High impedance

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "High impedance" – news · newspapers · books · scholar · JSTOR (January 2021) (Learn how and when to remove this message)

In electronics, high impedance means that a point in a circuit (a node) allows a relatively small amount of current through, per unit of applied voltage at that point. High impedance circuits are low current and potentially high voltage, whereas low impedance circuits are the opposite (low voltage and potentially high current). Numerical definitions of "high impedance" vary by application.

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 high internal impedance.

Analog electronics

In

a high impedance node is one that does not have any low impedance paths to any other nodes in the frequency range being considered. Since the terms low and high depend on context to some extent, it is possible in principle for some high impedance nodes to be described as low impedance in one context, and high impedance in another; so the node (perhaps a signal source or amplifier input) has relatively low currents for the voltages involved.

High impedance nodes have higher

can match a high-impedance input source to a low impedance amplifier.

Digital electronics

In

, among many other uses.

The high-impedance state of a given node in a circuit cannot be verified by a voltage measurement alone. A

pull-down resistor

) can be used as a medium-impedance source to try to pull the wire to a high (or low) voltage level. If the node is not in a high-impedance state, extra current from the resistor will not significantly affect its voltage level.

References