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I'm working on a high speed ADC/DAC board. I saw some reference designs for the device, there are matching series resistors connected between output digital pins & controller.
Though, resistor network's value is given in the schematic. I'm curious to know, How do you calculate What resistors to be used for impedance matching.
What parameters of the input pins should be taken into account. Is there any formula for calculating the same ?
There are matching series resistors connected between output digital pins & controller
In these circumstances (fast digital signals crossing a significant distance on a PCB) you choose matching resistors to suit the impedance of the copper interconnection. The copper interconnection, just like coax cable or twisted pair cable exhibits characteristics that if not properly matched, can cause reflections when the fast edges of the signal reach the receiving device. This will inevitably lead to data corruptions.
On the other hand, if the tracks are not too long (compared to the wavelength of the fastest parts of the signal), maybe the resistors are just pull-ups. There are decent rules of thumb that govern the need to apply terminations of course.
If you need a more definitive answer, a section of the circuit would help as well as a picture of the copper tracks on the circuit board.
