LNA Bypass Circuit With Floating Active Devices for Better Linearity
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Solution Overview
Problem
LNAs operating in bypass mode suffer from performance degradation due to capacitive loading of active devices, leading to non-linear performance issues and unacceptable noise-figure degradation, especially in RF receiver front-ends.
Innovation Solution
Decouple the amplifying element from ground by using additional switches to minimize capacitive loading in the bypass path, thereby improving the input third-order intercept point (IIP3) and non-linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the active and bypass paths share the same input and output terminals due to space limitations, then the device complexity is reduced, but the non-linearity performance and insertion loss in bypass mode deteriorate due to capacitive loading of active devices
Solution Approach 1:
The patent divides the LNA into separate active and bypass paths with independent input/output terminals. This segmentation allows the bypass path to be electrically isolated from the active devices, eliminating capacitive loading effects while maintaining a compact integrated structure. The active path includes amplifying elements for signal amplification, while the bypass path provides a direct signal path with minimal interference.
Solution Approach 2:
The patent extracts the bypass path from the active path by providing separate input and output terminals for the bypass mode. This extraction removes the harmful capacitive coupling between active devices and the bypass signal path, allowing the bypass mode to achieve superior linearity performance independent of the active amplifying elements.
2Reliability
If an input switch is implemented to switch out active elements from the bypass path, then the non-linearity performance is improved, but the noise-figure degrades by approximately 0.3 dB
Solution Approach 1:
The patent extracts the bypass path completely from the active path by providing separate input and output terminals. This eliminates the need for switching mechanisms and prevents any noise-figure degradation that would result from switch insertion loss and non-ideal switch characteristics, while still achieving superior linearity performance in bypass mode.
Solution Approach 2:
The patent segments the LNA into distinct active and bypass paths with independent terminals, allowing simultaneous optimization of both paths without interference. The bypass path can be optimized for minimum insertion loss and best linearity, while the active path handles amplification, without requiring switches that would degrade noise performance.
3Device complexity
If the amplifying element remains coupled to ground in bypass mode, then the circuit simplicity is maintained, but the input third order intercept point and non-linearity performance deteriorate
Solution Approach 1:
The patent segments the bypass path from the active amplifying elements by providing separate input and output terminals. This segmentation naturally decouples the amplifying element from the bypass signal path, eliminating capacitive loading effects without requiring additional decoupling switches or complex circuit reconfiguration, thus maintaining circuit simplicity while improving IIP3.
Data Source
AI summary
Methods and devices to improve nonlinearity performance of low noise amplifiers (LNAs) are disclosed. The described methods and devices reduce the capacitive loading of the LNA amplifying devices on the bypass path of the LNAs when operating in the bypass mode. This is performed by decoupling the active devices from ground to put the amplifying devices in a floating state, thus minimizing the impact of the gate-source capacitances of the amplifying devices on the overall linear performance of the LNA operating in the bypass mode.