Hi
I have to test an IC with 50 ohm logic at 20 MHz. The input signal is a 20 MHz square wave. The original test fixture has 26 AWG wire for transmission lines and does not distort the signals. I made a "paddle board" with 50 ohm transmission lines and connected to the test fixture through a cable with 50 ohm twisted pairs. The cable is 4 feet long. The signal is so distorted that the circuit is loaded down and the input signal resembles a sine wave at the paddle board. To add insult to injury the input signal is connected to 5 inputs of the test fixture by means of said 26 AWG wire.
I got a reasonable response by attaching a 50 ohm coax to one pin (disconnecting the others) and jumpering using 26 AWG to the other 5 pins. But the response loads the generator so I do not have amplitude control.
Any suggestions. I am going to respin the paddle board but do not know how to change it.

 

I am having a hard time visualizing what you had and what you have changed it to. Can you post a sketch with a better explanation?

 

Below is a picture of the setup. The green paddle board is shown with the cable to the test fixture. It consists of 24 pairs of twisted pair cable selected for the right impedances. The old test fixture made of 26 awg wire is in the aluminum box. There are only three grounds on the IC. The paddle board on which the IC sits has 50 ohm traces except for the diff pairs. They have 100 ohm.
Thanks for reading.