2022-09-23 10:57 Status: #blank # Input Impedance This should illustrate the importance of input impedance; it determines how an electrical signal interacts with a circuit network, including whether a signal reflects or produces artifacts like ringing. This is also the reason that circuit networks, transmission lines, and arbitrary DUTs are represented with network parameters, transfer functions, input impedance values, and other quantities for cascaded networks. [^1]   Input impedance for a lossless transmission line. - The input impedance (i.e., the actual impedance signals see after transients decay to zero) is just the characteristic impedance when the line and load are matched, regardless of line length. This is shown in the flat gray line above. - The reflection coefficient is zero. You don’t need to worry about a stair-step increase in the voltage that is seen at the load (for digital signals). For analog signals, you don’t need to worry about [standing waves forming](https://www.nwengineeringllc.com/article/analog-signal-resonance-in-pcb-interconnects.php) on the transmission line. - Maximum power will transfer across the transmission line to the load. Similarly, maximum power will transfer from the source into the transmission line. Note that some signalling standards (e.g., LVDS) take advantage of high input impedance at the load. [^2] --- # References [^1]: [Understanding Characteristic Impedance in Your Circuits and PCBs | NWES Blog (nwengineeringllc.com)](https://www.nwengineeringllc.com/article/understanding-characteristic-impedance-in-your-circuits-and-pcbs.php) [^2]: [How to Use Input Impedance in Circuits and Transmission Lines | Blog | Altium Designer](https://resources.altium.com/p/how-use-input-impedance-circuits-and-transmission-lines)