Most simple impedance calculators assume this situation. This type of situation corresponds to a single trace routed on a dielectric with infinite thickness. The surrounding dielectric also affects the impedance. First, simply selecting the geometry, arrangement, and material used to form traces will affect their impedance. The basic idea is to set the impedance encountered by signals to a specific value, ideally limiting any impedance mismatches to small values. Obviously, no fabrication process is perfect, and any PCB that comes off the manufacturing line will have some variations in trace impedance. Impedance control and impedance management are two terms that are loosely interchangeable and refer to different methods for setting the impedance seen by signals in a PCB. There are some simple design strategies that can help ensure your signals are not distorted during operation.
In the RF range and beyond, controlling the impedance encountered by your signals will ensure that your device will operate as designed. Once you start working with high-speed or high frequency signals, you’ll find that the impedance of your traces and mismatch at sources and loads can have a major affect on signal integrity. Controlled impedance on a circuit board is a PCB layout issue that I didn’t feel completely comfortable in handling as a PCB designer for some time. Once I started working on electro-optics systems that required high sampling rates, controlling impedance was always a critical design issue. It was just an amplifier circuit on a single layer PCB, and controlling the impedance was not even an afterthought. My first PCB was far from a high-speed digital device.