The impact of oscilloscope noise interference on measurement

Noise floor:
usually refers to the "baseline noise floor" of the oscilloscope, which is the vertical noise generated by the analog front end and digital conversion process of the oscilloscope. The size of the noise floor is indicated by the signal-to-noise ratio. The larger the value, the smaller the noise interference of the signal, that is, the smaller the noise floor of the measuring instrument.

The impact of background noise on vertical measurement:
The background noise is reflected on the oscilloscope screen as the noise waveform generated when the oscilloscope is placed in the most active vertical gear. Of course, the background noise of the oscilloscope is related to the equipment used in the instrument, hardware scheme, signal processing and other aspects, so the background noise of oscilloscopes from different companies or different types is different, as shown in Figure 1.

Figure 1 Oscilloscopes from different companies have different noise floors.
⑴ When the noise floor of the oscilloscope is large, it will mask small signals and affect the accuracy of the measurement of delicate signals, resulting in inaccurate vertical measurements.
⑵ When the noise floor of the oscilloscope is low, the signal measurement will be more accurate.
For example, as shown in Figure 2 below, a sinusoidal signal with a peak-to-peak value of 4mV is input to oscilloscopes from two different companies, and their peak-to-peak values ​​are measured respectively to understand the impact of the noise floor on the measurement.

Figure 2 Comparison of peak-to-peak measurements of oscilloscopes from different companies

If you want to reduce the impact of background noise on the measurement, you can use the following methods:
 Use "average" capture as the capture method of the oscilloscope. Average capture can evenly display the periodic signal triggered multiple times, making the signal slightly fluctuate around a certain value, closer to the actual value, to reduce the impact of noise.

 The oscilloscope can use the "digital filtering" method to filter out noise signals greater than the cutoff frequency (less than the cutoff frequency) under low-pass filtering (high-pass filtering) to improve the measurement accuracy.