Multiband LNA Resonant Feedback for Low Noise Across RF Bands
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Solution Overview
Problem
Implementing multiple low noise amplifiers (LNAs) for multiple receive bands is costly and inefficient, while using a single LNA with resistive feedback can lead to signal degradation and increased noise figure at certain frequencies.
Innovation Solution
A multiband low noise amplifier with parallel resonant feedback, featuring an amplifier element with resistive feedback and series-coupled resonant circuits that operate as open circuits at specific frequencies to decouple resistive feedback, allowing a single amplifier to effectively cover multiple frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple LNAs are implemented for multiple receive bands, then noise figure requirements are met for multiple receive frequencies, but cost increases, semiconductor die area is consumed, and signal degradation occurs
Solution Approach 1:
A single LNA is designed to serve multiple receive bands (e.g., 800 MHz, 1.8 GHz, 2.1 GHz, 2.6 GHz) through the use of resonant circuits that can be tuned to different frequencies. The resonant circuits enable the amplifier to selectively amplify signals at different bands while maintaining acceptable noise figure performance across all bands, eliminating the need for separate LNAs for each band.
Solution Approach 2:
The noise figure and gain characteristics of the LNA are adjusted by changing the resonant frequency of the resonant circuits. By tuning the resonant circuits to different frequencies corresponding to different receive bands, the LNA can optimize its performance for each band without requiring separate amplifier designs.
2Device complexity
If a single LNA is implemented to cover multiple receive frequencies, then cost and area are reduced, but resistive feedback degrades reverse isolation, return loss, and increases noise figure at certain frequencies
Solution Approach 1:
Resonant circuits are introduced into the feedback path of the LNA. These resonant circuits exhibit frequency-selective behavior where they present low impedance at their resonant frequency and high impedance at other frequencies. This allows the resistive feedback to be effectively bypassed at resonant frequencies, preventing the degradation of reverse isolation, return loss, and noise figure that would otherwise occur with continuous resistive feedback.
Solution Approach 2:
Resonant circuits are inserted as intermediary elements between the input and output of the LNA in the feedback path. These resonant circuits mediate the feedback signal by allowing it to pass at resonant frequencies while blocking it at non-resonant frequencies, thereby controlling when resistive feedback is active and preventing its harmful effects at frequencies where it would degrade performance.
3Adaptability or versatility
If resistive feedback is used in a single LNA for multiple bands, then the LNA can cover multiple frequencies, but reverse isolation and return loss are degraded
Solution Approach 1:
Resonant circuits are placed in the feedback path to exploit their frequency-selective impedance characteristics. At resonant frequencies, the resonant circuits present low impedance, allowing feedback signals to pass and maintaining adaptability across multiple bands. At non-resonant frequencies, they present high impedance, blocking feedback signals and preserving reverse isolation and return loss performance.
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 solution reduces noise figure, maintains flat gain and linearity across multiple bands, and simplifies impedance matching, enabling efficient operation with a single amplifier for multiple bands without signal degradation.
Implementation Method 1
each of the resonant circuits is configured to operate as an effective short circuit at a frequency other than a resonant frequency and configured to operate as an effective open circuit at the resonant frequency
Data Source
AI summary
A multiband low noise amplifier (LNA) with parallel resonant feedback includes an amplifier element configured to receive a radio frequency (RF) signal at an RF input and provide an amplified version of the RF signal at an RF output, a resistive feedback circuit coupled between the RF input and the RF output, and a plurality of series-coupled resonant circuits coupled in series with the resistive feedback circuit between the RF input and the RF output of the amplifier element, wherein each of the resonant circuits is configured to operate as an effective short circuit at a frequency other than a resonant frequency and configured to operate as an effective open circuit at the resonant frequency to decouple the resistive feedback from the amplifier element at each resonant frequency.