ADS1298: ADS1298 ECG FE Low Pass Filter

Van Tu Hoang

Part Number: ADS1298

Hi TI E2E Support Team,

I have a question about the circuit that IT had designed on ADS1298 ECG FE Board (On the picture). Right at the beginning of the circuit, from there i can see that IT is using a low pass filter 2.order which is a component of resistances and capacitors. So from those values of resistances and capacitors i have got a cut off frequency of more than 200 kHz, it means that the filter will let the frequency under this value through and block the uppers. So my question is: Why should this cut off frequency be so high, when you mainly want to filter out the 50 Hz from power supply? And why not low pass filter 1.order?

Your answers would help me very much.

Thank you,

Van Tu, Hoang

over 4 years ago

0 Alexander Smith over 4 years ago

TI__Mastermind 47595 points

Hi Van Tu,

You actually don't want to cancel out the 50Hz noise with the RC filters. The purpose of the RC filters is to filter out high frequency signals that would alias back into the sampling frequency band. This cutoff frequency for an RC filter is typically at least 10x the frequency of the signal of interest and at least 2x less than the modulator sampling frequency.

In order to cancel the 50Hz noise, you will want to rely on the RLD function of the device and the common-mode rejection ratio of the input PGAs.

There is an application note that covers this in the BIOFAQ located here: https://e2e.ti.com/support/data-converters/f/73/p/772058/2855202

0 Van Tu Hoang over 4 years ago in reply to Alexander Smith

Prodigy 190 points

Hi Alex,

Thank you very much for your quick answer.

Have a nice weekend.

Van Tu, Hoang

0 Alexander Smith over 4 years ago in reply to Van Tu Hoang

TI__Mastermind 47595 points

Happy to help and you too!

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ADS1298: ADS1298 ECG FE Low Pass Filter