Patent ID: 7486386

Claim:
A proximity sensor comprising: one or more wavelength transmitting light-emitting diodes; one or more wavelength receiving photodiodes; a photocurrent receiver connected to the photodiode and consisting of a transimpedance amplifier; an ambient correction circuit for calibrating DC ambient in a signal generated at the receiving photodiode(s) immediately prior to a reflectance measurement, the circuit constructed as a gyrator from a transconductance amplifier, a capacitor which stores the voltage analog of the DC correction current, and a voltage to current circuit, MOS transistor, for producing the correction current ambient signal at a known rate, the period above a fixed receive-detect threshold required to cancel the DC ambient used to produce a pulse width proportional to the DC ambient signal, the same gyrator circuit used during a subsequent proximity cycle to convert an increase in input signal due to reflection above a fixed receive detect threshold into a pulse width proportional to the reflectance signal; a pulse width comparator circuit for comparing a pulse width signal proportional to the reflected signal against a preset pulse width value to detect proximity; a transmitter connected to light-emitting diode(s), which emit light pulses that are reflected by an object in proximity and received at the photodiode; and a controller system that controls the these elements by continuously alternating a DC calibration cycle with a proximity measurement cycle or on demand first performs the DC calibration cycle followed by the proximity measurement cycle.