LNA Bypass Path with Series Isolation Switch Against RF Distortion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional Low Noise Amplifiers (LNAs) with bypass modes suffer from unwanted distortion due to unintended field-effect transistor (FET) behavior when handling strong radio-frequency signals, leading to signal corruption in receivers.
Innovation Solution
An amplifier circuit with a signal amplifying path and a parallel bypass path, including switches and transistors configured to allow signal bypassing, attenuation, or blocking, utilizing isolation and shunting transistors to manage RF energy and prevent distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an LNA is used with a bypass switch configuration to handle strong RF signals, then the LNA can be bypassed to avoid distortion, but the FET may still be unintentionally turned on by high RF signal strength modulating the gate, causing unwanted distortion and signal corruption
Solution Approach 1:
An isolation transistor is introduced as an intermediary component between the bypass switch and the LNA. This isolation transistor acts as a mediator that prevents the high RF signal from directly modulating the gate of the LNA's FET, thereby blocking the harmful effect while maintaining the bypass functionality. The isolation transistor is controlled to remain in a non-conducting state during bypass mode, effectively isolating the LNA from the strong RF signal.
Solution Approach 2:
The circuit is segmented into distinct functional sections: a bypass path with a bypass switch, an isolation section with the isolation transistor, and the LNA section. This segmentation allows independent control of each function - the bypass switch can route signals around the LNA while the isolation transistor separately manages the protection of the LNA's FET gate from RF signal modulation, preventing unintended turn-on.
2Reliability
If a bypass switch is used to route strong signals around the LNA, then the LNA is protected from overload, but additional circuit components and switching mechanisms are required that increase circuit complexity
Solution Approach 1:
The isolation transistor serves multiple functions: it acts as an isolator to protect the LNA from RF signal modulation, functions as a switch to control signal flow to the LNA, and helps manage the bypass operation. By making the isolation transistor multi-functional, the circuit achieves reliable protection without requiring separate dedicated components for each function, thereby limiting the increase in overall circuit complexity.
Data Source
AI summary
An amplifying circuit for receiving a signal in a wireless network includes an amplifier and two switches. The amplifier includes an isolation switch having a gate connected to a control signal for activating the isolation switch transistor in a bypass mode and a source/drain connected to the input for receiving the signal and the other source/drain connected to the gate of an amplifier transistor. The amplifier also includes a bypass transistor having a gate connected to a control signal for activating the bypass transistor in a bypass mode. The bypass switch is connected in parallel with the series combination of the isolation switch and amplifier between the input and output, enabling the received signal to bypass the amplifier. In the bypass mode, the isolation switch prevents RF energy from voltage modulating the gate of the amplifier transistor gate thus reducing undesirable distortion and harmonics from the amplifier.