What is the impedance control or a controlled impedance?

Impedance is the result of the interaction between the resistance and reactance in a circuit and expressed in Ohms. Impedance is an AC characteristic, which means it is related to frequency. A controlled impedance is important to maintain signal integrity, especially for high-frequency products.

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How to achieve the impedance control?

Generally, the impedance is uncontrolled unless we have specific traces designs and other related operations. Impedance control or the controlled impedance means ensuring the impedance mismatches are within the allowable limits through some design for the PCBs.

We can achieve the impedance control in PCB design and PCB manufacturing in two ways: one is a well-defined PCB stack-up, and another is well-designed traces with different configurations. What’s more, the impedance of the PCBs also depends on the size and material used in the manufacturing process.

Why need impedance control in PCB design?

The traces in the PCBs are used to transfer maximum signal power from the source to the load. If the source's impedance value does not match the impedance value of the load, some signals will be reflected back to the source. Then only part of the signals travels to the destination. As the demand for high-density and high-speed PCBs has increased dramatically, the PCB designs with controlled impedance have become very popular.

We may be no need to worry about the impedance control if the traces are short or low-frequency. But the reactance and the impedance are vital factors for high-frequency circuits. The higher the frequency, or the longer the traces, the more necessary it is to control the traces' impedance.

The impedance control of APOLLOPCB

A controlled impedance requires a degree of accuracy to function properly.  Usually, PCB designers will specify the impedance values and tolerances, and PCB manufacturers select suitable materials and fabricate the boards according to the specifications. At APOLLOPCB, we have professional engineers to solve any of your problems.

As we are impossible to plan the order without clear impedance callouts, please let us know in advance if you have desired impedance value and tolerance. We will confirm the specifications with you before PCB manufacturing to achieve your expectations with the best quality. Most of the controlled impedance PCBs will be tested, but the impedance calculation is very complicated. If you have questions about the impedance control or other techniques, contact us!