IMPLEMENTATION AND MEASUREMENT RESULTS

The dual-bias network is verified with a DPA designed for 5G mobile communications in the frequency band of 3.4 to 3.6 GHz. Figure 5 is a photograph of the dual-bias DPA. It is fabricated on a 30 mil thick Rogers RO4350B substrate with a 3.48 dielectric constant. Cree CGH40010F GaN HEMTs are used for both the carrier and peaking amplifiers. The carrier amplifier is set to Class AB with a gate bias of -2.75 V. The peaking amplifier operates in Class C with gate bias of -6 V. Referring to the transistor datasheet, the drain operating voltages of both amplifiers are set to 28 V.

Figure 5

Figure 5 Fabricated GaN DPA.

Figure 6

Figure 6 Measured and simulated gain and drain efficiency vs. output power, 3.4 to 3.6 GHz.

 
Figure 7

Figure 7 Measured ACLR at 3.5 GHz.

The curves of the gain and efficiency of the DPA as a function of output power are shown in Figure 6. Saturated output power can reach more than 43 dBm. Compared with the simulated efficiency, at low output power, the measured efficiency is higher and at higher output power, the measured efficiency is about three percentage points lower. The drain efficiency at saturation is above 70 percent. When the output power is backed off 6 dB, it is in the range of 51 to 55 percent. The efficiency is higher than 43 percent when the output power is backed off by 8 dB. Measured gain is slightly lower than simulated. When approaching saturated output power, gain appears to compress, but the average measured gain is greater than 10 dB.

At the 3.5 GHz center frequency a 20 MHz LTE modulation signal with a peak-to-average power ratio of 7.1 dB is used to drive the DPA. The measured ACLR is shown in Figure 7. Upper and lower sidebands are -32.1 and -31.9 dBc, respectively, with an output power of 42.7 dBm. After the addition of DPD they are -46.6 and -47.5 dBc, respectively.

Table 1 provides a performance comparison with other published DPAs, showing improved drain efficiency and ACLR.

t1.jpg

CONCLUSION

A new type of dual-bias network structure widens RFPA VBW and reduces the memory effect. To verify this, a DPA operating from 3.4 to 3.6 GHz is designed and fabricated. The ACLR measured with DPD is lower than -46 dBc when using a 20 MHz LTE modulation signal with a PAPR of 7.1 dB. This shows that the dual-bias structure not only widens the VBW and reduces the memory effect, but is also easily implemented.

ACKNOWLEDGMENTS

This work is supported by National Natural Science Foundation of China (No. 61871169).

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