Transient Thermal Response Impact of 3.5GHz GaN HEMT Amplifier on TDD LTE Spectrum and Its Improvement Based on a Thermal Equivalent Circuit Approach

Thermal response of GaN HEMT amplifier under TDD operations causes ACLR degradation due to the fluctuation of output power. Transient response of the transistor channel temperature and corresponding output power is obtained analytically and numerically. Layered structure is modelled by Cauer thermal equivalent circuit where every thermal resistor and thermal capacitor is obtained assuming that the heat travels within a 45 degree angle range of mounting materials. The model also takes it into account that the amount of heat applied is changing according to the channel temperature because the dissipated power is determined by the output power that changes according to the channel temperature. It will be shown the model explains the experimental transient response of the ACLR degradation of a 2W-class 3.5GHz power amplifier. A potential measure to improve the response is also discussed.