Thevenin Line Termination

[shrtCrct]

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.

 

[mneary]

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.)