Abstract
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.
