Programmable LNA Branch Switching for Linearity and Impedance Match
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Solution Overview
Problem
Current low-noise amplifiers (LNAs) face challenges in maintaining high linearity and low noise figure across various gain and bias current modes while ensuring minimal distortion and impedance matching, which limits their ability to handle a wide range of input signal levels and data rates in communications receivers.
Innovation Solution
The LNA is designed with multiple amplifier branches of binary-weighted FETs, allowing for adjustable bias current and impedance control through capacitors and resistors, maintaining constant current density and impedance across different modes, and using post-fabrication tuning for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the LNA operates in high gain and high bias current mode, then the gain and linearity are improved, but the power consumption increases and the noise figure deteriorates in lower modes
Solution Approach 1:
The LNA is divided into multiple parallel branches (first branch, second branch, third branch) with different bias current levels. Each branch is designed to operate optimally at specific gain modes, allowing the system to segment the operating range and select appropriate branches to maintain linearity while reducing power consumption in lower gain modes.
Solution Approach 2:
The system dynamically switches between different LNA branches based on the required gain mode. Control logic activates specific branches (e.g., first branch for high gain, second branch for medium gain, third branch for low gain) to adapt the power consumption and performance characteristics to the current operational requirements.
2Use of energy by moving object
If the bias current is reduced for lower gain modes, then the power consumption is reduced, but the linearity and noise figure deteriorate
Solution Approach 1:
Different LNA branches are segmented with optimized bias currents for specific gain modes. The third branch is designed for low gain operation with lower bias current, while maintaining acceptable noise figure through targeted design optimizations specific to that branch's operating conditions.
Solution Approach 2:
Each LNA branch is designed with local quality optimizations tailored to its specific operating range. The third branch for low gain mode has specific component values and transistor sizing optimized for that regime, allowing it to achieve acceptable noise figure despite lower bias current.
3Reliability
If the LNA is designed for high gain mode, then the gain and linearity are optimized, but the impedance matching deteriorates in lower gain modes
Solution Approach 1:
The input and output impedance matching networks are segmented into branch-specific designs. Each LNA branch has dedicated matching components (inductors, capacitors) optimized for its operating conditions, ensuring that impedance matching is maintained across all gain modes rather than compromising when switching between modes.
Solution Approach 2:
Impedance matching is optimized locally for each branch's operating conditions. The matching network parameters (L1, L2, L3, C1, C2, C3 values) are specifically tuned for each branch's gain and bias current characteristics, ensuring optimal impedance matching in each operational mode.
4Adaptability or versatility
If multiple LNA branches are used for different gain modes, then the adaptability is improved, but the device complexity increases
Solution Approach 1:
The LNA is segmented into three parallel branches that can be independently controlled. This segmentation allows the system to achieve wide gain range adaptability (0-21 dB) by selectively activating combinations of branches, while the modular structure helps manage complexity through systematic design.
Solution Approach 2:
Multiple LNA branches share common structural elements and control mechanisms. The branches use similar topologies with unified control logic for switching between modes, and share common input/output coupling structures, which reduces the overall complexity increase compared to completely separate amplifier designs.
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.