Patent ID: 8148903

Claim:
An apparatus comprising a light emitting diode (LED) driving circuit configured to drive at least one LED, wherein the circuit comprises: an optical sensor configured to receive light emitted from said at least one LED and generate a feedback signal corresponding to an amount of light received by the optical sensor; and a current regulator configured to regulate an amount of current flowing into said at least one LED according to a comparison of the feedback signal with a first reference signal, wherein the current regulator comprises: a first reference signal generator configured to generate the first reference signal, a comparator configured to compare a level of the feedback signal with a level of the first reference signal; a first transistor connected between a negative electrode of said at least one LED and a reference voltage source, where the first transistor is driven in response to the comparison of the feedback signal with the first reference signal; and a first load connected between the first transistor and the reference voltage source, wherein the first reference signal generator comprises: an operational amplifier comprising a positive input terminal configured to receive a second reference signal; a second load connected between a negative input terminal of the operational amplifier and the reference voltage source; a second transistor configured to supply a reference current to the second load in response to an output of the operational amplifier; a current mirror configured to generate a mirror current of the reference current; and a first resistor, wherein the mirror current flows into the first resistor and wherein the first reference signal corresponds to a voltage across both ends of the first resistor.