Gain Boosting in Distributed Amplifiers for Close-to-f_max Operation in Silicon

In this paper, the challenges of designing distributed amplifiers at frequencies close to $f_{\text {max}}$ of transistors are tackled. By using bandpass transmission lines, the maximum operation frequency of the distributed amplifier is increased compared to low-pass transmission lines. Moreover, a novel gain-boosted cascode structure with an internal feedback is employed to cancel a part of the loss in the input line and boost the bandwidth and the highest operation frequency of the amplifier. The proposed amplifier operates up to frequencies as high as 0.67 $f_{\text {max}}$ of the transistors. Two proof-of-concept prototypes are fabricated in a 0.13- $\mu \text{m}$ SiGe process with $f_{\text {max}}$ of 210 GHz. The first prototype shows an average gain of 14.4 dB from 52 to 142 GHz (bandwidth of 90 GHz at the center frequency of 97 GHz) while the second one achieves an average gain of 18.6 dB from 48 to 135 GHz (bandwidth of 87 GHz at the center frequency of 91.5 GHz).