Key result
A two-wired current modulator active electrode prototype achieved total input-referred noise voltages of 3.9 μVRMS for ECG and 0.7 μVRMS for EEG, with a common-mode rejection ratio up to 120 dB.
The proposed two-wired current modulator active electrode reduces cost and complexity for wearable ECG/EEG bioamplifiers while maintaining low noise and high common-mode rejection.
May support compact biopotential sensors; leaves open clinical validation before routine use.
This paper presents an innovative current modulator active electrode (CMAE) with only two outgoing wires that reduces cost and complexity of wearable bioamplifiers based on dry electrodes. The CMAE can be considered as an operational transconductance amplifier, which modulates the supply current by input voltage signal through its two supply rails. The CMAE prototype is implemented with only two discrete op-amps for ECG and EEG recording with current consumption of 60 μA and 100 μA, respectively. The CMAE's built-in preamplifier has utilized a dc feedback loop, instead of the conventional dc servo loop, which suppresses electrode offset in almost rail-to-rail. Total input-referred noise voltages of the ECG and EEG type CMAEs are 3.9 μVRMSand 0.7 μVRM S, respectively, in 0.5-100 Hz bandwidth. By using bipolar pseudoresistors, sub-hertz high-pass corner frequency but with fast settling time is achieved. The common-mode noise due to the disparate channels imbalances is digitally rejected by using an online adaptive noise canceler, which boosts the common-mode rejection ratio up to 120 dB with assisting the driven right leg circuit.
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Pourahmad et al. (2018) studied this question. Current modulator active electrode (CMAE) was evaluated on Total input-referred noise voltages and common-mode rejection ratio. A two-wired current modulator active electrode prototype achieved total input-referred noise voltages of 3.9 μVRMS for ECG and 0.7 μVRMS for EEG, with a common-mode rejection ratio up to 120 dB.
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