Common Mode vs Differential Mode Signals
In the realm of signal integrity and high-speed circuit design, understanding the behavior of differential pairs is crucial. A fundamental aspect of differential pairs is the concept of even mode and odd mode propagation, which governs how signals travel along the pair. Additionally, various impedance parameters play a significant role in characterizing the differential pair's behavior. This includes even mode impedance (Zeven), odd mode impedance (Zodd), differential impedance (Zdiff), common mode impedance (Zcom), and characteristic impedance (Zo). By comprehending these concepts and equations, engineers can design differential pairs with optimized performance and ensure reliable signal transmission in their electronic systems.
Differential impedance, odd mode propagation, and odd mode impedance are key concepts in differential high speed signals design, where differential pairs are used in board layout.
In real design, we are given a differential impedance of 100 ohms which is measured by Time Domain Reflectometry (TDR). TDR will given both a odd and even impedance.
Due to the fact differential traces are tightly coupled to reference ground planes in PCB stripe line design, Zdiff=2xZodd=2xZo
A differential driver A (e.g. H-Bridge) transmits complementary signals on a communication interface usually postfixed as _TX_P and _TX_N
Reference and Further Reading:
For more detailed information on the topics of Time Domain Reflectometry (TDR) and differential impedance, you can refer to the provided reference and further reading links: "The basics of Time Domain Reflectometry" at https://hvtechnologies.com/blog/basics-time-domain-reflectometry-tdr and "What is Differential Impedance and Why do We Care?" at https://www.signalintegrityjournal.com/blogs/12-fundamentals/post/1665-what-is-differential-impedance-and-why-do-we-care.