Design of SiGe HBT power amplifiers for microwave radar applications
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A novel modification to the standard cascode amplifier architecture is presented in SiGe which allows for an optimal separation of gain and breakdown functions through the mixed breakdown cascade architecture, opening the door for moderate power amplifiers in SiGe. Utilizing this technique, a two-stage, high-gain amplifier operating at X-Band is fabricated and measured. The 20 dB of gain per stage represents the highest gain at X-Band at the time of publication. Additionally, a near one Watt power amplifier is designed and fabricated at X-Band, which represents the highest output power in SiGe at X-Band at time of publication. Related to the power amplifier design, thermal considerations are also investigated. The validity of utilizing lumped mutual thermal coupling in SiGe devices is presented. Using this finding, a thermal coupling model and network which are compliant for use with commonly available HBT models and circuit simulators is presented. This model and network is used to thermally optimize SiGe PA cells based upon layout spacing.