40-Gb/s High-Gain Distributed Amplifiers With Cascaded Gain Stages in 0.18-μm CMOS

A novel circuit topology for high-gain distributed amplifiers is presented in this study. Based on the conventional distributed architecture, the gain cells are realized by cascading cas- code stages for gain enhancement. In addition, the stagger-tuning technique is extensively utilized in the design of the cascode stages as well as the cascaded stages, leading to significant improvement in terms of the operating bandwidth and the gain flatness. With the proposed circuit architecture, two amplifiers are implemented in a standard 0.18-mum CMOS technology. The amplifier with a 3 times 3 configuration exhibits a gain of 16.2 dB and a 3-dB bandwidth of 33.4 GHz, while the one in a form of 2 times 4 demonstrates a gain of 20 dB and a bandwidth of 39.4 GHz. Consuming a dc power of 260 mW from a 2.8-V supply voltage, both circuits provide clear eye-opening with a pseudorandom bit sequence (PRBS) at 40 Gb/s.