A High-Gain, Two-Stage, X-Band SiGe Power Amplifier

SiGe technology is becoming well-known for its capabilities as a high-speed IC design platform, and is being increasingly employed to address a wide variety of communications circuit applications. Unfortunately, the ever-increasing speed of the requisite SiGe transistors comes at a cost that significantly constrains their use in power amplifier design: available breakdown voltage. We demonstrate here that by using an optimized cascode amplifier architecture employing both the high speed (low breakdown voltage) and high breakdown voltage (low speed) SiGe transistors, one can relax these design constraints considerably. Using this approach, a two stage, X-Band amplifier has been fabricated exhibiting maximums of more than 40 dB of stable gain, an output power greater than 20 dBm, and a power-added efficiency of 25% over the X-band operating frequency of 8.5 to 10.5 GHz, and is suitable for emerging X-band phased array radar applications.