Light-controlled transducer with pulse width modulated output based on non-equilibrium metal oxide semiconductor capacitors

A novel conception of practical applications of non-equilibrium processes in illuminated metal-oxide-semiconductor capacitors is presented. It is shown that the time dependent variations of the displacement current in such capacitors, biased in strong inversion condition by a functional voltage generator, is the basis of the new transducers. Triangular or sawtooth voltage waveforms supplied by a generator together with a dc voltage bias are used in the processing circuit containing a semiconductor capacitor as the sensitive optical transducer. The main advantages of these proposed low-cost transducers is the direct pulse width modulated (PWM) output electric signal, with a duty that can change from 2 to 98% under microwatts´ variations of the incident light intensity. This transducer does not need an A/D converter, which may be important for several applications, such as automatic control, robotic, feedback electronic systems, and non-contact optical position sensing for nulling and centering measurements. The operating principles, mathematical modeling and experimental results of this novel transducer are considered in detail in this work.