Design of an integrated sensor for noninvasive optical mammography based on frequency-domain NIR spectroscopy

Time-resolved techniques for optical spectroscopy are emerging as a promising diagnostic tool for mammography providing richer information content of optical images and improved tumor detectability. This paper presents the design of an integrated optical sensor for phase and amplitude detection of RF-modulated optical signals up to 110 MHz in the near-infrared (NIR) region (650-850 nm) for use in frequency-domain instruments that measure both amplitude and phase changes in photon migration between source and detector. The sensor consists of an NIR-sensitive photodetector monolithically integrated with front-end analog amplifier and signal processing circuitry for amplitude and phase detection in an unmodified CMOS process. The differential transimpedance amplifier (TIA) achieves a transimpedance-bandwidth product of 28 THzOmega and input-referred current noise of 1.92 pA/radicHz at 110 MHz. The amplitude detector exhibits 49.2 mV/muA resolution with 0.5% linearity and 26 dB dynamic range. The proposed phase detector can detect 360 degree phase difference with phase resolution of 5 mV/degree. The sensor is implemented in a 0.18 mum CMOS technology and consumes 22.5 mW from a 1.8 V supply voltage. The integrated sensor presented is envisaged as a building block towards a low-power, low-cost optical sensor array system for concurrent measurement of multiple tissue sites, thus improving spatial resolution.