Monolithic distributed amplifier with active control schemes for optimum gain and group-delay flatness, bandwidth, and stability

In this paper, active control schemes are presented to optimize the performance of the distributed amplifier (DA) subject to the process variation. A detailed analysis of the DA with mismatched termination loads has been performed, which reveals that pronounced gain and group-delay ripple arises at the low-frequency end from the reflected waves in the artificial transmission line. To solve this problem, an active variable resistor is proposed as the gate-line termination load. The gain and stability of the cascode DA has also been analyzed, which identifies the most critical component determining the tradeoff between the gain-bandwidth product (GBP) and the stability to be the gate feedback resistor of common-gate field-effect transistor. It is also replaced with the active resistor to maximize GBP, while avoiding oscillations. A nine-section cascode DA with active control features is designed and fabricated using commercial GaAs pseudomorphic high electron-mobility transistor foundry. The measurement shows that the gain and group-delay ripple can be minimized, and GBP can be maximized without oscillations by the active bias controls. Active control schemes allow the monolithic DAs to be fine tuned after the fabrication and, thus, can be a robust DA design methodology against process variation and inaccurate device models.