MAX2831 Power Amplifier (PA) Output Power and Bias-Current Optimization

Introduction

The MAX2831 is a fully integrated transceiver with power amplifier (PA) for 802.11b/g applications. The bias current and output-matching network for the two-stage PA have been optimized to nominally deliver +18.5dBm while consuming 209mA from a 3.3V supply (at less than 5.6% EVM in 54Mbps (64-QAM) mode) while meeting 802.11g spectral mask requirements. At lower output-power levels, reprogramming the PA Bias Current Registers allows the bias current and overall PA current to be reduced for improved Tx efficiency while still meeting 802.11g requirements. When the PA bias current is optimized for +17dBm transmit power, a current savings of 26mA is achieved as compared with the nominal register setting. When operating at +3dBm transmit power, a current savings of 62mA is achieved as compared with nominal register setting. Further current savings can be achieved for a specific output-power level through optimization of the simple two-capacitor output-matching network.

Programming

Register 10 (A3:A0 = 1010) allows programming of the two-stage PA bias current. Bits D2:D0 allow optimization of the first-stage bias current, and bits D6:D3 allow programming of the second-stage bias current. Table 1 summarizes the register settings and the equivalent MAX2831 EV kit bias-current settings.

Results

Figure 1 and Table 2 summarize the current savings that can be achieved by optimizing the PA bias current. Table 3 and Figure 2 summarize the performance for nominal register settings. Figures 3, 4, and 5 summarize performance for register settings optimized for +17dBm and +15dBm and their output spectrums, respectively. Figure 6 summarizes performance for register settings optimized for +12dBm and +9dBm. Figure 7 provides the measurement setup.