RF Power Amplifier Noise Cancellation via Baseband Feedback Loop
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Solution Overview
Problem
Co-located RF transmission and reception systems in telecommunications networks experience significant interference due to out-of-band noise, particularly in UHF or VHF frequencies, where existing solutions like multiple filterings are energy-consuming, costly, and inefficient, especially as power amplifiers generate substantial noise near saturation, making it difficult to filter effectively.
Innovation Solution
An RF power amplifier with an additional analog feedback loop active in the baseband, connecting the output and input via decoupling inductors, injects part of the output noise back into the input to cancel noise, using a noise loop that operates below the useful amplification band to reduce noise without affecting the amplifier's gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If multiple filters are used to reduce emission noise, then noise reduction is achieved, but energy consumption increases and equipment space is consumed
Solution Approach 1:
The patent implements a feedback circuit that captures a portion of the amplifier's output signal and feeds it back to the input through a feedback network. This feedback mechanism automatically adjusts the amplifier's operating parameters to reduce noise emission at the source, eliminating the need for additional filter components and reducing both energy consumption and equipment space requirements.
Solution Approach 2:
The patent extracts and eliminates the noise-generating mechanism by modifying the amplifier's internal feedback loop. By taking out the problematic noise generation process and replacing it with a controlled feedback mechanism, the system achieves noise reduction without requiring external filter components that would consume energy and occupy space.
2Object-affected harmful factors
If multiple filters are used to reduce emission noise, then noise reduction is achieved, but equipment cost increases
Solution Approach 1:
The feedback circuit uses standard electronic components (resistors, capacitors, and operational amplifiers) to create a noise-reduction mechanism that is integrated into the existing amplifier design. This approach eliminates the need for expensive specialized filter components, thereby reducing overall equipment cost while maintaining noise reduction effectiveness.
Solution Approach 2:
The feedback network serves multiple functions simultaneously: it stabilizes the amplifier's gain, reduces noise emission, and improves linearity. This multi-functionality eliminates the need for separate dedicated noise filter components, reducing equipment cost through component consolidation.
3Loss of energy
If power amplification operates near saturation for optimal efficiency, then power efficiency is improved, but noise generation increases
Solution Approach 1:
The feedback circuit continuously monitors the amplifier's output and adjusts the input signal to maintain optimal operating conditions. This automatic adjustment allows the amplifier to operate near saturation for efficiency while the feedback mechanism compensates for noise generation, keeping noise levels acceptable despite high-power operation.
Solution Approach 2:
The feedback network dynamically changes the amplifier's operating parameters (gain, bias points) based on the operating conditions. By adjusting these parameters in real-time, the system maintains high efficiency near saturation while minimizing noise generation through optimal parameter selection.
4Object-affected harmful factors
If highly selective filters are implemented at high power levels, then noise filtering is improved, but overall transmitter efficiency is reduced due to losses
Solution Approach 1:
The patent extracts the noise reduction function from the output stage and implements it at the input stage through feedback. By taking out the noise filtering requirement from the high-power output path and moving it to the low-power input path via feedback, the system achieves noise filtering without the energy losses associated with high-power filtering components.
Solution Approach 2:
The feedback mechanism provides noise reduction at the input signal level, preventing noise from being amplified in the first place. This approach eliminates the need for lossy high-power filters at the output stage, maintaining transmitter efficiency while achieving effective noise filtering.
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 approach significantly reduces noise at the carrier's foot by 15 dB without the need for additional filtering, maintaining amplifier efficiency and compactness, and can eliminate the need for output filters in co-site applications.
Implementation Method 1
The amplifier includes a feedback loop, active in the baseband, connecting the output and the input of the amplifier via decoupling inductors
Implementation Method 2
A first inductor is connected between the feedback loop and the drain of the transistor, and a second inductor is connected between the feedback loop and the gate of the transistor
Data Source
Figure 1~3
Figure 2
Figure 4
AI summary
Disclosed is an RF power amplifier in which added emitted noise is greatly reduced. The invention applies for example in co-located RF transmission and reception systems belonging to different telecommunications networks, where each system is likely to pollute the other. The power amplifier comprising at least one transistor (Q1), said transistor comprising a feedback circuit (10) determining its amplification gain, it further comprises a feedback circuit (30) effective in a band base frequencies in which noise is produced at the output of said transistor, so that part of the output noise is injected at the input of said transistor.