Meet the challenge of high-pass filter and ST-segment requirements with a DC-coupled digital electrocardiogram amplifier

Forward-filtered triangle simulating the QRS complex of an ECG. The digital filter with linear phase and cutoff frequency beyond the required standards is producing an ST-segment depression. The difference of the input and output signal shown is equivalent to the suppressed signal part.

Forward-filtered triangle simulating the QRS complex of an ECG. The digital filter with linear phase and a low cutoff frequency is producing a smaller but longer ST-segment depression that may even influence the end of the T wave. The difference of the input and output signal shown is equivalent to the suppressed signal part.

Forward-backward, zero-phase filtered triangle simulating the QRS complex of an ECG with the same cutoff frequency. Such filter results in an ST-segment change as well as a PQ-segment change. The result of the forward filter only including the ST-segment depression is shown as well.

Comparison between a digital AC-coupled and a digital DC-coupled ECG amplifier. For the digital DC-coupled amplifier, the analogue HPF is replaced by a digital HPF located after the ADC. In this case, the overall signal behavior is almost identical. Both concepts, when fulfilling the corresponding standards, are safe; but the digital DC-coupled ECG amplifier gives a higher degree of freedom for future design improvements. Furthermore, the digital DC-coupled ECG amplifier allows easy testing because no HPF is present in the raw digital signal.