ADS127L01: Aliasing behavior

Hello Mochi-san,

Thank you for your post.

Is the customer applying a windowing function to their data? Typically, we use a 7-term Blackmann-Harris window. 

Best regards,

Ryan-san,

Thank you for your prompt reply.

I am asking the customer what was thier windowing function.

Regards,

Mochizuki

Ryan-san,

They are using Hanning window function.

However this time, peak frequency of aliasing spectrum is on the FFT point.

The reading level have been verified it is no impact when changed windowing function.

Would you give us the other suggestion to see specified stopband attenuation?

Regards,

Mochizuki

Ryan-san,

Any update?

This socket  is focused business project, there are full of TI’s OPA, ADC,DSP and PM devices.

We really want to keep this ADC DIN.

Regards,

Mochizuki

Hello Mochi-san,

Please excuse the delay as yesterday was a holiday in the U.S.

Can you share some example FFTs from the test results you discussed?

One concern is that the out-of-band signal may be too large for the modulator to handle properly. This means that the modulator may be saturating, as described in section 9.1.4 of the data sheet. This phenomenon becomes apparent is when there is an obvious rise in the noise floor of the FFT. If there is also a fundamental signal present, the peak of the signal in the FFT may be shifted above the normal level as well. Please refer to Table 31 for suggested out-of-band amplitude limits.

Notice that, for input signals near 100 kHz to 200 kHz and fMOD = 16.384 MHz, we put a "-" in the Table 31. At those input frequencies, there was almost no apparent change to the noise floor and no aliased signal measured. So to me, it's possible that something else is causing the phenomenon observed by the customer. To validate this theory, try reducing the amplitude of the out-of-band signal in 100-mVp increments and see if anything improves. 

Best regards,

Ryan-san,

Thank you very much for your prompt reply during holiday evening.

I will commicate it to our customer in this morning at our time zone.

Regards,

Mochizuki

Hello Ryan-san,

I have get our customer's FFT data, but it is their ES sample test result.

Can I send it to your ti mail address directly?

Regards,

Mochizuki