Noise observed when 150 Hz test tone data is captured using EVAL-ADAS1000 EVM.

Hi Subbash,

Since you have 150Hz test tone configured and you are doing 500Hz sampling rate but decimating the data by 4, you effectively have 125Hz sampling rate which is lower that your 150Hz sine wave. Ideally, your sampling rate should be twice the frequency of you input signal. You can try outputting every frame.

You might also need to check your FILTCTL to make sure that LPF is set to 250Hz to make sure that the 150Hz sine wave can pass through, 

The ADAS1000 datasheet has details on how to configure and measure 150Hz testone in ADAS1000. 

ADAS1000/ADAS1000-1/ADAS1000-2 (Rev. C) (analog.com)

Regards,

Mark

Dear Mark, 

Actually, We are Capturing data at 2kHz and decimating by 4. So the effective sampling frequency is 500Hz. The sampling frequency is 3 time the input signal (150Hz sine wave).

at 2kHz sampling frequency, without decimation, the sine wave looks to be fine.

Hi Mark, 

Can you review and comment

Ping

Ping

Hi Subbash,

With 500Hz sampling, you're capturing only 3 points of your sine wave so the data you're getting is probably right. 

Just to make sure that you have configured the part properly, have you tried following the example from the datasheet?

Example 4: Configure 150 Hz Test Tone Sine Wave on Each ECG Channel and Stream Conversion Data

regards,

Mark

Dear Mark, 

I have verified the configuration settings. They are set as per Example 4. Except for Frame control register where We have used 0x8A1F961C. (Skip interval is selected as Output every 4th frame to achieve 500 Hz data rate).

If We set FRMCTL as 0x8A1F9610. We are able to obtain proper 150Hz sine wave plot.

Are you also able to obtain the same result on EVM. ..?

Thanks and Regards,

Subbash

ping

Hi Subbash,

I am also getting the same output on Eval Board. The frequency is correct but because you are only sampling 3 points per period of the 150Hz sine wave, you won't be able to replicate the sine wave in your setup.

regards,

Mark