What is an Impedance Control PCB?

What is Impedance?

Impedance refers to the sum of electric resistance, inductive reactance, and capacitive reactance. While talking about DC signals, there are no inductive reactance and capacitive reactance because these depend on the frequency of the signal, and the frequency of DC is zero. Thus, there is no reactance for DC signals, and the only thing that matters is resistance.

In the case of AC signals, we need to consider electric resistance, inductive reactance, and capacitive reactance. The impact of electric resistance is not affected by frequency, but the inductive reactance and capacitive reactance change with the frequency, and their impact is significant when the frequency is high. Thus, while dealing with high-frequency signals, we need to consider and control impedance to get the desired results.

What is an Impedance Control PCB?

An impedance control PCB is a special PCB that has calculated impedance according to the requirement. In such PCBs, the desired impedance is maintained so that they can offer the desired results. Conventional PCBs do not have any restriction on impedance, so they cannot be called impedance control PCBs.

The transmission of high-frequency signals is affected by impedance, so it is important to have control over it. Such PCBs can deal with high-frequency signals and prevent distortion and errors during transmission.

There are two ways to control the impedance of the PCB. You can either fix the dielectric thickness of the PCB or mention the impedance in Ohms. Fixing the dielectric thickness is a bit difficult, and you might not get the desired results as the impedance depends on many factors. The best way is to select the desired impedance in Ohms and inform the PCB manufacturer. Now, it is the responsibility of the manufacturer to provide the desired impedance with a tolerance of ±10 Ohms. However, the manufacturer might require some changes in the design or dimensions to ensure the required impedance, and in this case, the manufacturers discuss everything with the buyer before taking any step.

Why Impedance Control PCB?

This question tickles the mind of beginners that do not know much about PCBs. We need to understand why there is any need for such a PCB.

Impedance control PCBs can provide a safe path that other PCBs cannot provide for high-frequency signals. The most important thing in a high-frequency signal is Signal Integrity, which means the ability to retain the signal in its original shape during transmission. If the signal at the receiver end is nearly the same as at the sender end, then there is signal integrity. It gives a measurement of signal distortion.

While talking about high-frequency signals, signal integrity becomes more important. It is because these signals carry a message which is created using amplitude or frequency modulation. The message is hidden in the signal and decoded at the receiver ends. But if there is any change in the signal, such as a change in frequency and amplitude, then the signal at the receiver end will not be the same as the sender end. It will change the information or message conveyed.

Moreover, there is a signal reflection in the case of a difference in the impedance between the sender end and the receiver end. The reflected signal is superimposed over the primary signal and creates distortion. If the difference between the impedance is higher, the reflected signal will be greater. Thus, to minimize the reflection, it is essential to match the impedance of the traces.

Due to the above issues, it is necessary to use impedance controlled PCBs for high-frequency applications. It will ensure that the signal is transmitted without any distortion.