EVAL-ADuCM355 Output Data Rate

Hi Analog,

We are using the new EVAL-ADuCM355 to measure up to 16 sensors sequentially, in a 2-wire configuration. We want the highest possible output data rate from those sensors, so I am looking for suggestions on how to maximize this. So far, to maximize the output data rate, using the M355_Biased_EIS example in IAR, I have:

  • Removed any unnecessary delay_10us() calls
  • Fixed the sine wave freq at 10 kHz
  • Set the number of DFT points to 1024 or 2048 (1024 is empirically the minimum number of points in the DFT we need to retain sufficient measurement accuracy)
  • Set the DFT source to the SINC3 filter (to bypass the SINC2 filter) and reduced the number of points in this to 2.
  • Bypassed the low pass filter (LFPBYPEN_BYP)
  • Set HSDACCON [8:1] to 7 MHz (DacCon |= (0x07<<BITP_AFE_HSDACCON_RATE);)

As far as I can see, the actions above should result in the following output rate:

Impedance Data Output Rate = 1600KSPS/2 = 800KSPS SINC3 output. 800KSPS/1024 = 781 SPS DFT output.

However, when recording timestamped measurements on RealTerm, I only get an output frequency of 83 Hz - quite far from the 781 Hz output from the DFT engine. 

Do you have any suggestions for how to resolve this? We want to get as close as possible to the 781 Hz data rate.

I have attached the .c file I have modified from the M355_Biased_EIS example in order to get the 83 Hz output frequency here: 5050.M355_ECSns_EIS.zip



Clarified question further
[edited by: andyy at 2:28 PM (GMT 0) on 29 Mar 2019]