Low-Noise Front-End Receiver Dedicated to Biomedical Devices: NIRS Acquisition System

This paper concerns the design and the implementation of a fully integrated front-end intended to Near-Infrared Spectroscopy System (NIRS) acquisition system. A low-noise transimpedance amplification (TIA) circuit followed by adjustable cut-off frequency and a low-pass filter (LPF) was implemented in order to decrease noise circuit of NIRS detectors. For TIA, a single ended common source, common gate input stage based on a cascode structure is used to get a higher gain-bandwidth closed-loop transimpedance amplifier. To enhance the circuit noise performance, a single feedback transistor technique is used, compared to passive feedback, to achieved high quality data from NIRS acquisition channel. The proposed LPF combines two control methods to adjust the low cut-off frequency. Simulation results show a TIA gain of 104.2 dBΩ, −3dB bandwidth of 19 MHz and an equivalent input noise current spectral density of 446 fA/√Hz. LPF filter exhibits a relatively constant noise 201nV/√Hz from 0 Hz to 700 KHz and linearity performance over its entire tuning range. The proposed front-end of NIRS preamplifier is implemented using 0.18 μm CMOS technology.