184.108.40.206.2. Determine the Bandwidth
Figure 44 shows that the voltage at any instant t is:
At 10 percent of the curve, you have:
At 90 percent of the curve, you have:
The 10 percent equation divided by the 90 percent equation gives:
The time constant variable is related to the 3-dB frequency by the equation:
From the previous equation, we can determine the equation for the time constant, r.
Plug the time constant into the voltage equation to get:
Use the following equation to determine the bandwidth for sinusoidal signal
The highest frequency component for a signal with a rise time of Tr have a frequency given by this equation.
The signal previously discussed had a rise time of 300 ps, which means that the highest frequency component present in the signal be:
Using the equation with the bandwidth and speed numbers, you can determine that:
If the transmission line is longer than wavelength/10, then termination is required. In this design example, the transmission line is two inches long, so termination is required.