Hi All,
I would like to ask some questions on impedance matching resistors.
I.
The formula for impedance-matching resistor value is:
Rdriver + Rresistor = Zo,
Therefore,
Rresistor = Zo - Rdriver
Zo can be calculated using many calculators on the Internet, but how can I know the resistance of the driver?
II.
In the attached picture, there are termination resistors of different values {10, 22, 30}, and even 0 value. However, the tracks connected with these pins are all of 5mil width.
|
|
Width (mil) |
Termination resistor (Ohm) |
|
D16 |
5 |
22 |
|
H15 |
5 |
10 |
|
G19 |
5 |
0 |
|
D19 |
5 |
22 |
|
H3 |
5 |
33 |
If tracks having equal width, and since all copper layers have the same height, they should be all of a same characteristic impedance, so Zo are the same. They why their termination resistors are different? Is this due to the difference in Rdriver?
III.
For what reason is those 0-value resistors are used? What are their purposes?
Thanks,
Zheng