# The Evolution of Integrated Interfaces for MEMS Microphones

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## Abstract

**:**

## 1. Introduction

## 2. Capacitive MEMS Microphones

## 3. MEMS Microphone Interface Circuits

#### 3.1. Preamplifier

#### 3.2. A/D Converter

## 4. Example 1: Third-Order DT $\mathbf{\Sigma}\Delta $ Modulator

#### Experimental Results

## 5. Example 2: Second-Order Multi-Bit DT $\mathbf{\Sigma}\Delta $ Modulator

#### Experimental Results

## 6. Example 3: Fourth-Order MASH DT $\mathbf{\Sigma}\Delta $ Modulator

- Low-Power (LP) mode (second order, ${f}_{S}=768$ kHz, 4-kHz bandwidth, 50% bias current level);
- Standard (ST) mode (fourth order, ${f}_{S}=2.4$ MHz, 20-kHz bandwidth, 75% bias current level);
- High-Resolution (HR) mode (fourth order, ${f}_{S}=3.6$ MHz, 20-kHz bandwidth, 100% bias current level).

#### Experimental Results

## 7. Example 4: Third-Order CT $\mathbf{\Sigma}\Delta $ Modulator

#### Experimental Results

## 8. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**The microphone market in million units since 2005 [3].

**Figure 5.**Block diagram of the preamplifier without (

**a**) and with (

**b**) parasitic capacitance bootstrapping.

**Figure 8.**Schematic of the SC implementation of the third-order DT $\mathrm{\Sigma}\Delta $ modulator (example 1).

**Figure 11.**Block diagram of the DT analog second-order $\mathrm{\Sigma}\Delta $ modulator (example 2).

**Figure 12.**Schematic of the SC implementation of the DT analog second-order $\mathrm{\Sigma}\Delta $ modulator (example 2).

**Figure 13.**Block diagram of the fourth-order, digital $\mathrm{\Sigma}\Delta $ modulator (example 2).

**Figure 15.**Block diagram of the reconfigurable DT MASH $\mathrm{\Sigma}\Delta $ modulator (example 3).

**Figure 16.**Schematic of the SC implementation of a single stage of the reconfigurable DT MASH $\mathrm{\Sigma}\Delta $ modulator (example 3).

**Figure 17.**Measured $\mathit{SNDR}$ as a function of the input signal amplitude in the three main operating modes (example 3).

**Figure 19.**Schematic of the active-RC implementation of the third-order CT $\mathrm{\Sigma}\Delta $ modulator (example 4).

Parameter | Value |
---|---|

Technology | 0.35-$\mathsf{\mu}$m CMOS |

Bandwidth (B) | 20 kHz |

Dynamic range ($\mathit{DR}$) | 76 dB |

Signal-to-noise and distortion ratio ($\mathit{SNDR}$) | 61 dB |

Effective number of bits ($\mathit{ENOB}$) | 9.8 |

Power supply voltage | 3.3 V |

ADC power consumption | 360 $\mathsf{\mu}$W |

ADC figure of merit (${\mathit{FoM}}_{S}$) | 153 dB |

Total power consumption | 1 mW |

Parameter | Value |
---|---|

Technology | 0.35-$\mathsf{\mu}$m CMOS |

Bandwidth (B) | 20 kHz |

Dynamic range ($\mathit{DR}$) | 77 dB |

Signal-to-noise and distortion ratio ($\mathit{SNDR}$) | 71 dB |

Effective number of bits ($\mathit{ENOB}$) | 11.5 |

Power supply voltage | 3.3 V |

ADC power consumption | 760 $\mathsf{\mu}$W |

ADC figure of merit (${\mathit{FoM}}_{S}$) | 148 dB |

Total power consumption | 1 mW |

${\mathit{f}}_{\mathit{S}}$ [MHz] | B [kHz] | Second-Order | Fourth-Order | ||
---|---|---|---|---|---|

Single-Bit Output | Multi-Bit Output | ||||

$\mathit{DR}$ [dB] | P [mW] | $\mathit{DR}$ [dB] | P [mW] | ||

0.768 | 4 | 85 (LP) | 0.10 | 99 | 0.48 |

20 | 59 | 97 | |||

2.4 | 4 | 95 | 0.15 | 98 | 0.73 |

20 | 77 | 96 (ST) | |||

3.6 | 4 | 96 | 0.20 | 102 | 0.97 |

20 | 85 | 99 (HR) |

Parameter | HR Mode | ST Mode | LP Mode |
---|---|---|---|

Bandwidth (B) [kHz] | 20 | 20 | 4 |

Clock frequency (${f}_{S}$) [MHz] | 3.6 | 2.4 | 0.768 |

Noise-shaping order (L) | 4th | 4th | 2nd |

Dynamic range ($\mathit{DR}$) [dB] | 99 | 96 | 85 |

ADC power consumption [mW] ^{§} | 0.97 | 0.73 | 0.10 |

ADC figure of merit (${\mathit{FoM}}_{S}$) [dB] | 172 | 170 | 161 |

Total power consumption [mW] ^{§} | 1.33 | 1.01 | 0.18 |

Signal-to-noise and distortion ratio ($\mathit{SNDR}$) [dB] * | 80 | ||

Power supply voltage [V] | 1.7–3.6 | ||

Technology | 0.18-$\mathsf{\mu}$m CMOS |

^{§}Measured with a power supply voltage equal to 1.8 V.

**Table 5.**Passive component values in the third-order $\mathrm{\Sigma}\Delta $ modulator (example 4).

Resistor | Value | Capacitor | Value |
---|---|---|---|

${R}_{i}$ | 47 k$\mathsf{\Omega}$ | ${C}_{1}$ | 18.5 pF |

${R}_{1}$ | 5.7 M$\mathsf{\Omega}$ | ${C}_{2}$ | 18.7 pF |

${R}_{3}$ | 57 k$\mathsf{\Omega}$ | ${C}_{f}$ | 2.1 pF |

${R}_{4}$ | 1 M$\mathsf{\Omega}$ | ${C}_{4}$ | 1 pF |

Parameter | Value |
---|---|

Technology | 0.16-$\mathsf{\mu}$m CMOS |

Bandwidth (B) | 20 kHz |

Dynamic range ($\mathit{DR}$) | 103.1 dB |

Dynamic range A-weighted (${\mathit{DR}}_{\mathrm{A}}$) | 106 dB |

Signal-to-noise and distortion ratio ($\mathit{SNDR}$) | 91.3 dB |

Effective number of bits ($\mathit{ENOB}$) | 17 |

Power supply voltage | 1.6 V |

ADC power consumption | 390 $\mathsf{\mu}$W |

ADC figure of merit (${\mathit{FoM}}_{S}$) | 180 dB |

Parameter | Example 1 | Example 2 | Example 3 | Example 4 | |
---|---|---|---|---|---|

LP | HR | ||||

Year | 2008 | 2011 | 2015 | 2016 | |

Technology | 0.35 $\mathsf{\mu}$m | 0.35 $\mathsf{\mu}$m | 0.18 $\mathsf{\mu}$m | 0.16 $\mathsf{\mu}$m | |

Bandwidth (B) [kHz] | 20 | 20 | 4 | 20 | 20 |

Noise-shaping order (L) | 3rd | 4th | 2th | 4nd | 3rd |

Dynamic range ($\mathit{DR}$) [dB] | 76 | 77 | 85 | 99 | 103 |

$\stackrel{\phantom{\rule{85.35826pt}{0ex}}\mathrm{Evolution}\phantom{\rule{85.35826pt}{0ex}}}{\to}$ | |||||

ADC power consumption [mW] | 0.36 | 0.76 | 0.10 | 0.97 | 0.39 |

ADC figure of merit (${\mathit{FoM}}_{S}$) [dB] | 153 | 151 | 161 | 172 | 180 |

$\stackrel{\phantom{\rule{85.35826pt}{0ex}}\mathrm{Evolution}\phantom{\rule{85.35826pt}{0ex}}}{\to}$ | |||||

Power supply voltage [V] | 3.3 | 3.3 | 1.7–3.6 | 1.6 |

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**MDPI and ACS Style**

Malcovati, P.; Baschirotto, A.
The Evolution of Integrated Interfaces for MEMS Microphones. *Micromachines* **2018**, *9*, 323.
https://doi.org/10.3390/mi9070323

**AMA Style**

Malcovati P, Baschirotto A.
The Evolution of Integrated Interfaces for MEMS Microphones. *Micromachines*. 2018; 9(7):323.
https://doi.org/10.3390/mi9070323

**Chicago/Turabian Style**

Malcovati, Piero, and Andrea Baschirotto.
2018. "The Evolution of Integrated Interfaces for MEMS Microphones" *Micromachines* 9, no. 7: 323.
https://doi.org/10.3390/mi9070323