I've read some of the other threads regarding the accuracy of the Edge Coupled Microstrip Impedance Calculator. I still think there is a problem, but I'd like to approach it from a different perspective.
For starters, if you use the Microstrip calculator with the following parameters:
T = 1.4 mil
H = 8 mil
W = 8 mil
Er = 4
you'll get a Z of 67.8 Ohms, which is in agreement with a J. Nicolle calculator I've been using, as well as a home-spun MS Excel calculator.
Now, using the Edge-Coupled Microstrip calculator with similar parameters:
T = 1.4 mil
H1 = 8 mil
W = 8 mil
S = 99.9 mil
Er = 4
you'll get a Zdiff of 157 Ohms, versus 135.7 Ohms for the J. Nicolle calculator and 135.6 for my spreadsheet calculator.
It seems to me that with such a large trace separation, Zodd and Zeven should be within 0.1 or 0.2 Ohm on either side of 67.8 Ohms. Instead, Zodd and Zeven are 78.6 and 64.2 Ohms, respectively, How can there be that much mutual coupling when the traces are so far apart?
For starters, if you use the Microstrip calculator with the following parameters:
T = 1.4 mil
H = 8 mil
W = 8 mil
Er = 4
you'll get a Z of 67.8 Ohms, which is in agreement with a J. Nicolle calculator I've been using, as well as a home-spun MS Excel calculator.
Now, using the Edge-Coupled Microstrip calculator with similar parameters:
T = 1.4 mil
H1 = 8 mil
W = 8 mil
S = 99.9 mil
Er = 4
you'll get a Zdiff of 157 Ohms, versus 135.7 Ohms for the J. Nicolle calculator and 135.6 for my spreadsheet calculator.
It seems to me that with such a large trace separation, Zodd and Zeven should be within 0.1 or 0.2 Ohm on either side of 67.8 Ohms. Instead, Zodd and Zeven are 78.6 and 64.2 Ohms, respectively, How can there be that much mutual coupling when the traces are so far apart?
