A Multiple-Time-Scale Analog Circuit for the Compensation of Long-Term Memory Effects in GaN HEMT-Based Power Amplifiers

In this article, we present an analog circuit for the compensation of long-term memory effects in power amplifiers (PAs) based on GaN high-electron-mobility transistors (HEMTs). The analog compensation circuit (ACC) is supported on a charge-trapping behavioral model that features a state-dependent variable emission time constant, rather than a fixed emission time constant. This allows not only for the more accurate modeling and compensation of the nonlinear long-term memory effects experienced by GaN HEMT-based PAs, but also for the adaptation of the dynamics of the ACC to varying operating conditions, such as the ambient temperature. We demonstrate that the proposed ACC is able to successfully eliminate any multiple-time-constant transient symptom of current collapse following a high-power radio-frequency pulse or two-tone excitation and accurately preserve the class of operation of a GaN HEMT-based PA. Moreover, we also demonstrate that the proposed ACC can aid the linearization of GaN HEMT-based PAs for fifth-generation (5G) New Radio (NR) communications, allowing for the reduction in the complexity of the digital predistorter. For a 5G NR time-division duplexing signal with a bandwidth of 20 MHz, the inclusion of the ACC improved out-of-band emissions by over 15 dB and improved the error-vector magnitude by over 10 p.p. at essentially no cost to the PA's power-added efficiency.