A fully differential capacitively-coupled high CMRR low-power chopper amplifier for EEG dry electrodes

Abstract

The use of dry electrodes is increasing rapidly. Since their impedance is high, there is a high impedance node at the connecting node between the electrode and amplifier. This leads to absorb powerline signal and high CMRR amplifiers are essential to eliminate this. In this article, we propose a low-power low-noise chopper-stabilized amplifier with high CMRR. In order to minimise the input-referred noise, an inverter-based differential amplifier is utilized. Meanwhile, a DC servo loop is designed to reject the DC offset of the electrode. Since all of the stages required a common-mode feedback, for each of the amplifiers a suitable circuit was used. Furthermore, a chopping spike filter is implemented at the final stage to attenuate the choppers’ spike. Finally, to eliminate the offset effect from the mismatch and post-layout, a DC offset rejection technique is used. The designed circuit is simulated in a standard 180 nm CMOS technology. The designed chopper amplifier consumes just 1.1 μW at a 1.2 V supply. The mid-band gain is 40 dB while the bandwidth is from 0.5 to 200 Hz. The total input-referred noise is 1 μVrms in its bandwidth. Thus the NEF and PEF of the designed circuit is 2.7 and 9.7, respectively. In order to analyse the performance of the proposed chopper amplifier against process and mismatch variation, Monte Carlo simulation is done. According to 200 Monte Carlo simulations, CMRR and PSRR are 124 dB with 6.9 dB standard deviation and 107 dB with 7.7 standard deviation, respectively. Ultimately, the total area consumption is 0.1 mm2 without pads.