Noise Measurements of Discrete HEMT Transistors and Application to Wideband Very Low-Noise Amplifiers

The noise models of InP and GaAs HEMTs are compared with measurements at both 300 and 20 K. The critical parameter, T-drain, in the Pospieszalski noise model is determined as a function of drain current by measurements of the 1-GHz noise of discrete transistorswith 50-Omega generator impedance. The dc I-V for the transistors under test are presented and effects of impact-ionization are noted. InP devices with both 100% and 75% indium mole fraction in channel are included. Examples of the design and measurement of very wideband low-noise amplifiers (LNAs) using the tested transistors are presented. At 20-K physical temperature the GaAs LNA achieves <10-K noise over the 0.7-16-GHz range with 16 mW of power and an InP LNA measures <20-K noise over the 6-50-GHz range with 30 mW of power.