A 10-Gb/s laser/modulator driver IC with a dual-mode actively, matched output buffer

A laser/modulator driver IC for 10-Gb/s-SONET OC-192-fiber optic transmitte rs is described. Depending on the user application, the IC is capable of dr iving more than 100 mA of current into a laser diode or over 50 mA into an electro-absorption or Mach-Zehnder modulator. Rise and fall times below 20 pS are achieved. The driver employs a novel dual-mode actively matched outp ut buffer that provides a dc-coupled back termination of either 25 or 50 Om ega. Compared to an output buffer with a resistive termination, this buffer dissipates only half as much power. In addition, the buffer has the abilit y to reject external bias and mill therefore not load bias sources used to set laser threshold currents and modulator offset voltages. The low power c onsumption makes the IC most suitable for co-packaging with uncooled lasers and electro-absorption modulators. The driver is fabricated in a 0.25-mum gate length production GaAs PHEMT process with substrate thru vias, thin-fi lm resistors, and MIM capacitors.