Patent ID: 8592742

Claim:
A circuit for controlling current supplied to an optical sensor having a light emitting diode and photo-detector, the circuit comprising: a controller to generate a pulse width modulated signal at a first node, the controller coupled to the photo-detector of the optical sensor to receive signals indicative of light being detected by photo-detector; a low pass filter coupled to the first node, the low pass filter filtering the pulse width modulated signal into a constant voltage signal that is dependent on a duty cycle of the pulse width modulated signal and outputting the constant voltage signal on a second node; and a current amplifier coupled to the second node, the current amplifier converting the constant voltage signal into a current that is dependent upon the constant voltage signal and outputting the current to the light emitting diode of the optical sensor to cause the light emitting diode to illuminate, wherein the controller changes the duty cycle of the pulse width modulated signal based on the signals received from the photo-detector thereby changing the current that is supplied to the light emitting diode.