• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 47 subscribers
  • Views 1491 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM334 output impedance measurement

Overjoyed_Android
Prodigy 205 points
Other Parts Discussed in Thread: LM334

For the LM334, how is the output impedance measured?  We want to to know what the test setup is so we can replicate the results.

  • 0
    TI__Guru* 95195 points

    I'm not absolutely sure how they made the measurement. I'll see if I can find out who made the measurement in the datasheet. In the meantime, I'll give a method that I think is similar to how it was made and you can go through and try to replicate it.

    First, you could use gain/phase analyzer that has the ability to drive the AC signal. You would need a test resistor that can give you an output that is easy to measure and that doesn't drive the output of the current source out of compliance.

    If you look at the small signal model of the output the current source as attached to this post, you drive the output of the current source through a test resistor. Then you measure back the output of the driving source (Vref) and the voltage looking back into the current source (Vtest).

    The voltage at the output of the current source comes from the voltage divider of ro and rtest coming from the source of Vref. Therefore:

     (Vtest/Vref) = (ro)/(ro + rtest)

    If Vref=Vtest, then ro is basically infinite comparted to rtest.

    In putting this together, you may need to consider the size of the signal so that it doesn't show a non-linear behavior, the size of the resistor so that it doesn't hit the current source compliance, the frequency range of the that you're measuring, and the size of the test and the reference signals so that they aren't too subject to gain error and offsets.

    You also might consider using an instrumentation amplifier so that you can read a larger signal for Vtest-vref, or using a function generator for the Vref signal and measuring the data by hand.

    Regardless, there a few different ways to make this measurement. As long as you consider the potenial errors, it should give you something reasonable as a result.


    Joseph Wu