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INA223: 0.1Hz to 10Hz Voltage Noise Measurement

Intellectual 380 points

Replies: 17

Views: 910

Part Number: INA223

Hi Sir

 

 

For correlating figure 28 “0.1Hz to 10Hz Voltage Noise”

We builds up active filter as TI verified design mentioned in document #SLAU522

And take OPA827 as DUT, briefly connecting and wiring without shielding can.

 

The resulting waveform is approximate and satisfied as the attachment (PK-Pk = 24.2mV) but not INA223 while using as DUT instead

 

OPA827

 


 

 

 

According to figure 28 of INA223, the estimation should be

 


(1) Gain = 20

VOUTPK-PK = 200nV/ Div x 6 Div x 20 (Gain) X 100 (Filter Gain) = 2.4mV

 

(2) Gain = 300

VOUTPK-PK = 200nV/ Div x 1 Div x 300 (Gain) X 100 (Filter Gain) = 6mV

 

The resulting is 10 times more than expectation; we have no idea what dominate the measurement, and how to identify

 

We simply set VCM about 1V and VIN+ - VIN- is about 5mV via voltage divider (200 ohm and 1 ohm), tie VIN – to GND.


Thanks for recommendation and measurement guide!

Regards

Ben

 


  • Hello Ben,

    Thanks for considering to use Texas Instruments. What are you using to supply the input? If it is an AC to DC converter plus a switch mode power supply source, that can potentially introduce a lot of input noise even with a large cap across the VCC and GND. For the lowest input noise, you should use a battery. One of the best battery sources you could use would be a NiCad battery.

    Best Regards,

    Patrick Simmons, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Patrick Simmons:

    Hi Patrick

    Thanks for recommendation!

    Actually the differential voltage developed across is from the dividing of linear power supply or Alkaline battery

    Where

    VS = Linear power supply

    VBUS = Linear power supply or Alkaline battery

    Conventionally the output noise of OPA is measured by shorting the input to GND.

    As understanding, the incorrect input common mode voltage will lead INA incorrect as well

    Since INA is symmetrical and balanced, is it suitable to connect the both inputs to GND?

    Or all I have to do is to find a clear source?

    Is it possible to show how you measure the noise of INA?

    Regards

    Ben

  • In reply to Ben Huang1:

    Hello Ben,

    Can you set up the INA223 like shown below?

    Also one test you could do is measure the noise of the output for the following configuration.  This will show if these op amps are contributing more noise than expected.

    Lastly, if you apply a 1mV sine-wave at the input here, do you see a 100mV sine-wave output?

    At the moment having some difficulty tracking down the engineer and the test apparatus used for the noise measurements we took.  Will let you know when I am able to track them down. Also I would not connect the inputs of the INA223 to ground for your measurement.

    Best Regards,

    Patrick Simmons, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Patrick Simmons:

    Hi Patrick

    Thanks for the reminder and comment!

     

    The transfer function and noise floor of BPF have been checked.

    The corner frequency and gain are close to your design but I am not sure what the expectation of noise floor is. since there is no mention in this document # SLAU522

    Noise floor of BPF

    INA223 @ Shut voltage mode (Gain =20V/V)

    According to the waveform, the pk-pk is much worse than expectation

    Please refer to the set-up picture, is there anything required to have an improvement? Maybe I should not take something as granted!

     


     


    Appreciate for paying much attention and effort on this case

     

    Regards

    Ben


     

  • In reply to Ben Huang1:

    Hello Ben,
    When you say the gain is close, does that mean when you passed a 1mV signal at 1Hz and saw a 100mV output? If it was greater than 100mV, how big was it? I noticed that your fabricated board is a little different than what is shown in SLAU522. Can you give me a list of the board modifications you made? As for your setup, could you this time include the INA223 and ground the inputs. Also can you set the output mode to shunt voltage measurement in the configuration register if you have not already done so previously?

    Best Regards,

    Patrick Simmons, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Patrick Simmons:

    Board Modification for INA223 20190110.pptxBoard Modification for INA223 20190110.pptxHi Patrick

    Thanks for reply and sorry for not describing clearly!

    Patrick:

    When you say the gain is close, does that mean when you passed a 1mV signal at 1Hz and saw a 100mV output? If it was greater than 100mV, how big was it?

    Ben:

    Yes! Where the close gain and corner frequency I mentioned is the active BPF (I am trying to matching the components as the design recommended as possible)

    Patrick:

    I noticed that your fabricated board is a little different than what is shown in SLAU522. Can you give me a list of the board modifications you made?

    Ben:

    Please find the attached ppt for more details, Basically, the difference is for INA223 only and leave others unchanged.

    Patrick:

    As for your setup, could you this time include the INA223 and ground the inputs.

    Ben:

    Does it mean tie both input to GND directly as conventional noise measurement of OPA? As memory, you would not connect the input to GND for this measurement, what is the intention for grounding the input to GND this time?

    Patrick:

    Also can you set the output mode to shunt voltage measurement in the configuration register if you have not already done so previously?

    Ben:

    Also I am always configuring the measurement to shut voltage mode, thanks for reminder!

    Patrick:

    At the moment having some difficulty tracking down the engineer and the test apparatus used for the noise measurements we took.  Will let you know when I am able to track them down

    Ben:

    Is it possible to track them down?

    Ben:

    I am planning to make a board revision, please find the same ppt for reference as well.

    Any recommendations and ideas are welcome

    Regards

    Ben

  • In reply to Ben Huang1:

    Hello Ben,

    The intent of having both inputs tied to ground was to remove any noise that comes from the common mode supply. In hindsight, this part is a unidirectional part and it would be better to have a IN- tied to ground with the voltage divider output from the battery tied to the IN+.

    Unfortunately I was not able to track down the engineer responsible for those measurements. Consequently, I am building up my own noise filter board to collect my own noise measurements. Once I have collected some measurements, I will update you on any tips or recommendations. This may take a few days. Sorry to keep you waiting so much.

    Best Regards,

    Patrick Simmons, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Patrick Simmons:

    Hi Patrick

    Appreciate for continuing paying much attention on this measurement!

    This item is the most critical in the precision measurement!

    Much more time consumption is reasonable but it is worthy.

    I am also studying anything possible to make this measurement better!

    To make sure what I understand clearly and avoid any misleading, I may draw a simple schematic for discussing!

    (1) Stimulus from battery

    (2) Tie both inputs to GND

    Does it also require? (Too much closer to GND)

    I am going to follow your recommendation once the revised board is available.

    Looking forward to your own measurement and another application report publication as SLAU522, that someone can easily Google it and get satisfied guide to the beginner as me

    Regards

    Ben

  • In reply to Ben Huang1:

    Hi Ben,

    I hope you shield the whole circuit? Put the OPAmp circuit into a shield and experiment with the best GND connection for this shield. Properly shielding can dramatically improve the noise performance!

    Kai
  • In reply to kai klaas69:

    Hi Kai

     

     

    Thanks for recommendation!

    I made a brief ptt file to show how the measurement is taking

    Since the revised board is not ready, I using the previous one still

     

    INA223 Set up for noise measurement.pptx

     

     

    Have you ever evaluated the shielding effectiveness of mental box?

    I put a mobile phone inside the box and make a 3G/4G phone call,

    but the ringtone is still perceived.

    As you mentioned, properly shielding can dramatically improve the noise performance, I have no idea how to define the “properly”

     

     

    Regards

    Ben

     


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