10-Gb/s driver amplifier using a tapered gate line for improved input matching

The use of a tapered gate line in a distributed amplifier (DA) is investigated and applied to the design of a GaAs monolithic microwave integrated circuit 10-Gb/s optical driver amplifier. Improved input matching is achieved near the cutoff frequency by reducing the characteristic impedance successively along the gate line toward the termination. With the improved matching conditions, the voltage ripple on the final resistor termination is reduced. The degree of tapering that can be employed is limited by the low-frequency gain and matching requirements. Detailed analysis and simulation results are used to investigate the advantage of this technique. To demonstrate its practical use, the performance of a 10-Gb/s DA fabricated with Filtronic Compound Semiconductor´s 0.5-μm pseudomorphic high electron-mobility transistor technology is presented.