Why is high input impedance important for a differential amplifier?

High input impedance in a differential amplifier is crucial for ensuring the accuracy of weak signals. When an amplifier has high input impedance, it minimally loads the source signal it is measuring. This characteristic is particularly important when dealing with weak bioelectric signals, such as those obtained from the nervous system or muscular activity, where even slight changes can be significant.

If the input impedance were low, it could draw significant current from the signal source, potentially distorting the signal and reducing the fidelity of the measurement. High input impedance allows the differential amplifier to pick up these weak signals without introducing substantial additional noise or altering the original signal characteristics. This measurement accuracy is essential in neurophysiologic intraoperative monitoring, where precise interpretation of data can impact surgical outcomes.