Last month’s quiz was a very fundamental question in signal integrity. “The open circuit output voltage of a driver is 1v. Its output impedance is 5 ohms. It is driving a 50 ohm transmission line. What is the initial voltage launched into the transmission line?”

This question is really about how to think of a transmission line. Once you realize that when the signal looks into the transmission line, the initial impedance it sees is the characteristic impedance of the line, then the answer will be obvious.

Initially, the transmission line looks like a resistor of 50 ohms. With this perspective, the signal sees a voltage divider, with 5 ohms in series with the 50 ohms of the transmission line. The voltage launched into the line is just 1 v x 50 ohms/55 ohms = 0.91 v.  The answer was number 2.

As you can see on the results table to the left, most of you got the right answer. For those that want to understand this better, take a look at OLL-115 and BTS002.

In addition, we’ve just launched our first hands on labs. The first one, HOL-101 allows you to explore this question of the voltage launched into a transmission line. I invite you to take it for a spin. We love feedback, so let me know what you think of this type of hands on lab. I have plans for many more.

Check out the latest quiz which is about our new webinar series. See you in cyberspace!