I have a digital output from an FPGA that I would like to drive over a 50 ohm coax cable. The pulse is +5V for 10 us. What is the proper way to match the impedance of the cable?
I'd start with a pseudo line driver, like a 74AC04 and a 51 Ohm series resistor. At the other end you can have a high impedance line receiver with a 51 Ohm resistor to GND.
Then I'd rent a network analyzer and check it out. You will need to unlimber your checkbook for one of those however.
If that is too rich for your blood then a TDR might fill the bill. That will tell you if reflections are a problem with your termination.
Thanks for the quick response Papabravo. Is there another solution that doesn't require the line receiver at the other end? This triggers another device and I would like to avoid an intermediate step on that end.
How much cable are we talking about? Skimping on line drivers and receivers is usually penny wise and pound foolish for anything over about 6-18 inches. Trust me on this.
I understand the advantages of using a line driver / receiver. I only struggle with one thing: When I hook a 50 ohm coax into a pulse generator, it can drive the pulse easily over a 2 m cable. No receiver is require. Could a unity gain, non-inverting op amp to accomplish the same result the driver / receiver setup achieves? Or is there a method to recreate what is being done in the pulse generator?
Depends on the opamp. A 741 won't cut the mustard. A TL081 might do the job, and a BUF634 would probably work as well. Why are you so resistant to using the part you require. If you test it with 2m of cable and it works: end of story. If you want to build a bunch of them,then you need to worry about how repatable the design is. Why take a chance?