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Presented is the linearity improvement technique of a power amplifier (PA) using a digitally-controlled tunable output matching network implemented in GaAs BiFET technology. The load impedance of the heterojunction bipolar transistor (HBT) power device in the last stage of the PA is adjustable in terms of output power levels by a metal-insulator-metal (MIM) capacitor array with pHEMT switches in the output matching network. A 2.4 GHz two-stage PA for IEEE 802.11g, Wireless Local Area Network (WLAN) application, is implemented to demonstrate the technique. Not only is the maximum linear output power of the PA increased by 2.5 dB, but the linearity is also improved by 4 dB at the output power of 15 dBm for the error vector magnitude specification of -28 dB.
Presented is the linearity improvement technique of a power amplifier (PA) using a digitally-controlled tunable output matching network implemented in GaAs BiFET technology. The load impedance of the heterojunction bipolar transistor (HBT) power device in the last stage of the PA is adjustable in terms of output power levels by a metal-insulator- metal (MIM) capacitor array with pHEMT switches in the output matching network. A 2.4 GHz two-stage PA for IEEE 802.11g, Wireless Local Area Network (WLAN) application, is implemented to demonstrate the technique. Not only is the maximum linear output power of the PA increased by 2.5 dB, but the linearity is also improved by 4 dB at the output power of 15 dBm for the error vector magnitude specification of 228 dB. Introduction: The continuous increase in high data rate requirements over the past several years drives the dominance of the wireless standard, IEEE 802.11 a/b/g/n, which is called WLAN. The WLAN uses maximum 64 quadrature amplitude modulation (QAM) signal with the OFDM scheme, which can transmit the data rate up to 54 Mbits. The 64-QAM OFDM signal allows high data rate transmission, however it requires a highly linear power amplifier (PA) because of a high peakto- average ratio. The linearity of the WLAN PA is generally evaluated through the error vector-magnitude (EVM) because information is carried on both the magnitude and the phase of a signal. Therefore, EVM is one of the key parameters for WLAN PA development along with gain and efficiency.
There have been efforts...