Trapping Compensation for Transient Recovery in GaN LNAs

This study reports on the development of a novel trapping-effect compensation circuit (TECC) for improving the transient recovery of a transistor in GaN low-noise amplifiers (LNAs). The proposed TECC uses a transistor with the same type of traps as a compensated transistor in the LNA. The transient change in the on-resistance, caused by the traps of the transistor in the TECC, can be used to adaptively change the gate bias of the compensated transistor to improve the recovery characteristics immediately after the overdrive input. Moreover, the recovery characteristics at different temperatures can also be improved by the TECC because the time constant of the traps of the transistor in the TECC varies with the temperature in the same manner as the compensated transistor in the LNA. The recovery characteristics of GaN-HEMT with the TECC were simulated using a large-signal model that considers the trapping effect. The test elementary group (TEG) of the GaN-HEMT with the TECC for the measurement of recovery characteristics was fabricated, and the recovery characteristics were measured at 28 GHz. The output power change
$\Delta P_{\mathrm{out}}$
in the recovery characteristics was reduced from 2.4 to 0.2 dB at room temperature (300 K) and from 1.9 to 0.2 dB at high temperature (350 K) by applying the TECC. The measurements confirm the usefulness of the proposed circuit.