A noise reconfigurable current-reuse resistive feedback amplifier with signal-dependent power consumption for fetal ECG monitoring

This paper presents a noise-reconfigurable resistive feedback amplifier with current-reuse technique for fetal ECG monitoring. The proposed amplifier allows for both tuning of the noise level and changing the power consumption according to the signal properties, minimizing the total power consumption while satisfying all application requirements. The amplifier together with its amplitude detector and dynamical biasing circuit is implemented in a standard 0.18- $\mu \text{m}$ CMOS process. Measurements demonstrate that the proposed current-reuse resistive feedback topology improves the power efficiency of the conventional resistive feedback amplifier, achieving at the same time a good noise efficiency factor (NEF $=2.8$ ) and an input impedance of 20 $\text{M}\Omega $ . The amplitude detector and the dynamical biasing circuit, which tunes the current in the amplifier according to the signal amplitude, save up to 40% of the total power consumption. The amplifier achieves a measured noise level of 0.34 $\mu \text{V}_{\mathrm{ rms}}$ in a 0.6–175-Hz band, consuming 6.3- $\mu \text{W}$ power.