IMD elimination and CPR improvement for an 800 MHz HBT MMIC power amplifier

This paper describes a novel technique for reducing the third order intermodulation (IMD) product and ACPR levels in HBT power amplifiers. This technique is based on the dynamic control of the injection/feedback of the second harmonic frequency signal to the amplifier. For a cellular frequency HBT MMIC power amplifier, a reduction of 44 dB in the 3rd order IMD level is measured at 28 dBm output power. By controlling the phase and amplitude of the injected/fedback second harmonic, a total rejection of IMD products over a wide dynamic range of input power is achieved without any change in the fundamental signal levels. The ACPR for CDMA system (IS-98 standard) over a 30 kHz bandwidth with /spl plusmn/900 KHz offset shows a 6 dB improvement. No degradation in the CDMA signal quality factor (/spl rho/) and PAE (40%) are observed. To the best of our knowledge this is the first application of this technique to HBT power amplifiers.