Patent ID: 7601940

Claim:
An optical system, comprising: a room lighting unit comprising a light emitting diode (LED) operable in the visible spectrum; and a communication system comprising: the LED of the room lighting unit configured for providing illumination and further configured for operating in a pulsed mode of operation at a pulse rate that is unnoticeable to a human eye; and an optical communications unit configured to receive light transmitted by the LED and derive therefrom, data embedded in the light using the pulsed mode of operation, the optical communications unit comprising: a photodetector configured to receive light transmitted by the LED of the room lighting unit and generate therefrom, a photodetector output signal; a high-pass filter coupled to the photodetector, the high-pass filter configured for blocking frequencies corresponding to ambient room light that is incident upon the photodetector while passing a filtered signal containing frequencies corresponding to the pulsed mode of operation; a variable gain amplifier coupled to the high-pass filter, the variable gain amplifier configured to receive the filtered signal and provide a variable gain that is dependent upon a desired amplitude of an output signal of the variable gain amplifier; and a gain control circuit coupled to the variable gain amplifier, the gain control circuit comprising: a low-pass filter coupled to an output node of the variable gain amplifier, the low-pass filter configured for blocking frequencies corresponding to the pulsed mode of operation while passing a control voltage that varies linearly in correspondence to a peak-to-peak voltage of the output signal of the variable gain amplifier; and a gain control amplifier coupled to the low-pass filter, the gain control amplifier including a pair of gain-setting resistors and a reference voltage, which are used by the gain control amplifier for generating a gain control signal, wherein the reference voltage is selected based upon the desired amplitude of the output signal of the variable gain amplifier.