I just solved a problem in my homework. I had to calculate the reflection waves and I was given the following data:
Resistance
R0 = 120 Ω line impedance
Ri = 90 Ω resistance at input
Rb = 1 kΩ termination resistance
Line
l = 0.5m length of the line
δ = 6 ns/m
Source voltage
U0 = 0.4 V logical 0 - low voltage
U1 = 4.8 V logical 1 - high voltage
I was also given the following graph:
Showing I have to calculate reflections for when signal goes from 0>1
/ low to high voltage basically when we have a pulse.
First I calculated Tau, T = l * δ = 3 ns
, and then I calculated the reflection coefficients at R0 and Rb using formula ρx = \$ \frac{Rx - R0}{Rx = R0} \$
With that I was able to calculate for the part before the pulse:
ui(0-) = ub(T-) = U0 \$ \cdot \$ \$ \frac{Rb}{Rb + Ri} \$
Followed by the rise:
ui(0+) = ui(0-) + ΔU \$ \cdot \$ \$ \frac{R0}{R0 + Ri} \$
And then I was simply able to calculate reflection voltages at certain time for instance first traveling voltage from the change:
u0(1) = ΔU \$ \cdot \$ \$ \frac{R0}{R0 + Ri} \$
And then reflection voltage at T on the end of the line:
ub(T+) = ub(T-) + u0(1) + u0(2)
After that I can just calculate the reflections until 5 Tau to see if the signal stabilizes anyhow.
- My question is how do my calculations and formulas change when the graph provided would be inverse showing a drop in the pulse from 4.8V to 0.4V ?