Post-Amplifier Receive Filter for 5G Intermodulation Distortion
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Solution Overview
Problem
Radio frequency (RF) systems face challenges in effectively filtering out noise and crossover leakage across wide channel bandwidths, leading to intermodulation distortion and desense issues, particularly in 5G NR applications where channel bandwidths can exceed 50 MHz.
Innovation Solution
Incorporating a configurable receive filter circuit with a post-low-noise amplifier (LNA) and single-throw, multi-pole switches to selectively connect a notch filter or acoustic wave filters, such as BAW or SAW filters, between the LNA output and the receive path, providing at least 30 dB of noise rejection and mitigating intermodulation distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a receive filter is placed before the LNA to filter out noise and interference, then the filtering effectiveness is improved, but the system noise figure deteriorates due to the filter's insertion loss
Solution Approach 1:
The patent inverts the conventional filter placement by positioning the receive filter after the LNA instead of before it. This reversal allows the filter's insertion loss to occur after amplification, minimizing its impact on the overall noise figure while still achieving effective filtering of out-of-band signals and interference from the received RF signal.
Solution Approach 2:
The LNA performs preliminary amplification of the weak received signal before the signal passes through the receive filter. This ensures that the signal is already amplified to a sufficient level before filtering, so that the filter's insertion loss does not significantly degrade the signal-to-noise ratio or increase the effective noise figure.
2Productivity
If the channel bandwidth is increased to accommodate 5G NR applications, then the data transmission capacity is improved, but the intermodulation distortion and desense issues worsen due to TX leakage and crossover leakage
Solution Approach 1:
The receive filter acts as an intermediary component placed in the signal path after the LNA to specifically target and remove TX leakage and crossover leakage signals. This intermediary filtering stage provides the necessary isolation between transmit and receive frequencies, enabling wider channel bandwidths to be used without suffering from intermodulation distortion and desense problems.
3Object-generated harmful factors
If a filter is placed after the LNA to reject TX leakage, then the intermodulation distortion is reduced, but the receive sensitivity may deteriorate due to additional insertion loss
Solution Approach 1:
The LNA performs preliminary amplification of the weak received signal before it passes through the receive filter. By ensuring the signal is already amplified to a sufficient level before filtering, the subsequent insertion loss of the filter has minimal impact on the overall receive sensitivity, as the signal-to-noise ratio has already been improved by the LNA's low-noise amplification.
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 significantly improves receive sensitivity by rejecting TX leakage and crossover leakage, maintaining system noise figure and performance across wide channel bandwidths, even in 5G NR bands, thereby reducing intermodulation distortion and desense issues.
Implementation Method 1
a downlink filter configured to filter a receive signal received by an antenna and having a passband corresponding to a receive channel
Implementation Method 2
the uplink filter configured to filter an amplified transmit signal for transmission via the antenna and having a passband corresponding to a transmit channel
Implementation Method 3
a receive amplifier configured to amplify the filtered receive signal output by the downlink filter to output an amplified receive signal
Implementation Method 4
a post-amplifier receive circuit including a first noise filter having a stopband corresponding to the transmit channel
Implementation Method 5
the first noise filter is a bulk acoustic wave (BAW) filter, a surface acoustic wave (SAW) filter, a Temperature-compensated SAW (TC-SAW) filter
Data Source
AI summary
A radio frequency front-end system includes an FDD duplexer. a receive amplifier amplifies a filtered receive signal output by the duplexer to output an amplified receive signal. the receive amplifier including a first amplified output and a second amplified output. A first noise filter connected to the first amplified output and having a stopband corresponding to the transmit channel. A switch selectively outputs either 1) the receive signal filtered by the noise filter or 2) the second amplified output.