LNA Bypass Circuit to Cut Capacitive Loading and Improve Linearity
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Solution Overview
Problem
Low noise amplifiers (LNAs) face challenges in maintaining high linearity performance and low insertion loss when operating in bypass mode, due to capacitive loading from active devices in the active gain mode path.
Innovation Solution
The LNA is configured to operate in high gain, low gain, or bypass mode, with the amplifying element decoupled from ground in bypass mode, reducing capacitive loading and improving non-linearity performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the active and bypass paths share the same input and output terminals, then space limitations on the die are satisfied, but the bypass mode performance suffers due to capacitive loading of the active devices
Solution Approach 1:
The patent divides the input signal path into separate segments: one for the active path and another for the bypass path. By providing dedicated input terminals for each path, the capacitive loading effect on the bypass path is eliminated while maintaining compact die area through shared output terminal and integrated layout.
2Reliability
If an input switch is implemented to switch out active elements from the bypass path, then capacitive loading is reduced, but noise-figure degradation occurs
Solution Approach 1:
The patent introduces a bypass capacitor as an intermediary element that provides a low-impedance path to ground for the amplifying element in bypass mode. This eliminates the need for input switches while maintaining low noise-figure, as the capacitor effectively decouples the amplifying element without introducing switch-related noise degradation.
3Device complexity
If the amplifying element is coupled to ground in bypass mode, then circuit simplicity is maintained, but nonlinearity performance degrades due to capacitive loading
Solution Approach 1:
The patent implements dynamic coupling of the amplifying element to ground through a bypass capacitor that is activated only in bypass mode. In active gain mode, the amplifying element operates with normal DC biasing, while in bypass mode, the capacitor provides AC ground coupling to reduce capacitive loading effects, thus improving nonlinearity performance without compromising circuit simplicity.
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.