How to change AD5940's sampling frequency

Hi,

  With the default AFE configuration, max allowed ODR is 10Hz. 

For ODR more than this, ADC filter parameters must be changed.

If you are running the code through IDE (Keil or IAR), you may add the below code ) inside AppBIASeqMeasureGen () and add to watch “AppBIACfg.MaxODR”, to know the maximum sampling rate allowed for the set configuration.

  AppBIACfg.MeasSeqCycleCount = AD5940_SEQCycleTime();

  AppBIACfg.MaxODR = 1/((( AppBIACfg.MeasSeqCycleCount + 10) / 16.0)* 1E-6)  ; //If Sysclk is16MHz

  if(AppBIACfg.BiaODR > AppBiaCfg.MaxODR)

  {

  /* We have requested a sampling rate that cannot be achieved with the time it takes to acquire a sample.*/

AppBIACfg.BiaODR = AppBIACfg.MaxODR;

  }

Akila said:

With the default AFE configuration, max allowed ODR is 10Hz. 

thanks,Actually it already exists.But the sampling frequency does not change.so I want to know what BiaODR is for.  

Hi,

Changing the below parameters in  BodyImpedance.c file changes maxODR:

AppBIACfg.DftNum

AppBIACfg.ADCSinc2Osr

AppBIACfg.ADCSinc3Osr

Hello Akila,

Thank you for the prompt response! I was wondering what exactly should be changed within those lines of code. I was looking at the BIOZ-2Wire example and I don't see any numerical values for me to change given the codes you just provided. 

This is what I am currently seeing: 

OR

Thank you!

Very similar to your question about the sampling rate for the AD5940 Board

Hi,

Because  I calculated the value of maxodr is 47 , So no matter how I change the Biaodr value, there is no effect on the output frequency.

so can I delete the  configuration of maxodr in here? only use the Biaodr。

Hi,

 If MaxODR is 47 samples/s and if you are setting BiaODR =50, it is not going to provide 50Hz Output rate. Hence keeping the MaxODR block ensures clarity.

Hi,

Then how can I increase the output frequency to more than 50hz?

Do I have to raise the MAXODR, and how do I increase the value of this?

Change 

pBIACfg->DftNum = DFTNUM_8192;

pBIACfg->ADCSinc3Osr = ADCSINC3OSR_2;

in AD5940Main.c

and

  .ADCSinc2Osr = ADCSINC2OSR_22,

in BodyImpedance.c

But when I change these values,the accuracy of the data decreases

Hello Akila, 

Are these parameter changes also applicable in the BIOZ-2Wire example as well?.

I can only locate  AppBIOZCfg.DftNum, AppBIOZCfg.ADCSinc20sr, and AppBIOZCfg.ADCSinc30sr in the BIOZ-2Wire.c within the AppBIOZSeqCfgGen() section. Would directly replacing the codes with the changes you suggested work?

Thank you 

It would be good to know the FULL code modfications to get to 1000Hz sampling rate, which would be similar to a benchtop Zurich instrument, which we would like to compare to. There seems to be lots of partial code answers - please provide the full code and maximum sampling rate and ideally the loss in accuracy from the 4Hz example in the documentation and the desirable 1000Hz sampling rate.

It would be good to know the FULL code modfications to get to 1000Hz sampling rate, which would be similar to a benchtop Zurich instrument, which we would like to compare to. There seems to be lots of partial code answers - please provide the full code and maximum sampling rate and ideally the loss in accuracy from the 4Hz example in the documentation and the desirable 1000Hz sampling rate.