Figure 1 Multiple loads schematics
How the value of series termination resistor, Rs can be calculated in a system where a single clock output is used to drive multiple separate loads?
Consider point A in the figure. To its right, point A sees a resistance of Zo. To its left, point A
observes a resistance consisting of:
Rs + (Rd || (Rs + Zo) || (Rs +Zo)) Equation 1
Equating both sides of point A yields the following formula:
Zo = Rs + (Rd || (Rs + Zo) || (Rs +Zo)) Equation 2
If we substitute Zo = 50 and Rd =25 into Equation 2 and solve for Rs, we will find that Rs is
equal to 38.4.
Note that Equation 2 only covers a system with 3 separate loads. Use Equation
3 for a system with N parallel loads.
Zo = Rs + (Rd || Rx) Equation 3
where Rx = (Rs +Zo) / (N-1)