CTLE-Coupled Variable Gain Amplifier With Low Parasitic Capacitance
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Solution Overview
Problem
Conventional variable gain amplifiers (VGAs) are inadequate due to limitations in gain range, linearity, distortion, tunability, and bandwidth, as well as high parasitic capacitance that impairs frequency response and introduces phase shift and group delay.
Innovation Solution
A variable gain amplifier architecture that incorporates a continuous-time linear equalizer (CTLE) section and a VGA section, utilizing a transistor with adjustable resistance based on both common mode voltage and control signal, and a digital-to-analog converter (DAC) to generate a control voltage for gain control, allowing for high SNR and tunability while minimizing parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional variable gain amplifier architectures are used, then basic amplification function is achieved, but parasitic capacitance is high which impairs frequency response and introduces phase shift and group delay
Solution Approach 1:
The patent segments the VGA into two independent sections: a CTLE section for signal equalization and a VGA section for gain control. This segmentation allows each section to be optimized independently, with the CTLE section handling frequency response compensation and the VGA section providing clean amplification with minimal parasitic capacitance effects.
Solution Approach 2:
The patent introduces common mode resistors as intermediary elements that connect the CTLE section to the VGA section. These resistors serve as mediators that transfer the common mode voltage information while isolating the parasitic capacitance effects, thereby improving frequency response without compromising gain control.
2Adaptability or versatility
If existing VGA designs are used, then amplification is provided, but gain range and tunability are limited
Solution Approach 1:
The patent employs dynamic control of the transistor resistance values through common mode voltage adjustment. By dynamically varying the common mode voltage, the resistance of the transistors in the VGA section changes, enabling continuous gain adjustment across a wide range while maintaining linearity through the differential configuration.
Solution Approach 2:
The patent changes the resistance parameter of the transistors by adjusting the common mode voltage level. This parameter change mechanism allows for continuous gain control without requiring switching between discrete resistor values, thereby improving linearity and reducing distortion while expanding the adjustable gain range.
3Reliability
If conventional VGA sections are used, then gain control is achieved, but signal-to-noise ratio is compromised
Solution Approach 1:
The patent merges the equalization function and amplification function into a unified architecture where the CTLE section and VGA section work together. This merging allows the common mode voltage to serve dual purposes: equalizing the frequency response in the CTLE section and controlling the gain in the VGA section, thereby improving SNR without proportionally increasing complexity.
Solution Approach 2:
The common mode voltage signal serves multiple functions simultaneously: it provides equalization control for the CTLE section, gain control for the VGA section, and establishes the operating point for the differential transistors. This multi-functionality improves SNR by coordinating signal conditioning and amplification while avoiding the need for separate control circuits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed architecture achieves high signal-to-noise ratio (SNR), fine tunability, and reduced parasitic capacitance, enhancing the performance of VGAs in communication systems by leveraging existing CTLE configurations and manufacturing processes.
Implementation Method 1
a transistor whose resistance value is based on both the common mode voltage and the control signal
Implementation Method 2
A DAC generates a control signal based on a control code
Data Source
AI summary
The present invention is directed to electrical circuits and techniques thereof. In various embodiments, the present invention provides a variable gain amplifier architecture that includes a continuous-time linear equalizer (CTLE) section and a variable gain amplifier (VGA) section. The CTLE section provides both a pair of equalized data signals and a common mode voltage. A DAC generates a control signal based on a control code. The VGA section amplifies the pair of equalized data signals by an amplification factor using a transistor whose resistance value is based on both the common mode voltage and the control signal. There are other embodiments as well.