Source-Switched Split LNA 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 low front-end losses when handling intraband non-contiguous carrier aggregate (CA) signals, particularly due to the limitations of passive splitters which result in interference, distortion, and degradation of sensitivity and noise figure.

Innovation Solution

The use of multiple low noise amplifiers configured in a cascode architecture with switchable transistors and capacitors allows for operation in both single and split modes, eliminating the need for power splitters and ensuring consistent input impedance, thereby enhancing isolation and reducing losses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a passive splitter is used to split the signal to multiple downconverters, then the signal can be distributed to multiple channels, but the output-to-output isolation between channels is insufficient (only 18-20 dB) causing interference and distortion

Engineering Contradiction:

Improvesignal distribution capabilityVSAvoidinterference and distortion between channels

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The invention divides the single LNA output into multiple independent LNA paths, with each LNA dedicated to a specific channel. This segmentation eliminates the need for a passive splitter and provides superior isolation between channels, as each LNA operates independently without cross-coupling to other channels.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention introduces a mode selector switch as an intermediary device that controls the connection between the LNA output and the downconverter inputs. This switch enables selective coupling to different channels and provides better isolation compared to a passive splitter by actively managing signal paths rather than passively dividing them.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If a passive splitter is used to handle multiple channels, then signal distribution is achieved, but the isolation degrades significantly when operating frequency deviates from the splitter's optimal frequency

Engineering Contradiction:

Improvemulti-channel handling capabilityVSAvoidisolation performance across frequency range

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The invention employs a mode selector switch that can dynamically reconfigure the signal paths based on the operating mode (single channel or dual channel). This dynamic switching capability allows the system to maintain optimal performance across different frequency ranges by selecting the appropriate LNA and path configuration, unlike a fixed-frequency passive splitter.

Inventive Principle:

Principle #15Dynamics

3Adaptability or versatility

If a passive splitter is used in the signal path, then signal distribution to multiple downconverters is enabled, but significant power loss occurs reducing receiver sensitivity

Engineering Contradiction:

Improvesignal routing flexibilityVSAvoidpower loss in signal path

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

By segmenting the signal path into multiple independent LNA channels, the invention eliminates the need for a passive splitter that inherently divides power. Each LNA provides full-gain amplification to its dedicated channel without the 3 dB power division loss characteristic of passive splitters, thereby improving overall receiver sensitivity.

Inventive Principle:

Principle #1Segmentation

4Adaptability or versatility

If the LNA output is coupled to multiple downconverters through a splitter, then both channels can be received simultaneously, but the noise figure and linearity are degraded due to losses

Engineering Contradiction:

Improvesimultaneous multi-channel receptionVSAvoidnoise figure and linearity performance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The invention segments the reception system into independent LNA channels, with each LNA providing clean, low-noise amplification to its dedicated channel. This eliminates the cumulative losses from the mode selector switch and passive splitter that would otherwise degrade the noise figure and linearity, maintaining superior RF performance in both single and dual channel modes.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS11005425B2Source switched split LNA

Publication Date: 2021.05.11 PSEMI CORP

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” 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 caps for each legs can be used to further improve the matching performance of the invention.