AC Coupling vs. DC Coupling on an Oscilloscope

Written by j.t. barett
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AC Coupling vs. DC Coupling on an Oscilloscope
An oscilloscope's AC and DC input coupling lets you work with different signal types. (electrical signals image by Albert Lozano from

If you're learning electronics, knowing how to use an oscilloscope will help you in building and repairing circuits. The oscilloscope's AC and DC coupling options let you examine different kinds of electrical signals conveniently.


Every oscilloscope has at least one input channel. You can set it to read direct current (DC) or alternating current (AC) signals by pushing a switch marked "coupling."

DC Signals

With DC coupling, the oscilloscope acts as a voltmeter. The screen will show a flat trace moved up or down by the DC voltage you're measuring. By touching the scope probe to different circuit points, you can get rough voltage readings.

DC offset

A signal with AC and DC combined, where a waveform "floats" on top of a constant voltage, has what's called DC offset. With DC coupling, the offset will push the waveform off-screen. AC coupling removes this offset.

AC Signals

You can use either coupling type to see AC signals. By pressing the switch to go from AC to DC and back again, you can detect small offsets. A signal with offset will move vertically on the screen.

Low Frequencies

Because of the vague distinction between DC and low-frequency AC, AC coupling may not be useful for frequencies below a few cycles per second. Use DC coupling instead.

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