# A Band-Pass Instrumentation Amplifier Based on a Differential Voltage Current Conveyor for Biomedical Signal Recording Applications

^{1}

^{2}

^{*}

## Abstract

**:**

^{2}. It is shown that the designed DVCCII benefits from good linearity over a wide range of input signals and provides a low input impedance at terminal X. Two versions of the proposed band-pass instrumentation amplifier using pseudo resistances were designed with different specifications for two different applications, namely for EEG and ECG signals. Numerical analyses of both designs show proper outputs and frequency responses by eliminating the undesired artifact and DC component of the EEG and ECG input signals.

## 1. Introduction

_{1}and Y

_{2}, and one high-impedance output node Z.

_{X}= V

_{Y1}− V

_{Y2}, I

_{Z}= I

_{X}

_{1}and Y

_{2}, appears at the terminal X, and the current injected into terminal X is being replicated to the output terminal Z. Thus, in an ideal DVCC the input resistance at terminal X is zero, and the resistance at terminal Z and both Y terminals is infinity. Therefore, a current flowing through Y

_{1}and Y

_{2}terminals is ideally zero. In practice, however, the input resistances and currents in DVCCs are different from the ideal case. Another desirable characteristic is the linearity of the device.

## 2. Methods

#### 2.1. DVCCII Circuit

_{1}to M

_{10}. These two stages should have equal output currents. The voltage follower stage is connected to the outputs of these two identical transconductors, such that the I3 and I4 currents are equal in magnitude. Thus:

_{3}) is grounded, the voltage at terminal X follows the voltage difference of the terminals Y

_{1}and Y

_{2}. Note that this is valid, as long as both output currents are linear and M

_{1}–M

_{4}are in saturation.

_{15}and M

_{16}. Thus, for achieving unit current gain, M

_{15}and M

_{16}must be matched with M

_{13}and M

_{14}, respectively. All transistors are sized to operate in the saturation region. The size of the transistors is listed in Table 1.

#### 2.2. Post Layout Simulation Results

_{x}and I

_{z}to depict the $\frac{{\mathrm{I}}_{\mathrm{z}}}{{\mathrm{I}}_{\mathrm{x}}}$ curve, both ports are terminated with 5 KΩ resistances. Moreso, note that port X is an output voltage port that has a small output resistance. Therefore, it should be loaded with a relatively large resistor. A 5 KΩ resistor seems to be large enough for this purpose.

_{id}= V

_{Y1}− V

_{Y2}are depicted in Figure 3a. The figure shows good linearity for differential input voltages between ±0.4 V. The offset voltage is also measured 2.24 mV and it is small enough. The offset voltage is the voltage of terminal X when V

_{id}is equal to zero or is grounded.

_{x}/V

_{id}) of 80 MHz and a 3 dB bandwidth of 450 MHz.

_{x}current source is injected into terminal X, is shown in Figure 4a. The figure shows a ±0.85 mA linear range. Figure 4b shows the current frequency response of the DVCC. As seen, this DVCC has a good flat I

_{z}/I

_{x}response with a unity gain up to about 80 MHz and its 3 dB bandwidth is equal to 450 MHz.

_{X}, is smaller than 20 ohm at DC and low frequencies. Variations of R

_{x}versus frequency is depicted in Figure 5. The value of Rx is also lower than 1 KΩ up to 3 dB frequency, demonstrating that port X can operate as a low impedance output port.

^{2}.

#### 2.3. Design of DVCC-Based Instrumentation Amplifier

_{2}are depicted in Figure 7. The gain of the instrumentation amplifier is given by $\mathrm{Av}=\frac{{\mathrm{V}}_{\mathrm{out}}}{{\mathrm{V}}_{\mathrm{id}}}\approx \frac{{\mathrm{R}}_{2}}{{\mathrm{R}}_{1}}$.

Parameter | Technology | Power Supply | Gain | BW (−3 dB) | On-Chip Area | Power Dissipation |
---|---|---|---|---|---|---|

[11] | 0.18 μm CMOS | ±0.9 V | 25–27.6 dB | 100 MHz | NA | 1.15 mW |

[25] | 0.18 μm CMOS | ±1.2 V | 19 dB for R_{L} = 8 KΩ | 18.1 MHz | NA | 383.4 μW |

[33] | 0.5 μm CMOS | ±1.5 V | 9–23 dB | 20 MHz | NA, Large size, due to use 7 off-chip resistors | 3.99 mW |

[36] | 0.18 μm CMOS | 1.8 V | Maximum of 40 dB | 2 KHz | 0.087 mm^{2} | 39.6 μW |

This work | 0.18 μm CMOS | ±0.9 V | 10 dB for R_{L} = 20 KΩ | 450 MHz | 460 μm^{2} | 148 μW * |

_{1}and C

_{Z}are required to achieve the small cut-off frequencies ${\mathrm{f}}_{\mathrm{L}}$ and ${\mathrm{f}}_{\mathrm{H}}$, respectively.

## 3. Results

_{1}and C

_{z}are set to 1 pF and 1.5 pF, respectively, and W/L sizing of the MOS pseudo resistors M

_{a}, M

_{b,}and M

_{RL}are set to $\frac{0.5\mathsf{\mu}\mathrm{m}}{5\mathsf{\mu}\mathrm{m}}$ and $\frac{15\mathsf{\mu}\mathrm{m}}{0.5\mathsf{\mu}\mathrm{m}}$, respectively. The frequency response of the designed band-pass IA is shown in Figure 10A. An input EEG test signal, which was recorded at the Neuro-Technology Lab in the Biomedical Engineering Department, the University of Isfahan, during the eyes-closed condition, followed by the eyes-open resting condition, was used to validate the designed circuit.

_{1}and Y

_{2}. After removing the DC component, the signal is filtered and amplified in the desired frequency band and then appears at the Voutput.

_{z}to 0.25 pF and the W/L ratio of Ma and Mb to $\frac{0.5\mathsf{\mu}\mathrm{m}}{10\mathsf{\mu}\mathrm{m}}$, to pass the frequency band of 0.13–160 Hz (Figure 11A) for ECG applications. Again, an ECG sample input, recorded at the Biomedical Instrumentation Lab in the Biomedical Engineering Department, the University of Isfahan, was applied and the output signal is shown in Figure 11B. Again, the quality of the output ECG signal proves the performance of the redesigned circuit for ECG recordings.

_{p-p}and a frequency of 10 Hz. It is worth mentioning that this THD is small enough, and the existence of this level of distortion in a large amplitude of an ECG signal is not an issue for the diagnoses of cardiac arrhythmia and other illnesses.

## 4. Conclusions

_{x}/V

_{id}) of 80 MHz. The power consumption of 148 µW was measured by a post layout simulation. The layout of the DVCC circuit occupies a total area of 0.378 µm

^{2}. In the following, using the presented DVCC, an instrumentation amplifier has been implemented and a new configuration has been presented to realize a band-pass amplifier using IA. In order to validate the proposed band-pass amplifier, two versions of the circuit with different specifications have been designed and recorded EEG and ECG signals have been successfully amplified and filtered. The proposed current-mode band-pass instrumentation amplifiers have applications in improving the quality of various biomedical signals for clinical diagnosis, including electrocardiography and electroencephalography.

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 2.**CMOS realization of the designed DVCC. The differential voltage between two input terminals, Y1 and Y2, appears at the X terminal and the current injected at X terminal is being replicated to the output.

**Figure 3.**(

**a**) The X terminal output voltage versus changes of V

_{id}. (

**b**) Frequency response of the DVCC.

**Figure 4.**(

**a**) Output current of terminal Z versus terminal X input current, when terminal Z is shorted. (

**b**) Current frequency response (I

_{z}/I

_{x}) of the DVCC.

**Figure 5.**The X terminal input resistance R

_{X}versus frequency changes. It is measured less than 20 ohm in low frequency and DC operation regions.

**Figure 6.**The layout of the proposed DVCCII using Cadence with TSMC 0.18 μm standard CMOS technology.

**Figure 7.**(

**a**) The block diagram of the instrumentation amplifier implemented using the presented DVCC, (

**b**) Voltage gains for different resistances at the output of this instrumentation amplifier.

**Figure 8.**The schematic of the proposed configuration for separating the required frequency bands for various biomedical signals through the IA.

**Figure 10.**(

**A**) The frequency response of the gain and phase of the band-pass bioamplifier. (

**B**) The original EEG input signal (Vinput) (

**C**). The EEG output signal after amplification and filtering using the designed circuit of Figure 8. (

**D**) Power spectral density plots under eyes-open and eyes-closed conditions for the EEG recordings.

**Figure 11.**(

**A**) The frequency response of the gain and phase of the band-pass amplifier for ECG recording. (

**B**) The ECG input and its related output signal after amplification and filtering using the designed circuit of Figure 8.

Transistors | W (µm) | L (µm) |
---|---|---|

M1–M4 | 1.8 | 3 |

M5–M8 | 0.9 | 0.8 |

M9–M10 | 9.5 | 1.4 |

M11–M12 | 0.5 | 0.3 |

M13–M16 | 5 | 0.2 |

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

Technology | 0.18 μm TSMC CMOS |

Power Supply | ±0.9 V |

Linear Dynamic Range for V_{x} vs. V_{id} | ±400 mV |

X Terminal Offset Voltage | 2.24 mV |

Linear Dynamic Range for I_{z} vs. I_{z} | −0.85 mA~0.87 mA |

X Terminal Voltage BW, f_{u} | BW = 450 MHz, f_{u} = 80 MHz |

Z Terminal Current BW, f_{u} | BW = 450 MHz, f_{u} = 80 MHz |

RinX (X Terminal Input Resistance) | f < 1 MHz: R = 20 ohm f up to 100 MHz: R < 600 ohm |

On-chip area | 378 μm^{2} |

Total Power Dissipation | 148 μW |

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**MDPI and ACS Style**

Karami Horestani, F.; Karami Horastani, Z.; Björsell, N. A Band-Pass Instrumentation Amplifier Based on a Differential Voltage Current Conveyor for Biomedical Signal Recording Applications. *Electronics* **2022**, *11*, 1087.
https://doi.org/10.3390/electronics11071087

**AMA Style**

Karami Horestani F, Karami Horastani Z, Björsell N. A Band-Pass Instrumentation Amplifier Based on a Differential Voltage Current Conveyor for Biomedical Signal Recording Applications. *Electronics*. 2022; 11(7):1087.
https://doi.org/10.3390/electronics11071087

**Chicago/Turabian Style**

Karami Horestani, Fatemeh, Zahra Karami Horastani, and Niclas Björsell. 2022. "A Band-Pass Instrumentation Amplifier Based on a Differential Voltage Current Conveyor for Biomedical Signal Recording Applications" *Electronics* 11, no. 7: 1087.
https://doi.org/10.3390/electronics11071087