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Evolution of and Perspectives on Differential-Pair-Based CMOS Variable
Gain Amplifiers with Linear-in-Decibel Gain Control: A Tutorial
- Siqi Wang,
- Zhenghao Lu,
- Zhong Tang,
- Xiaopeng Yu,
- Hanming Wu,
- Kiat Yeo,
- Yong Chen
Siqi Wang
Zhejiang University College of Information Science and Electronic Engineering
Author ProfileZhenghao Lu
Soochow University School of Electronic and Information Engineering
Author ProfileXiaopeng Yu
Zhejiang University College of Information Science and Electronic Engineering
Author ProfileKiat Yeo
Singapore University of Technology and Design Engineering Product Development
Author ProfileAbstract
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A variable gain amplifier (VGA) is an essential building block used in
the automatic gain control (AGC) loop to provide a continuous,
adjustable gain for the signal strength. To maintain the stability and
consistency of the AGC loop, it is necessary to ensure that the gain of
the VGA has an accurate dB-linear characteristic. This tutorial provides
a detailed overview of the development of dB-linear VGAs based on
differential pair structures over recent years. We categorise various
VGA cells based on differential pair structures, analyse their operating
principles, and explain the key features of each topology. Based on
observation and extraction of the dB-linear implementation schemes used
by these VGAs, we summarise three basic methods for achieving dB-linear
gain control. We also discuss specific methods for realising the
exponential function, using a true exponential and a mathematical
approximation, and present the different types of approximation
functions adopted in the works described here. Considerations in regard
to the tuning range, gain error, bandwidth, linearity,
process-temperature robustness, and circuit simplicity are also
discussed. Finally, we draw comparisons and give perspectives for future
dB-linear VGAs.Submitted to International Journal of Circuit Theory and Applications 16 Jun 2024Review(s) Completed, Editorial Evaluation Pending
26 Jun 2024Reviewer(s) Assigned
20 Aug 2024Editorial Decision: Revise Minor
24 Aug 20241st Revision Received
27 Aug 2024Submission Checks Completed
27 Aug 2024Assigned to Editor
27 Aug 2024Review(s) Completed, Editorial Evaluation Pending
27 Aug 2024Reviewer(s) Assigned
27 Sep 2024Editorial Decision: Accept