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AMC1306M05-Q1: Difference between settling time and latency on delta sigma modulator?

Yoshiki Ochi
Expert 7515 points
Part Number: AMC1306M05-Q1

Hi team, 

Referring to https://www.ti.com/lit/wp/sbaa359a/sbaa359a.pdf, "Table 2. Performance Trade-Off Between ENOB and Settling, Latency or Bandwidth for the AMC1306 at CLKIN = 20 MHz Using a Sinc3 Filter", it says "latency" and "settling time". What is difference between "latency "and "settling time"? Do you have any picture to explain it?

Regards,
Ochi 

  • 0
    TI__Mastermind 22950 points

    Hi Ochi-san,

    I unfortunately don't have any images to share but the settling time is the time required for the SINC filter to settle with a stepped input. This time is typically 3*Data Rate where the data rate can be calculated as OSR/fCLK. The latency is typically measured with a marginally varying input signal. So for a continuous signal, the latency can be seen has half of the settling time of the filter. 

    In either case, the delay from the modulator can be ignored as the dominant source of delay will come from the filter. 


    Regards,
    Aaron

  • 0 in reply to Aaron Estrada
    TI__Expert 7515 points

    Hi Aaron, 

    Thank you for your instruction. I understand what settling time is, but cannot understand what latency is... When step input signal comes, the digital output will changed; its digital output value has transient duration and steady (=settled) state.

    • For settling time = 3*Data rate, where "3" indicates Sinc"3" filter? If CPU uses Sinc"2" filter, then settling time = 2*Data rate?
    • For latency, does settling time include latency? Or do we have to consider consider delta sigma response time as "only settling time" or "settling time + latency"? This response time is important for over current fast response loop.  
    • Do you know C2000 MCU could configure as other than 3rd order digital SINC filter? 

    Regards,
    Ochi

  • 0 in reply to Yoshiki Ochi
    TI__Mastermind 22950 points

    Hi Ochi-san,

    • For settling time = 3*Data rate, where "3" indicates Sinc"3" filter? If CPU uses Sinc"2" filter, then settling time = 2*Data rate?
      • You are correct. My apologies for not being clear. The settling time can be seen as Filter Order * Data Rate
    • For latency, does settling time include latency? Or do we have to consider consider delta sigma response time as "only settling time" or "settling time + latency"? This response time is important for over current fast response loop.  
      • The latency can be seen as the 'delay time' and is measured with a varying analog input/continuous signal. 
    • Do you know C2000 MCU could configure as other than 3rd order digital SINC filter? 
      • Yes, I believe that Sinc1, Sinc2, and Sinc3 filter options are available. 

    Regards,

    Aaron