Electronic – Do I need a 50/60Hz notch filter for battery powered devices


Given that battery powered devices are not plugged in the mains power, can I assume that there will be no 50/60 Hz frequency noise?

This question came up while thinking about what the circuit for a portable ECG monitor would look like and it seemed obvious that the 50 Hz notch filter could be eliminated. But is it so?

Thank you

Best Answer

Assuming you're talking about the input signal, you may still want the filter because the long leads running to the chest pads (or wherever your detection location is) could pick up a 50/60Hz signal like a transformer's secondary from a nearby loaded mains cable.

If you're only referring to the power supply, you're correct, a battery produces very stable DC voltage, any instantaneous fluctuation in battery voltage would predominantly come from sudden loading/unloading of the battery. Therefore no filter would be needed.