# A Fully-Differential CMOS Instrumentation Amplifier for Bioimpedance-Based IoT Medical Devices

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Principle of Operation

#### 2.1. Block Diagram

#### 2.2. Transistor Level Implementation

## 3. Design Considerations

## 4. Experimental Results

## 5. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 9.**Transient response of the IA output voltage (green) to a 100-mV${}_{pp}$ input square wave (yellow).

**Figure 12.**Spectral density of noise vs. frequency: simulated (green) and measured (blue) responses.

Device | W/L ($\mathsf{\mu}$m/$\mathsf{\mu}$m) | Device | W/L ($\mathsf{\mu}$m/$\mathsf{\mu}$m) |
---|---|---|---|

MDI | 200/1 | MDO | 200/1 |

MFI | 80/0.5 | MFO | 80/0.5 |

MFCI | 20/0.5 | MFCO | 20/0.5 |

MSDI | 16/1 | MSDO | 16/1 |

MSUI | 48/1 | MSUO | 48/1 |

M1A, M2A | 80/0.5 | M1B, M2B | 80/0.5 |

M1C | 20/0.5 | M2C | 20/0.5 |

M3, M4 | 30/0.5 | M3C, M4C | 60/0.5 |

**Table 2.**Simulated vs. experimental performance of the FD IA (Technology: 180 nm CMOS, ${V}_{DD}$ = 1.8 V, ${A}_{v,nom}$ = 4 V/V).

Parameter | Simulated | Measured |
---|---|---|

Voltage gain (V/V) | 3.69 ± 0.07 | 3.78 ± 0.06 |

Voltage gain error (%) | −7.7 | −5.5 |

BW (MHz) | 10.27 ± 4.70 | 5.83 |

$\sigma $(${v}_{O}$) (mV) | 5.14 | 3.63 |

${v}_{I}$${\mid}_{THD=-40dB}$ @ 1 kHz (mV) | 53.5 | 59.6 |

${v}_{I}$${\mid}_{THD=-40dB}$ @ 10 kHz (mV) | 53.5 | 57.6 |

${v}_{I}$${\mid}_{THD=-40dB}$ @ 100 kHz (mV) | 53.2 | 59.0 |

${v}_{I}$${\mid}_{THD=-40dB}$ @ 1 MHz (mV) | 44.8 | 38.0 |

$S{R}^{+}$/$S{R}^{-}$ (V/$\mu s$) | 10.4/10.4 | 8.3/8.3 |

CMRR @ DC (dB) | 95.1 ± 9.2 | 73.3 |

CMRR @ BW (dB) | 70.8 ± 6.2 | 42.0 |

${V}_{iN,rms}$ [100 Hz-BW] ($\mu {V}_{rms}$) | 74.7 | 86.4 |

${I}_{DD}$ ($\mu $A) | 199.1 | 266.4 |

Parameter | [11] TCAS-I’11 | [12] IMCSSD’12 | [22] IJEC’20 | [26] TCAS-II’21 | [29] Electronics’22 | This Work |
---|---|---|---|---|---|---|

Technology | 0.35-$\mathsf{\mu}$m CMOS | 0.35-$\mathsf{\mu}$m CMOS | 0.35-$\mathsf{\mu}$m CMOS | 0.18-$\mathsf{\mu}$m CMOS | 0.18-$\mathsf{\mu}$m CMOS | 0.18 $\mathsf{\mu}$m CMOS |

Technique ${}^{(\ast )}$ | LCF | LCF | ICF | ${G}_{m}$-TI | ICF | ICF |

Results | Meas. | Sim. | Sim. | Sim. | Meas. | Meas. |

V${}_{DD}$ (V) | 3 | 2 | 3 | 1.8 | 1.8 | 1.8 |

I${}_{DD}$ ($\mu $A) | 285 | 240 | 250.6 | 162 | 219.3 | 266.4 |

Gain (dB) | 34 | 8 | 34 | 0/40 | 11.4 | 11.4 |

BW (MHz) | 2.0 | 4.0 | 7.6 | 6.7 $\times {10}^{-6}$/87.0 | 8.0 | 5.83 |

CMRR (dB) | >90 @ DC | 80 @ 1 MHz | 99.5 @ DC | 164.4 @ 100 kHz | 80.6 @ DC | 73.3 @ DC |

THD (dB) @ ${v}_{I}$ (m${V}_{pp}$) | −56.2 @ 10 | N.A. | −57.4 @ 10 | N.A. | −61.6 @ 20 | −64.9 @ 20 |

${v}_{I,max}$ (mV) | 30 | N.A. | 8 | N.A. | 53 | 59.6 |

${V}_{iN,rms}$ ($\mu {V}_{rms}$) | 16 | 36 | 32.4 | N.A. | 92.0 | 86.4 |

Area (mm${}^{2}$) | 0.068 | 0.037 | — | 0.0569 | 0.0291 | 0.0304 |

NEF | 5.9 | 10.8 | 7.2 | N.A. | 26.3 | 21.3 |

DR | 65.5 | N.A. | 47.9 | N.A. | 52.2 | 56.8 |

^{(∗)}LCF: local current feedback; ICF: indirect current feedback; G

_{m}-TI: transconductance-transimpedance.

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**MDPI and ACS Style**

Corbacho, I.; Carrillo, J.M.; Ausín, J.L.; Domínguez, M.Á.; Pérez-Aloe, R.; Duque-Carrillo, J.F.
A Fully-Differential CMOS Instrumentation Amplifier for Bioimpedance-Based IoT Medical Devices. *J. Low Power Electron. Appl.* **2023**, *13*, 3.
https://doi.org/10.3390/jlpea13010003

**AMA Style**

Corbacho I, Carrillo JM, Ausín JL, Domínguez MÁ, Pérez-Aloe R, Duque-Carrillo JF.
A Fully-Differential CMOS Instrumentation Amplifier for Bioimpedance-Based IoT Medical Devices. *Journal of Low Power Electronics and Applications*. 2023; 13(1):3.
https://doi.org/10.3390/jlpea13010003

**Chicago/Turabian Style**

Corbacho, Israel, Juan M. Carrillo, José L. Ausín, Miguel Á. Domínguez, Raquel Pérez-Aloe, and J. Francisco Duque-Carrillo.
2023. "A Fully-Differential CMOS Instrumentation Amplifier for Bioimpedance-Based IoT Medical Devices" *Journal of Low Power Electronics and Applications* 13, no. 1: 3.
https://doi.org/10.3390/jlpea13010003