RF Amplifier Feedback Ladder for Multi-Band Gain and Linearity
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Solution Overview
Problem
Recent RF front-end low-noise amplifiers (LNAs) for mobile communication devices face challenges in achieving ultra-low noise figure with high gain performance across multiple frequency bands, requiring flexible gain modes and improved linearity while minimizing power gain variation and complexity.
Innovation Solution
The implementation of a radio frequency amplifier circuit with a feedback circuit comprising a resistive feedback circuit and a shunt feedback circuit, arranged in a ladder structure with switches to adjust impedance and provide multiple gain modes, enabling accurate gain reduction with good linearity and low noise figure degradation across various frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a common-source input stage with external matching component is used to achieve ultra-low noise figure with high gain, then noise figure performance is improved, but device complexity increases due to high number of different frequency bands
Solution Approach 1:
The LNA core is designed to support a wide range of frequency bands (e.g., 600 MHz to 3.8 GHz) with a single circuit implementation, enabling the same core to be reused across multiple bands. This multi-functionality reduces the need for separate LNA designs for each band, thereby reducing overall device complexity while maintaining ultra-low noise figure performance through the common-source input stage with external matching component
2Adaptability or versatility
If multiple gain modes are implemented to support different applications, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent implements multiple gain modes (e.g., high gain mode with 21 dB gain and passive bypass mode with -12 dB gain) through dynamic switching mechanisms that allow the LNA core to adapt its operating state. This dynamic capability enables the circuit to switch between different gain configurations based on application requirements, improving adaptability while managing complexity through controlled switching rather than multiple static circuits
Solution Approach 2:
The patent achieves different gain modes by changing circuit parameters such as switching between different feedback configurations and adjusting impedance values. By varying parameters like feedback factor and operating point rather than creating entirely separate circuits for each mode, the patent reduces complexity while maintaining the ability to support multiple gain modes with different linearity and noise figure characteristics
3Manufacturing precision
If gain is reduced by 3 dB to improve linearity, then linearity performance is improved, but power gain decreases
Solution Approach 1:
The patent achieves linearity improvement while managing power gain by changing circuit parameters such as feedback factor and operating point. Through parameter adjustment rather than simple gain reduction, the patent can improve linearity metrics (e.g., IIP3) by 3 dB while controlling the impact on power gain, allowing flexible trade-offs between linearity and gain based on application requirements
Data Source
AI summary
An RF amplifier circuit includes an amplifier and a feedback circuit. The feedback circuit includes a resistive feedback circuit coupled between an input and output of the amplifier and a shunt feedback circuit coupled between the output of the amplifier and a reference input. The resistive feedback circuit includes a first set of serially coupled resistors and a first set of switches. The first sets of resistors and switches are arranged in a ladder structure with each switch of the first set of switches configured to bypass one of the resistors of the first set of resistors. The shunt feedback circuit includes a second set of serially coupled resistors and a second set of switches. The second sets of resistors and switches are arranged in a ladder structure with each switch of the second set of switches configured to bypass one of the resistors of the second set of resistors.