Multichannel Systems MPA2I Manual - Manual (Page 7)

Welcome to the MPA2I
3
2 Welcome to the MPA2I Miniature Preamplifier
The 2-Channel Miniature Preamplifier MPA2I is connected to the microelectrodes for providing
the initial tenfold amplification stage.
It has additional common ground and reference electrode inputs. The reference electrode is
ideally identical to the recording electrodes and placed into a comparable but inactive area or tissue.
Background or noise signals that are picked up by both the reference electrode and the recording
electrodes are removed.
The metal case provides electrical shielding. Electrode damage is prevented by the very low bias
current. The high input impedance ensures stable long-term recordings: Ideally, the input
impedance would be infinite. As low voltages are generally recorded, a high current would flow
if the input impedance were low. As a result, the amplifier would not be able to deliver the current,
and the voltage would break down. The miniature preamplifier has a high input impedance to avoid
this problem.