What must the amplifier input impedance of a differential amplifier be at a minimum?

The minimum input impedance of a differential amplifier should be at least 10 MOhms. This high input impedance is crucial in neurophysiologic monitoring, as it prevents loading of the electrode and the underlying tissue, which can distort the recorded signals. High input impedance reduces the current draw from the biological signals being measured, such as EEG or EMG, ensuring that the integrity of the signals remains intact and allows for accurate measurements.

When input impedance is too low, it can create a voltage drop across the input circuit, which reduces the effective amplitude of the signals being monitored. Therefore, a high-impedance input is necessary to ensure minimal interference and maximum fidelity of recordings, particularly in sensitive intraoperative settings where precision is paramount.