ADS1298: Ads1298 raw data waveform baseline is very high

Annie Liu

Part Number: ADS1298

Hi Team,

One customer asked what is the 8-channel raw data from the ADS1298? He uses the electrocardiograph to send signals, but the baseline of the original data is very high. Customer would like to know what processing does the lower computer need to do to pull the baseline to a fixed position?

Best Regards,

Annie

over 6 years ago

0 Alexander Smith over 6 years ago

TI__Guru 57662 points

Hi Annie,

This can be found in the datasheet, it is a 24 bit status word, followed by 24 bits for each channel.

Is the baseline fixed to a DC level? If so, simply subtract that DC value from the measurement after it has been converted to volts.

Is the baseline wandering (Changing)> If so, this is typically due to a changing impedance. If this is the case, the RLD loop may need some de-bugging. I recommend turning off lead-off detection, ensuring a secure electrode connection, making sure that the patient does not move, and experimenting with which leads derive the RLD signal. Typically, using less leads to derive the signal is better than too many.

If your customer has not seen it yet, we have a BIOFAQ which may help answer some questions: https://e2e.ti.com/support/data-converters/f/73/p/772058/2855202

0 Annie Liu over 6 years ago in reply to Alexander Smith

TI__Genius 10295 points

Hi Alex Smith,

The baseline value is now an electrocardiograph, and the value is fixed. After the original 8-channel data voltage value is converted into a voltage value, For example, the lowest value of channel 1 is -4.3mv ~ the highest value is -5mv. The change baseline is basically -4.5mv.
The official did not give the range of the baseline of each channel. Isn't the baseline fluctuating around 0mv like the square wave?

Annie

0 Annie Liu over 6 years ago in reply to Alexander Smith

TI__Genius 10295 points

Hi Alex Smith,

Another question is:

The square wave signal voltage difference is 2mv, but not positive and negative 1mv, but positive 0.5mv negative -1.5mv Is this normal?

Annie

0 Alexander Smith over 6 years ago in reply to Annie Liu

TI__Guru 57662 points

Hi Annie,

Offsets from the electrode measurements are to be expected since the patient and the circuit are not necessarily at the same potential. The offset will be worse when using lead-off detection and not using the RLD function of the device. If using the RLD function of the device, I would expect the measurement to have less of an offset. It is also possible that there is an error in the code to voltage conversion, which can be verified using the post in the BIOFAQ. Variation in offset for the test signal is normal.

0 Annie Liu over 6 years ago in reply to Alexander Smith

TI__Genius 10295 points

Hi Alex Smith,

Is there any way to process the baseline to near baseline 0, because the waveform is displayed to print the graph.

Annie

0 Alexander Smith over 6 years ago in reply to Annie Liu

TI__Guru 57662 points

Hi Annie,

From my previous post:

Is the baseline fixed to a DC level? If so, simply subtract that DC value from the measurement after it has been converted to volts.

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ADS1298: Ads1298 raw data waveform baseline is very high