超低功耗芯片实现高动态范围麦克风读出，有效消除信号失真。
A 399uW 114.3 dB DR Companding Readout ASIC for MEMS Microphones Employing a Multirate Time-Domain ADC
- 采用多速率时间域调制技术，实时捕捉信号细节以减少边界失真
- 实测动态范围达114.3dB，功耗低于400μW，性能指标领先
- 适合对功耗和音质敏感的智能语音设备，如降噪耳机与可穿戴产品
数字微机电麦克风在高级降噪与语音识别等应用中，对动态范围和灵敏度要求日益提高。低成本解决方案是采用压缩-扩展模数转换架构（companding ADC），该架构将动态范围划分为多个量化噪声水平不同的段落，从而缓解功耗限制。然而，传统压缩麦克风在信号跨越不同幅度段落边界时易产生可闻失真。本文提出一种基于压控振荡器（VCO）的新型压缩型模数转换架构，通过高分辨率时间域信号表示机制，有效抑制边界失真。多速率频率-数字转换设计使量化噪声与VCO频率解耦，同时保持标准音频采样率。驱动电路与振荡器电路协同优化，使该VCO-ADC在无反馈数模转换器条件下实现超过112dBc的峰值无杂散动态范围（SFDR），并维持吉欧姆级输入阻抗，兼容电容式MEMS结构。本文展示了基于0.13μm工艺的完整数字麦克风读出集成电路实现，包含两个模拟通道及数字信号处理与校准模块，输出标准单比特脉冲密度调制（PDM）信号。实测结果表明，该芯片动态范围达114.3dB，功耗低于400μW，SNDR的施雷耶尔因子（Schreier FoM）为171.0dB，DR因子为191.3dB。
原文摘要 · Abstract (English)
Improvements in the dynamic range and sensitivity of digital MEMS microphones are essential in applications like advanced noise canceling and voice recognition. A cost effective solution to achieve these goals is the companding ADC architecture. Companding ADCs split the dynamic range in several segments with different quantization noise levels, relaxing power constraints. A common problem of companding microphones are audible artifacts generated when the input signal crosses the boundaries between different amplitude segments. We show in this paper a companding ADC architecture that mitigates the boundary artifacts by leveraging the instantaneous and high-resolution time-domain representation of the input signal in a VCO-based ADC. The use of a multi-rate frequency-to-digital converter allows to decouple quantization noise from the VCO frequency, keeping standard audio sampling rates. Co-optimization of the driver and oscillator circuits enables our VCO-ADC to reach \textgreater 112dBc of peak SFDR without a feedback DAC, keeping a Giga-Ohm input impedance compatible with a capacitive MEMS. We show measurements of a 0.13 $μ$m ASIC implementing a complete readout circuit for a digital MEMS microphone. This includes two analog channels and the digital signal processing and calibration blocks required to deliver a standard single-bit PDM output. This ADC reaches a dynamic range of 114.3dB with a power budget under 400 uW, a Schreier FoM_{SNDR} of 171.0 dB and a FoM_{DR} of 191.3 dB.
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