Direct-coupled distributed baseband amplifier IC's for 40-Gb/s optical communication

We have developed GaAs MESFET baseband amplifiers using novel distributed amplification schemes. The key feature of their design is a direct coupling architecture employing two kinds of new distributed DC transformers. One is a distributed level-shift circuit and the other is a distributed source coupled FET logic (SCFL) level transformer. A two-stage distributed amplifier IC cascaded with the distributed level-shift circuit has a gain of 17 dB with a 0-to-30 GHz bandwidth. This is the best performance so far among all reported GaAs MESFET baseband amplifier ICs. A distributed baseband amplifier IC with the distributed SCFL level transformer connected by another distributed level-shift circuit also has a 0-to-30 GHz bandwidth with a gain of 7 dB. This is the first IC with an SCFL interface to have such broad-band characteristics.