Filter Circuit Impedance Switching With Parasitic LC Compensation
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Solution Overview
Problem
Existing filter circuits with external control terminals face instability in characteristics due to parasitic inductance from long connection lines, affecting transmission and reception performance.
Innovation Solution
A filter circuit configuration with an external connection capacitor between the external control terminal and the connection point between the antenna-side and reception-side circuits, allowing impedance control to switch between transmission and reception modes, and minimizing the impact of parasitic inductance by forming an LC circuit with the external connection capacitor and parasitic inductor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the external control terminal is connected to ground via a long line, then the impedance control for switching between transmission and reception is achieved, but parasitic inductance increases causing unstable filter circuit characteristics
Solution Approach 1:
An external connection capacitor is introduced as an intermediary element between the external control terminal and the connection point between the antenna-side circuit and reception-side circuit. This capacitor compensates for the parasitic inductance of the connection line, allowing the external control terminal to effectively control the impedance state while maintaining stable filter circuit characteristics independent of line length.
Solution Approach 2:
The invention changes the electrical parameters of the control path by adding capacitance in series with the parasitic inductance. This parameter modification creates an LC circuit whose impedance characteristics can be controlled to compensate for the unwanted inductive effects, stabilizing the filter circuit performance across different mounting conditions.
2Adaptability or versatility
If the line length is increased to connect the external control terminal, then the control function is implemented, but the parasitic inductance changes causing transmission filter circuit characteristics to become unstable
Solution Approach 1:
The external connection capacitor serves as a mediator that decouples the filter circuit characteristics from the connection line length. By introducing this capacitor, the system achieves adaptability in control terminal connection while maintaining reliable transmission filter circuit characteristics through compensation of the variable parasitic inductance.
3Productivity
If the external control terminal impedance is set low for transmission mode, then transmission signal passes through the filter circuit, but the parasitic inductance influences the transmission filter circuit characteristics
Solution Approach 1:
By adding the external connection capacitor, the electrical parameters of the control path are modified to compensate for parasitic inductance. This allows the system to maintain precise filter circuit characteristics while achieving the required transmission signal throughput through proper impedance control.
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 filter circuit achieves stable characteristics independent of mounting form and line length, ensuring reliable switching between transmission and reception with minimal influence from parasitic inductance, maintaining performance across the desired frequency bands.
Implementation Method 1
forming an LC circuit with the external connection capacitor and parasitic inductor
Implementation Method 2
external connection capacitor between the external control terminal and the connection point
Implementation Method 3
the impedances of the external circuit CTL and the external circuit TX are set to be sufficiently high. Thus, the filter circuit 1P becomes equivalent to a reception filter circuit
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A filter circuit (1) includes an antenna-side circuit (11), a transmission-side circuit (12), a reception-side circuit (13), and an external connection capacitor (C11). The antenna-side circuit is connected to an antenna-side terminal (T1). The transmission-side circuit is connected to a transmission-side terminal (T2) and the antenna-side circuit. The reception-side circuit is connected to a reception-side terminal (T3), the antenna-side circuit, and ground. The external connection capacitor is connected between an external control terminal (T11) and a connection point (16) between the antenna-side circuit and the reception-side circuit. The antenna-side circuit and the transmission-side circuit constitute a low pass filter. The antenna-side circuit and the reception-side circuit constitute a band pass filter. The reception-side circuit includes an LC parallel resonant circuit (LCP1).