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WiMAX is an innovative communication technology which is generally applied in latest commercial communication products. It uses of orthogonal frequency division multiple access (OFDMA) modulation to suit multi-path environments that gives network operators higher throughput and capacity. Although this technology is of much benefit to users and applications, it is a real challenge of hardware circuit design, especially on power amplifier (PA) circuits. One reason is that OFDMA modulation scheme in WiMAX system requires very high linearity of PAs. Thus, the design methodology of board level integration which is one solution of system in package (SiP) is proposed to solve non-linear effect and thermal problem of PAs. Multilayer organic substrate process and high dielectric constant material (DK 40) is used to realize the design. Eventually, 50% of the entire passive components, such as the output matching circuit, RF chokes, and some of the decouple capacitors of power amplifier have been integrated into the substrate. The measured data of small-signal response for the designed PA is with 29 dB gain, -12 dB input reflection, -22 dB output reflection, and the reverse isolation is more than 45 dB between 2.5 and 2.7 GHz. And with WiMAX OFDMA/64-QAM modulation signal testing, under error vector magnitude (EVM) conditions at -30 dB, the designed PA can output 24.5 dBm at 2.499 GHz; 24 dBm at 2.599 GHz; 24 dBm at 2.68725 GHz, fully satisfying the standard requirements. These studies show that board level integration technology can be utilized in linearity demands and high power circuit designs, and can substantially shrink the sizes of the circuits and the cost. Furthermore, it also provides a new solution for next generation communication systems.