The impedance of traces is also defined by the PCB materials used on the board. Why is it good to specify the dielectric of the board instead of CI? If not, your boards will vary from each other, making debugging performance-related issues very difficult. You must ensure that your manufacturer provides you the right size, position, and tolerance of your etched features. We manufacture your PCB with the right pattern sizes and positions within certain tolerances. When you give Sierra your PCB design– copper patterns, hole patterns, and final material thicknesses– we laminate the copper layers into a single circuit board. Factors that affect the controlled impedanceįactors that influence the PCB impedance tolerances include materials’ resin content percentage, Dk values of the resin and the type of the glass cloth used, and other physical PCB tolerances like trace height and width at the top and bottom of the trace. For better understanding, read the effects of high-speed signals in a PCB design.Ī uniform transmission line on a PCB has a definite trace width and height and is at a uniform distance from the return path conductor, usually a plane at a certain distance from the signal trace. This is the first step to improve the integrity of the signals on the PCB traces. Therefore, to have undistorted signal travel, the PCB signal traces must have a uniform controlled impedance to minimize signal distortions caused by reflections. The distortion may be so much that the signal may not be able to perform the desired function. This reflection will travel in the opposite direction of the signal, which means that the reflected signal will superimpose on the primary signal.Īs a result, the original signal will be distorted: the signal intended to be sent from the transmitter side would have changed once it gets to the receiver side. The larger the difference is, the greater the reflection will be. If this impedance varies from one point to the next one, there will be a signal reflection whose magnitude will depend on the difference between the two impedances. Typically, you will need controlled impedance for PCBs used in high-speed digital applications, such as RF communication, telecommunications, computing using signal frequencies above 100MHz high-speed signal processing, and high-quality analog video such as DDR, HDMI, Gigabit Ethernet, etc.Īt high-frequency, the signal traces on a PCB act like transmission lines, which have impedance at each point on the signal trace trajectory. Understanding why controlled impedance is necessary.Types of PCB transmission lines that require controlled impedance are single-ended microstrip, single-ended stripline, microstrip differential pair, stripline differential pair, embedded microstrip, and co-planar (single-ended and differential) The impedance of circuits is determined by the physical dimensions and the dielectric materials of the PCB. Controlled impedance is important for solving signal integrity problems, which is the propagation of signals without distortion. It is relevant when high-frequency signals are propagating on the PCB transmission lines. What is a controlled impedance?Ĭontrolled impedance is the characteristic impedance of a transmission line formed by PCB traces and its associated reference planes. Hence, the controlled impedance of traces plays an important role in signal integrity and the performance of circuit boards. Nowadays, the speeds of the circuits are increasing day by day, and signals in the GHz range are common. The time of simple interconnecting traces and conductors is over. It is now crucial to understand your critical nets and traces, impedances, and how the board impacts the performance of the signal. RLC Resonant Frequency and Impedance CalculatorĮvery day, PCB designs and components become smaller, faster – in other words, more complicated.Bandwidth, Rise Time and Critical Length Calculator.Transmission Line Reflection Calculator.Trace Width and Current Capacity Calculator.