Investigation of direct-coupled amplifier topologies for wireless communication systems using normally-on mHEMT technology

This paper presents direct-coupled DC-50 GHz two-stage baseband amplifier topologies realized in a 35nm gate-length InAlAs/InGaAs mHEMT technology. These are key components of future single-chip receiver MMICs for point-to-point communication systems. Three interstage coupling approaches are investigated: resistive coupling, a diode-level-shifter and a Kukielka amplifier. The Kukielka amplifier features the best performance in terms of gain-bandwidth-product and represents the state of the art for this topology. The investigated two-stage amplifier circuits achieve up to 21 dB gain and a 3 dB bandwidth of 53 GHz, requiring less than 300x300um2 chip area. The presented level-shifter circuit has a 3 dB bandwidth of up to 150 GHz and an insertion loss of less than 3.5 dB.