Patent ID: 7714515

Claim:
A system for driving at least one light-emitting diode (LED) comprising: an output terminal connectable to an anode of the LED and at which an output voltage can be provided for the LED; and a driver loop connectable to a cathode of the LED and operable to maintain a LED current flowing through the LED at a desired level, thereby attenuating modulation error attributable to voltage variations at the cathode of the LED, wherein the driver loop comprises: a first transistor through which a bias current flows, the first transistor having a drain, a source, and a gate; a second transistor through which the LED current flows, the second transistor having a drain, a source, and a gate; and a modulation error attenuation component connected to the first transistor and the second transistor and operable to maintain the drain of the first transistor at the same voltage level as the drain of the second transistor and further operable to maintain the gate of the first transistor at the same voltage level as the gate of the second transistor, wherein the modulation error attenuation component comprises: a third transistor connected in series with the first transistor; a first operational amplifier having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is connected to the drain of the third transistor, the second input terminal is connected to the output terminal, and the output terminal is connected to the gates of the first and second transistors; and a second operational amplifier having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is connected to the drain of the second transistor, the second input terminal is connected to the drain of the first transistor, and the output terminal is connected to the gate of the third transistor.