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MSP430FR6047: SDHS, amplitude convesion

Thierry Soubie
Prodigy 30 points
Part Number: MSP430FR6047

Hi,

I have a simple question. Is there a simple formula to link amplitude from ADC capture to the input signal of the ADC?

I'm trying to link the amplitude of the input signal of ADC (observed on scope) with the values given in the USS Design Center (observed on ADC capture TAB).

Below is what I measure, with gain control=21.5 dB (means amplification is 11.88):

Approximatively we have 1800 peak-to-peak amplitude on ADC capture and 50mVpp on scope.

I would expect to get 50mV * 11.88 = 594mVpp on ADC capture. If the amplitude unit is in mV...

Obviously I miss something...

Also,  what is the unit of the amplitude scale?

Appreciate your help.

Best Regards,

Thierry Soubie

  • 0
    TI__Mastermind 38620 points
    Hello Thierry,

    I am researching this and expect to have an answer for you tomorrow.
  • 0
    TI__Mastermind 38620 points
    Hello Thierry,

    The units for the ADC capture is ADC counts. If you wanted to equate the voltage to ADC counts, you could simply multiply the measured voltage by the gain(11.88) and then divide this number by the number of ADC counts. In your case, it would be 594mV / 1800 = 0.33mV per ADC count.

    Also, you will want to have a lower gain setting as there is internal saturation that can occur above ~1,000 counts for 1MHz transducers. Take a look at item 4 on page 8 of the document below.

    www.ti.com/.../slaa837.pdf
  • 0 in reply to Eddie LaCost
    Prodigy 30 points

    Hello Eddy,

    Thanks for your answer. And for your comment regarding the saturation, it improves my measurement. :)

    I understand your expplabation but I'd like to get the LSB (volt per ADC count) in a theoritical way. Usually we can calculate the LSB as follow LSB=Vsupply/4096 for 12bit ADC.  

    How can I get the LSB for the ADC of SDHS?

    Best Regards,

    Thierry

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