• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 48 subscribers
  • Views 2461 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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:

Nanovolt range amplifier

Nanovolt range amplifier

Subash Chandra bose M
Intellectual 280 points
Other Parts Discussed in Thread: OPA1642, OPA1611

Hi team,

                  I need to amplify nano voltage using opamp  opa1642. This is for leakage current(suspension insulator in transmission line ) monitor application.Kindly suggest me some information to proceed further.

  • 0
    Guru 140200 points
    Hi Subash,

    DC or AC?

    Can you show a schematic or your circuit?

    Kai
  • 0
    TI__Genius 12680 points

    Hi Subash,

    Do you need to measure single nanovolt voltages, or nanoamp currents?

    Nanovolt voltage measurement will be nearly impossible with an op amp by itself, simply due to input voltage noise. Our lowest voltage noise op amp, the OPA1611, has a voltage noise density of 1.1nV/rtHz, which already exceeds your signal of interest (even before considering the input frequency range of interest).

    In order to accomplish the low noise level required, you'll have to build a hybrid op amp using a matched pair of low-noise JFETs (IFN146, for example) and an op amp such as the OPA1611. Bob Cordell has a good application note for such a circuit here. A similar circuit is also used in the old Agilent 34420A DMM, and is described in detail in the third edition of The Art of Electronics. Some searching should turn up the service manual and schematics for this DMM, for reference. DC precision at this level will require much care in the design and construction of the circuit, and may require autocalibration in order to ensure consistent DC performance. 

    Nanoamp current measurement, by comparison, is fairly straightforward using a FET input op amp configured as a transimpedance amplifier. 

    As Kai mentions, if you have more information on your application, or a sketch of a schematic, please include this, as we can then suggest solutions for that specific application. 

  • 0 in reply to kai klaas69
    Intellectual 280 points

    Hi Kai,

             Actually it is AC 60hz.

  • 0 in reply to Alex Davis
    Intellectual 280 points

    Hi Alexander Davis,
    Thank you for such a detailed explanation. Actually we take output from the insulator ends . For example , if the leakage current flows on the insulator say 1mA, we take output from two terminals from the same insulator. Based on the resistivity,area and length, we will be getting some nano voltages across it ,So that needs to be amplified.

  • 0 in reply to Subash Chandra bose M
    TI__Genius 12680 points
    Hi Subash,
    As I mentioned above, we don't have an op amp or reference design for a nanovolt-range amplifier. There are a few resources (linked above) which may help with a solution, but if possible, the best solution may be to purchase an existing commercial product (such as a high-end DMM) which already implements this function, as this level of performance is very difficult to achieve.