Patent ID: 7630422

Claim:
A driver for a vertical-cavity surface emitting laser (VCSEL), comprising: a bias current source having an input and operable to generate at a first output a bias current and an output voltage for the VCSEL and to generate at a second output a replica output voltage; a modulation current source coupled to the bias current source by at least one switch and operable to generate a modulation current for the VCSEL when the switch is closed; and an output tracking circuit having first and second inputs coupled, respectively, to the first and second outputs of the bias current source, the output tracking circuit operable to compare the output voltage and the replica output voltage and generate at an output a feedback signal based on a result of the comparison, the output of the output tracking circuit coupled to the input of the bias current source, the bias current source further operable to generate the output voltage and the replica output voltage by matching the output voltage and the replica output voltage based on the feedback signal; wherein the bias current source comprises a digital-to-analog converter having a plurality of cells, each cell comprising (i) a first transistor operable to generate the bias current and the output voltage for the VCSEL and (ii) second and third transistors operable to generate the replica output voltage.