Split Cascode LNA Switching for Carrier Aggregation Isolation
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Solution Overview
Problem
Current low noise amplifiers (LNAs) in communications receivers face challenges in achieving high output-to-output isolation and maintaining linearity and noise figure when handling intraband non-contiguous carrier aggregate (CA) signals, especially due to the limitations of passive splitters which result in significant losses and degradation of performance across a broad frequency range.
Innovation Solution
The use of multiple cascode low noise amplifiers (LNAs) with switchable configurations, including a source switching split (SSS) configuration that allows for independent control of the input FETs and the elimination of power splitters, ensures consistent input impedance across single and split modes, thereby enhancing isolation and reducing noise figure and linearity issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a passive power splitter is used to split the LNA output to multiple DBCs, then the receiver can handle multiple channels, but the isolation between outputs is limited to 18-20 dB and insertion loss increases
Solution Approach 1:
The invention divides the LNA into multiple independent amplifier segments (first LNA and second LNA), each dedicated to a specific channel. This eliminates the need for a passive splitter and enables independent control of each channel's signal path, achieving superior isolation between channels while maintaining multi-channel handling capability.
Solution Approach 2:
The invention introduces dynamic switching mechanisms (switches coupled to the LNA) that allow selective activation of individual LNA segments based on which channel is being received. This dynamic control enables the system to adapt to different channel configurations and achieve high isolation by activating only the necessary amplifier segment.
2Adaptability or versatility
If a passive power splitter is used to split the LNA output, then the signal can be distributed to multiple DBCs, but significant power loss occurs
Solution Approach 1:
By segmenting the LNA into multiple independent amplifier units, each capable of direct connection to a specific DBC, the system eliminates the passive splitter that causes 3 dB inherent loss plus additional insertion loss. Each LNA segment drives its designated channel directly, preserving signal power.
Solution Approach 2:
The dynamic switching mechanism allows the system to activate only the LNA segment needed for the current channel, avoiding the continuous power division and loss associated with passive splitters. This reduces overall power consumption and signal loss while maintaining the ability to distribute signals to multiple DBCs as needed.
3Adaptability or versatility
If the LNA operates over a broad frequency band to handle CA signals, then the receiver can support carrier aggregation, but maintaining consistent performance across the band is challenging
Solution Approach 1:
The LNA is divided into multiple frequency-optimized segments, where each LNA segment can be designed to operate optimally at a specific frequency or frequency range within the broad band. This segmentation allows each segment to maintain consistent performance at its designated frequency without being compromised by the requirements of other frequency ranges.
Solution Approach 2:
The switching mechanism dynamically selects which LNA segment to activate based on the frequency of the received signal. This dynamic frequency-based selection ensures that the system always uses the LNA segment best suited for the current operating frequency, maintaining consistent performance across the entire broad frequency band.
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.