Integrated circuits for 10-20 Gb/s lightwave systems

In order to determine the suitability of any integrated circuit technologies for regenerators at data rates of 10-20 Gb/s, it is necessary to consider the requirements generated by the overall system. The most stringent requirements, on a given IC technology, occur at the laser driver, in the linear channel (photoreceiver and post amplifiers), and in the timing recovery circuitry. The digital functions (demultiplexer, decision circuit, etc.), although consisting of straightforward digital building blocks, require careful optimization to attain the necessary speed with reasonable power dissipation. The laser or external modulator have drive requirements which include large AC current swings, as well as DC offsets. A typical DFB laser has a threshold of approximately 10-15 mA, and may require a drive current as large as 70-90 mA_p-p. If the laser is impedance matched to 50 ohms this translates to a drive voltage requirement of 4-5 V. External modulators have similar or greater voltage drive requirements, depending on their input impedance and type