# Highly Linear 2.6 GHz Band InGaP/GaAs HBT Power Amplifier IC Using a Dynamic Predistorter
## 3 Implementation and Measurement Results  
Figure 6a displays a photograph of the implemented PAIC measuring 1.2 \(\times\) 1.1 mm\({}^{2}\), employing Winsemiconductor's 2 \(\times\) 1m InGaP/GaAs HBT process. Figure 6b shows a photograph of the module measuring 5 \(\times\) 5 mm\({}^{2}\) using a four-layer laminate. The diode-connected transistor and the shunt capacitor for the predistorter are integrated, whereas the \(R_{E}\) and \(L_{E}\) are external for tuning. The output-matching network consists of bond wires, surface-mount capacitors, and lines on the laminate. A \(V_{REF}\) of 3.1 V is supplied to the active bias circuits for both the driver and main stage.  
Figure 4: Schematic of the two-stage PA, including the proposed predistorter.  
Figure 5: Simulated performances of the two-stage HBT PAIC with and without the predistorter: (a) AM\(-\)AM and AM\(-\)PM characteristics, (b) ACLR using the 5G NR modulated signal.  
0.05 dB according to the AM\(-\)AM characteristics. These characteristics appear noticeably flatter. The AM\(-\)PM characteristics also demonstrate an improvement of more than \(3^{\circ}\).  
Figure 9 illustrates the measured performances of the PAIC for the carrier frequencies of 2.55-2.65 GHz using a 5G NR QPSK CP-OFDM signal with 273 RBs and a signal bandwidth of 100 MHz. Figure 9 presents the gain and PAE, while Figure 9 outlines the ACLR with and without the predistorter. At an average output power of 24.0 dBm, an ACLR below \(-40.0\) dBc was achieved with the predistorter, compared to approximately \(-34.4\) dBc without it. The gain and PAE at an average power of 24 dBm were recorded as 26.5-27.1 dB  
Figure 8: Measured AM\(-\)AM and AM\(-\)PM characteristics using a CW signal with and without the predistorter: (**a**) 2.55 GHz, (**b**) 2.65 GHz.  
Figure 7: Measured gain and PAE of the PAIC using a CW signal with and without the predistorter.  
and 11.8%, respectively. The measurement results of this study are summarized in Table 1. Compared to previous works, this study demonstrates exceptional ACLR performance using a modulated signal with a wide signal bandwidth of 100 MHz and a high PAPR of 9.7 dB. The relatively low PAE is primarily attributed to the significantly large OBO of 11 dB.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Ref.** & **Freq.** & **Ppeak** & **Modulated** & **PAPR** & **ACLR** & **Pavg** & **OBO** & **PAEavg** \\  & **(GHz)** & **(dBm)** & **Signal** & **(dB)** & **(dBc)** & **(dBm)** & **(dB)** & **(\%)** \\ \hline
[8] & 2.6 & 32.14 & LTE 20M & **-** & \(-47\) & 25.6 & 6.5 & 17.2 \\
[11] & 1.7–2.05 & 31 & LTE 20M & 7.88 & \(-30\) & 28 & 3 & 40 \\
[12] & 2.3–2.6 & 32.8 & 64-QAM & 6.1 & \(-33.2\) & 16.4 & 16.4 & 5 \({}^{*}\) \\
[13] & 2.3–2.7 & 35 & NR 20M & 10.83 & \(-34\) & 28–29 & 6–7 & 27 \\ This work & 2.5–2.7 & 35 & NR 100M & 9.7 & \(-40\) & 24 & 11 & 11.8 \\ \hline \hline \end{tabular}  
* Graphically estimated.  
\end{table}
Table 1: Performance summary and comparison to previously reported GaAs HBT PAICs.  
Figure 9: Measured performances of the PAIC using the 5G NR modulated signal for the carrier frequencies of 2.55\(-\)2.65 GHz: (**a**) gain and PAE, (**b**) ACLR with and without the predistorter.