AWR Software for the Design of a High-Efficiency Broadband GaN HEMT Doherty Amplifier for Cellular Transmitters
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Figure 10 shows the measured power gain and drain efficiency of a transmission-line GaN HEMT inverted Doherty amplifier
across the entire frequency bandwidth for five frequencies. In this case, a power gain of more than 9dB was achieved in a
frequency range of 1.8-2.7GHz. At the same time, the drain efficiencies of more than 55 percent at saturation power P
3dB
and
around 50 percent at 7dB backoff output powers were measured across the entire frequency bandwidth, with maximum drain
efficiency of more than 70 percent at lower bandwidth frequencies below 1.95GHz and peak efficiency points at maximum
backoff output powers of around 6dB over the entire frequency range. The test conditions for concurrent transmission of
4-carrier global system for mobile communications (GSM) signal and a 10MHz LTE signal with a PAR of 8dB are shown Table 1.
Figure 10: Test performance of broadband two-stage inverted Doherty amplifier
Table 1: Test conditions for concurrent signal transmission.
As a result, the drain efficiency of 51 percent with an average total output power of 45.5dBm (18.2W for the GSM signal and
17W for the LTE signal) was achieved using an in-house digital predistortion (DPD) linearization scheme. Figure 11 shows
the spectral performance after dual-band DPD linearization of the broadband two-stage inverted Doherty amplifier: for the
four-carrier GSM signal with an out-of-band intermodulation level lower than −70dBc, as shown in Figure 11a, and for the
10MHz LTE signal with adjacent channel leakage ratio (ACLR) lower than −57dBc, as shown in Figure 11b.
Figure 11: Dual-band DPD linearization of broadband two-stage inverted Doherty amplifier: a) four-carrier GSM signal and b) 10MHz LTE signal
Test Conditions
DUT 1.8-2.7GHz 2 x 80W GaN HEMT
Signals Tested: 1850 4C GSM + 2650 10MHz LTE
GSM 4xCarrier Power 42.62dBm (18.2W)
LTE 10MHz 1 Carrier Power 8dB PAR 42.3dBM (17W)
Composite Signal PAR 7.1dB
Total RF Power 35.2W (45.5dBm)
Drain Efficiency 51%
a) b)
