High Frequency Component Diplexer Impedance Mismatch
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Solution Overview
Problem
Impedance mismatch in SAW filters within mobile communication apparatuses leads to degraded transmission characteristics and cutoff characteristics across different frequency bands, increasing circuit complexity and module size.
Innovation Solution
A high-frequency component configuration featuring a diplexer with a high-frequency filter and a low-frequency filter connected in parallel to the antenna port, where the low-frequency filter includes a series and parallel resonant circuit, allowing for impedance matching and preventing undesired attenuation poles by setting resonance frequencies to match predetermined attenuation poles in the high-frequency filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a SAW filter is provided in a reception path for each communication system, then signals from transmission path to reception path are prevented, but impedance mismatch occurs at frequencies outside passband leading to degraded transmission and cutoff characteristics
Solution Approach 1:
A matching circuit is introduced as an intermediary component between the SAW filter and the reception path. This matching circuit compensates for the impedance mismatch that occurs at frequencies outside the SAW filter's passband, thereby maintaining desired transmission characteristics without compromising the signal isolation function of the SAW filter.
Solution Approach 2:
The impedance parameters of the circuit are adjusted by introducing a matching circuit with specific impedance characteristics. This changes the overall impedance profile to achieve better matching at frequencies outside the passband, preventing degradation of transmission and cutoff characteristics while maintaining the SAW filter's signal isolation capability.
2Manufacturing precision
If phase adjusting circuits and multistage filters are added to achieve impedance matching, then transmission characteristics are improved, but circuit complexity and module size increase
Solution Approach 1:
The complex phase adjusting circuits and multistage filter structures are extracted and replaced with a simpler matching circuit design. This matching circuit achieves the necessary impedance matching function with fewer components and lower complexity, maintaining transmission characteristics while avoiding the drawbacks of overly complex circuit configurations.
Solution Approach 2:
Instead of adding multiple circuit stages, the solution changes the impedance parameters through a single matching circuit configuration. This approach achieves impedance matching with minimal additional components, thereby improving transmission characteristics without significantly increasing circuit complexity or module size.
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 maintains desired transmission characteristics at high frequencies and prevents degradation due to impedance mismatch, simplifying the circuit design and reducing module size without requiring phase adjusting circuits or multistage filters.
Implementation Method 1
The low-frequency filter includes a parallel resonant circuit constituted by a line connected to the antenna port and a capacitor connected in parallel with the line. An impedance of each of constituent elements of the low-frequency filter is set such that a high-frequency transmission/reception signal is attenuated and a low-frequency transmission/reception signal is allowed to pass through.
Implementation Method 2
The high-frequency filter may be constituted by a plurality of capacitors cascaded to the antenna port and a series resonant circuit having one end connected between the capacitors and the other end grounded. An impedance of each of these constituent elements of the high-frequency filter is set such that a low-frequency transmission/reception signal is attenuated and a high-frequency transmission/reception signal is allowed to pass through.
Data Source
Figure 1
Figure 2
Figure 3(A)~3(C)
AI summary
There is provided a high-frequency component in which, even when a SAW filter is provided in a low-frequency circuit and there is an impedance mismatch, high-frequency transmission characteristics are not degraded. The high-frequency component includes a diplexer (1) in which a high-pass filter (102) and a low-pass filter (101) are connected in parallel with an antenna port, a high-frequency circuit cascaded to the high-pass filter (102), and a low-frequency circuit cascaded to the low-pass filter (101). A filter which causes an impedance mismatch to occur is connected to the low-frequency circuit. The low-pass filter (101) includes a line (Lt1). The low-pass filter (101) is constituted by a parallel resonant circuit (101A) including the line (Lt1) and a series circuit (101B) including the line (Lt1). A resonance frequency of the parallel resonant circuit (101A) is a trap frequency of a high-frequency transmission/reception signal. A frequency of resonance of all elements of the low-pass filter (101) is a trap frequency of undesired resonance that occurs at high frequencies.