AWR Application Notes

Design of a HighEfficiency Broadband GaN HEMT Doherty Amplifier for Cellular Transmitters

Issue link: https://resources.system-analysis.cadence.com/i/1355092

Contents of this Issue

Navigation

Page 4 of 7

AWR Software for the Design of a High-Efficiency Broadband GaN HEMT Doherty Amplifier for Cellular Transmitters 5 www.cadence.com/go/awr The impedance conditions at different points of the load network of the peaking amplifier when it is turned off are shown in Figure 6, where Z match shown in Figure 6a indicates low reactance at the output of the load network over the required frequency range from 1.8-2.7GHz, having near-zero reactance at the mid-band frequency with some inductive and capacitive reactances when the operating frequency approaches the bandwidth edges. At the same time, by using a series transmission line one quarter-wavelength long at high-band frequency, an open-circuit condition is provided at higher band frequencies with suffi- ciently high inductive and capacitive reactances across the frequency bandwidth, indicated by Z peaking shown in Figure 6b. Hence, the broadband performance of such an inverted Doherty structure can potentially be achieved in a practical realization. Figure 6: Impedances for peaking amplifier Figure 7a shows the load-network equivalent circuit for a carrier amplifier with a frequency behavior of the impedance Z carrier seen by the carrier device, whose real component slightly varies around 10ohms, shown in Figure 7b. This means that, taking into account the device output shunt capacitance C out of about 5pF and series output inductance L out provided by the overall bond wire and package leadframe inductances, the impedance seen by the device multi-harmonic current source at the fundamental frequency across the entire frequency bandwidth of 1.8-2.7GHz has been increased by two times from the initial 5ohms at the input of the broadband output impedance transformer. This is a high enough impedance to achieve high efficiency at backoff output power levels. Figure 7: Matching network and load impedance for carrier amplifier a) b) a) b)

Articles in this issue

Links on this page

view archives of AWR Application Notes - Design of a HighEfficiency Broadband GaN HEMT Doherty Amplifier for Cellular Transmitters