A 100 W GaN HEMT SPA-D with 57% fractional bandwidth for DVB-T applications

Abstract

This paper presents the design of a high power, broadband sequential power amplifier with Doherty-type active load modulation (SPA-D) for DVB-T applications. By designing the SPA-D at device level, the bandwidth limitation due to device parasitics and the frequency dependence of peaking output impedance can be mitigated. External capacitors are used in combination with the device output capacitances and package parasitics to form very short transmission lines (TL) having characteristic impedances of the corresponding device optimum impedances. In this way, the fractional bandwidth (FB) of SPA-D can be extended up to 60%. The high power SPA-D demonstrator exhibits measured drain efficiency of 45%-67.5% at 8 - 10 dB power back-off (BO) and 54%-79% at peak power of ≥ 100 W over 460 MHz-830 MHz (~ 57% FB). At 710 MHz, a measured power added efficiency (PAE) of 70 % and 62.5 %are achieved at 50.5 dBm output power and 8 dB BO, respectively. To the best of our knowledge, this PA has the highest performance in terms of efficiency and bandwidth for DVB-T application to date.