A CMOS VGA with DC offset cancellation for direct-conversion receivers

• Main Authors: Zheng, Yuanjin, Yan, Jiangnan, Xu, Yong Ping
• Other Authors: School of Electrical and Electronic Engineering
• Format: Article
• Language: English
• Published: 2010
• Subjects: DRNTU::Engineering::Electrical and electronic engineering
• Online Access: https://hdl.handle.net/10356/92153; http://hdl.handle.net/10220/6276
• Institution: Nanyang Technological University

A CMOS dB-linear variable gain amplifier (VGA) with a novel I/Q tuning loop for dc-offset cancellation is presented. The CMOS dB-linear VGA provides a variable gain of 60 dB while maintaining its 3-dB bandwidth greater than 2.5 MHz. A novel exponential circuit is proposed to obtain the dB-linear gain control characteristics. Nonideal effects on dB linearity are analyzed and the methods for improvement are suggested. A varying-bandwidth LPF is employed to achieve fast settling. The chip is fabricated in a 0.35-µm CMOS technology and the measurement results demonstrate the good dB linearity of the proposed VGA and show that the tuning loop can effectively remove dc offset and suppress I/Q mismatch effects simultaneously.