A monolithic based NIRS front-end wireless sensor

This paper concerns a novel analog front-end of a wireless brain oxymeter smart sensoring instrument based on near-infrared spectroreflectometry (NIRS). The NIRS sensor makes use of dynamic threshold transistors (DTMOS) for low voltage (1 V), low power and low noise enhancement. The design is composed of a transimpedance amplifier (TIA) and an operational transconductance amplifier (OTA). The OTA differential input pairs use DTMOS devices for input common mode range enhancement. The OTA was fabricated in a standard 0.18 μm CMOS process technology. Measurements under a 5 pF capacitive load for the OTA gave a DC open loop gain of 67 dB, unity frequency gain bandwidth of 400 kHz, input and output swings of 0.58 and 0.7 V, a power consumption of 18 μW, and an input referred noise of 134 nV/√Hz at 1 kHz without any extra noise reduction techniques. The achieved features of the proposed oxymeter front-end will allow ultra low-light level measurements, high resolution and good temperature stability.