CMOS mixed-signal phase detector for integrated chemical sensor systems

The development of a portable chemical sensor system based on the measurement of the excited-state lifetimes of luminophore doped xerogels in the frequency-domain is described. The prototype sensor system is demonstrated for oxygen (O₂) monitoring and consists of a silicon photodiode as the detector followed by a current-to-voltage converter, an amplifier, a band-pass filter and a custom-designed CMOS phase detector. The variation in the lifetime, due a change in the analyte concentration, is measured as a phase shift between a sinusoidally modulated reference excitation and the fluorescence emission using the designed CMOS phase shift detector. The CMOS mixed-signal phase detector is fabricated using the AMI 1.5 mum process available through MOSIS. A highly accurate, low cost, and hand-held prototype oxygen sensor is demonstrated using this CMOS phase detector