44% efficiency operation of power heterojunction FET at near pinch-off for 3.5 V wide-band CDMA cellular phones

Abstract

This paper describes 1.95 GHz power performance of a double-doped AlGaAs/InGaAs/AlGaAs heterojunction FET (HJFET) operated at 3.5 V drain bias voltage for Wide-band CDMA (W-CDMA) cellular phone systems. An HJFET with a novel multilayer cap and a narrow recess structure showed a low on-resistance ( R on) of 1.4 ohm mm. With an optimum output impedance matching at a reduced quiescent drain current of 80 mA (less than 1% of the maximum drain current), the HJFET exhibited a high power added efficiency (PAE) of 44.2% with an output power of 600 mW (28.0 dBm) and an adjacent channel leakage power ratio (ACPR) of −43 dBc at 5 MHz off-center frequency. This high PAE obtained was ascribed to an ACPR dip behavior with respect to the input power at around the W-CDMA criteria. Through an ACPR simulation with measured AM–AM and AM–PM conversion characteristics, the AM–AM conversion characteristic was found to dominate the W-CDMA ACPR rather than the AM–PM conversion.