Correlated Noise Reduction in a CMOS ECG Amplifier: Opportunities and Limitations

Low-noise front-end amplifiers are essential for the acquisition of weak biopotential signals, such as electrocardiograms (ECGs), where the noise introduced by the first amplification stage directly limits the overall signal quality. While correlated noise-cancellation techniques have been extensively investigated for radio-frequency (RF) low-noise amplifiers, their application to low-frequency biomedical interfaces remains largely unexplored because of the different dominant noise mechanisms. This work investigates the applicability of an RF-inspired correlated noise-cancellation methodology to a low-frequency CMOS biomedical preamplifier core intended for ECG front-end applications. The proposed architecture extends a conventional resistive-feedback common-source amplifier by introducing an auxiliary feedforward path designed to attenuate the internally generated correlated noise components without significantly affecting the useful signal. The amplifier was designed in a 150 nm CMOS process and evaluated through AC, noise, Monte Carlo, PVT and time-domain analyses. Compared with the reference single-stage implementation, the proposed architecture achieves approximately a 20% reduction in integrated input-referred noise and a 14% reduction in integrated output-referred noise while marginally improving the voltage gain. Statistical analyses confirm that the proposed technique maintains its effectiveness under process, voltage, temperature, and mismatch variations. Time-domain evaluations with representative ECG waveforms further validate the methodology at the amplifier-core level and indicate its potential integration into complete low-noise biomedical analog front-ends.