Tunable LNA Gain Linearization for Extended Dynamic Range
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Solution Overview
Problem
Low Noise Amplifiers (LNAs) face challenges in maintaining a high signal-to-noise ratio for weak signals, as existing LNAs can introduce noise that degrades the quality of received signals, particularly in direct conversion transceivers.
Innovation Solution
The proposed solution involves a cascaded LNA architecture with tunable bandpass stages, including a variable gain stage and a tunable tank circuit with a cross-coupled compensation transistor pair biased in the sub-threshold region, allowing for adjustable transconductance and quality factor (Q) to enhance signal amplification while minimizing noise injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional LNA architecture is used, then gain can be achieved, but noise is introduced that degrades signal quality
Solution Approach 1:
The LNA is divided into multiple cascaded stages (first LNA stage, second LNA stage) with different functions. The first stage provides initial amplification with optimized noise performance, while the second stage provides additional gain. This segmentation allows each stage to be optimized for its specific role, achieving high overall gain while controlling noise introduction at each stage.
Solution Approach 2:
Different LNA stages are designed with different characteristics optimized for their specific positions in the cascade. The first stage uses input matching networks optimized for noise figure, while subsequent stages are optimized for gain. This local optimization of quality factors and matching networks at different stages achieves high gain overall while minimizing noise introduction.
2Adaptability or versatility
If LNA operates at high output swings, then dynamic range increases, but linearity degrades and adjacent channel rejection decreases
Solution Approach 1:
The LNA incorporates dynamically adjustable parameters including variable gain control and tunable quality factors. The quality factors of resonant circuits can be adjusted based on operating conditions to maintain optimal linearity across different output swing levels. This dynamic adjustment allows the LNA to adapt to high output swing conditions while preserving linearity and adjacent channel rejection.
Solution Approach 2:
The patent employs parameter changes in the form of adjustable quality factors and gain settings. By changing the quality factor parameters of resonant circuits and adjusting gain parameters, the LNA can maintain linear operation even at high output swings. This parameter adjustment compensates for non-linear effects that would otherwise degrade linearity and adjacent channel rejection.
3Object-generated harmful factors
If narrow band selection is implemented, then adjacent channel rejection improves, but frequency tuning range is limited
Solution Approach 1:
The LNA design incorporates multiple resonant circuits with different quality factors that can be selectively activated. The same hardware structure serves multiple functions: narrow band selection for adjacent channel rejection and wider tuning range for frequency agility. By selectively engaging different resonant circuits or adjusting their quality factors, the LNA achieves both narrow band rejection and wide tuning capability.
Solution Approach 2:
The quality factors of the resonant circuits are made dynamically adjustable rather than fixed. This allows the LNA to switch between narrow quality factor settings for adjacent channel rejection and wider effective bandwidth settings for frequency tuning. The dynamic quality factor adjustment enables the same hardware to provide both narrow band selection and wide frequency range adaptability.
Data Source
AI summary
A low noise amplifier including a variable gain amplifier stage configured to accept an input signal and to provide a load driving signal; a tunable bandpass filter connected as a load to the variable gain amplifier stage, wherein the bandpass filter includes a cross-coupled transistor pair, and at least one cross-coupled compensation transistor pair biased in a subthreshold region configured to add a transconductance component when the load driving signal is of a magnitude large enough to decreases a transconductance of the cross-coupled transistor pair; and, a controller circuit configured to tune the bandpass filter. The filter can be tuned in respect to the frequency and the quality factor Q.