Abstract
Optical brain imaging using functional near infra-red spectroscopy (fNIRS) offers a portable and noninvasive tool for monitoring of blood oxygenation. In this paper we have introduced a new miniaturized photodetector front-end on achip to be applied in a portable fNIRS system. It includes silicon avalanche photodiodes (SiAPD), Transimpedance amplifier (TIA) front-end and Quench-Reset circuitry to operate in both linear and Geiger modes. So it can be applied for both continuous-wave fNIRS (CW-fNIRS) and also single-photon counting. Proposed SiAPD exhibits high-avalanche gain (>100), low-breakdown voltage ( V) and high photon detection efficiency accompanying with low dark count rates. The proposed TIA front-end offer a low power consumption ( mW), high-transimpedance gain (up to 250 MV/A), tunable bandwidth (1 kHz - 1 GHz) and very low input and output noise (~few fA/√Hz and few μV/√Hz). The Geiger-mode photon counting front-end also exhibits a controllable hold-off and rest time with an ultra fast quench-reset time (few ns). This integrated system has been implemented using submicron (0.35 μm) standard CMOS technology.
Highlights
Optical sensors and systems are widely applied in biological and biomedical imaging
Optical brain imaging using functional near infra-red spectroscopy offers a portable and noninvasive tool for monitoring of blood oxygenation
In this paper we have introduced a new miniaturized photodetector front-end on a chip to be applied in a portable functional near infra-red spectroscopy (fNIRS) system
Summary
Optical sensors and systems are widely applied in biological and biomedical imaging. Optical coherent tomography (OCT), pulse-oximetry, Brillouin scattering (BLS) imaging, Optical dermatology, and spectroscopy are some examples. FNIRS is a non-invasive, minimally intrusive, safe, and high-temporal resolution imaging technique for real-time and longterm monitoring of the brain function and biological tissues It is considered as one of the most efficient diagnosis and investigation techniques of different neurological diseases, such as, stroke and epilepsy seizures that require continuous monitoring of the patient at the hospital, which is a costly endeavor. FNIRS is compact when compared to other brain imaging systems, but current commercially available NIRS devices are still too bulky to be wearable or portable for monitoring brain function They are not miniaturized enough in order to be integrated with other wireless and portable medical imaging systems intended for bedside real-time brain monitoring. It suffers from low spatial resolution, high-level noise, susceptible to the internal and ambient light/temperature and bias voltage variations.
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