Author Topic: Measuring On-chip resistive termination (impedance adaptation)  (Read 922 times)

0 Members and 1 Guest are viewing this topic.

Offline steamedhamsTopic starter

  • Regular Contributor
  • *
  • Posts: 65
  • Country: fr
Measuring On-chip resistive termination (impedance adaptation)
« on: September 08, 2021, 04:04:07 pm »
I am measuring the resistive termination of an FPGA's internal complex IO (single ended for now).
I've been wondering how to do this..

I was thinking, if I added an ammeter to the pad and then ground to the other side, i could see the current flow.. but doesn't this also draw current from the output buffer causing issues??

However, if I were to somehow deactivate the output buffer, then I am just creating a circuit from Vref/2 across the resistor and then to ground through my ammeter.

Seems simple enough but I am not really sure.



 

Online NorthGuy

  • Super Contributor
  • ***
  • Posts: 3242
  • Country: ca
Re: Measuring On-chip resistive termination (impedance adaptation)
« Reply #1 on: September 08, 2021, 05:26:51 pm »
Connect a 50 Ohm resistor between the pad and Vref (or between the pad and ground). Measure the voltage on the pad and calculate using Ohm's law.
 

Offline steamedhamsTopic starter

  • Regular Contributor
  • *
  • Posts: 65
  • Country: fr
Re: Measuring On-chip resistive termination (impedance adaptation)
« Reply #2 on: September 08, 2021, 08:21:07 pm »
wouldnt an ammeter be more accurate? why 50 ohm?
 

Online NorthGuy

  • Super Contributor
  • ***
  • Posts: 3242
  • Country: ca
Re: Measuring On-chip resistive termination (impedance adaptation)
« Reply #3 on: September 08, 2021, 08:42:11 pm »
wouldnt an ammeter be more accurate?

I don't think so. It also measures voltage difference across a resistor, but it's resistor is much smaller than yours.

why 50 ohm?

Mathematically, you'll get the least error if both DUT resistor and yours are the same.
 

Offline steamedhamsTopic starter

  • Regular Contributor
  • *
  • Posts: 65
  • Country: fr
Re: Measuring On-chip resistive termination (impedance adaptation)
« Reply #4 on: September 09, 2021, 04:10:09 pm »
turns out i had the correct approach just connected to the wrong pad.  |O
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf