Portal de Periódicos da CAPES

A CMOS VGA With DC Offset Cancellation for Direct-Conversion Receivers

2008; Institute of Electrical and Electronics Engineers; Volume: 56; Issue: 1 Linguagem: Inglês

10.1109/tcsi.2008.2010592

1558-0806

Yuanjin Zheng, Jiangnan Yan, Yong Ping Xu,

Electrostatic Discharge in Electronics

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-mum 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.