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Original question:

XTR117: XTR117 output nosie level

XTR117: Broadband noise level

Ole Mjos
Prodigy 10 points
Part Number: XTR117
Other Parts Discussed in Thread: XTR115, XTR116

The datasheet specifies input referred noise as 0.6uVpp 0.1-10Hz. 

I want to use the loop to transmit signals into the kHz range.

Do you have a specificaion or graph showing input referred spectral noise density?

  • 0
    TI__Guru 56641 points

    Hi Ole, 

    Ole Mjos said:
    Do you have a specificaion or graph showing input referred spectral noise density?

    We do not have spectral noise density data/plots for the IC. Typically, we can simulate the noise spectral behaviors in our op amp products. Since we do not have an actual Spice model, we are unable to get this done. Perhaps, I should ask our modeling engineer to create a spice model for the family, which are XTR115/XTR116 and XTR117.

    Ole Mjos said:
    I want to use the loop to transmit signals into the kHz range.

    Since the application is operating at kHz range, the 1/f noise can be ignored due to the broadband BW is >10*f_h, where f_h refers to upper cutoff frequency of the 1/f region (say f_h = 10Hz or 100Hz). The 1/f noise contribution will be insignificant when the broadband BW is 10X or higher than the upper cutoff frequency of the 1/f region. 

    I could convert the 0.6uVpp (0.1-10Hz) to Vrms and extract the nominalized 1/f voltage noise spectral density based on this figure (normalized at 1 Hz). However, it has insignificant meaning since your application's broadband is operating at kHz range. In other words, you need to concern about the broadband noise effects, which are the dominated noise sources in the system per the application. 

    If you have other questions, please let us know. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Prodigy 10 points

    Thanks Raymond,

    I would appreciate if you could create a Spice model.

    Best regards

    Ole

  • 0 in reply to Ole Mjos
    TI__Guru 56641 points

    Hi Ole, 

    I have to submit a request for it. Once the inquiry is accepted, and it will be queued among a list of Spice model requests. I do not know when it will be ready to be posted on the part's website. It definitely will not be in the remaining month this year. What is your end application? Could we resolve this via other meanings for now?

    If you have other questions, please let me know. 

    Raymond

  • +1 in reply to Raymond Zhang1
    Prodigy 10 points

    The end application is a system with different sensor signals time multiplexed into the current loop. Some sensors are DC/slow varying signals, one is a hydrophone with signals into the kHz range. I have built a first prototype and the measured input noise of the hydrophone channel was higher than I expected from my simulations. I increased the gain of the hydrophone preamp and found that this brought the measured input referred noise down close to the simulation result. I then bypassed the current loop and inserted the signal from the preamp directly into the ADC with its preceding buffer, this also gave results close to simulation. So what I will do for now is to increase the preamp gain, although this will somewhat reduce the dynamic range of the system. 

    But I would definitely like to have a Spice model for the future, so I can explore these tradeoffs in a simulator instead of building and tweaking a prototype.

    Thanks,

    Ole

  • 0 in reply to Ole Mjos
    TI__Guru 56641 points

    Hi Ole, 

    If you want to simulate the noise performance of XTR117, we have to have the Spice model. I have submitted the Spice model inquiry in our team, but it will take time to be released. 

    Alternative, you can build a discrete 2-wire current loop transmitter, which then you may be able to analyze the noise performance. 

    https://www.ti.com/lit/an/slaa866/slaa866.pdf?ts=1701442135415&ref_url=https%253A%252F%252Fwww.google.com%252F

    Best,

    Raymond