Linearized Darlington Cascode Amplifier Employing GaAs PHEMT and GaN HEMT Technologies

This paper reports on the results of a new Darlington cascode (DCAS) feedback amplifier topology implemented with 0.5 mum E-mode GaAs PHEMT technology. The Darlington cascode employs active self-bias and a linearizing Darlington cascode circuit for achieving enhanced gain and IP3-bandwidth performance. The Darlington cascode achieves 12.5 dB gain with a 16 GHz 3 dB bandwidth (BW)-a 60% BW improvement over an equivalent conventional Darlington amplifier design. The DCAS obtains an IP3 of 29 dBm with a 13 GHz BW-an 80% improvement in IP3-BW over the conventional Darlington approach. These improvements have been obtained without significantly compromising noise figure, stability, or bias robustness. The DCAS amplifier design approach was also successfully applied to a high-voltage GaN HEMT technology and resulted in greater than 1 W output power over a multi-octave 1-4GHz band. The DCAS topology offers an approach for compacting high microwave performance into a small area without the use of distributed or reactive matching techniques.