an extra active circuit [13]. Bear in mind that the dummy capacitor does not participate in the input sampling since it is involved in the noise extraction process.…”

A hybrid Sigma-Delta modulator with reusable SAR quantizer

“…In addition, the offset mismatch among the constituent comparators in flash quantizers can degrade the resolution and linearity of the modulators. Several quantization techniques [2,3,4,5] have been proposed to deal with those disadvantages in multi-bit Sigma-Delta modulators.…”

A Compact Switched-Capacitor Multi-Bit Quantizer for Low-Power High-Resolution Delta-Sigma ADCs

“…Alternatively, the use of capacitive summation based on passive charge sharing is an attractive solution because of its simplicity and low-power operation, although the corresponding signal attenuation may require pre-amplification or reference scaling [3]. Other trends in hybrid multi-bit ΔΣMs [4] replace the flash quantizer by another type of Nyquist-rate ADC, like pipeline, two-step flash, cyclic, tracking, integrating or synchronous/asynchronous successive-approximation register (SAR) [5]- [7]. In many cases, the overall ADC sensitivity and robustness against circuit non-idealities (e.g.…”