Variable Gain Amplifier Circuit for Wide RF Gain Control
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Solution Overview
Problem
Conventional variable gain amplifiers face challenges in achieving a wide gain variable range while maintaining excellent linearity and low noise figure (NF), often requiring a large circuit scale and increased complexity due to the need for multiple stages and bias current control.
Innovation Solution
The proposed solution involves a variable gain amplifier configuration with a first and second variable gain amplifier circuit, an attenuation circuit, and a variable resistance circuit, where the gain control section adjusts the gains of both amplifier circuits and the resistance value of the variable resistance circuit using a gain control voltage, allowing for a reduced circuit scale and improved linearity by optimizing gain distribution and attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple variable gain amplifier circuits are used to achieve a wide gain variable range, then the gain control range is improved, but the circuit scale and complexity increase
Solution Approach 1:
The amplifier is divided into two parallel signal paths: a first variable gain amplifier circuit for high gain amplification and a second variable gain amplifier circuit for low gain amplification. This segmentation allows each circuit to be optimized for its specific gain range, achieving wide overall gain control without requiring a single complex amplifier
Solution Approach 2:
An attenuation circuit is introduced as an intermediary element in the second signal path. This attenuation circuit, controlled by the gain control voltage, works together with the second variable gain amplifier circuit to provide precise gain control in the low gain range while maintaining circuit simplicity
2Adaptability or versatility
If multiple stages are used to achieve wide gain range, then the gain variable range is improved, but the noise figure increases
Solution Approach 1:
By segmenting the amplification into two parallel paths with different gain characteristics, the system can select the optimal path for the current signal level. The first variable gain amplifier circuit handles high gain requirements with minimal stages, while the second path handles low gain requirements, thereby minimizing the number of amplification stages and reducing cumulative noise figure
Solution Approach 2:
Each signal path is designed with locally optimized characteristics: the first path is optimized for high gain amplification with appropriate noise figure characteristics, while the second path is optimized for low gain amplification. This local quality optimization ensures that each path performs optimally in its designated gain range, maintaining low overall noise figure across the full gain variable range
3Adaptability or versatility
If multiple variable gain amplifier circuits are used to achieve wide gain range, then the gain control range is improved, but the linearity deteriorates
Solution Approach 1:
The gain control range is segmented into two distinct regions handled by separate optimized circuits. The first variable gain amplifier circuit is optimized for high gain operation with improved linearity in that range, while the second variable gain amplifier circuit combined with the attenuation circuit is optimized for low gain operation. This segmentation prevents the linearity deterioration that would occur if a single circuit attempted to cover the entire wide gain range
Solution Approach 2:
Each amplifier circuit is designed with local quality optimization for its specific operating range. The first circuit parameters are optimized for high gain linearity, while the second circuit parameters are optimized for low gain linearity. This ensures that each circuit operates in its optimal linearity region, maintaining excellent overall linearity across the wide gain control range
Data Source
AI summary
A variable gain amplifier of the present invention connects an input and an output of a first variable gain amplifier circuit to an RF input terminal and an RF output terminal, respectively, connects one terminal of an attenuation circuit is to an RF input terminal, connects an input and an output of a second variable gain amplifier circuit to the other terminal of the attenuation circuit and an RF output terminal, respectively, connects one terminal of the variable resistance circuit to a node between the attenuation circuit and the second variable gain amplifier circuit, and grounds the other terminal of the variable resistance circuit. A gain of the first variable gain amplifier circuit, a gain of the second variable gain amplifier circuit, and a resistance value of the variable resistance circuit are then varied by a gain control voltage outputted from a gain control section.