# 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

- Minhee, K.; Eunkyoung, P.; Hwan, C.B.; Kyu-Sung, L. Recent Patient Health Monitoring Platforms Incorporating Internet of Things-Enabled Smart Devices. Int. Neurourol. J.
**2018**, 22, S76–S82. [Google Scholar] - Gope, P.; Gheraibia, Y.; Kabir, S.; Sikdar, B. A Secure IoT-Based Modern Healthcare System With Fault-Tolerant Decision Making Process. IEEE J. Biomed. Health Inf.
**2021**, 25, 862–873. [Google Scholar] [CrossRef] [PubMed] - Grimnes, S.; Martinsen, V.G. Bioimpedance and Bioelectricity Basics, 3rd ed.; Academic Press: Cambridge, MA, USA, 2015. [Google Scholar]
- Steyaert, M.S.J.; Sansen, W.M.C. A micropower low-noise monolithic instrumentation amplifier for medical purposes. IEEE J. Solid-State Circuits
**1987**, 22, 1163–1168. [Google Scholar] [CrossRef] - van den Dool, B.J.; Huijsing, J.K. Indirect current feedback instrumentation amplifier with a common-mode input range that includes the negative rail. IEEE J. Solid-State Circuits
**1993**, 28, 743–749. [Google Scholar] [CrossRef] [Green Version] - Martins, R.; Selberherr, S.; Vaz, F.A. A CMOS IC for portable EEG acquisition systems. IEEE Trans. Instrum. Meas.
**1998**, 47, 1191–1196. [Google Scholar] [CrossRef] - Harrison, R.R.; Charles, C. A low-power low-noise CMOS amplifier for neural recording applications. IEEE J. Solid-State Circuits
**2003**, 38, 958–965. [Google Scholar] [CrossRef] - Zhao, Y.Q.; Demosthenous, A.; Bayford, R.H. A CMOS instrumentation amplifier for wideband bioimpedance spectroscopy systems. In Proceedings of the 2006 IEEE International Symposium on Circuits and Systems, Kos, Greece, 21–24 May 2006; pp. 5079–5082. [Google Scholar]
- Yazicioglu, R.F.; Merken, P.; Puers, R.; Van Hoof, C. A 60 μW 60 nV/√Hz readout front-end for portable biopotential acquisition systems. IEEE J. Solid-State Circuits
**2007**, 42, 1100–1110. [Google Scholar] [CrossRef] - Denison, T.; Consoer, K.; Santa, W.; Avestruz, A.; Cooley, J.; Kelly, A. A 2 μW 100 nV/√Hz chopper-stabilized instrumentation amplifier for chronic measurement of neural field potentials. IEEE J. Solid-State Circuits
**2007**, 42, 2934–2945. [Google Scholar] [CrossRef] - Worapishet, A.; Demosthenous, A.; Liu, X. A CMOS instrumentation amplifier with 90-dB CMRR at 2-MHz using capacitive neutralization: Analysis, design considerations, and implementation. IEEE Trans. Circuits Syst. I Regul. Pap.
**2011**, 58, 699–710. [Google Scholar] [CrossRef] - Ramos, J.; Ausín, J.L.; Duque-Carrillo, J.F.; Torelli, G. Wideband low-power current-feedback instrumentation amplifiers for bioelectrical signals. In Proceedings of the International Multi-Conference on Systems, Signals and Devices, Chemnitz, Germany, 20–23 March 2012; pp. 1–5. [Google Scholar]
- Abdelhalim, K.; Jafari, H.M.; Kokarovtseva, L.; Velazquez, J.L.P.; Genov, R. 64-channel UWB wireless neural vector analyzer SOC with a closed-loop phase synchrony-triggered neurostimulator. IEEE J. Solid-State Circuits
**2013**, 48, 2494–2510. [Google Scholar] [CrossRef] - Ong, G.T.; Chan, P.K. A power-aware chopper-stabilized instrumentation amplifier for resistive Wheatstone bridge sensors. IEEE Trans. Instrum. Meas.
**2014**, 63, 2253–2263. [Google Scholar] [CrossRef] - Van Helleputte, N.; Konijnenburg, M.; Pettine, J.; Jee, D.; Kim, H.; Morgado, A.; Van Wegberg, R.; Torfs, T.; Mohan, R.; Breeschoten, A.; et al. A 345 μW multi-sensor biomedical SoC with bio-impedance, 3-channel ECG, motion artifact reduction, and integrated DSP. IEEE J. Solid-State Circuits
**2015**, 50, 230–244. [Google Scholar] [CrossRef] - Worapishet, A.; Demosthenous, A. Generalized analysis of random common-mode rejection performance of CMOS current feedback instrumentation amplifiers. IEEE Trans. Circuits Syst. I Regul. Pap.
**2015**, 62, 2137–2146. [Google Scholar] [CrossRef] - Chang, C.; Zahrai, S.A.; Wang, K.; Xu, L.; Farah, I.; Onabajo, M. An analog front-end chip with self-calibrated input impedance for monitoring of biosignals via dry electrode-skin interfaces. IEEE Trans. Circuits Syst. I Regul. Pap.
**2017**, 64, 2666–2678. [Google Scholar] [CrossRef] - Rezaeiyan, Y.; Zamani, M.; Shoaei, O.; Serdjin, W.A. A 0.5 μA/channel front-end for implantable and external ambulatory ECG recorders. Microelectron. J.
**2018**, 74, 79–85. [Google Scholar] [CrossRef] [Green Version] - Nasserian, M.; Peiravi, A.; Moradi, F. A fully-integrated 16-channel EEG readout front-end for neural recording applications. AEU–Int. J. Electron. Commun.
**2018**, 94, 109–121. [Google Scholar] [CrossRef] - Lee, C.; Song, J. A chopper stabilized current-feedback instrumentation amplifier for EEG acquisition applications. IEEE Access
**2019**, 7, 11565–11569. [Google Scholar] [CrossRef] - Psychalinos, C.; Minaei, S.; Safari, L. Ultra low-power electronically tunable current-mode instrumentation amplifier for biomedical applications. AEU–Int. J. Electron. Commun.
**2020**, 117, 153120. [Google Scholar] [CrossRef] - Carrillo, J.M.; Domínguez, M.A.; Pérez-Aloe, R.; de la Cruz Blas, C.A.; Duque-Carrillo, J.F. Low-power wide-bandwidth CMOS indirect current feedback instrumentation amplifier. AEÜ–Int. J. Electron. Commun.
**2020**, 123, 153299. [Google Scholar] [CrossRef] - Kwon, Y.; Kim, H.; Kim, J.; Han, K.; You, D.; Heo, H.; Cho, D.i.; Ko, H. Fully differential chopper-stabilized multipath current-feedback instrumentation amplifier with R-2R DAC offset adjustment for resistive bridge sensors. Appl. Sci.
**2020**, 10, 63. [Google Scholar] [CrossRef] [Green Version] - Han, K.; Kim, H.; Kim, J.; You, D.; Heo, H.; Kwon, Y.; Lee, J.; Ko, H. A 24.88 nV/√Hz Wheatstone bridge readout integrated circuit with chopper-stabilized multipath operational amplifier. Appl. Sci.
**2020**, 10, 399. [Google Scholar] [CrossRef] - Matthus, C.D.; Buhr, S.; Kreißig, M.; Ellinger, F. High gain and high bandwidth fully differential difference amplifier as current sense amplifier. IEEE Trans. Instrum. Meas.
**2021**, 70, 1–11. [Google Scholar] [CrossRef] - Pérez-Bailón, J.; Sanz-Pascual, M.T.; Calvo, B.; Medrano, N. Wide-band compact 1.8 V-0.18 μm CMOS analog front-end for impedance spectroscopy. IEEE Trans. Circuits Syst. II Express Briefs
**2022**, 69, 764–768. [Google Scholar] [CrossRef] - Pérez-Bailón, J.; Calvo, B.; Medrano, N. 1.0 V-0.18 μm CMOS tunable low pass filters with 73 dB DR for on-chip sensing acquisition systems. Electronics
**2021**, 10, 563. [Google Scholar] [CrossRef] - Ashayeri, M.; Yavari, M. A front-end amplifier with tunable bandwidth and high value pseudo resistor for neural recording implants. Microelectron. J.
**2022**, 119, 105333. [Google Scholar] [CrossRef] - Corbacho, I.; Carrillo, J.M.; Ausín, J.L.; Domínguez, M.A.; Pérez-Aloe, R.; Duque-Carrillo, J.F. Compact CMOS wideband instrumentation amplifiers for multi-frequency bioimpedance measurement: A design procedure. Electronics
**2022**, 11, 1668. [Google Scholar] [CrossRef] - Banu, M.; Khoury, J.; Tsividis, Y. Fully differential operational amplifiers with accurate output balancing. IEEE J. Solid-State Circuits
**1988**, 23, 1410–1414. [Google Scholar] [CrossRef]

**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