Dual-Path LNA Architecture for Gain-Linearity Tradeoff
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Solution Overview
Problem
The tradeoff between output impedance and linearity in low-noise amplifiers (LNAs) is challenging, particularly in low-power receiver front-ends, where increasing output impedance to compensate for noise leads to non-linear behavior and signal degradation due to blockers.
Innovation Solution
A dual output path LNA architecture is implemented, where the LNA drives a low impedance for high linearity in the presence of blockers and a high impedance for increased voltage gain, with isolation circuits and control circuits to switch between these paths based on power mode, and a local oscillator offset circuit with reduced spur generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the LNA output impedance is increased to increase voltage gain, then the voltage gain is improved, but the LNA becomes more susceptible to non-linear behavior due to blockers
Solution Approach 1:
The LNA output is segmented into two separate output paths: a first output path with a first output impedance and a second output path with a second output impedance. This allows the system to select different impedance characteristics depending on the operating conditions, resolving the contradiction between voltage gain and linearity by providing specialized paths for different signal conditions.
Solution Approach 2:
The system dynamically switches between the first and second output paths based on the presence of blockers. A control mechanism selects which output path to use, allowing the LNA to adapt its output impedance characteristics in real-time to maintain optimal performance under varying signal conditions.
2Reliability
If the LNA voltage gain is increased to compensate for increased noise in low-power components, then the noise-related performance degradation is improved, but the LNA exhibits non-linear behavior and gain compression
Solution Approach 1:
By segmenting the output into two paths with different impedance characteristics, the system can select the appropriate path based on whether noise compensation or linearity is the priority, avoiding the need to increase gain to the point of non-linearity.
Solution Approach 2:
The system changes the output impedance parameter dynamically by switching between the first and second output paths. This allows optimization of voltage gain when noise compensation is needed while maintaining linearity when blockers are present, without requiring a fixed high-gain design that would always suffer from non-linearity.
Data Source
AI summary
The present disclosure is directed to a dual output path LNA that can be used to break the tradeoff between the output impedance and linearity of an LNA without the problems of a programmable output impedance LNA. In an embodiment, the dual output path architecture includes an LNA driving a low level of impedance in a low voltage gain path, thus achieving high linearity in the presence of large blockers, and driving a high level of impedance in a high voltage gain path to increase the LNA's voltage gain and minimize performance degradation due to a noisier, low power receiver front-end chain following the LNA. The present disclosure is further directed to a local oscillator (LO) offset circuit with low power and reduced spur generation.