Differential oscilloscope inputs

Some oscilloscopes are equipped with a differential input. A differential input is not referenced to ground, but both sides of the input are "floating".

Differential input

It is therefore possible to connect one side of the input to one point in the circuit and the other side of the input to the other point in the circuit and measure the voltage difference directly.

Differential measuring

Advantages of a differential input:

  • No possibility to create a short circuit to ground through the oscilloscope.
  • Only one channel is used to measure the signal.
  • More accurate measurement, since only one channel introduces a measurement error.
  • The Common Mode Rejection Ratio of a differential input is high. If both points have a relative high voltage, but the voltage difference between the two points is small, the voltage difference can be measured in a low input range, resulting in a high resolution.
Warning: The maximum common mode voltage a differential input can handle is limited. When the common mode voltage exceeds that limit, the input will clip and the measured signals will be distorted. Refer to the specifications of your instrument for the maximum common mode voltages.