RC-Filter @ ADS1298R ECGFE

Andreas Schunkert

Other Parts Discussed in Thread: ADS1298R

Hi everybody!

I made some testings with the ADS1298R Evaluation Board and now I'm designing a own Board for our aplication with the ADS1298R Device. While I worked on my schematics I notice the RC-Filter on the ADS1298R ECGFE Board between the Sub-D Input and the ADS1298R on each channel.

Can you please explain the reason of this Hardware filter? Because I calced the 3dB cut off frequency with 127kHz. Is that correct? And why aren't the filter designed with a lower cut off frequency? I think 127kHz is verry high for desired signals less than 10Hz.

Thanks for your answers and greetings from Germany!

Andreas

over 9 years ago

0 Greg Hupp over 9 years ago

TI__Mastermind 23235 points

The filter you are referring to is the anti-aliasing filter of the circuit. It's purpose is to attenuate the higher frequencies approaching the modulator frequency to prevent aliased signals back into your band of interest. It is not intended to filter your band of interest, the reason that the cutoff is much higher.

There is a small mention of it in the datasheet on page 51, right above the filter frequency response graphs.

0 Andreas Schunkert over 9 years ago in reply to Greg Hupp

Prodigy 60 points

Thanks for the Information!

0 Andreas Schunkert over 9 years ago in reply to Andreas Schunkert

Prodigy 60 points

Ok..... one more question about this filter.

If this filter is using as a Aliasing-Filter and the Data Rate is adjusted to 500SPS. Am I wrong, or isn't the samplingfrequency in this case 500 Hz. That means, that the Nyquist-Frequency is 250 Hz. For that I Need a Antialiasing-Filter with a cutoff-frequncy of 250 Hz to prevent that there will be higher frequenzy back in my band of intrest.

Where is my error in reasoning?

0 Greg Hupp over 9 years ago in reply to Andreas Schunkert

TI__Mastermind 23235 points

ADS1298R is a delta-sigma (or over-sampling) converter. You may want to review the operation of this ADC to understand better the relationship between the output data-rate and the actual sampling rate.

Data converters

Data converters forum

RC-Filter @ ADS1298R ECGFE