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

Abstract

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 discretecomponent 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.

Multi-Electrode EMG Spatial-Filter Implementation Based on Current Conveyors

“…In previous work by the authors [26], an extension of the CCII-based instrumentation amplifier was found, highlighting that a passive network could perform the doubledifferential calculation in current mode. A generalization of this characteristic can be found by examining the network in Figure 3a, for which the Thévenin equivalent impedance of the electrodes can be found for the case Z 2 = Z 3 .…”

“…However, in order to realize a board-level implementation, instead of a CCII circuit, which is not easy to find as an off-the-shelf component, a surrogate has been used. In particular, noting that since the output taken from the CCII amplifier is the voltage on impedance Z o (due to the output current from the CCII Z node), we can achieve the same result by using an operational amplifier (OA) connected as in Figure 4a, which implements an equivalent function to the CCII [26]. Indeed, thanks to the virtual ground property, the voltage v i at the OA non-inverting input is accurately replicated at the OA inverting input, as occurs in the CCII at nodes Y and X.…”

“…Recently, Guerrero et al proposed an efficient and practical method for acquiring EMG signals for double-differential (DD) electrodes [26]. It exploits the current mode approach and, in particular, uses a type II current conveyor (CCII) to good effect [27,28].…”