• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 79 subscribers
  • Views 1773 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

MSP430F2013: Sigma Delta 16 bit resolution vs Sigma Delta 24 bit resolution

Yonathan Foto
Prodigy 40 points
Part Number: MSP430F2013
Other Parts Discussed in Thread: ADS1256

I was hoping someone can clarify the maximum resolution that can be achieved if using 16 bit Sigma Delta ADC with the internal reference voltage (Vref = 1.2V, Vfsr=+-0.6V) compared to the 24 bit Sigma Delta ADC using the same reference voltage.

From the ADC names I would assume an 16 bit Sigma Delta ADC would output a value between the range of 0-16bits depending on the OSR chosen and the 24 bit Sigma Delta ADC would output a value between the range of 0-24 bits depending on the OSR chosen.

But when reading the family user guide. It says that the number of bits output by the digital filter is dependent on the over sampling ratio and ranges from 15 to 30 bits for both SD_16 &SD_24.

*From pg.604 of the family user guide:
http://www.ti.com/lit/ug/slau144j/slau144j.pdf

If anyone can clarify the max resolution that can be achieved for both these ADC and the difference between the two, it would be much appreciated.

  • 0
    TI__Guru 56685 points
    Yonathan,

    I'll have to get back to you on this, but I am looking into getting you some more information.
  • 0 in reply to Jace H
    Prodigy 40 points

    Much Appreciated!

  • 0 in reply to Jace H
    TI__Guru 56685 points

    Hello Yonathan,

    There is no simple answer to what you are asking is choosing your SD ADC depends on a variety of factors and trade-offs. One aspect is your sampling frequency is a lower on over sampled schemes as you have to sample more times to get a certain SNR and resolution. There are other trade-offs as well. I would highly encourage you to check out TI's ADC Learning center for more information on the subject. these guides and application notes are written from a general ADC perspective and will apply to the ADCs integrated within the MSP430 due to their general nature. Link below.

    www.ti.com/.../data-converters-learning-center.page

  • 0 in reply to Jace H
    Prodigy 40 points
    Hello Jace,

    Thank you for taking the time to look in to this. Maybe I was not clear in my original question because i feel there should be a simple answer to this. I am aware of the basic operation of sigma delta ADCs, I am not asking how to choose an SD ADC, I am aware that choosing a higher OSR will reduce my sampling frequency but allow for a greater resolution.

    What I am asking is what is the maximum bit resolution that the 16 bit Sigma Delta (SD_16) and the 24 bit Sigma Delta (SD_24) can achieve.

    I would assume from their names the maximum resolutions would be 16 bit and 24 bits but from the family user guide. It says that the number of bits output by the digital filter is dependent on the over sampling ratio and ranges from 15 to 30 bits for both SD_16 &SD_24. This is why I am confused, what is the difference between the two SD ADCs?

    *From pg.604 of the family user guide:
    www.ti.com/.../slau144j.pdf


    The following is the type of information I am looking for:

    The ADS1256 :www.ti.com/.../ADS1256

    "allows the user to optimize between resolution of up to 23 bits noise-free and data rate of up to 30k samples per second (SPS)."
    Features
    24 Bits, No Missing Codes
    All Data Rates and PGA Settings
    Up to 23 Bits Noise-Free Resolution
  • 0 in reply to Yonathan Foto
    TI__Guru 56685 points

    Hello Yonathan,

    I have some clarification now on the differences between SD16 and SD24 that are featured on our MSP430F2xxx family devices.

    1.    The F2013 SD16 is different from the rest of the SDs in the sense that it has mux-ed input channels with a buffer versus simultaneous conversion.
    2.    The operation and design is exactly the same between the SD16 to SD24 (minus the variants).
    3.    The resolution of all our converters are not easily explained, but simply put, it is the reference voltage divided by the 2^16 in the unipolar mode. This doesn’t change when the mode is changed to 24-bit. Increasing the bit mode will only ensure that the ENOB improves, not the resolution
    4.    However, in order to get the effectiveness of both types, we need to get the SINAD values at the highest OSR to determine the ENOB and this will truly represent the quality of the SD. So when you compare the 16-bit mode versus the 24-bit mode, the ENOB will be better for the 24-bit version.
    5.    With the ENOB, we can determine the noise bits versus the signal bits.

    Basically, both the SD16 and the SD24 modules are very similar, but the SD24 will have better ENOB in general.

  • 0 in reply to Jace H
    Prodigy 40 points
    Thanks for the help!

**Attention** This is a public forum