Hybrid Variable Gain Amplifier Switching for Wide-Range Linearity
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Solution Overview
Problem
Conventional variable gain amplifiers (VGAs) exhibit significant deterioration in linearity at both high and low gain levels, leading to signal distortion and inefficiency, particularly in wide dynamic range applications like 5G phased array systems.
Innovation Solution
A hybrid variable gain amplifier (VGA) with dual modes of operation, utilizing cross-connected and tied-to-Vdd topologies, allows for improved linearity by selectively enabling and disabling current paths through transistors, maintaining high linearity across a wide dynamic range without increasing power consumption or circuit complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional VGA circuits are used to achieve wide dynamic range gain control, then the gain range is sufficient, but linearity deteriorates significantly at upper or lower ranges of gain
Solution Approach 1:
The VGA is divided into two separate VGAs: a first VGA handling low gain ranges and a second VGA handling high gain ranges. Each VGA is optimized for its specific range, preventing the linearity deterioration that occurs when a single VGA operates across the entire dynamic range. The gain control signal selectively activates one VGA based on the required gain level.
Solution Approach 2:
The system dynamically switches between the first and second VGAs based on the desired gain level. A gain control signal determines which VGA is active, allowing the system to adapt to different operating conditions while maintaining optimal linearity for each gain range.
2Device complexity
If a single VGA is used for wide dynamic range operation, then the device complexity remains low, but linearity and noise performance degrade at extreme gain levels
Solution Approach 1:
The VGA system is segmented into two specialized amplifiers rather than using one general-purpose amplifier. This segmentation allows each VGA to be optimized for its specific gain range, improving linearity without requiring a complex multi-stage architecture for the entire system.
Solution Approach 2:
Each VGA is designed with specific characteristics optimized for its operating range. The first VGA is optimized for low gain operation while the second VGA is optimized for high gain operation, allowing each component to have local quality tailored to its function rather than requiring a uniformly complex design.
3Power
If gain is increased to amplify low level signals, then signal strength is sufficient, but sensitivity to low level signals is reduced due to noise
Solution Approach 1:
The segmented VGA architecture allows the system to use the first VGA for low gain applications where noise would be problematic, and only switches to the second VGA for high gain when absolutely necessary. This prevents unnecessary noise introduction while still providing sufficient signal strength when needed.
Solution Approach 2:
The system changes the operating parameters by selecting different VGAs based on the required gain level. This parameter change allows optimization of the noise figure for each operating condition, using the VGA with the better noise characteristics for the current signal level.
Data Source
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AI summary
Hybrid variable gain amplifiers and methods of controlling hybrid VGAs are disclosed. The hybrid VGA includes a first portion that provides a current path between a positive input and a positive output, and a current path either between the positive input and a negative output, in a first mode of operation, or between the positive input and a voltage source, in a second mode of operation. A second portion of the VGA provides a current path between a negative input and the negative output, and a current path either between the negative input and the positive output, in the first mode of operation, or between the negative input and the voltage source, in the second mode of operation. Control voltages selectively enable the paths in the first or second mode of operation. The control voltages further control amount of current flow in the enabled paths.