High impedance

In electronics, high impedance means that an electrical contact point in a circuit (a node) allows a relatively small amount of current through, per unit of voltage applied to that point. High impedance circuits show low current for (possibly) high voltage, whereas low impedance circuits are the opposite: they show low voltage for (possibly) high current. Values for electrical impedance are measured in units of Ohms (Ω), similar to resistance.

High-impedance inputs are preferred on measuring instruments such as voltmeters or oscilloscopes. In audio systems, a high-impedance input may be required for use with devices such as crystal microphones or other devices with inherently high internal impedance.