Design of a Programmable Gain Instrumentation Amplifier in a 45 nm CMOS Process

This paper presents the design of a Programmable Gain Instrumentation Amplifier (PGINA) intended for electrocardiogram (ECG) acquisition in wearable biomedical systems. The design flow includes analytical modeling, electrical simulation, layout implementation, and process, voltage, and temperature (PVT) variability analysis. In the proposed PGINA architecture, the Operational Transconductance Amplifier (OTA) is designed to balance performance and power efficiency, while the programmable gain stage incorporates transmission gate (TG) structures to ensure low on-resistance and minimal signal distortion. Gain control is implemented with 4-bit resolution, enabling linear-in-dB steps up to 30 dB, with bandwidth preserved across all configurations. Post-layout simulations show a maximum Common-Mode Rejection Ratio (CMRR) of 134 dB and an Input-Referred Noise (IRN) of $85.94 \mu$ Vrms. The amplifier consumes $373 \mu \mathrm{~W}$ from a 1.1 V supply and occupies a total layout area of $0.038 \mathrm{~mm}^{2}$, designed in a 45 nm CMOS process. These results highlight a favorable trade-off among linearity, noise performance, and power efficiency, supporting the suitability of the proposed solution for low-power, high-fidelity biomedical signal acquisition in portable applications.