An 11 GHz–Bandwidth Variable Gain Ka–Band Power Amplifier for 5G Applications

A Ka–band, 32–43 GHz, differential power amplifier (PA) for millimeter wave applications is presented. The PA is a three stage design with a nominal gain of 36 dB. A device periphery ratio of 1:2:4 is adopted for pre–driver, driver and final stage, respectively. To enable use of 2.7 V supply, a cascode topology was employed in all three stages. The input is 80 Ω differential and the output load is 50 Ω single ended. The PA has a variable gain of 36 ± 11 dB for use as variable gain amplifier. A saturation power of 17.8 dBm was measured at 35 GHz with a small signal gain of 34.5 dB, including output losses of 2–2.5 dB over band. The design is based on magnetically coupled parallel resonators to obtain the required bandwidth. A SiGe HBT BiCMOS process with fMAX = 330 GHz was used for fabrication. The PA is part of a front–end design, and its output thus faces an antenna interface with integrated LNA and TX/RX switches, and the input is connected to an on-chip variable gain amplifier.