Analysis and Compensation of Phase Variations Versus Gain in Amplifiers Verified by SiGe HBT Cascode RFIC

The transmission phase variations versus gain in common emitter and common base amplifiers are analyzed revealing that these stages can be tuned to yield opposite phase characteristics versus gain. By cascading these two stages, e.g., on the basis of a cascode, and optimizing added feedback elements, it is possible to compensate these phase variations. A universal analysis based on bipolar transistors is derived. However, the insights can be mapped to other transistors such as field-effect transistors. The analysis is verified by implementation of a low-noise cascode amplifier in 0.25-mum silicon germanium heterojunction bipolar transistors. At 50-Omega terminations, 1.6-V supply voltage, 1-mA current consumption, and a gain of 7 dB plusmn 0.25 dB, a noise figure of less than 3.2 dB, and a third-order output intercept point of -3 dBm are measured within a frequency range from 5.2 to 5.9 GHz. For a gain control range of 12 and 20 dB, the transmission phase variations are reduced to 3deg and 6deg, respectively, which is around a factor of 7 better than for a conventional noncompensated cascode topology. The fully integrated circuit is well suited for wireless local area network systems applying adaptive antenna combining and operating in accordance to the 802.11 a/n standards.

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