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10 February 2009 Improved sensitivity of portable bio-sensor systems using lock-in detection method
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Recently, a number of portable biosensors have been developed to check the health condition of human beings regardless of time and place. Though those sensors have a merit of a handy one, the signals are inevitably measured with intensive background noises. In order to detect a weak signal concealed in intensive background noises such as Johnson noise, 1/f noise, and shot noise, a special technique is essentially required. As of a special technique, the lock-in detection method is able to minimize the effects of these noises using modulated signal and reference signals. Previously, we applied the lock-in detection method to infrared detection system. The sensitivity of this system was decided by the 1/f noise at the photodetector. In this work, we have demonstrated the portable bio-sensor system using high frequency infrared laser diode and photodetector. Therefore, the main signal of interest may keep away from the effect of the 1/f noise with hybrid-type highly sensitive lock-in detection module. This technique provides the minimum detection range of 3 mV and the dynamic range of 25.8 dB at the noise level of 120 mV.
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Ho-Hyun Son, In-Il Jung, Doo Gun Kim, Do-Gyun Kim, and Young-Wan Choi "Improved sensitivity of portable bio-sensor systems using lock-in detection method", Proc. SPIE 7219, Optoelectronic Integrated Circuits XI, 72190N (10 February 2009);

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