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PGA205: The noise issue

Tao_2199
Genius 5740 points
Part Number: PGA205

Hello,

 

Regarding to PGA205, my customer is asking some question.

Currently, they are checking PGA205 on their board and face noise issue.

(Please refer below.)


 

They confirmed other frequency(14kHz,20kHz) in addition input signal(17kHz) at ADC output by frequency analysis(FFT) .

To making clear to cause , they confirmed following.

(1) They configured PGA205 gain(x1,x2,x4,x8) by A0/A1 pin and confirmed ADC output data.

(Result)

Input signal(17kHz) -> The signal is output with each gain multiplier(x1,x2,x4,x8).

14kHz/20kHz -> Regardless of gain multiplier, the signal is output approximately 1 time(x1).

From above result, they think it possible that noise issue(14kHz/20kHz) won’t be occurred from the front stage of PGA 205.

(2) They confirmed noise on only ADC block by frequency analysis.

(ADC input -> GND: R312 Removed. C316 shorted to GND.)

(Result)

They couldn’t confirmed two noise(14kHz/20kHz) and input frequency(17kHz).

(Question)

Could you please give us comment, points or advice?

Is there any possible causes?

 

Regards,

Tao2199

  • 0
    TI__Expert 5830 points
    Hello,

    I will look into this for you.

    Best regards,

    Errol Leon
    Texas Instruments
    Precision Op Amp Applications
  • 0
    TI__Expert 5830 points

    Hello,

    I have a couple of questions on the schematic.  

    • What is the amplitude of the signal from the generator?
    • What device is the amplifier before the PGA205?
      • What is the gain of the amplifier?
      • What are the power supplies?
      • What is the expected output?
    • What ADC device is the PGA205 interfacing?
    • What is the acquisition time and conversion time of the ADC?
    • What is the value of the reference?

    Best regards,

    Errol

  • 0 in reply to Errol Leon6
    Genius 5740 points

    Hello Errol

    Thank you for reply.

    I’m asking your confirmation items to my customer.

    And I will ask you a confirmation about your questions.

    >What is the value of the reference?

    It is meaning about the reference for ADC.

    My understanding is correct?

    I'm asking that just in case.

     

    Regards,

    Tao2199

  • 0 in reply to Tao_2199
    TI__Expert 5830 points

    Hello Tao2199,

    Yes, your understanding is correct. 

    Best regards,

    Errol

  • 0 in reply to Errol Leon6
    Genius 5740 points

    Hello Errol

     

    Thank you for reply.

    My customer confirmed about your questions.

    I will summarize some information as block diagram.

    Please refer attached file.

     

    (Answer about confirmations from you)

    (1)What is the amplitude of the signal from the generator?

    (Ans.) 20mVp-p

     

    (2)What device is the amplifier before the PGA205?

    (Ans.) ADTL084ARUZ (ADI)

     

    a)What is the gain of the amplifier?

    (Ans.) G=100

    b)What are the power supplies?

    (Ans.) +12V/-12V

    c)What is the expected output?

    (Ans.)30mVp-p(SG) x 100(Gain) =3Vp-p

    SG-> Amp(G=100)->Low pass filter(fc=5kHz) -> PAG205

     

    (3)What ADC device is the PGA205 interfacing?

    (Ans.) LTC2326HMS-16#PBF (LTC)

     

    (4)What is the acquisition time and conversion time of the ADC?

    (Ans.)

    Acquisition time: 3.460us(min)

    Conversion time: 3us(max) 1.9us(min)

    Please refer attached file.

     

    (5)What is the value of the reference?

    (Ans.) Internal reference: 2.048V

    Please refer attached file.

     

    *And I have a question about their block diagram.

    (Question)

    One inverting amp is used as single-end to differential converting for PGA205 input．

    I think that in this case, generally dedicated single-end to differential converter amp(circuit) should be used.

    Could you please give comment or advice?

     

    Regards,

    Tao2199

    pga205_Block_diagram.pdf

  • 0 in reply to Tao_2199
    Genius 5740 points
    Sorry. I misled you.
    c)What is the expected output?
    (Ans.)20mVp-p(SG) x 100(Gain) =2Vp-p

    Regards,
    Tao2199
  • 0 in reply to Tao_2199
    Genius 5740 points

    Hello Errol,

     

    Could you please let know current status?

     

    Regards,

    Tao2199