A K-Band CMOS Variable Gain Amplifier for Phased Array Applications

This paper presents a hybrid topology integrating passive attenuation and active amplification units for highperformance digitally controlled variable gain amplifiers (VGAs). The passive unit employs a π-type symmetric structure with embedded switches to achieve a wide attenuation range, while the active unit adopts a common-source common-gate current-steering multiplexing architecture for precise dB-linear control. A K-band VGA prototype was implemented in a 55 nm CMOS process. Measurement results show an amplitude control range of -13.4 to 3.1 dB with 0.5 dB steps over the 17–22 GHz frequency range of interest. The root-mean-square amplitude error (RMSA) is below 0.19 dB, and the root-mean-square phase error (RMSP) is better than 3.55°. The VGA achieves an input 1 dB compression point (IP1dB) above -1 dBm while consuming less than 7.5 mW. The total chip area, including all test pads, is 0.49 mm², with a core footprint of 0.17 mm².