# What Is Impedance of a Circuit?

#### What is impedance of a circuit?

If you want to understand what is impedance of a circuit, think of it as the resistance to current flow that a device or part of a system presents. It includes both the resistance component that arises from collisions of charged particles with the internal structure of a conductor as well as the reactance component that reflects any inertia that is present.

The first thing that you must understand about impedance is that it varies with the frequency of the electricity passing through it. This is a big difference from the idea of resistance, which doesn’t take into account the frequency of the signal.

Impedance can be measured using a combination of hardware and software tools, such as an oscilloscope, signal generator, and a load with a known impedance. Impedance measurements are often used in the design stage of a project to ensure that a design is suitable for the intended use.

#### Symbols for Impedance

There are two types of symbols for impedance: cartesian and polar. These can be used in a variety of calculations, including finding the total impedance of multiple components in parallel.

Cartesians are useful for simple calculations where quantities need to be added or subtracted and polar forms are more convenient when multiple quantities are multiplied or divided. For example, when calculating the total impedance of multiple resistors in series, the polar form can be more accurate.

#### Detecting Impedance Discontinuities

Vias and through holes in multilayer boards will have parasitics between neighboring conductive elements that can change the impedance of signals transmitted over them. This can cause transmission line discontinuities that may interfere with the performance of a system.

Similarly, conductors and traces on a PCB will have noise coupling between them that can also affect the impedance of signals that are carried over them. Fortunately, most multilayer boards use conductors and traces that are designed to minimize these discontinuities.

The inverse of impedance is admittance, which can be determined by measuring the amplitudes and phase angles of a signal and comparing these to those seen from other components or the load with unknown impedance. This can be done with a circuit analyzer or signal generator that is connected to the circuit and can display the amplitude and phase of an input signal against the output from each component or the load.

In addition to analyzing the amplitude and phase of a signal, a circuit analyzer can also display the total impedance for each component in a given circuit. This can be particularly helpful if you’re trying to determine the effects of a particular component on the overall performance of a circuit.

#### Understanding Impedance for Nonlinear Components

The impedance of a circuit that contains nonlinear components can be tricky to calculate. Typically, circuit impedance is calculated using a transfer function, which is a plot of the magnitude and phase shift of a given input signal compared to the output of each circuit element. However, if the circuit contains elements like transistors or diodes that are designed to produce output based on the input signal, then it is more complicated to calculate the total impedance for each element.