Fully integrated wide dynamic range optical receiver for near infrared spectroscopy

This paper presents a low power and wide dynamic range optical receiver dedicated to the frequency domain near infrared spectroscopy (FD-NIRS). The proposed optical receiver is fabricated using a 0.18 μm CMOS technology with a 0.5 mm ² integrated PIN photodiode (PD). This large area of the PD is necessary to collect a sufficient amount of the weak optical power which is reflected from the human scalp. Moreover, an automatic gain control (AGC) is used to account for the large individual variations and to enable connecting different inter-optodes separations to the same amplifier chain. This adopted AGC extends the maximum overloading input photocurrent of the optical receiver to 6.4 μApp resulting in a 17.04 dB dynamic range extension and a total dynamic range of 50.1 dB. The chip consumes 2.35 mW of power, has an integrated input referred noise current of 20 nArms, a maximum gain of 109.6 dBΩ, and a 10.7 MHz bandwidth.