Supplementary Material for "A Fully-Differential Biopotential Amplifier with a reduced number of parts"
Objective: Fully differential topologies are well-suited for biopotential amplifiers, mainly for single-supply battery-powered circuits such as portable wearable devices where a reduced number of parts is desired. A novel fully differential biopotential amplifier is proposed with the goal of providing electrode offset rejection, bandwidth limitation, and a temporal response compliant with biomedical standards with only a single commercial quad operational amplifier (OA) integrated circuit. Methods: A novel compensation strategy was used to provide a transfer function with only one zero at the origin, which makes it easy to comply with the transient response imposed by biomedical standards. A topology with no grounded components was leveraged to obtain a common-mode rejection ratio (CMRR) ideally infinite and independent of components mismatches. Results: Design equations are presented and, as an example, an electrocardiogram (ECG) amplifier was built and tested. It features a CMRR of 102 dB at 50 Hz, 53 dB gain that supports DC input voltages up to ±300 mV when powered from a 0 V to 5 V single-supply voltage, and a cutoff frequency of less than 0.05 Hz with a first order response. Conclusion: A fully-differential biopotential front-end was designed and validated through experimental tests, demonstrating proper operation with only 4 OAs. Significance: The amplifier is intended for board-level design solutions, it can be built with off-the-shelf components that can be selected according to specific needs, such as reduced power consumption, low noise, or proper operation from a low-voltage power source.
“A Fully-Differential Biopotential Amplifier with a reduced number of parts” Supplementary material: It includes simulation models, experimental data, scripts, and PCB designs to reproduce the results in the article. 1. Simulation Models Some simulation circuits (TINA by Texas Instruments) are provided to reproduce the results presented in the manuscript. DifferentialModeGain.TSC: It allows to obtain frequency and transient responses. NoiseAnalysis.TSC: Amplifier noise simulation for TLC2274 and OPA4344. CMRR.TSC: This circuit allows to simulate the CMRR of the amplifier. The model of A1H was lightly modified to introduce a CMRR imbalance between A1H and A1L. 2. Experimental setup The following test circuit was used to measure the Differential Gain GDD, CMRR, and Noise. The circuit was placed inside a grounded metallic cabinet (an old PC) to avoid power-line interference. Measurements were made with an Agilent DSO-X 2024A and its built-in signal function generator. 3. Experimental data Measured_Noise_TLC2274.txt: Noise spectral density of the built amplifier. Column #1: Frequency [Hz]; Column #2: PDS at the output x 51 [nV/sqrt(Hz)] ecg03.txt: ECG signal acquired at 512 samples/sec. Column #1: amplifier output voltage [V] Pulse_IEC.mat: Experimental transient response to a 3 mV 100 ms width pulse. A 3V pulse with a 1000x attenuator was used and a 1.5V battery was added to produce a DC shift. A periodic 1 Hz pulse train was applied for averaging. Agilent Oscilloscope in Average Mode (32 frames) Column #1: time [s], Column #2: vin [mV], Column #3: vOUT [V] 4. MATLAB script Paper_Figures_R3_F: This script was used to produce the figures of the manuscript. Some experimental data such as Differential Gain (GDD) and CMRR measurements are embedded in the script. 5. Printed Circuit Board (PCB) PCB_Design.zip: This zip contains a proposed PCB design and all the files to reproduce it.