Duplexer Ladder Layout for Low-Reflectivity Band Isolation
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Solution Overview
Problem
Conventional duplexers face challenges in achieving adequate isolation and low insertion loss when operated in carrier aggregation mode, particularly with closely spaced frequency bands, leading to increased reflectivity and insertion loss due to the use of inductances in parallel branches near the antenna terminal.
Innovation Solution
The duplexer design involves connecting inductances in series with parallel resonators furthest from the antenna terminal, with the first parallel arm connected directly to ground, and using phase shifters to rotate impedance for frequencies outside the passband, improving reflectivity and isolation between TX and RX bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If inductances are connected in series with parallel resonators near the antenna terminal to improve TX/RX isolation, then isolation between bands is improved, but reflectivity increases and insertion loss increases
Solution Approach 1:
The patent extracts the inductance from its conventional position near the antenna terminal and relocates it to the parallel resonator furthest from the antenna terminal. This extraction from the problematic location eliminates the harmful reflection effect while preserving the isolation function. The inductance is completely removed from the first parallel arm near the antenna terminal, which directly resolves the contradiction by eliminating the source of high reflectivity and insertion loss.
Solution Approach 2:
The patent changes the spatial dimension of inductance placement within the filter structure. Instead of placing inductance in the first parallel arm (nearest to antenna terminal), it places inductance in the last parallel arm (furthest from antenna terminal). This dimensional repositioning within the ladder structure transforms the electrical characteristics, allowing isolation to be maintained while reflectivity and insertion loss are improved.
2Object-generated harmful factors
If inductances are added to parallel branches to improve isolation for closely spaced bands, then band isolation is improved, but reflectivity increases leading to signal losses
Solution Approach 1:
The patent extracts the inductance from the first parallel arm near the antenna terminal where it causes harmful reflections. By removing the inductance from this critical location, the reflectivity problem is eliminated while the isolation function is preserved through the inductance placed in the furthest parallel resonator.
Solution Approach 2:
The patent applies different local qualities to different parts of the filter structure. The first parallel arm near the antenna terminal has no inductance (pure capacitive resonator) to minimize reflections, while the last parallel arm has inductance for isolation. This local differentiation of structure quality resolves the contradiction between isolation and reflectivity.
3Ease of manufacture
If conventional diplexers are used for closely spaced frequency bands, then simple implementation is achieved, but adequate isolation between bands cannot be achieved
Solution Approach 1:
The patent segments the diplexer structure into distinct parallel arms with different configurations. The first parallel arm is simplified (no inductance) for ease of manufacture and low reflection, while the last parallel arm includes inductance for isolation. This segmentation allows the diplexer to maintain structural simplicity while achieving adequate isolation for closely spaced bands.
Solution Approach 2:
The patent changes the electrical parameters of the parallel arms by selectively adding or removing inductance. The first parallel arm uses only capacitance (simpler), while the last parallel arm uses LC combination (more complex but provides isolation). This parameter differentiation resolves the contradiction between simplicity and isolation performance.
4Object-generated harmful factors
If phase shifters are used to rotate impedance towards infinity for frequencies outside passband, then isolation is improved, but device complexity increases
Solution Approach 1:
The patent extracts the phase shifting function from separate phase shifter circuits and integrates it into the passive LC resonator structure itself. The inductance in the parallel resonator naturally provides the required phase rotation for impedance transformation without requiring active phase shifter components, thereby reducing device complexity while maintaining isolation performance.
Solution Approach 2:
The LC resonator structure serves multiple functions simultaneously: it provides frequency selection, impedance transformation, and phase shifting all through its passive reactive elements. The inductance and capacitance values are designed to automatically provide the required phase rotation for frequencies outside the passband, eliminating the need for separate phase shifter circuits.
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 design enhances RX/TX insulation and reflectivity, reducing dependence on the quality factor of inductances, allowing for effective operation in quadplexer mode with improved bandwidth and reduced insertion loss, even with closely adjacent bands, and supports various duplex methods and band combinations.
Implementation Method 1
a phase shifter circuit (PS1, PS2) is arranged in each case between the antenna terminal (AT) and the input of the respective duplexer which rotates the impedance in the passband of the other duplexer towards infinity
Implementation Method 2
The duplexer, therefore, must have a high reflection coefficient at the antenna terminal for frequencies of the other band, that is to say outside its passband. This can be achieved by the impedance being rotated towards infinity with the aid of a phase shifter in the same frequency band
Implementation Method 3
The resonators can be constructed as SAW or BAW resonators
Data Source
AI summary
A duplexer and a quadplexer are disclosed. In an embodiment, the duplexer includes an antenna terminal and two sub-paths including a transmit path and a receive path, the two sub-paths being connected to the antenna terminal, wherein the transmit path includes serially interconnected series resonators and, in parallel therewith, n parallel paths connected to ground, wherein each parallel path includes one parallel resonator or a cascade of serially interconnected parallel resonators, wherein n is an integral number with 0<n<8, wherein at least one of the n parallel resonators is connected to ground in series with an inductance in the transmit path, and wherein a parallel resonator is connected directly to ground in a first parallel path that is nearest to the antenna terminal and no inductance is arranged in the first parallel path.