Bandwidth, Rise Time and Critical Length Calculator

The characteristics of transmission lines in any high-speed design should be uniform to avoid degradations such as signal distortions and crosstalk. To help you achieve this feat, Sierra Circuits has introduced the Bandwidth, Rise Time and Critical Length Calculator. Using this tool, you can calculate 3dB bandwidth (BW), fastest signal rise time (tr), critical length (lc), maximum data transfer rate (DTR), and maximum frequency content (Fmax).

High-speed PCBs operate in the range of hundreds of MHz to several GHz. These boards are prone to signal integrity issues. Hence, it is important to analyze the high-speed trace properties and calibrate their values as per the standards.

Features of the tool

This has the following features:

• Calculates the high-speed transmission line parameters for coated and uncoated microstrip models.
• Most importantly, it computes the critical length of the trace. Note that if the trace is longer than its critical length, it should be treated as a transmission line with a controlled impedance.
• Also computes effective dielectric constant, propagation delay per unit length, wavelength, etc.
  The units of the input parameters can be changed using the dropdowns.

How to use Bandwidth, Rise Time and Critical Length Calculator

The first step is to select the model of the transmission line. You can choose between uncoated and coated microstrips using the drop-down on the left.

Next, you will have to key in the input parameters. The required inputs for this tool are dielectric constant (mandatory) and anyone among of the following:

Maximum data transfer rate (DTR)
Fastest signal rise time (tr)
Maximum frequency content (Fmax )
3 dB bandwidth (BW_3dB)

You can pick the second input parameter by selecting the checkbox right next to the field that you wish to enter. For instance, if you go with fastest signal rise time as your second parameter and hit calculate, then the tool will compute DTR, tr, BW_3dB along with the values of the following parameters:

1. Effective dielectric constant (Ereff)
2. Propagation delay per unit length (Pd)
3. Propagation speed (Vp)
4. Rise time length (Sr)
5. Wavelength (λ)
6. Critical length (lc)
7. Maximum short length (Lmax)

Analysis of trace parameters such as bandwidth, rise time, and critical length is one of the key steps when it comes to high-speed designs. These parameters directly affect the impedance matching which in turn influences the overall performance of your board. This Bandwidth, Rise Time and Critical Length Calculator will assist you to compute these important characteristics with ease. By using this tool, you can also calculate the values of various other vital transmission line properties in real-time. This not only ensures optimum functionality of your board but also speeds up the design process.