Lucent Technologies Inc.

Agere Systems Inc.

Gregory C Salvador

Johannes Gerardus Ransijn

James D Yoder

Fridolin L Bosch

Dwight David Daugherty

James Daniel Yoder

Kenneth D Gaynor

A system and method are provided for providing an impedance match of an output buffer to a transmission line without significantly increasing the power consumption of the output buffer. A system and method are also provided for providing an impedance match of an output buffer to a transmission line, while still allowing for an adjustable output swing as is required for loads such as laser transmitters and optical modulators.

System and method for providing an impedance match of an output buffer to a transmission line

A digital driver circuit with increased maximum output voltage amplitude and therefore also increased maximum current amplitude for constant power supply voltages is provided. A current sensing resistor replaces the conventional current source transistor in the output stage of the driver circuit. In addition, the output current control circuit is applied to an earlier stage of the driver. An automatic output current control scheme is created which keeps the voltage across the current sensing resistor equal to a DC reference and therefore maintains the output current or voltage amplitude by actively level shifting the DATA and DATA drive signals for the output stage to the correct level. This eliminates the necessity to incorporate a voltage safety margin and simultaneously increases the maximum available output voltage amplitude. Therefore, by utilizing the current sensing resistor and by moving the output amplitude control circuit to an earlier stage of the driver circuit, the driver circuit of the present invention provides increased output voltage and current amplitudes to drive modulated devices. In another embodiment, the automatic output amplitude control scheme is created by keeping the voltage across the current sensing resistor equal to a Mark-Bar reference signal corresponding to input data.

Digital driver circuit

A dynamic laser diode drive circuit is formed so that the gain of the final gain stage is controlled in association with the level of the drive current supplied to the laser diode. In particular, the current sources associated with the final gain stage and the output stage and commonly controlled so that the gain tracks the current level. That is, in situations required a relatively low current, the gain is minimized to prevent overdriving the output stage (a situation common in prior art arrangements). When a larger laser drive current is required, the gain of the final stage is adjusted to increase the output from this stage and provide a sufficient voltage differential to drive the output stage.

Dynamic control for laser diode drivers

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Wernersville, PA, United States of America

Gregory C Salvador