Ring Resonator Bandpass Filter With Parallel Signal Branches
Solution Overview
Problem
Existing bandpass filters face challenges in achieving low insertion loss while effectively attenuating interference signals in stop bands, particularly in multi-band front-end modules like WLAN modules, where steep flanks and efficient signal processing are required.
Innovation Solution
A bandpass filter design featuring parallel signal branches forming a ring resonator with complex wave modes and equal amplitude, 180° phase difference, utilizing LC elements and impedance jumps, which allows for equal transmission coefficients in both directions, enabling efficient signal circulation and notch formation at specific frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional bandpass filter designs are used, then basic filtering function is achieved, but insertion loss is high and attenuation in stop bands is insufficient
Solution Approach 1:
The filter is divided into multiple parallel signal branches (first and second signal branches) forming a ring resonator structure. Each branch processes signals independently with specific phase characteristics, allowing selective cancellation of stop band frequencies while maintaining pass band transmission with minimal loss.
Solution Approach 2:
The signal branches are designed with asymmetric impedance transformations and different phase shift characteristics. The first signal branch has impedance transformation ratio k1 and the second has k2, where the branches exhibit different amplitude and phase responses to create the required 180° phase difference at stop frequencies for destructive interference.
2Object-affected harmful factors
If steep flanks are achieved in transfer function, then stop band attenuation is improved, but device complexity increases
Solution Approach 1:
The ring resonator structure creates resonant conditions where signals circulating in opposite directions (clockwise and counterclockwise) interfere constructively in the pass band and destructively in the stop bands. This resonance-based approach achieves steep flanks and high attenuation through natural wave interference patterns rather than complex multi-stage filtering.
Solution Approach 2:
The filter utilizes frequency-dependent impedance transformations in the signal branches, where the impedance transformation ratios k1 and k2 vary with frequency. This allows the same structure to provide different amplitude and phase responses at different frequencies, achieving steep flanks through parameter variation rather than structural complexity.
3Object-affected harmful factors
If multiple signal branches with different characteristics are used, then stop frequencies are effectively suppressed, but manufacturing precision requirements increase
Solution Approach 1:
The signal branches are designed to have equal transmission coefficients in both passage directions, creating a balanced ring resonator structure. This equipotential design ensures that waves circulating in opposite directions have equal amplitudes, making the phase cancellation at stop frequencies more robust and less sensitive to manufacturing variations.
Solution Approach 2:
The ring resonator structure provides feedback paths where signals circulating in opposite directions continuously interact. The feedback mechanism naturally reinforces the phase cancellation effect at stop frequencies, as any deviation from the ideal 180° phase difference is corrected by the resonant feedback, reducing sensitivity to manufacturing tolerances.
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
The solution achieves low insertion loss and high attenuation in stop bands with steep transmission characteristics, suitable for integration in LTCC substrates, enhancing the performance of multi-band front-end modules like WLAN modules by effectively managing signal branches and phase relationships.
Implementation Method 1
For the resulting wave Ūout at the output of the bandpass filter, for at least two stop frequencies, the condition Ūout=ŪCW+ŪCCW≈0 applies, wherein the amplitudes of opposed wave modes are approximately equal |ŪCW|≈|ŪCCW|, and wherein the phase difference of these wave modes equals 180°
Implementation Method 2
Two signal branches form a ring resonator, in which a wave mode with a complex amplitude ŪCW=|ŪCW|exp{−jφCW} running in the clockwise direction and a wave mode with a complex amplitude ŪCCW=|ŪCCW|exp{−jφCCW} running in the counterclockwise direction can propagate
Implementation Method 3
The signal branches feature a frequency-dependent runtime, and each acts as a phase shifter
Implementation Method 4
The ring resonator includes concentrated LC elements, i.e., capacitors, inductors. In principle, an inductor can be replaced by a section of a delay or transmission line
Data Source
AI summary
A bandpass filter is described herein. The bandpass filter has two parallel signal branches, each connected, on an input side, to an input node and, on an output side, to an output node. The two signal branches form a ring resonator, having a wave mode with a complex amplitude of {right arrow over (U)}CW=|{right arrow over (U)}CW|exp{−jφCW} propagating in a clockwise direction and a wave mode with a complex amplitude of {right arrow over (U)}CCW=|{right arrow over (U)}CCW|exp{−jφCCW} propagating in a counterclockwise direction. The vector sum of a resulting wave {right arrow over (U)}out at the output node of the bandpass filter at two or more stop frequencies is: {right arrow over (U)}out={right arrow over (U)}CW+{right arrow over (U)}CCW=0, and |{right arrow over (U)}CW|=|{right arrow over (U)}CCW| and |φCW−φCCW|=180°. The stop frequencies are arranged such that a passband is formed between two stop frequencies.