• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 30 subscribers
  • Views 458 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.

EK-TM4C1294XL: ADC 1LSB

Genatco
Guru 55913 points
Part Number: EK-TM4C1294XL

Does 1LSB=0 - 820µV or just 820µV? If only 820µV what about the voltages between 2LSB to 3LSB? It would seem sample switches/caps could capture any defined analog voltage and had the entire Bit range (0-4096) to convert the analog voltage into a digital value anywhere between two 820µV steps.   

So 2^12 = 4096*820µV=3.358V and 1LSB should = 0V? But +/-3LSB precision error % adds noise into the digital conversion results or 0v-2460µV?

Oddly it does not seem like VDDA is actually 0V and has a much higher offset value, even when tied to DGND plane. Conversion results <50mV are not possible and maintain <1/4 LSB precision if any channel noise drives an odd offset state from that of VDDA. 

  • 0
    TI__Guru**** 191486 points

    Hi,

      1LSB is equal to (Vrefh - Vrefl)/2^12. If your Vrefh is 3.3V and Vrefl is 0 then 1LSB = 805uV or 820uV if your Vrefh = 3.358V.

      If you are looking for the differential non-linearity error the it is listed in the datasheet. 

    Although not the same ADC, but a similar 12-bit ADC from a different TI MCU has the below diagram depicting the DNL that might help understanding. 

  • 0 in reply to Charles Tsai
    Guru 55913 points

    Hi Charles,

    Charles Tsai said:
    If your Vrefh is 3.3V and Vrefl is 0 then 1LSB = 805uV

    Perhaps this may be part of the problem and the added low pass SW filter adds >3LSB error to each sample. Most could live with 1/2LSB (DL) error each step but it seems adding a LP filter, for example (x3/4) extends lower LS-Bits above the actual sample data value. The net result is we loose low end precision (0-50mV) in order to gain precision further up the ADC FS, 50mV to 3v1 with SW low pass filter..