FIELD OF INVENTION
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The present disclosure relates to the field of radiofrequency (RF) technologies, and the present invention in particular to a directional coupler for differential signal processing which focuses on reducing production costs and improving efficiency by eliminating the need for RF loads while maintaining excellent performance in coupling and isolation.
BACKGROUND
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In RF systems, the management of high-frequency signals requires precise and efficient components capable of routing, sampling, and monitoring signals with minimal distortion and interference. Directional couplers are critical to these systems, widely used in telecommunications, RF measurement equipment, and other signal-processing applications. These devices are passive components that couple a fraction / portion of an RF signal from the main signal path while maintaining isolation to prevent interference. Despite their widespread use, traditional directional couplers exhibit several limitations, particularly when considering an adaptation to differential signal environments.
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Indeed, a standard directional coupler usually consists of four ports: an input port, a through port, a coupled port, and an isolated port. The coupled port extracts a small portion of the input signal for measurement or monitoring, while the isolated port is terminated, typically with a resistive load, such as a 50-ohm resistor. This termination is designed to prevent reflections that could degrade the performance of the coupler by ensuring that unwanted signals are absorbed. While this design works well for single-ended signals, it is not applicable easily to differential signal systems.
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Differential signaling is a method of transmitting signals over two complementary lines, with one line carrying the original signal and the other carrying its inverse. At the receiving end, the difference between the two signals is processed, with the aim of canceling out common-mode noise and interference. This technique is highly effective in improving signal integrity and is widely used in high-speed, high-frequency systems prone to electromagnetic interference.
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When differential signals are used with directional couplers, additional complexities arise. Indeed, traditional coupler designs are inherently optimized for single-ended signals, meaning they are not naturally suited to handle the paired, complementary nature of differential signals. This mismatch creates challenges in achieving the required balance and directivity for differential applications.
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Another critical limitation of traditional directional couplers is their reliance on discrete RF resistive loads to terminate the isolated port. These components increase the cost and complexity of manufacturing, in particular because they often require precise tuning or trimming during production. In compact and high-density electronic systems, the use of discrete components further consumes valuable space on printed circuit boards (PCBs), complicates routing, and limits the scalability of designs. These issues are particularly problematic in modern multilayer PCBs, where space is a scarce resource, and efficient use of the available area is critical.
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There are no specific solutions for differential directional couplers in the prior art, even if traditional single-ended directional couplers are known to be inadequate for differential signal environments. Indeed, existing couplers do not address the unique requirements of processing paired signals with complementary phases, nor do they mitigate the challenges introduced by phase or amplitude mismatches in differential systems. Moreover, the integration of directional couplers into PCBs remains constrained by the physical and design limitations of discrete components, which hinder the development of compact, cost-effective solutions.
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Therefore, the limitations of traditional directional couplers in handling differential signals, coupled with the challenges of integrating these devices into modern electronic systems, highlight a significant gap in the prior art. There is a clear need for an innovative solution that addresses these issues while providing robust, scalable, and cost-effective performance in differential signal environments.
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The aim of the present invention is therefore to provide a differential directional coupler that eliminates the need for discrete RF resistive loads at the isolated ports, thereby simplifying manufacturing, reducing costs, and enabling compact integration into PCBs. The proposed solution addresses the challenges of traditional directional couplers in differential signal environments by ensuring robust performance, maintaining balance and symmetry between complementary signals, and minimizing the effects of phase or amplitude mismatches. Additionally, it offers scalability and enhanced shielding by embedding the coupler directly into the PCB substrate, making it suitable for high-density and high-performance RF systems.
SUMMARY
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Embodiments provide a differential directional coupler, a method thereof and a PCB comprising the differential directional coupler.
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In one aspect of the invention, a differential directional coupler for processing differential signals is provided. The differential directional coupler comprises a differential feed line including a positive signal path and a negative signal path. A first directional coupler is coupled to the positive signal path, and a second directional coupler is coupled to the negative signal path. The first and second directional couplers are interconnected to form a virtual ground.
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In an embodiment of this aspect, the first and second directional couplers each further comprise an isolation port, and the first and second directional couplers are interconnected by being shorted at their isolation ports.
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In another embodiment of this aspect, a first coupled port of the first directional coupler is configured for extracting a controlled fraction of a positive signal in the positive feed line, and a second coupled port of the second directional coupler is configured for extracting a controlled fraction of a negative signal in the negative feed line.
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In another embodiment, the extracted controlled fractions of the signals are used for monitoring or measurement.
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In another embodiment, the first coupled port and the second coupled port are connected together to form a path between the first and second directional couplers, that is to say that a first and a second isolated port are connected together, thus forming the virtual ground.
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In another embodiment, the positive signal path and the negative signal path each comprise a through port.
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In another embodiment, the positive signal path and the negative signal path each comprise an input port.
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In a second aspect of the invention, a method of processing differential signals using a differential directional coupler is provided. The method comprises transmitting a differential signal through a differential feed line, the feed line including a positive signal path and a negative signal path; coupling the positive signal path to a first directional coupler and coupling the negative signal path to a second directional coupler; and interconnecting the first and second directional couplers to form a virtual ground.
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In an embodiment of this second aspect, the first and second directional couplers each further comprise an isolation port, and the method further comprises coupling the first and second directional couplers by shorting them at their isolation ports.
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In another embodiment, a first coupled port of the first directional coupler extracts a controlled fraction of a positive signal in the positive feed line, and a second coupled port of the second directional coupler extracts a controlled fraction of a negative signal in the negative feed line.
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In another embodiment, the method further comprises using the extracted controlled fractions of the signals for monitoring or measurement.
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In another embodiment, the first coupled port and the second coupled port are connected together to form a path between the first and second directional couplers, thus forming the virtual ground.
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In another embodiment, the positive signal path and the negative signal path each comprise a through port.
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In another embodiment, the positive signal path and the negative signal path each comprise an input port.
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In a third aspect of the invention, a printed circuit board, PCB, is provided. The PCB comprises a differential directional coupler according to any of the preceding embodiments, wherein the feed line of the differential directional coupler is embedded within the PCB substrate.
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The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
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- Fig. 1 is a standard directional coupler according to a related art.
- Fig. 2 is differential directional coupler according to one embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
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Hereinafter, the embodiments will now be described in detail with reference to the accompanying drawings. However, the disclosure cannot be limited to the embodiment in which the idea of the disclosure is presented, and another embodiment included within range of ideas of another backward disclosure or the present disclosure may be easily proposed by addition, change, deletion and the like of another element.
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The terms used in this specification were selected to include current, widely used general terms. In certain cases, a term may be one that was arbitrarily established by the applicant. In such cases, the meaning of the term will be defined in the relevant portion of the detailed description. As such, the terms used in the specification are not to be defined simply by the name of the terms but are to be defined based on the meanings of the terms as well as the overall description of the present disclosure.
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Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the same reference numerals are used to designate the same or similar elements throughout the drawings.
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Fig. 1 presents the architecture and functionality of a standard directional coupler 100 according to a related art. It represents a standard coupler design from the prior art, which is used in RF systems for signal sampling, measurement, and monitoring. It illustrates the essential structure of a single-ended directional coupler, highlighting its key components.
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In this design, the input port Pin 101 serves as the primary entry point for the RF signal. The majority of the input signal continues along the main transmission line to the through port Pthru 102, which carries the main output signal. This port ensures the efficient transmission of the signal with minimal loss.
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A controlled fraction of the input signal is diverted to the coupled port Pout,couple 104. This port is designed to extract a small, precise portion of the signal for monitoring or measurement purposes while maintaining high isolation from the main signal path.
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The isolated port, labeled as Piso 103, is terminated with a resistive load RL 105, which could be 50 ohms. This termination is aimed at preventing reflected signals from interfering with the operation of the coupler and ensures optimal performance by absorbing unwanted energy. The resistive load is a key component of standard coupler, as it guarantees impedance matching and minimizes reflections, preserving the coupler's directivity and signal integrity.
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The coupler 100 comprises a coupling section 106 (or segment or portion, these terms being similar in this context) between the coupled port Pout,couple 104 and the through port Pthru 102, depicted as a line connecting the ports and having a part close to (for instance running in parallel to) the main transmission line between the coupled port Pout,couple 104 and the through port Pthru 102, represents the mechanism by which the fraction of the signal is transferred to the coupled port. This structure is designed to achieve the desired level of coupling while maintaining minimal loss and high directivity between the input and through ports.
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However, this exemplary design illustrates the fundamental limitations of such standard couplers in terms of their reliance on discrete resistive components, such as the resistor RL 50-ohm load, which adds cost, complexity, and space requirements in modern compact RF systems. It also highlights the challenge of integrating such couplers into densely packed PCB designs while maintaining performance. Most importantly, this design is inherently suited for single-ended signals and is not adapted for differential signaling, where two complementary signal lines carry equal and opposite signals. Indeed, standard couplers lack the structural capability to process both lines of a differential signal pair simultaneously while maintaining the required symmetry and balance. They are also unable to address the critical challenges of phase and amplitude mismatches that can occur in differential environments, which can degrade performance and compromise directivity.
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Fig. 2 is a differential directional coupler architecture 200 according to one embodiment of the present invention. It is specifically designed to process differential signals while overcoming the limitations of prior art couplers discussed above, in particular as it offers a solution to eliminate the need for discrete RF resistive loads and enables robust, broadband, and cost-efficient integration into compact systems such as PCBs.
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The differential input signal enters the structure via the input ports Pin + 201 and Pin - 202. These ports represent the positive and negative components of the differential feed line 203, which is composed of two complementary signal paths 203a, 203b carrying equal and opposite signals. This feed line 203 provides the differential signal transmission with minimal interference and high signal integrity.
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The feed lines or paths 203a and 203b are each connected to one of two directional couplers, a first coupler 204a and a second coupler 204b, which therefore process the positive and negative signal lines, respectively. Each coupler 204a and 204b operates as a two-port coupling structure. The coupling is achieved by any suitable means, typically through parallel or broadside coupling in coupling sections, allowing the signals to be isolated and processed independently. The couplers 204a and 204b extract and process fractions of the signals while maintaining high isolation and minimal power loss. The coupling is done at the level of two coupling sections 206a and 206b, for each feed lines 203a and 203b, respectively.
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The main output of the differential signal is delivered at the through ports Pthru + 207a and Pthru - 207. Indeed, these ports ensure that the majority of the signal's power continues along the main path while preserving the differential nature of the signal. The coupled ports, Pout,couple + 205a and Pout,couple - 205b, form the path for the first and second coupler 204a and 204b which extract controlled fractions of the positive and negative signals, respectively, at the level of the coupling sections 206a and 206b. These extracted signals can be used for monitoring, measurement, or other purposes without significantly affecting the integrity of the main signal.
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An aspect of the invention is the treatment of the isolated ports of the two couplers. In conventional coupler designs, these ports each require discrete RF resistive loads RL as discussed previously to terminate the signals and prevent reflections. The present approach allows to eliminate the need for such resistive loads by interconnecting the coupled ports, Pout,couple + 205a and Pout,couple - 205b, of the first and second coupler 204a and 204b to form a virtual ground 208 (in other words, the couplers are shorted at their isolation ports resulting in forming this virtual ground 208). The virtual ground 208 is achieved by shorting these ports in RF domain, which creates a stable reference point for the differential signal without the need for galvanic connections or physical resistors. In some cases, this design can minimize signal reflections, enhance directivity, and reduce complexity.
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This proposed architecture offers several critical advantages over prior art, among other, the elimination of discrete resistive components reduces production costs and simplifies manufacturing, as there is no need for tuning or trimming of resistors during assembly.
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Additionally, the configuration allows the integration of the coupler directly into a PCB substrate which further enhances its utility. This embedded structure not only reduces space consumption but also provides electromagnetic shielding, which minimizes external interference and improves the overall reliability of the system.
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Unlike traditional couplers, which are limited to single-ended signal processing, the coupler of the present invention is specifically tailored for differential signal environments. The coupling structure proposed preserves the symmetry and balance required for differential signals, thereby addressing the challenges posed by phase and amplitude mismatches.
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In summary, the present invention introduces a differential directional coupler that addresses the limitations of prior art by eliminating discrete resistive loads, supporting robust and broadband operation, and enabling compact integration into PCBs. The configuration of the virtual ground mechanism ensures minimal reflections and high directivity, while the design's scalability and cost-efficiency make it a significant advancement in RF signal processing technology.
List of signs:
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- 101: Input port.
- 102: Through port.
- 103: Isolated port.
- 104: Coupled port.
- 105: Resistive load.
- 106: Coupling section.
- 201: Positive input port.
- 202: Negative input port.
- 203: Differential feed line.
- 203a: Positive signal path.
- 203b: Negative signal path.
- 204a: First directional coupler (positive line).
- 204b: Second directional coupler (negative line).
- 205a, 205b: Coupled ports for positive and negative signals.
- 206a, 206b: Coupling sections of the couplers.
- 207a, 207b: Through ports for positive and negative signals.
- 208: Virtual ground.