Size Constraint to Limit Interference in DRL-Free Single-Ended Biopotential Measurements

Purpose: In this work, it is shown that small, battery-powered wireless devices are so robust against electromagnetic interference that single-ended amplifiers can become a viable alternative for biopotential measurements, even without a Driven Right Leg (DRL) circuit. Methods: A power line interference analysis is presented for this case showing that this simple circuitry solution is feasible, and presenting the constraints under which it is so: small-size devices with dimensions less than 40 mm × 20 mm. Results: A functional prototype of a two-electrode wireless acquisition system was implemented using a single-ended amplifier. This allowed validating the power-line interference model with experimental results, including the acquisition of electromyographic (EMG) signals. The prototype, built with a size fulfilling the proposed guidelines, presented power-line interference voltages below 1.2 µVPP when working in an office environment. Conclusion: It can be concluded that a single-ended biopotential amplifier can be used if a sufficiently large isolation impedance is achieved with small-size wireless devices. This approach allows measurements with only two electrodes, a very simple front-end design, and a reduced number of components.

A Low Noise High Input Impedance Chopper-Stabilized Biopotential Amplifier with Ripple Reduction Technique

Biopotential signals are created as a result of the electrochemical activity of the many cells that comprise the nervous system, and they represent both normal and pathological organ function. These signals must be identified with extreme caution because they are surrounded by a great deal of noise when detected by sensors. This article explores a novel biopotential amplifier that incorporates the chopper stabilization technique to increase noise performance and minimize offset. However, by introducing the chopper modulator into the proposed design, the amplifier's overall input impedance was lowered, which was then increased to greater than 200 MΩ by adding the forward auxiliary path to the input branch. Additionally, the output ripple, produced due to switching activity and up-sampling, was reduced by inclusion of the R-C ripple removing block at the output of the operational transconductance amplifier (OTA). The designed architecture had a mid-band gain of 40dB with a power consumption of 9 µW and an offset of 10µV and a CMRR of 82 dB. It generated a noise of 42nV/√Hz. Also, the obtained results were compared with a conventional amplifier. The proposed design was verified by carrying out simulations using 180nm technology parameters. Cadence Virtuoso (Schematic editor), Spectre (Simulator), Symica and Magic (Layout) tools were used to complete the implementation and simulation of the proposed design. HIGHLIGHTS Biopotential signals are created as a result of the electrochemical activity of the many cells which must be identified with extreme caution because they are surrounded by a great deal of noise when detected by sensors It explores a novel biopotential amplifier that incorporates the chopper stabilization technique to increase noise performance and minimize offset By introducing the chopper modulator into the proposed design, the amplifier's overall input impedance was lowered, which was then increased to greater than 200 MΩ by adding the forward auxiliary path to the input branch The output ripple, produced due to switching activity and up-sampling, was reduced by inclusion of the R-C ripple removing block at the output of the operational transconductance amplifier (OTA) The designed architecture had a mid-band gain of 40dB with a power consumption of 9 µW and an offset of 10 µV and a CMRR of 82 dB. It generated a noise of 42 nV/√Hz GRAPHICAL ABSTRACT