A low-light-level sensor for medical diagnostic applications

A low-level light sensor and preprocessor for a disposable medical probe is described. A 10-Hz 4-muA/cm(2) input optical signal in the visible spectru m is assumed in chemoluminant diagnostic applications. A single-bit first-o rder sigma-delta modulator has been employed for analog-to-digital conversi on, thanks to its robustness, simplicity, inherent linearity, and high sign al-to-noise ratio. A current buffer has been used to replicate the weak sig nal with sufficient bandwidth. Tests have shown the feasibility of this app roach, and have also enabled improvements of the design.