Wide-band CDMA distortion characteristics of an AlGaAs/InGaAs/AlGaAs heterojunction FET under various quiescent drain current operations

Wide-band CDMA (W-CDMA) distortion characteristics of a fabricated double-d oped heterojunction FET (HJFET) are presented, Measured results demonstrate that the first and second adjacent channel W-CDMA adjacent channel leakage power ratios (ACPRs) of the HJFET are correlated to the third- and fifth-o rder intermodulation (IM3 and IM5) distortions respectively under various q uiescent drain current operation (I-q). A first channel ACPR dip phenomenon is observed under a low I-q condition, resulting in improved power added e fficiency. Due to its close correlation to the IM3 distortion, the ACPR dip phenomenon is explained in terms of the similar IM3 characteristic. Simula ted results reveal that the dip is a consequence of the cancellation of dis tortions generated by the third- and fifth-order nonlinearities at the IM3 frequency. The conditions for the cancellation are detailed.