Multiplexer Cancellation Circuit Layout for Band Isolation
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Solution Overview
Problem
Existing multiplexers face challenges in improving attenuation characteristics and bandpass characteristics due to increased size and impedance issues caused by capacitances in cancellation circuits, leading to reduced bandwidth and isolation between filter circuits.
Innovation Solution
A multiplexer design that includes a cancellation circuit with a longitudinally-coupled resonator and a capacitive element, where the capacitive element is only arranged on the common terminal side of the resonator, reducing the size of the cancellation circuit and enhancing impedance matching, thereby improving attenuation and bandpass characteristics without compromising the bandwidth of the second filter circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitances are arranged on both sides of the longitudinally-coupled elastic wave resonator in the cancellation circuit, then the attenuation characteristics are improved, but the size of the multiplexer increases
Solution Approach 1:
The patent extracts the capacitive element from one side of the longitudinally-coupled elastic wave resonator, retaining only the necessary capacitance on the antenna terminal side. This selective removal maintains the cancellation effect while reducing the overall circuit size and eliminating unnecessary components.
Solution Approach 2:
The patent introduces asymmetric arrangement of capacitive elements, with capacitance provided only on the antenna terminal side of the resonator rather than symmetrically on both sides. This asymmetric configuration achieves the required attenuation characteristics while minimizing circuit size.
2Reliability
If capacitance is increased to secure necessary cancellation circuit performance, then the cancellation effect is improved, but the impedance decreases causing ripples in the passband and reduced bandwidth
Solution Approach 1:
The patent optimizes the capacitance value to a specific range (0.3-0.8 pF) that provides sufficient cancellation effect while maintaining appropriate impedance levels. This parameter optimization prevents both over-capacitance (which would cause ripples) and under-capacitance (which would reduce cancellation effectiveness).
Solution Approach 2:
The patent applies partial capacitance rather than full symmetric capacitance on both sides. By providing capacitance only on the antenna terminal side with optimized value, the patent achieves the minimum necessary cancellation effect without excessive capacitance that would degrade impedance and bandwidth.
3Stability of the object's composition
If capacitances are arranged on both sides of the resonator, then the cancellation circuit is balanced, but the impedance matching becomes difficult and isolation between filter circuits decreases
Solution Approach 1:
The patent removes the capacitive element from the transmission terminal side, keeping capacitance only on the antenna terminal side. This extraction simplifies the circuit structure and improves impedance matching characteristics, thereby enhancing isolation between filter circuits.
Solution Approach 2:
The patent applies capacitance locally only where needed (antenna terminal side) rather than uniformly on both sides. This localized capacitance placement optimizes the cancellation effect at the critical interface while maintaining good impedance matching and isolation characteristics.
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 proposed design achieves improved attenuation characteristics in the first filter circuit and enhanced bandpass characteristics in the second filter circuit, while maintaining a smaller chip size and preventing signal leakage, thus improving isolation between the filter circuits.
Implementation Method 1
a cancellation circuit that generates an offset component that offsets a component in a certain frequency band flowing through the path connecting the common terminal and the first terminal
Implementation Method 2
a capacitive element for amplitude and phase adjustment is connected in series with the cancellation circuit
Data Source
AI summary
A multiplexer includes a transmission filter and a reception filter that are connected to a common terminal, and a cancellation circuit that is connected to the common terminal and a node on a transmission path and that offsets a component in a certain frequency band flowing through the transmission filter. The cancellation circuit includes a capacitive element connected to the common terminal, and a longitudinally-coupled resonator including a first end connected to the capacitive element and a second end connected to the node with no capacitive element interposed therebetween. An impedance in a reception band when viewing the cancellation circuit from the common terminal side is higher than an impedance in the reception band when viewing the cancellation circuit from the node side.