Patent ID: 7496121

Claim:
A laser modulating and driving device comprising: a modulation signal generating unit provided in a first substrate and configured to generate and output a laser modulation signal consisting of a pair of symmetrical small swing differential signals based on pixel data, the pair of symmetrical small swing differential signals swinging between a predetermined high voltage and a predetermined low voltage, wherein the predetermined high voltage is less than a supply voltage of a small swing differential signal output circuit of the modulation signal generating unit, and the predetermined low voltage is more than a ground voltage of the small swing differential signal output circuit and less than the predetermined high voltage, the modulation signal generating unit includes a modulation circuit configured to produce a modulation signal and the small swing differential signal output circuit configured to convert the modulation signal to the pair of small swing differential signals, the modulation signal generating unit has an output-stage inverter or buffer using a transistor, and at least one of a high potential and a low potential that defines a swing of said pair of small swing differential signals is generated by an ON resistance of the transistor; and a driving unit provided in a second substrate spatially separated and distinct from the first substrate and configured to drive a laser according to the laser modulation signal output and supplied from the modulation signal generating unit, the driving unit including a small swing differential signal input circuit configured to receive the pair of small swing differential signals.