Analysis and Demonstration of Mm-Wave Distributed Amplifiers With Modified Artificial Transmission Line Model

In this article, we analyze the mm-wave distributed amplifiers (DAs) with a modified artificial transmission line (M-ATL) model which includes the parasitic inductance and capacitance of the transistors. The characteristic impedance and the cutoff frequency are analytically derived with the M-ATL model. It is found that the parasitic inductance reduces the cutoff frequency, thus limiting the DA bandwidth and can be optimized for the group-delay equalization. To confirm the accuracy of the M-ATL model, two mm-wave DAs - ultra-wideband DA (UWDA) and variable-gain DA (VGDA) - were demonstrated using a 250-nm InP DHBT process. The on-chip bias network and group-delay equalization of the DAs are analyzed to improve the bandwidth and gain flatness. The measurement shows that the UWDA exhibits an average gain of 11 dB over the frequency from 6 to 261 GHz. The VGDA shows an average gain variation from 1.5 to 11.1 dB over the frequency from 6 to 200 GHz.