Split LNA Source Switching for Stable Input Impedance
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Solution Overview
Problem
Existing receiver front ends face challenges in achieving high output-to-output isolation, low losses, and maintaining linearity and noise figure when amplifying intraband non-contiguous carrier aggregate signals due to limitations of passive splitters and varying input impedance in single and split modes.
Innovation Solution
A receiver front end utilizing multiple low noise amplifiers (LNAs) with cascode architecture, source switching, and optional gate and degeneration switches to maintain consistent input impedance and reduce losses, enabling operation in both single and split modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a passive splitter is used to split the signal to multiple downconverters, then the signal can be distributed to multiple channels, but the isolation between outputs is insufficient (only 18-20 dB) causing interference and distortion
Solution Approach 1:
The patent divides the single LNA output into multiple independent LNA paths, with each LNA dedicated to a specific frequency channel. This segmentation eliminates the isolation problem of passive splitters by providing electrically independent amplification paths for each carrier frequency in the carrier aggregation signal.
2Adaptability or versatility
If the LNA operates in split mode with passive splitter, then multiple channels can be received, but losses increase and linearity degrades
Solution Approach 1:
The receiver front end is segmented into multiple independent LNA branches, each handling a specific frequency channel. This allows direct connection from each LNA to its dedicated downconverter without passing through a lossy passive splitter, thereby reducing signal losses while maintaining multi-channel reception capability.
3Adaptability or versatility
If the LNA is designed for broad frequency band operation, then it can handle carrier aggregation signals, but the input impedance varies between single and split modes causing performance degradation
Solution Approach 1:
By segmenting the receiver into multiple independent LNA paths with each LNA tuned to a specific frequency channel, the input impedance remains stable and consistent for each channel regardless of whether other channels are active. This eliminates the impedance variation problem that occurs in single-LNA designs operating in both single and split modes.
4Device complexity
If a single LNA is used with mode selector switch, then the architecture is simple, but the isolation between different downconverter paths is insufficient
Solution Approach 1:
The patent uses multiple independent LNAs instead of a single LNA with switching, where each LNA is dedicated to a specific frequency channel. This segmentation provides superior isolation between downconverter paths because each LNA operates independently without sharing common amplification stages, eliminating the need for complex mode selector switches while improving reliability.
Data Source
AI summary
A receiver front end amplifier 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” configured input FET and a “common gate” configured output FET can be turned on or off using the gate of the output FET. A first switch is provided that allows a connection to be either established or broken between the source terminal of the input FET of each LNA. Further switches used for switching degeneration inductors, gate capacitors, and gate to ground capacitors for each leg can be used to further improve the matching performance of the invention.