GaN HEMT Low Noise Amplifiers for Radio Base Station Receivers

Licentiate thesis, 2012

Gallium nitride (GaN) high electron mobility transistor (HEMT) has been introduced as the technology of choice for high power microwave applications due to its material properties including high saturation electron velocity and breakdown field together with excellent thermal conductivity and robustness. It is also a promising candidate for receiver front-ends in the radio base station(RBS) where low noise figure and high linearity are key issues for low noise amplifier (LNA) design. The objective of this work has been to study the key properties of GaN HEMT LNAs in terms of linearity and noise performance, within frequency band of 1-3 GHz, for radio base station receiver front-end design. A well-designed GaN HEMT LNA technology would eventually challenge existing RBS commercial LNA platforms such as gallium arsenide (GaAs) pseudomorphic high electron mobility transistor (pHEMT). In the first part characterization and design of a highly linear single-stage common-source GaN HEMT MMIC LNA with operational frequency of 3 GHz is presented. The main target was to investigate linearity and the trade-off between key parameters such as output third order intercept point (OIP3), noise figure (NF) and dc power consumption (Pdc). At 3 GHz the single-stage LNA showed a measured OIP3 of 39 dBm with Pdc = 2.1 W. The measured minimum NF was 1.5 dB which was around 1 dB higher than existing commercial GaAs pHEMTs. The second part deals with two hybrid LNA solutions, two-stage commonsource cascade LNA with operating frequencies of 1-3 GHz and single-stage cascode LNA designed for 1.5 GHz. Both hybrid designs were based on available commercial GaN HEMTs. The objective was to obtain low NF (≤ 1 dB) and high OIP3 (≥ 40 dBm) with a maximum dc power consumption of 2 W. The fabricated two-stage common-source LNA produced an OIP3 of 42 dBm with a NF equal to 0.5 dB. The dc power consumption was measured to be 1.2 W. With a OIP3/Pdc ratio of 13.2 the LNA may challenge present commercial GaAs pHEMT LNA solutions for RBS. The single-stage cascode LNA exhibited minimum NF of 0.6 dB. Compared to two-stage common-source topology the single-stage cascode LNA introduced OIP3 = 35 dBm but at 50% less Pdc. Keywords: radio base station receiver, high electron mobility transistor (HEMT), gallium nitride (GaN), low noise amplifier, cascode, cascade, high linearity, low noise, robustness.