Split LNA Drain Sharing for Low-Noise Receiver 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 operating in split mode, especially when handling intraband non-contiguous carrier aggregate signals, due to limitations in passive splitters and mode selection switches, leading to interference, distortion, and degradation in sensitivity and noise figure.
Innovation Solution
The use of multiple low noise amplifiers configured as cascode amplifiers with switchable transistors and capacitors allows for operation in both single and split modes with enhanced isolation and reduced losses, by selectively turning on/off output FETs, matching input impedance, and using drain switches to couple/decouple drain terminals, thereby 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 signal to multiple DBCs, then the receiver can handle multiple channels, but the isolation between outputs is limited to 18-20 dB and degrades with frequency deviation
Solution Approach 1:
The invention divides the single LNA output path into multiple independent LNA paths, each with its own amplifier and switching network. This segmentation allows each LNA to independently drive its connected DBC, eliminating the isolation limitations of passive splitters while maintaining multi-channel handling capability.
Solution Approach 2:
The invention employs dynamic switching networks that can reconfigure the connection topology between LNAs and DBCs based on operating mode. In single-channel mode, the switch connects one LNA directly to a DBC; in multi-channel mode, multiple LNAs are connected to multiple DBCs. This dynamic reconfiguration optimizes both isolation and signal path for each operating condition.
2Adaptability or versatility
If a passive splitter is used to split the signal, then the receiver can operate in split mode, but significant power loss occurs (3 dB reduction plus 1.0-1.5 dB insertion loss)
Solution Approach 1:
Instead of using a single passive splitter that divides power, the invention segments the signal path into multiple active LNA paths. Each LNA independently amplifies its assigned signal, eliminating the inherent 3 dB power loss of passive splitting while enabling split mode operation.
Solution Approach 2:
The invention replaces the passive mechanical/electrical splitter with active electronic amplification paths. Each LNA path uses active transistors and switching networks to dynamically route and amplify signals, substituting the lossy passive splitting mechanism with active signal regeneration and routing.
3Adaptability or versatility
If the LNA operates over a broad frequency band to handle CA signals, then the receiver can process multiple frequency channels, but achieving desired isolation between DBCs becomes difficult
Solution Approach 1:
The invention uses dynamically controllable switching networks that can reconfigure the signal path based on the operating frequency and mode. Each LNA is independently controlled, allowing the system to optimize isolation at different frequencies by selectively activating specific LNA-DBC pairs and using switching networks to minimize cross-coupling across the broad frequency range.
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.