LNA Input Switch Attenuation With Lower Insertion Loss
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Solution Overview
Problem
RF receivers face challenges in minimizing insertion loss and noise figure while maintaining linearity, particularly due to the impact of automatic gain control (AGC) on the low noise amplifier (LNA) input, which is sensitive to insertion loss and linearity issues when handling large signal amplitudes.
Innovation Solution
The design incorporates a switching block with a series and shunt switch configuration that selectively couples or decouples the input signal to the LNA, using an OFF impedance in low gain mode for attenuation and an ON impedance in high gain mode, and includes matching resistors to ensure proper impedance matching, reducing layout complexity and insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If input AGC is used when input signal amplitude is large to improve linearity, then linearity is improved, but noise figure degrades due to increased insertion loss
Solution Approach 1:
The switching block is divided into multiple switching arrangements, each corresponding to a specific RF band. Each switching arrangement independently controls the signal path for its associated band, allowing selective activation of attenuation functionality only for the currently active band, thereby minimizing overall insertion loss while maintaining linearity when needed.
Solution Approach 2:
The switching block dynamically configures the signal path based on the selected RF band and signal conditions. The series and shunt switches are controlled to provide attenuation only when and where needed, adapting the insertion loss characteristics to match the operational requirements of the active band, thus optimizing both linearity and noise figure performance.
2Reliability
If multiple switches are added to reduce insertion loss and improve noise figure, then noise figure is improved, but device complexity and layout space increase
Solution Approach 1:
Each switching arrangement is designed to perform multiple functions: band selection, signal attenuation, and isolation of inactive bands. By making the switching block multi-functional, the patent reduces the need for separate dedicated components for each function, thereby minimizing the total number of switches while achieving insertion loss reduction and noise figure improvement.
Solution Approach 2:
The patent combines the attenuation functionality with the band switching functionality by integrating series and shunt switches within each switching arrangement. This merging of functions allows the same switch network to simultaneously perform gain control and band selection, reducing overall device complexity and layout space requirements.
3Stability of the object's composition
If attenuator is inserted in series with LNA input to provide attenuation, then linearity is improved for large signals, but insertion loss increases and noise figure degrades
Solution Approach 1:
The switching block provides localized attenuation control by configuring the series and shunt switches specifically for the active RF band. Attenuation is applied only in the local context of the selected band's signal path, rather than uniformly across all bands. This localized approach minimizes overall insertion loss while providing necessary linearity improvement for the active band.
Solution Approach 2:
The series and shunt switches act as intermediary elements that dynamically control the signal path. Instead of using a fixed attenuator that always introduces loss, the switches mediate between the signal source and LNA, providing attenuation only when and where needed based on signal conditions and band selection, thereby reducing overall energy loss while maintaining linearity.
Data Source
AI summary
Methods and devices to improve the insertion loss at the LNA input of RF receivers are disclosed. The described methods and devices make use of the band switches in OFF state to improve the layout design, insertion loss and NF. Exemplary embodiments incorporating the disclosed concept are also presented.