I am currently running the test AD8233 ECG chip on +/- 300mV half cell potential. In the details, I send a 1mVpp AC sine wave 10Hz with DC offset +300mV or -300mV and look at the output of the chip. In the DC +300mV or 0mV dc offset, the AD8233 is working ok and output the correct output amplitude i.e. in this case Gain is set 1100, so i get 1.1Vp-p sinewave signal. However, whenever i change to -300mV DC offset, the output is only less than half (about 400mVp-p sinewave) and the waveform looks distorted. So, i investigate more details, by decreasing the DC offset from -300mV back to 0mV, at about -150mV DC offset, i can get back 1.1Vp-p sine wave amplified signal.
One of important standard for ECG 60601-2-27 is that the ECG front end chip need to accept up to half cell potential +/-300mV DC offset when testing with small AC waveform sinewave, triangle wave or squarewave. In this case, it seemed to be the AD8233 did not do the job at -300mV DC offset. Could you please tell me whether I can change the configuration design to get it accept -300mV ?
The details circuit i used is AD8233CB Evaluation board default configuration.