| Summary: | A CMOS power amplifier is an important building block in the wireless systems design. The automatic gain control in CMOS power amplifier is mostly realized with a variable gain amplifier. In RF design, it is required for the variable gain amplifier to have high linearity, wide bandwidth and large gain range, and the relation between gain of the VGA and the control signal must be linear-in-decibel. In this project, a variable gain amplifier was designed with a self-biased differential amplifier and a linear-in-decibel variable amplifier. Design techniques including multistack transistors, body biasing resistor, impedance feedback loop and dynamic current bias were applied to improve design performance. Based on the simulation result, the variable gain amplifier proposed a 3dB bandwidth of 0.021~2.43GHz, and gain range is 10.1~-21.2dB. And the P1dB point and noise figure at 1.95GHz are -1.77dB and 17~48dB respectively.
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