Double-Differential Amplifier for sEMG Measurement by Means of a Current-Mode Approach

This work proposes a Double Differential (DD) amplifier topology which exploits the advantages of the current-mode approach. DD amplifiers are useful as front-ends in standalone active electrodes for superficial electromyography (sEMG) wearable applications and electroneurography (ENG) measurement devices. Front-ends for these applications need to attain low noise, high common-mode rejection ratio, and high input impedance to measure biopotential signals and can further benefit from low power operation, a small size, and an easily adaptable output. Presently published DD amplifiers are either complex in terms of a high part count, leading to higher power consumption and size, or suffer from limited interference-rejection capabilities and require further analog processing for compatibility with single-ended systems. Therefore, in this work, second-generation current conveyors have been leveraged to obtain a simple topology combining a small active-part count, a high common-mode rejection ratio, and a flexible output stage. The current-mode DD amplifier is presented and analyzed in detail to estimate its parameters and model the effects of nonidealities in the circuit. In order to validate the proposed topology, a discrete-component implementation was realized as a proof-of-concept. The results experimentally demonstrated the properties of the proposed topology and its feasibility for measuring superficial sEMG DD signals.