Thevenin Line Termination

Hi all,

I am providing a clock 20Mhz to a ds92lv1021 device. But my line length to the device is 12" with impedance of 100 Ohms. I need to do a Thevenin termination for the clock, but I am not sure how to calculate the two resistors R1 and R2 required for this. Vcc is 3.3V.

If anyone can help that will be of great.

Thanks in advance.

R1 and R2 in parallel will be 100 ohms. You need to choose a suitable open circuit voltage which will give the ratio between R1 and R2. So you have two equations and two unknowns.

Simple example: If you choose the open circuit voltage to be 3.3/2, then R1=R2 and they are 200 ohms.

(If you're sure the clock never quits and never actually goes open circuit this configuraton provides symmetrical load on the driver.)