Reconfigurable Balanced Bandpass Filters Using Varactor Tuning
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Solution Overview
Problem
Current high-frequency differential/balanced bandpass filters have limited tunability and common-mode suppression, often requiring mechanical tuning and achieving only low common-mode suppression and narrow frequency/narrow bandwidth tuning.
Innovation Solution
Design of high-order fully-reconfigurable balanced bandpass filters using a coupling matrix approach, allowing for tunability of center frequency and bandwidth through resonator tuning, with multiple transmission zeros and poles for enhanced common-mode suppression and quasi-elliptic differential-mode response, enabling intrinsic switching-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If mechanical tuning elements are used to achieve frequency and bandwidth tuning, then tunability is improved, but device complexity and insertion loss increase
Solution Approach 1:
The patent replaces mechanical tuning elements with electronic varactor diodes for frequency tuning and with electronic switches for bandwidth tuning and filter activation. This substitution eliminates mechanical moving parts, reducing complexity, improving reliability, and lowering insertion loss while maintaining full tunability across frequency and bandwidth parameters.
Solution Approach 2:
The patent achieves frequency and bandwidth tuning by changing the electrical parameters (capacitance and resistance) of the filter circuit through varactor diodes and electronic switches. By varying the capacitance values of varactors and the resistance values of switches, the filter's center frequency and bandwidth can be continuously adjusted without mechanical intervention.
2Ease of manufacture
If low-order transfer functions are used for planar integration, then manufacturing ease is improved, but common-mode suppression and selectivity deteriorate
Solution Approach 1:
The patent employs a high-order transfer function (5th order or higher) with multiple resonant sections that can be planarly integrated. The dynamic configuration of these sections, including series and parallel resonant circuits with carefully designed coupling, achieves both high common-mode suppression (>20 dB) and good differential-mode selectivity while maintaining compatibility with planar manufacturing processes.
Solution Approach 2:
The patent uses asymmetric coupling between resonant sections and asymmetric placement of resistive loads to achieve superior common-mode suppression. The asymmetric design creates different impedance transformations for common-mode and differential-mode signals, enabling the filter to reject common-mode noise effectively while passing differential-mode signals with minimal loss.
3Adaptability or versatility
If bandwidth tuning is implemented, then adaptability is improved, but in-band insertion loss increases due to coupling tuning requirements
Solution Approach 1:
The patent achieves bandwidth tuning by changing the resistance parameters of electronic switches rather than adjusting coupling coefficients. By varying the resistance values of switches connected in parallel with resonant sections, the effective Q-factor of the filter is modified, enabling continuous bandwidth control from narrow to wide without introducing additional coupling losses.
Solution Approach 2:
The patent replaces mechanical coupling adjustments with electronic switch-based bandwidth control. Electronic switches provide precise, lossless resistance modulation that does not require physical movement or contact, thereby maintaining low insertion loss across the entire bandwidth tuning range while enabling rapid reconfiguration.
4Measurement precision
If high-order filter sections are used to improve selectivity, then differential-mode selectivity is improved, but device complexity and common-mode suppression difficulty increase
Solution Approach 1:
The patent divides the high-order filter into multiple independent resonant sections (typically 3-5 sections), each contributing specific poles and zeros to the overall transfer function. Each section can be designed and optimized independently for its specific frequency and selectivity requirements, then combined through planar integration to achieve the cumulative effect of high differential-mode selectivity with manageable complexity.
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 provides wideband common-mode suppression (>70%) and tunability in center frequency and bandwidth, reducing in-band insertion loss and complexity, with prototypes demonstrating >22 dB isolation and >35 dB common-mode suppression across various states.
Implementation Method 1
multiple resonant sections cascaded between a differential RF input and a differential RF output. The sections include at least one multi-resonant cell (MRC), having four frequency tunable MRC resonators, a frequency tunable pole at a center frequency of the filter (f0), and two frequency tunable transmission zeroes (TZs) at resonating frequencies of MRC resonators
Implementation Method 2
The resonant sections are cascaded through impedance inverters
Data Source
AI summary
High-order balanced bandpass filters that are continuously tunable in terms of frequency and bandwidth (BW) and can be intrinsically switched-off. The filters include multiple resonant sections cascaded between a differential RF input and a differential RF output. The resonant sections comprise at least one multi-resonant cell and at least one transmission pole cell. The multi-resonant cell includes four frequency tunable resonators, and is configured to create a frequency tunable pole at the center frequency of the filter, and two frequency tunable transmission zeroes at resonating frequencies of the resonators of the multi-resonant cell. The transmission pole cells each include two resistively-terminated frequency-tunable resonators configured to resonate at the center frequency of the filter.