Sungchul Hong

Weighted Polynomial Digital Predistortion for Low Memory Effect Doherty Power Amplifier

We have proposed a simple and effective weighted polynomial digital predistortion algorithm, which consists of weighting, least square polynomial fit, and de-weighting. The weighting factor is introduced to describe the signal distribution statistics and high harmonic generation at a high power region to improve accuracy of the error function. A low memory linear Doherty power amplifier (PA) has been realized with two 90-W peak envelope power LDMOSFETs using memory effect reduction techniques, and the proposed algorithm has been applied to the PA. For the forward-link wideband code division multiple access 3FA signal, the adjacent channel leakage ratio performance at 5-MHz offset is -56 dBc with power-added efficiency of 20.78% at an average power of 40 dBm. The proposed weighting polynomial algorithm provides a significantly reduced error power and superior convergence behavior with improved linearization capability than the conventional polynomial. Moreover, the low memory Doherty amplifier could be linearized for a wideband signal using the simple algorithm without any memory effect compensation

High Efficiency GaN HEMT Power Amplifier optimized for OFDM EER Transmitter

We have proposed a highly efficient power amplifier (PA) for the envelope elimination and restoration (EER) transmitter using gallium nitride (GaN) HEMT. The class AB, B, C and F mode PAs have been implemented with EUDYNAs 10 watts GaN HEMT and compared the bias modulation performances in order to investigate the optimum PA structure. The proposed class F mode PA has been biased at class C and adopted a new output matching topology that improves the overall transmitter efficiency. For the WiMAX OFDM signal, the calculated overall drain efficiencies of the optimized EER amplifier, which are based on the measuremed bias dependent efficiencies, are about 73 % at an average power of 31 dBm at 2.14 GHz. The proposed highly efficient bias modulation PA for the EER transmitter provides a superior overall efficiency than that of any conventional switching or saturation mode PAs.

GaN HEMT Based Doherty Amplifier for 3.5-GHz WiMAX Applications

We have implemented a Doherty amplifier for 3.5- GHz world interoperability for microwave access (WiMAX) applications using Eudyna 90-W (P3dB) gallium-nitride (GaN) high electron mobility transistor (HEMT) because of the poor efficiency of a standard class AB amplifier when the linearity performance is good. The load modulation performance of the GaN HEMT device for the Doherty operation is rather moderate but workable. The linearity is improved using the in-band error cancellation technique of the Doherty amplifier. The implemented Doherty amplifier has been designed at an average output power of 43 dBm, backed-off about 8 dB from the 51 dBm (P3dB). For WiMAX signal with 28 MHz signal bandwidth, the measured drain efficiency of the amplifier is 27.8%, and the measured relative constellation error (RCE) is -33.17 dB, while those of the comparable class AB amplifier are 19.42% and -24.26 dB, respectively, at the same average output power level.