Drain-Sharing Split LNA Front End for CA Isolation and Linearity
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Solution Overview
Problem
Current receiver front ends face challenges in achieving high output-to-output isolation, maintaining third order intercept linearity, and minimizing noise figure when operating in Split mode, especially when handling intraband non-contiguous carrier aggregate (CA) signals.
Innovation Solution
The implementation of a receiver front end using multiple low noise amplifiers (LNAs) in a cascode configuration, with switches to control the operation of the output FETs and input impedance matching, allows for operation in both single and split modes while maintaining high isolation and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a passive splitter is used to split the LNA output to multiple DBCs, then the receiver can handle multiple channels, but the isolation between output channels is insufficient (only 18-20 dB)
Solution Approach 1:
The invention divides the single LNA output path into multiple independent amplifier paths (first LNA path and second LNA path), each handling a specific channel. This segmentation allows each path to be independently optimized and provides better isolation between channels compared to a passive splitter, resolving the contradiction between multi-channel handling and channel isolation.
2Adaptability or versatility
If a passive splitter is used to divide the signal to multiple DBCs, then channel aggregation is enabled, but the splitter introduces significant power loss and degrades noise figure
Solution Approach 1:
The invention segments the signal path into multiple active LNA paths instead of using a passive splitter. Each LNA path actively amplifies its designated channel, eliminating the power loss inherent in passive splitters. This approach enables carrier aggregation while maintaining signal power and improving noise figure, as each LNA can be optimized for its specific frequency channel.
3Adaptability or versatility
If the LNA operates over a broad frequency band to handle multiple channels, then carrier aggregation is supported, but maintaining linearity (third order intercept) becomes difficult
Solution Approach 1:
The invention divides the broad frequency operation into multiple narrower frequency bands, each handled by a dedicated LNA path. Each LNA can be optimized for its specific frequency range, maintaining high linearity and third order intercept performance within its operating band. This segmentation approach allows the overall system to handle broad frequency ranges through carrier aggregation while each individual LNA maintains excellent linearity characteristics.
4Device complexity
If a single LNA amplifies all channels before splitting, then the architecture is simple, but cross-coupling between DBCs causes interference and distortion
Solution Approach 1:
The invention segments the amplification function into multiple independent LNA paths, with each path dedicated to a specific channel. This eliminates the cross-coupling interference that occurs when a single LNA amplifies multiple channels simultaneously followed by passive splitting. Each LNA path operates independently, preventing distortion and interference between channels, though the architecture becomes more complex than a single LNA with splitter.
Data Source
AI summary
A receiver front end having 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. A drain switch is provided between the drain terminals of input FETs to place the input FETs in parallel. This increases the gm of the input stage of the amplifier, thus improving the noise figure of the amplifier.