Multi-Cascode Cell Design for Increased Broadband Power 0.1 um GaAs pHEMT MMICs up to V-Band

A comparative analysis of the DC and RF performance between single and multi-cascode cells for high frequencies (to V-band) and higher power MMIC operation is presented. This paper compares the power capabilities of a 0.1 µm GaAs pHEMT 2x25 µm single cascode cell with that of a 2x12 µm double-stacked (multi) cascode cell for the design of enhanced output power, broadband MMICs. A load line comparison for the two types of cascode cells shows that a similar maximum output power (Pdcmax) can be obtained from a 2x12 µm double-stacked cascode, when driven over a higher drain voltage swing at lower current, to that from a 2x25 µm single cascode. Moreover, measured data confirms higher Maximum Available Gain (MAG) up to 47 GHz and higher reverse isolation up to 75 GHz for double-stacked class-A operation. Also, a larger bandwidth can be achieved using the smaller devices with lower capacitances. Considering stability, 2x12 µm double-stacked configuration exhibits a lower negative output resistance as compared to the 2x25 µm single cascode. Thus, double-stacked (multi) cascode cell shows better RF performance, with no significant increase in unit cell layout width as compared to single cascode cell, leading to its potential utilization in the design of GaAs pHEMT based, high power MMICs such as Travelling Wave Amplifiers (TWA) up to V-band.