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Why does PCB impedance control really matter

Why-does-PCB-impedance-control-really-matter

What is PCB impedance control?

PCB impedance control is a concept that underlies many design solutions for printed circuit boards (PCBs). It’s an important part of any PCB because controlling the PCB’s impedances can help avoid interference and improve performance.

PCB impedance is the resistance or reactance of a circuit. It’s measured in ohms, and is represented by Z. A higher Z means that there’s more resistance than an equivalent-sized inductor and vice versa.

Properties of PCB impedance control

Some of the properties of PCB impedance control are as follows:

●   PCB Impedance Control is a promising technology that can help you reduce cost, reduce the size, and increase yield.
●   Impedance control improves performance by allowing designers greater flexibility when designing PCBs with multiple components connected through transmission lines or metal traces on board material substrate
● From a signal integrity standpoint, impedance control improves the ability of your system to handle high-frequency signals.

What PCB impedance control is used for?

Impedance control can be used in many different applications and it’s highly useful for medical devices.

● It’s a method of reducing energy loss in electrical circuits.
● Impedance control is used in automotive, telecommunications, and consumer electronics.
● Impedance control is used to create a smooth signal flow, without electrical noise.
● Impedance control can be used to reduce interference. 

How to calculate controlled impedance in PCB?

How-to-calculate-controlled-impedance-in-PCB

The impedance of a PCB is the ratio of the voltage to current, and it’s measured in Ω. Impedance control is an important part of designing high-performance amplifiers and other circuits.
The formula for calculating controlled impedance in PCB is:
Z = Zo + [(d/2)(Y/Yo)]

Where Zo is the controlled impedance of the ceramic capacitors, d is the thickness of dielectric and Y is power dissipation.

How to choose PCB impedance that you need?

The impedance of the PCB is a very important factor in  of high-speed PCB design. The impedance of the PCB is related to the signal transmission and signal integrity of the system.

The first thing you need to do is choose your type of electronic components or devices, as well as their amount and size (such as capacitors, and resistors). 

For example: if you want to build an analog-to-digital converter circuit with a 100MHz clock frequency at 5V supply voltage, then it will require more than 30000 resistors with a 1% tolerance value each; but if you want to build one with a 500MHz clock frequency at 25V supply voltage instead then only 2000 resistors are required instead!

The second thing is to decide how many signals you need and how many pins each signal should have. For example, if your circuit needs only 3 digital signals (for example for communication with a microcontroller), then it will only require 12 pins; but if it needs 24 analog inputs instead of 3 digital ones then it will require 96 pins! The third thing is to decide on the number of layers and their sizes. This depends on the size of your PCB, as well as the number of components and their type.

How to design PCB impedance control?

PCB Impedance control is a process that ensures that the impedance of a PCB is within the specified limits. this can be achieved by using capacitance and inductance at specific points on the board, as well as through interconnection between different boards.
Some of the methods for PCB impedance control are:

●   Resistor: this is a simple way to control PCB impedance. In this method, you will use resistors in series with your signal lines to reduce their potential.

●   Capacitor: this method works very well with low-frequency signals because it has a relatively high Q factor (a measure of how much energy can be stored in an entity). However, capacitors have limited bandwidth and can become highly stressed when driven by high-frequency signals.

●    Inductor: an inductor’s main advantage is its ability to provide power while being able to handle higher frequencies than other types of circuits. It also offers improved isolation from ground loops.

Brief introduction to impedance test

The impedance test is the most common method used by manufacturers to evaluate the effectiveness of their PCB design.
There are three major classes of impedance measurements:

●   Constant-current test (CCT) – in this type, power is applied at constant current but varying frequency; this causes changes in voltage drop across each capacitor/inductor pair and therefore produces changes in impedance values as well as power dissipation; CCT measurements can be made with just one or two instruments depending on how many capacitors/inductors you have on your board design;

●   Switching frequency test (SFT) – SFT generates sinusoidal signals whose frequencies vary linearly with time while varying intensity level remains constant over different periods; SFT generates AC voltages which vary linearly with time due to changing amplitudes of waveforms generated from switching transistors under control from controller ICs’ logic gates.

●   Resistance measurement – Resistance measurement provides information about electrical resistance between two points along conductors without affecting them

resistance-measurement

Factors affect the impedance control

The following is a list of the variables that impact PCB impedance control:

 ●Trace thickness: the copper foil’s thickness along with its covering is the trace width on a PCB. Impedance tends to decrease as trace thickness rises. Trace thickness standards for PCBs are based on a variety of variables, including performance and temperature increase.

●Copper width: impedance is also influenced by the width of the copper on the PCB. Impedance begins to reduce as copper width increases.

●Dielectric width: the insulating substance’s layer in between traces is known as the dielectric thickness. 

There is a logarithmic connection between dielectric width and impedance, meaning that a substantial rise in thickness often results in relatively mild gains in impedance. Manufacturers can significantly lower the width of the insulating layer to lower impedance.

Conclusion

Impedance control is an essential component of all printed circuit boards. It doesn’t matter if the PCB is for a mobile phone, a medical device, or an automotive component. The copper trace acts as the inductor, and another copper trace placed parallel to it, acts as the capacitor. The combined effect of these two traces is that they can produce a pure desired impedance.

In practice, this means that impedance control can be used to create greater controllability and reliability of the signal flow in your electronic devices without interference from external forces that may lead to electromagnetic interference (EMI).

We hope this blog post is helpful to provide you with enough information to understand the benefits of using PCB impedance control in your designs.

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