# Two-Channel Cross-Correlation Lowers the Oscilloscope Noise Floor

Subtopics

- How DSP Cross-Correlation Removes Measurement Errors

The two-channel cross-correlation technique can be performed when two copies of the same clock signal are input to two oscilloscope channels. The clock signal can be single-ended or differential (see Clock Signal Probing Options). Cross-correlation operations are then performed on the channels, as shown in the following figure.

Two-Channel Cross-Correlation Technique:

DUT noises through each channel are coherent and are not affected by the cross-correlation, whereas the internal noises generated by each channel are incoherent and are diminished by the cross-correlation operation at the rate of M1/2 (M being the number of correlations). This can be expressed as:

Where:

- Nmeas = the total measured noise
- NDUT = the DUT noise
- N1 and N2 = the internal noise from channels 1 and 2, respectively
- M = the number of correlations

The two-channel cross-correlation technique achieves superior measurement sensitivity without requiring exceptional performance of the hardware components. However, the measurement speed suffers when increasing the number of correlations.

## See Also

- How DSP Cross-Correlation Removes Measurement Errors

For more information on two-channel cross-correlation, see:

- Solutions for Exploring Phase Noise Measurement Methods and Techniques
- Phase Noise Measurement Solutions