Patent ID: 7167491

Claim:
A laser transmitter, comprising: an input stage receiving a first pair of differential signals and generating a second pair of differential signals with a steady voltage swing in response to the first pair of differential signals; a control circuit outputting a digital control signal; a limiting amplifier, comprising: a first variable resistor having an input terminal coupled to a rail; a second variable resistor having an input terminal coupled to an output terminal of the first variable resistor; a third variable resistor having an input terminal coupled to the output terminal of the first variable resistor, wherein at least one of the first, the second, and the third variable resistors has a control terminal couple to receive the digital control signal; a differential pair comprising: a first bipolar transistor having: a collector coupled to an output terminal of the second variable resistor; a base coupled to receive a first signal from the second pair of differential signals; a second bipolar transistor having: a collector coupled to an output terminal of the third variable resistor; a base coupled to receive a second signal from the second pair of differential signals; a first current source having: an input terminal coupled to the collector of the first bipolar transistor; a second current source having: an input terminal coupled to the collector of the second bipolar transistor; wherein output terminals of the first and the second current sources output a third pair of differential signals having (a) an improved rise and fall time over the second pair of differential signals and (b) an amplitude characteristic prescribed by the digital control signal; a laser driver receiving the third pair of differential signals and generating a drive signal in response to the third pair of differential signals; and a light source receiving the drive signal and generating a light in response to the drive signal.