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THS4551: Flicker noise

Mochi
Genius 3885 points
Part Number: THS4551
Other Parts Discussed in Thread: ADS127L01, OPA211, THS4561, OPA1637

Hello,

Our customer is developing wideband frontend for ADS127L01 by using THS4551.

They have observed flicker noise at THS4551 output pin even shorted input pin, it is 30uVpp random step noise at Gv=0dB.

Duration is 1-second to few10second period by the device. Around 30% of device has this flicker noise.

THS4551 is specified 3.3nV/rtHz noise density, but it is not specified flicker noise level.

30uVpp random noise is expected level on THS4551 performance.

 

Regards,

Mochizuki

  • 0
    Guru 47935 points

    Morning Mochi, 

    The physical silicon has a low incidence of the popcorn noise you are showing here. At one time, there was a finite time screen for this, but that may not be the case any more. Popcorn noise is not generally specified by anyone, the direct ADI comp to this part also has it, but they will not be describing it. 

    I did publish an upgraded 0.1Hz to 10Hz bandlimited high gain amplifier for this testing in the July 2020 AudioXpress magazine. There is an occasional e2e discussion of these issues, as here. 

    Popcorn noise pictures from e2e.docx

  • 0 in reply to Michael Steffes
    Guru 47935 points

    Incidentally Mochi, here is that upgraded low frequency noise preamp - using choppers so no 1/f or popcorn in the preamp stages itself. 

    Updated filter design 0.1Hz to 10Hz OPA388 2019 model for article.TSC

  • 0 in reply to Michael Steffes
    Genius 3885 points

    Hello Michael,

    Thank you for your prompt reply and confirm it is popcorn noise.

     

    HPF would be good idea for AC signal frontend, at this time end equipment is DC-Wideband measurement equipment.

    In this case I expect another workaround is simply select lower popcorn device.

    Do you have recommendation of lower popcorn noise THS amplifier in TI line up?

    CMOS top low noise differential amp will be nice.

     

    Regards,

    Mochizuki

  • 0 in reply to Mochi
    Guru 47935 points

    To settle on alternates, complete design goals would be helpful

    Current circuit would be a start. 

  • 0 in reply to Michael Steffes
    Genius 3885 points

    Hi Michael,

    Our customer is not comfortable to disclose their circuit to public forum space.

    Instead of that they want to find Flicker noise level specified amplifier, like OPA211 datasheet there is Voltage noise specification at f=0.1-10Hz, 80nVpp.

    Can we find such a THS device?

    Or is there any possibility to buy Flicker noise screened grade THS4551 with extra price?

     

    Regards,

    Mochizuki

  • 0 in reply to Mochi
    Guru 47935 points

    1. 0.1Hz to 10Hz noise is not the same thing as popcorn noise

    2. Only thing I can say is the THS4551 process has popcorn noise, FDA's on different processes include the THS4561 or OPA1637 or LME49724- but I cannot confirm popcorn free for those processes. 

    3. Screening? Well I gave you the measurement circuit to use, perhaps the distributor would like to quote that as a bench screen? 10seconds is a long time for ATE equipment to be tied up looking for a pop. What kind of volume are they talking, 100 parts a year would not be too much, 10k/month might be expensive. 

  • 0 in reply to Mochi
    TI__Genius 15555 points

    Hello Mochizuki,

    Our devices are tested to eliminate noise as much as reasonably possible, however due to the random nature of popcorn noise it possible for these issues to occur. Would you be able to share with me your schematic offline? Will send you a direct message to discuss further.

    Best,

    Hasan Babiker