A Wideband Gain-Enhancement Technique for Distributed Amplifiers

In this article, a new bandpass distributed amplifier (DA) using a wideband gain-boosting technique is presented. In particular, a feedback network, including a series inductor and a shunt capacitor, is used to generate two peaks at the lower and upper cutoff frequencies of the amplifier's bandpass response. This technique provides a gain enhancement over a wide bandwidth without sacrificing the upper cutoff frequency. A detailed analysis of the two frequencies peaking effect is carried out to support the theory. To verify the concept, a conventional and a gain-enhanced DA are fabricated in an indium-phosphide (InP) heterojunction bipolar transistor (HBT) process. The gain-enhanced DA exhibits a measured gain of 10.5 dB with a 4-dB gain improvement compared with the conventional one, covering a 3-dB bandwidth from 60 to 145 GHz. The maximum saturated (P-sat) is 20.9 dBm at 75 GHz with the measured 1-dB compression power (P-1dB) of 18.5 dBm. The dc power consumption is 440 mW, and the chip size is 1.6 mm x 0.6 mm. To the best of our knowledge, the proposed DA achieves the highest gain boosting over a broad bandwidth compared with the published works.