RF Filter Circuit With Dual Frequency Control for Low Passband Loss
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Solution Overview
Problem
Existing radio-frequency filters with variable-frequency capabilities face challenges in shifting the resonant frequency of the series arm circuit without increasing loss at the high edge of the pass band, leading to increased differences between resonant and anti-resonant frequencies.
Innovation Solution
Incorporating a series arm circuit with a variable frequency circuit that includes a switch and capacitor in parallel with the series arm resonator, allowing independent control of resonant and anti-resonant frequencies through switch states, and using interdigital capacitor electrodes with narrower electrode fingers to enhance the Q factor and reduce loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a switch is switched between ON and OFF to shift the anti-resonant frequency of the series arm circuit, then the frequency of the attenuation pole on the higher-frequency side of the pass band can be varied, but the resonant frequency of the series arm circuit does not change, which increases the difference between anti-resonant frequency and resonant frequency, thereby increasing the loss at the high edge of the pass band
Solution Approach 1:
The series arm circuit is divided into two independent frequency control mechanisms: a first switch (SW1) with a first capacitor (C1) connected in parallel to control the anti-resonant frequency, and a second switch (SW2) with a second capacitor (C2) connected in series to control the resonant frequency. This segmentation allows independent adjustment of resonant and anti-resonant frequencies, resolving the contradiction by enabling frequency variation while maintaining minimal difference between these frequencies, thus reducing loss at the high edge of the pass band.
2Ease of operation
If the resonant frequency of the series arm circuit is kept fixed while varying the anti-resonant frequency, then the attenuation pole frequency can be adjusted, but the difference between resonant and anti-resonant frequencies increases, degrading filter performance
Solution Approach 1:
The invention makes both the resonant frequency and anti-resonant frequency dynamically adjustable through two independent switch-capacitor circuits. The first switch-capacitor pair adjusts the anti-resonant frequency to position the attenuation pole, while the second switch-capacitor pair simultaneously adjusts the resonant frequency to maintain an appropriate difference from the anti-resonant frequency. This dynamic dual-control mechanism ensures optimal filter performance while providing ease of attenuation pole adjustment.
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
This configuration enables the radio-frequency filter to vary the attenuation pole frequency on the higher-frequency side without increasing loss, maintaining sharpness and reducing bulk wave loss, thereby improving the filter's performance and size efficiency.
Implementation Method 1
The series arm resonator and the first capacitor are connected in series with each other, and thus, the resonant frequency of the first series connecting circuit constituted by the series arm resonator and the first capacitor becomes higher than that of the series arm resonator alone.
Implementation Method 2
The series arm resonator and the first capacitor are connected in series with each other, and thus, the resonant frequency of the first series connecting circuit constituted by the series arm resonator and the first capacitor becomes higher than that of the series arm resonator alone.
Data Source
AI summary
A radio-frequency filter (10) includes a series arm circuit (11) and a parallel arm circuit (12). The series arm circuit (11) is disposed on a path connecting an input/output terminal (11m) and an input/output terminal (11n). The parallel arm circuit (12) is connected to a ground and to a node (x1) on the path. The series arm circuit (11) includes a series connecting circuit (11e) and a first variable frequency circuit (11a). The series connecting circuit (11e) includes a series arm resonator (s1) and a capacitor (C1). The first variable frequency circuit (11a) is connected in parallel with the series connecting circuit (11e) and varies the anti-resonant frequency of the series arm circuit (11). The first variable frequency circuit (11a) includes a capacitor (C2) and a switch (SW1) connected in series with each other. The series arm resonator (s1) and the capacitor (C1) are connected in series with each other.