Bio-signal processing using a novel lock-in detection technique for the portable bio-optical systems

摘要

Portable bio-optical systems have required not only small size but also high sensitive and precise detection technique. To achieve high sensitivity, portable bio-optical systems should be set up to minimize the effects of noises such as Johnson noise, 1lf noise, shot noise etc. In order to reduce the influence from these noises, we have applied a novel lock-in detection technique. The lock-in detection technique is able to effectively suppress these noises as choosing a frequency high enough to avoid 1lf noise and low enough to avoid parasitic noises occurred on high frequency. We use lock-in detection technique with a simple structure - several op-amplifiers and MOSFETs. Using the lock-in scheme, we recovered signals in the presence of overwhelming background noises without applying multistage amplifiers and filters. This technique provides high resolution measurements of relatively clean signals over several orders of magnitude and frequency by compared with conventional detection method. We have demonstrated portable bio-optical system using infrared LED and PD with our hybrid type lock-in detection module.