Directional Coupler Adjustable Termination High Directivity
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Solution Overview
Problem
Conventional directional couplers face limitations in achieving high directivity, especially in RF circuits, due to challenges in isolating incident waves from reflected waves, which affects the accuracy of power measurements in devices like cellular telephones and RF systems.
Innovation Solution
A directional coupler system with an adjustable termination impedance is implemented, allowing for tunable resistance and capacitance at the isolated and coupled ports, enhancing directivity by monolithic integration on a semiconductor substrate, and utilizing transformers and switchable impedance circuits to achieve high directivity across a wide frequency range with low insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional directional coupler architectures are used, then the device structure is simple, but the directivity is limited and cannot achieve high isolation between incident and reflected waves
Solution Approach 1:
The directional coupler is divided into multiple functional sections: a first coupler section with first and second transmission lines, and a second coupler section with third and fourth transmission lines. Each section has specific characteristic impedances and electrical lengths that work together to achieve high directivity. This segmentation allows independent optimization of each section's parameters to maximize isolation between incident and reflected wave measurements.
Solution Approach 2:
Different transmission lines within the coupler have different characteristic impedances specifically designed for their local functions. The first transmission line has impedance Z0, the second has impedance Z1, the third has impedance Z2, and the fourth has impedance Z3. These locally optimized impedance values create specific electrical properties at each port that collectively achieve the desired high directivity performance of 25 dB or greater.
2Measurement precision
If high directivity is achieved through complex coupler architectures, then measurement accuracy improves, but insertion loss increases
Solution Approach 1:
The invention achieves high directivity by precisely controlling electrical parameters rather than using complex architectures. The electrical lengths of the transmission lines are set to specific values (θ1, θ2, θ3, θ4) and the characteristic impedances are set to specific ratios (Z0:Z1:Z2:Z3). By optimizing these parameters, the coupler achieves 25 dB or greater directivity while maintaining low insertion loss through efficient signal coupling paths.
3Adaptability or versatility
If fixed termination impedance is used, then the circuit is simple, but the directivity cannot be optimized across wide frequency ranges
Solution Approach 1:
The termination impedance at the isolated port is made adjustable rather than fixed. A variable resistor or programmable impedance element allows the termination to be dynamically tuned to match different frequency operating conditions. This dynamic adjustment capability enables the directional coupler to maintain high directivity across a wide frequency range from 0.5 GHz to 3.8 GHz and beyond, adapting to different RF operating environments.
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 system achieves high directivity of over 25 dB within the 0.5 GHz to 3.8 GHz frequency range, enabling accurate power measurement and impedance mismatch detection with low insertion loss, suitable for RF front-end systems in handheld devices.
Implementation Method 1
There are many different types of coupler architectures that include electromagnetic couples and magnetic couplers
Implementation Method 2
An adjustable termination impedance is coupled to the isolated port and/or the coupled port
Implementation Method 3
The adjustable termination may include an adjustable resistance and/or an adjustable capacitance
Data Source
AI summary
In accordance with an embodiment, a circuit includes a directional coupler having a plurality of ports comprising an input port, a transmitted port, an isolated port and a coupled port, and an adjustable termination coupled to at least one of the plurality of ports.