N-Path Filter Branch Circuits for Flatter Passband Response
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Solution Overview
Problem
Conventional N-path filters have limited passband flatness and suffer from significant passband droop, which hinders their ability to effectively reject TX leakage frequencies and maintain high-quality filtering in wireless communication systems.
Innovation Solution
The N-path filter design incorporates multiple branches with common drain amplifier circuits, each comprising a transistor, capacitors, and switches, allowing for dynamic impedance adjustment and improved frequency response, including the addition of feedback capacitors and degeneration circuits to enhance rejection and flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional N-path filters are used, then the filter provides basic frequency selection, but the passband flatness is poor and significant passband droop occurs
Solution Approach 1:
The patent implements dynamic impedance adjustment in each filter branch by using switches controlled by non-overlapping clock signals. The impedance values are changed dynamically during operation to compensate for passband droop and achieve flatter frequency response, rather than using fixed passive components.
Solution Approach 2:
The patent changes the electrical parameters (impedance values) of the filter branches by switching between different circuit configurations. By adjusting the impedance parameters dynamically according to the clock phases, the filter achieves improved passband flatness and reduced droop while maintaining reliable filtering performance.
2Reliability
If conventional N-path filters are used, then the circuit structure is simple, but the out-of-band rejection is insufficient
Solution Approach 1:
The patent divides the filter into multiple independent branches, each with its own switch and impedance network. This segmentation allows each branch to contribute to the overall rejection performance, achieving steeper out-of-band rejection through the combined effect of multiple segmented filter paths.
Solution Approach 2:
The patent employs periodic switching of the filter branches using non-overlapping clock signals. This periodic action enables the filter to achieve higher effective order and steeper rejection characteristics by rapidly switching between multiple filter paths, enhancing out-of-band rejection without requiring a single complex high-order filter structure.
3Manufacturing precision
If the passband droop is reduced through component adjustment, then the frequency response improves, but the device complexity increases
Solution Approach 1:
The patent uses the same switch and impedance network structure in each filter branch, making the design universal and modular. This multi-functional approach allows the same circuit topology to simultaneously achieve frequency selection, passband flattening, and out-of-band rejection, reducing overall complexity compared to using different specialized components for each function.
Data Source
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AI summary
Certain aspects of the present disclosure provide N-path filters with wider passbands and steeper rejection than conventional N-path filters with only a single pole in each filter path. These N-path filters also have a flatter passband with decreased passband droop. One example N-path filter (402) includes a plurality of branches selectively connected with a common node, each branch of the N-path filter comprising a switch (M1, M2, M3, M4) connected in series with an impedance (ZA, ZB, ZC, ZD) comprising a common drain amplifier circuit (604A, 604B, 604C, 604D). In certain aspects, the amplifier circuit may include a degeneration circuit for stability and/or a polyphase feedback circuit to reduce in-band peaking.