Design of 85 GHz High Power Gain SiGe Buffer with Transformer Matching Network

An 85 GHz buffer with high power gain is shown in this paper. In order to obtain high power gain, two classic techniques to improve power gain are adopted. The first one is cascade structure of two power stages, and the other one is that each stage utilizes differential cascode structure. Meanwhile, the step-by-step pre-matching technique is applied to optimize the performance of buffer. The stability factor and output power are both improved with other critical design strategies, and a tradeoffis made between gain and efficiency. What's more, single-ended transformer matching network (TMN) is applied to simplify matching method. The simpli fied matching method is easy to use with smith chart and works very well, then a modi fied transformer model is adopted to analyze and optimize the performance of TMN with iterations of impedance matching. After fabricated by 0.13 mu m SiGe BiCMOS technology, the buffer shows 18.5 dB power gain and 2dBm output power of 1 dB gain compression point with 2.8V supply voltage and 40mA operating current, and the saturated output power is 6.33 dBm.