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CC2540: ADC signal delay (delay from analog input to decimation filter output)

Part Number: CC2540
Other Parts Discussed in Thread: ADS131E08,

Is there a specification on the ADC signal delay caused by the ADC sigma-delta modulator and decimation filter? Specifically I need to know the signal delay between the analog input pin and the output of the decimation filter. I am working on a project where this knowing this delay is critical.

Thanks,

George

  • Hi George,

    The conversion times for the various modes are listed in the datasheet.

    Cheers,
    Fredrik
  • Hi Fredrik,

    Thanks, but my question was not on the conversion times, I got those from the data sheet. What I need to know is the signal delay from the analog input pin to the output of the decimation filter. For example, a digital filter will cause a delay on the input signal according to the order of the filter, there should be a similar spec for the ADC decimation filter (and possibly the sigma delta modulator) depending on the order of the decimation filter, and possibly the number of samples decimated (I am using the 512 sample setting on the ADC).

    The information should be similar to the info found in this document, "Accounting for delay from multiple sources in delta-sigma ADCs" which can be found here:

    http://www.ti.com/lit/wp/slyy095/slyy095.pdf

    According to this document, the delay through the sigma-delta modulator should be small, much less than the 4.0 usec stabalization time (please correct me if this is not the case), and the delay through the digital decimation filter should be calculable if you know the design of the decimation filter. They use the digital filter of the ADS131E08 as an example and show the magnitude and phase response of the filter as well as the group delay. 

    The most useful information would be the delay, in samples (as shown in Table 1) and the group delay of frequency for the ADC on the CC2540/1.

    Thanks,

    George 

  • Hi George,

    I talked to our analog designers today, and this is what they told me:

    This is an accumulate and dump filter. The samples are filtered as they come in and after the set number of samples are accumulated an output sample is provided. We do not really have any better definition on the delay than the conversion time stated in the datasheet.

    Regards,
    Fredrik