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Reduction of Crosstalk at High-Speed Transmission in Dual-Channel TVS packaged using DFN12102020/01/09

    It has become a basic requirement today for electronic products to be lightweight and compact in size. However, the result is that the size on a PCB that is available for use becomes smaller and the layout density becomes significantly larger. For high-speed transmission, the frequency has to be increased in order to boost the transmission speed and the period of signal increase becomes shorter with the evolution of transmission protocols. All of the above make the signal integrity issues trickier than before and reduce the flexibility design for hardware engineers. Among all signal integrity issues, crosstalk has to be one of the toughest. Crosstalk is the jumping of interference signals from a dynamic line to the neighboring static lines, and exists in every pair of signal line. Crosstalk has been found in physical layers such as chipsets, packages, PCBs, connectors and cables, and it may render electronic products inoperable when it exceeds a certain level through overlapping. For this, it is imperative for engineers to find out and understand how crosstalk comes to be and how to reduce its impacts. 

 

    Crosstalk can come from the unexpected interference of voltage and current in neighboring transmission lines due to the electromagnetic coupling of signals on these lines. These magnetic fields extend into the surrounding space and become what we know as the fringing fields. Interference noises on a static line are generated due to the change in current and voltage on dynamic line, which leads to fringing field that leads to inductive coupling and capacitive coupling between the dynamic and static lines. 

 

    For the capacitive coupling, when there are signals transmitting on the dynamic line, the variation in the fringe voltage of signals leads to the induction of time-varying electric field in the coupling capacitor on the dynamic line; induction current is generated in the static line due to the change of time-varying electric field, and this fringe of signals is considered the source of electric current displacement along the dynamic line. During this process of current source displacement, noises of electric current interference are generated on the static line via coupling capacitor. 

 

    For inductive coupling, the variation of current signals on the dynamic line induces time-varying magnetic field in the vicinity of signal variation via coupling inductance and this time-varying magnetic field generates noises of induction current on the static line through induction. 

 

    The coupling noises of the static line have the following features:

  1. The level of instantaneous coupling voltage and current noises depends on signal strength; the stronger the voltage and current intensity of the signal, the stronger the noises of instantaneous coupling noise.
  2. The noise level of instantaneous coupling voltage and current determines the coupling per unit length of mutual capacitance and mutual inductance per unit length, which is to say that the instantaneous coupling noises increase as the coupling length increases because the transmission line gets closer. 

 

    The fringing field is an important cause of crosstalk. The best possible way to reduce it is to keep the distance between signal lines large enough to reduce the impacts of fringing field to an acceptable level. 

 

    Amazing Microelectronic is focusing on the crosstalk challenge that comes with high-speed signal transmission and becomes the first to develop the dual-channel TVS AZ1023-02F in DFN1210 package (Figure 1). Unlike conventional DFN2510 where the pair to pair distance for high-speed signals is only 32mil, DFN1210 allows for the design flexibility of the best possible layout permitted by PCB size, thus keeping the impacts of crosstalk with an acceptable range (Figure 2). The control of parasitic capacitance is given lots of attention in the design of high-speed signal circuit and good performance is produced as AZ1023-02F features only 0.18pF of parasitic capacitance, not only providing outstanding flexibility of crosstalk control but also ensuring the stability of impedance control. 

 

    Amazing Microelectronic maintains its pace for the development of new protection elements and is dedicated to developing protection elements ahead of market demands in the constantly evolving field of high-speed signal transmission in the hope to respond to customers’ demands. For protection elements, Amazing Microelectronic is your best ESD solution provider. 



Figure 1 AZ1023-02F DFN1210 package Figure 2 Application example of AZ1023-02F in HDMI2.1 routing

 

 

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