Dual Receive Filter With Shunt Path for LNA Linearity
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Solution Overview
Problem
In wireless communications devices, full duplex radio systems face challenges with signal distortion and noise interference due to insufficient isolation between transmitter and receiver portions, leading to degradation in noise figure and linearity issues, especially in conventional low noise amplifiers (LNAs).
Innovation Solution
The implementation of a modified receiver structure with a matching network and a shunt path that includes a shunt filter and load to direct unwanted leaked transmission signal energy away from the amplifier, improving impedance matching and reducing distortion by dissipating or reflecting this energy with appropriate phase to prevent clipping and enhance linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If isolation between transmitter and receiver portions is increased to prevent transmitted signal leakage, then linearity of received signals is improved, but noise figure of the receiver deteriorates
Solution Approach 1:
The receiver filter is divided into two distinct sections: a first section with high isolation characteristics for frequencies near the transmitter output frequency to prevent leakage, and a second section with low insertion loss for frequencies at the receiver input frequency to maintain noise figure. This segmentation allows each section to be optimized for its specific frequency range, resolving the contradiction between linearity and noise figure.
2Reliability
If conventional receiver filters are used to block transmitted signal leakage, then isolation is improved, but insertion loss increases causing signal attenuation
Solution Approach 1:
Different sections of the receiver filter are designed with different quality characteristics tailored to their specific frequency requirements. The first section has high isolation quality for blocking transmitter leakage at transmitter frequencies, while the second section has low insertion loss quality for passing receiver signals at receiver frequencies. This local optimization of filter characteristics resolves the contradiction between isolation and insertion loss.
3Measurement precision
If LNA gain is increased to amplify weak received signals, then sensitivity is improved, but distortion from transmitted signal leakage worsens
Solution Approach 1:
The receiver filter performs preliminary filtering of transmitted signal leakage before the signals reach the LNA. By removing the strong transmitter leakage signals in advance, the LNA can amplify weak received signals with high gain without causing distortion from saturation or intermodulation. This preliminary action resolves the contradiction between sensitivity and distortion.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively improves the third-order intercept point (IP3) and intermodulation margins of the amplifier, maintaining noise figure and gain while reducing distortion, thus enhancing the overall linearity and sensitivity of the receiver.
Implementation Method 1
reflecting at least a portion of the unwanted leaked transmission signal energy with an appropriate phase to cancel the unwanted leaked transmission signal energy at an output of the amplifier
Implementation Method 2
cancel the unwanted leaked transmission signal energy at an output of the amplifier
Implementation Method 3
dissipating at least a portion of the unwanted leaked transmission signal energy
Data Source
AI summary
A stage is provided for a receiver of a wireless device. The stage comprises a matching network that separates amplified signals of interest received from an amplifier from amplified unwanted signals received from the amplifier in conjunction with additional downstream filters. The stage also comprises a signal path that comprises components for receiving and processing the amplified signals of interest, and a shunt path that comprises components for adjusting reflected energy sent back to the amplifier for limiting the output swing of the amplifier in a frequency band corresponding to the amplified unwanted signals.