Programmable LNA Branching for Stable Gain and Impedance
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Solution Overview
Problem
Current low-noise amplifiers (LNAs) face challenges in maintaining high gain, linearity, and low noise figure across various gain and bias current modes while ensuring minimal change in input and output impedance, leading to degradation in performance and increased complexity due to the use of attenuator modules.
Innovation Solution
The LNA is designed with split amplifier branches of binary-weighted FETs, input and output capacitors, and gain control resistors to maintain constant current density and impedance across gain modes, allowing for flexible operation with minimal impedance changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the LNA operates in different gain modes by reducing bias current, then the gain is reduced, but the linearity degrades and noise figure worsens
Solution Approach 1:
The LNA is divided into multiple parallel branches (first branch with first FET, second branch with second FET) where each branch can be independently controlled. By selectively enabling branches with different binary weights, the total gain can be adjusted while maintaining optimal operating conditions in each active branch, thus preserving linearity across different gain modes.
Solution Approach 2:
Each FET branch is designed with specific binary-weighted dimensions (width, length) optimized for its particular gain contribution. The first FET has dimensions optimized for higher gain mode, while the second FET has dimensions optimized for lower gain mode. This local optimization ensures that each branch maintains high linearity when active, regardless of the overall system gain setting.
2Power
If the LNA operates in different gain modes by reducing bias current, then the gain is reduced, but the noise figure degrades
Solution Approach 1:
The LNA is divided into multiple parallel branches (first branch with first FET, second branch with second FET) where each branch can be independently controlled. By selectively enabling branches with different binary weights, the total gain can be adjusted while maintaining optimal operating conditions in each active branch, thus preserving linearity across different gain modes.
Solution Approach 2:
Each FET branch is designed with specific binary-weighted dimensions (width, length) optimized for its particular gain contribution. The first FET has dimensions optimized for higher gain mode, while the second FET has dimensions optimized for lower gain mode. This local optimization ensures that each branch maintains high linearity when active, regardless of the overall system gain setting.
3Power
If the LNA uses attenuator modules to reduce gain, then the gain is reduced, but the device complexity increases
Solution Approach 1:
The patent extracts the gain control function from external attenuator modules and integrates it directly into the LNA structure through multiple parallel FET branches with binary-weighted dimensions. This eliminates the need for separate attenuator modules, reducing device complexity while maintaining the ability to provide programmable gain control across different modes.
Solution Approach 2:
The parallel FET branch structure serves multiple functions simultaneously: it provides gain control, impedance matching, and linearity maintenance without requiring separate attenuator modules. The binary-weighted branch configuration enables programmable gain while the shared circuit topology maintains consistent input/output impedance across different gain modes, reducing overall device complexity.
4Power
If the LNA uses attenuator modules to reduce gain, then the gain is reduced, but the impedance matching deteriorates
Solution Approach 1:
The parallel FET branch structure serves multiple functions simultaneously: it provides gain control, impedance matching, and linearity maintenance without requiring separate attenuator modules. The binary-weighted branch configuration enables programmable gain while the shared circuit topology maintains consistent input/output impedance across different gain modes, reducing overall device complexity.
Solution Approach 2:
The LNA dynamically switches between different parallel branch configurations to achieve different gain modes. By selectively enabling/disabling branches based on the desired gain level, the system maintains optimal impedance matching at each gain setting. The dynamic reconfiguration of active branches ensures that impedance matching is preserved across the full range of programmable gain modes.
Data Source
AI summary
A receiver front end capable of receiving and processing intraband non-contiguous carrier aggregate (CA) signals using multiple low noise amplifiers (LNAs) is disclosed herein. A cascode having a “common source” input stage and a “common gate” output stage can be turned on or off using the gate of the output stage. A first switch is provided that allows a connection to be either established or broken between the source terminal of the input stage of each cascode. Further switches used for switching degeneration inductors, gate/sources caps and gate to ground caps for each legs can be used to further improve the matching performance of the invention.