Microstrip PCB Impedance Calculator

Tools - Pcbcupid - Free and Simple Microstrip PCB impedance online calculator

Microstrip are transmission lines that are routed on the external layers of the PCB which are always routed above a large reference plane on the adjacent layer. As the name suggests microstrip lines are used to convey microwave-frequency signals and RF signals. You can read more about microstrip here.

Calculate the impedance, capacitance, propagation delay, and inductance of a Microstrip Line PCB using this convenient online calculator. Understand the characteristics of your electrical transmission lines and optimize your circuit design.

Microstrip PCB impedance

Understanding Microstrip PCB Impedance:

The characteristic impedance of a flat wire hanging above a ground plane with a dielectric separating them is referred to as microstrip PCB impedance. Printed circuit boards (PCBs) are typically used to build this structure, although other materials can also be used as long as a conductor is isolated from a ground plane by a dielectric substance. 

Calculating Microstrip Impedance:

The characteristic impedance of a microstrip can be estimated using a variety of online resources and calculators. A few of these calculators take into account variables like as the dielectric constant, trace width, trace thickness, and trace-to-ground plane distance. These findings are, however, limited to crude estimation and approximation. It is advised to use specialist software, such as Polar Instruments, for precise impedance calculations. 

Impedance Control in PCB Design:

Adhere to these five essential guidelines for PCB design in order to attain impedance control:

Comprehend the Fundamentals: Become familiar with the terms impedance matching, transmission lines, and characteristic impedance.

b. Choose the Appropriate Materials: To get the required impedance, select the right dielectric material and trace width.

c. Take into Account the Stack-up: Engineer the PCB stack-up to reduce impedance variances all around.

d. Apply the TDR Method: Use Time-Domain Reflectometry (TDR) to find potential differences in impedance over a broad range of frequencies.

e. Check Using Measurements: Measure the real impedance of the PCB with specialized equipment to verify the impedance control. 

Types of Microstrip Traces:

Microstrip traces come in two primary varieties: coated and uncoated. In contrast to coated microstrips, which have a soldermask coating above the trace, uncoated microstrips lack one. A microstrip’s characteristic impedance is determined by various factors, including the dielectric constant, trace width, thickness, and the distance between the ground plane and the trace. 

Trace width
mm
Trace thickness
mm
Dielectric thickness
mm
Relative dielectric constant
mm

Formula

\[Z = \frac{87}{\sqrt{e_r+1.41}} * ln \left(\frac{5.98h}{0.8w + t}\right) \]
\[ P = 3.333 * \sqrt{0.475e_r + 0.67} * dimension\]
\[C = \frac{P}{Z} \]
\[ R = \frac {17.2}{w * t * dimension^2} * 1000 \]
\[ L = \frac {P * Z}{1000} \]

where :

  • Z = Single Ended Impedance
  • er = Relative dielectric constant
  • h = Trace width
  • w = Trace height
  • t = Trace thickness
  • P = Propagation Delay
  • C = Capacitance
  • L = Inductance
  • R = Resistance
  • If the dimension unit is mm then dimension=1
  • If the dimension unit is mils then the dimension is 0.0254

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