Adjustable Amplifier Feedback Loop for Wideband RF Linearity
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Solution Overview
Problem
Designing RF circuits that can operate linearly over a wide frequency range is challenging due to non-idealities of semiconductor components, especially in multi-band and multi-system receivers that need to handle both in-band and out-band signals, leading to stringent linearity requirements.
Innovation Solution
An amplifier circuitry with a feedback loop incorporating a band-stop filter that adjusts to the current operating frequency, using frequency-selective impedance and polyphase filters to create a band-pass response, thereby mitigating interfering signals and improving linearity by attenuating out-band components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the amplifier circuitry operates over a wide frequency band to support multiple radio communication schemes, then the adaptability is improved, but the linearity deteriorates due to non-idealities of semiconductor components
Solution Approach 1:
The feedback loop is segmented into multiple frequency-selective filter branches, each targeting specific out-band frequency ranges. This segmentation allows the circuit to handle different frequency bands with optimized linearity compensation for each segment, resolving the contradiction between wide frequency coverage and maintained linearity.
Solution Approach 2:
Different frequency-selective filters are applied to different frequency ranges within the feedback loop. Each filter provides localized linearity improvement for its specific frequency band, allowing the amplifier to maintain high linearity across the entire wide frequency band by addressing each frequency range with tailored filtering characteristics.
2Reliability
If the amplifier circuitry attenuates out-band signals to improve linearity, then the linearity is improved, but the device complexity increases due to additional feedback loop circuitry
Solution Approach 1:
The feedback loop circuitry is designed to perform multiple functions simultaneously: it provides linearity improvement through frequency-selective filtering, maintains stability across wide frequency bands, and enables support for multiple radio communication schemes. This multi-functionality reduces the need for separate circuits for each function, thereby limiting the increase in overall device complexity.
Solution Approach 2:
The invention employs a feedback mechanism where out-band signals are captured, filtered, and fed back to the amplifier input with inverted polarity to cancel nonlinear distortions. This feedback approach provides automatic linearity correction without requiring complex external control systems, balancing linearity improvement with acceptable circuit complexity.
3Reliability
If frequency-selective filtering is applied in the feedback loop to cancel undesired signals, then the linearity is improved, but the phase shift increases due to filter characteristics
Solution Approach 1:
The filter characteristics, including cutoff frequencies and Q-factors, are optimized to achieve the desired linearity improvement while minimizing phase shift. By carefully adjusting these parameters, the circuit achieves effective out-band signal attenuation with acceptable phase characteristics, resolving the contradiction between linearity and phase stability.
Data Source
AI summary
An amplifier circuitry having adjustable parameters is presented. The present amplifier circuitry includes a feed-back loop, wherein the feedback loop converts (26) a signal to another frequency, filters (20) the signal in the other frequency, and restores (24) the filtered signal back to the original frequency for inputting the signal to an input of the amplifier (22). The feed-back loop implements a band-stop filter (20) having an adjustable stopband causing the amplifier circuitry to have an adjustable band-pass response. A passband of the amplifier circuitry is changed from one operating frequency to another operating frequency by changing frequency conversion parameters of the feedback loop.