# Agnostic Envelope Linearization of Dynamically Supplied Power Amplifiers for Mobile Terminals
## 3 Experimental Setup and Linearization Results
### Experimental Results with the NR-60 MHz Test Signal
With the EOPT linearization approach, instead, since the ETM output is not available, canceling the RF leakage is not the objective. As observed in the AM-AM plot in Figure 11-right, the RF leakage is not compensated at the ETM output (\(Env_{out}\)) after EOPT linearization; instead, as it will be shown later, the resulting supply envelope is optimized for linearity at the ET PA output. Figure 9: Power efficiency, NMSE, and ACPR performance per iteration of different linearization approach. Time domain plots of different supply envelopes are depicted in Figure 12. As observed, \(Ent_{out,0}\), which is the envelope at the ETM output when no linearization is applied, contains high-frequency leakage in comparison to the generated envelope \(Ent_{gen}\). Most of the RF leakage can be compensated with the ELC linearization approach, as observed in \(Env_{out,ELC}\) in Figure 12. Instead, \(Ent_{out,EOPT}\) (i.e., the supply envelope after EOPT linearization) does not show any RF leakage compensation. However, the resulting supply envelope after EOPT linearization is optimized for linearity at the ET PA output. In any case, neither \(Ent_{out,ELC}\) nor \(Ent_{out,EOPT}\) envelopes exceed the ETM's linear amplification limitation (around 3.8 V). Figure 11: AM–AM plot of the normalized generated envelope (\(Env_{gen}\)) and the ETM output envelope difference (i.e., \(Env_{out}-Env_{gen}\)). Figure 10: AM–AM plot of the normalized baseband input and ET PA output. Figure 13 shows the spectra of different supply envelopes before and after applying different linearization methods. By considering a vertical margin of 40 dB, the generated SR envelope (\(Env_{gen}\)) has around 100 MHz bandwidth. The supply envelope at the ETM output without linearization has around 140 MHz bandwidth, i.e., the RF leakage has a bandwidth of around 140 MHz. Consequently, both the ELC or EOPT linearization approaches will generate an envelope optimization signal mostly within this bandwidth. After applying GMP-based I-Q DPD, the ETM output spectrum shows a spectral regrowth above 60 MHz. Despite the fact that the GMP-based I-Q DPD generates an I-Q predistorted signal targeting the linearization of the ET PA, part of the linearized RF signal is leaked to the ETM output and combined with the supply envelope, degrading again the linearity at the ET PA output. After ELC linearization, the spectrum of the ETM output is very close to the spectrum of the generated envelope \(Env_{gen}\), although there are some variations from 60 to 150 MHz. As observed, the purpose of EOPT linearization is not canceling the RF leakage, since the spectrum of the ETM output does not resemble the generated envelope. However, as shown in Figure 14, thanks to the EOPT linearization, the linearity requirements are met at the ET PA output. Figure 14 presents several ET PA output spectra when considering different linearization approaches. Without applying any linearization, the output spectrum shows strong leakage at its adjacent channels, with a significant spectral regrowth at around 60 MHz away from the center frequency. This specific spectral regrowth can be somehow compensated by the GMP-based I-Q DPD (including cross memory and high-order terms). However, as shown in Figure 14, the ET PA output spectra after GMP-based I-Q DPD fails to further compensate for the distortion at higher frequencies. Instead, when considering the linearization approaches at the supply envelope path (i.e., the ELC or EOPT), the overall spectral regrowth is mitigated, despite the fact that the peaks appearing at 60 MHz can still be appreciated. Although both envelope linearization approaches are enough to meet the linearity specifications (i.e., ACP \(<-36\) dBc), to further improve the overall ET PA linearity, these can be combined with the conventional I-Q DPD linearization. Figure 15 shows ET PA output spectra when both ELC and EOPT envelope linearization techniques are combined with GMP-based I-Q DPD (i.e., ELC+GMP and EOPT+GMP, respectively).