Distortion analysis of a power heterojunction FET under low quiescent drain current for 3.5 V wide-band CDMA cellular phones

The dependence of adjacent channel leakage power ratio (ACPR) of a heterojunction FET (HJFET) on quiescent drain current (I/sub q/) for wide-band CDMA (W-CDMA) cellular phones application is presented. Measured performance demonstrates an ACPR dip phenomenon under a low I/sub q/ condition resulting in a significant improvement on the power added efficiency of the HJFET with the ACPR maintained within the specification. It is found that the W-CDMA ACPR characteristic mainly correlates to the third-order intermodulation (IM/sub 3/) distortion of the HJFET. The ACPR dip arises from a similar characteristic on the IM/sub 3/ distortion under a low I/sub q/ operation.