Dry active electrodes (AE) make biosignal recording more convenient without needing conductive gel or skin preparation compared to conventional wet electrodes. Nowadays, the application of biosignals is being extended outside the health centers as AE-based wearable sensors and brain-computer interfaces (BCI). The term “active” refers to a built-in preamplifier on the electrode that transforms the low amplitude high impedance biosignal source to an amplified low impedance one, therefor improves the signal quality. Nevertheless, there are also some challenges such as existence of large and time variant electrode offset, CMRR degradation due to the AEs gain mismatch and the flicker noise that needs to be dealt with. This thesis presents a novel current modulator active electrode (CMAE) with only two outgoing wires, resulting in lower cost and complexity. The CMAE is actually an operational transconductance amplifier (OTA) that modulates the supply current by the input voltage signal through the two supply rails. The CMAE prototype is implemented with only two discrete opamps. The ECG and EEG signals are successfully recorded by the proposed CMAE with dry electrodes and corresponding total gain of 50 dB and 65 dB and current consumption of 60 µA and 100 µA. The CMAE’s built-in preamplifier employs a DC feedback loop instead of conventional DC servo loop (DSL) which suppresses the input offset voltage in rail-to-rail and attenuates the flicker noise at lower frequencies. Without using any chopper stabilization, the total input referred noise of ECG and EEG CMAEs are 3.9 µV RMS and 0.7 µV RMS respectively in 0.5-100 Hz bandwidth. By using bipolar pseudoresistors, sub-hertz low cut-off frequency but with fast settling time is attained. Since the CMAE performs single-ended amplification, a digitally boosted driven right leg (DbRL) scheme has been designed which typically boosts the gain of the Keywords: Bioamplifier, dry electrode, electroencephalogram, electrode offset voltage, DC servo loop, current modulator active electrode, bipolar pseudoresistor, digitally boosted driven right leg, adaptive noise canceler.
