• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 49 subscribers
  • Views 1012 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.

Original question:

OPA192: How to show current noise (pA/sqrt(Hz)) for a current source by using Noise Analysis?

OPA192: How to show current noise (pA/sqrt(Hz)) for a current source by using Noise Analysis?

James Ye1
Prodigy 50 points
Part Number: OPA192
Other Parts Discussed in Thread: TINA-TI

when use Noise Analysis for current source, the display still shows "V/sqrt(Hz)" as if the output is voltage.

How do I convert it to "A/sqrt(Hz)" (since output is now current)? 

  • 0
    Guru 48395 points

    well if the output is a current, use a current meter and that might work - without a TINA file, hard to tell what you are doing, 

  • 0
    TI__Guru* 93105 points

    Hi James,

    As Michael pointed out more information is needed to fully understand what kind of an noise analysis you are attempting.

    If it is Spice simulation noise analysis, the voltage noise V/sqrt(Hz) and current noise A/sqrt(Hz) sources are built-into the OPA192 model. The input current noise will be converted to voltage noise as it flows through the resistors in the circuit. When the noise analysis is completed the output will be available as input or output voltage noise in V/sqrt(Hz) units, or if Total Noise is selected the most often uV units.

    Note that the current noise for JFET or CMOS op amps such as the OPA192 the input current noise is extremely low. The OPA192 input current noise is specified at f = 1 kHz as 1.5 fA/√Hz (typical). When a complete noise analysis is accomplished the current noise contribution to the total noise is often found to be insignificant compared to the voltage noise.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 50 points

    Thomas:

    Attached is the Howland Current Pump I built using OPA192 in TINA-TI.

    When doing Noise Analysis, the output (which is current) noise density shows up as V/sqrt(Hz), not A/sqrt(Hz).  

    Do I need to covert or accept the display as A/sqrt(Hz)?

    thanks,

    James

    OPA192_CCS_for_TI.TSC

    OPA192_CCS_for_TI.TSC

  • 0
    Guru 140200 points

    Hi James,

    haven't we already discussed this a while ago?

    Kai

  • 0 in reply to James Ye1
    TI__Guru* 93105 points

    Hi James,

    I looked for more complete information about PSpice based simulator's (like TINA-TI) .NOISE analysis function. I have a PSpice manual from 1990 that provides detailed information about the analysis. It provides the details of the .NOISE lines syntax, and in one of the paragraph states, "The output noise units are always volt/Hertz1/2." Therefore, you cannot obtain a noise analysis with amp/Hertz1/2 noise units from a PSpice based simulator.

    Regards, Thomas

    Precision Amplifiers Applications Engineering