The noise of the oscilloscope can be reduced using a bandwidth limit filter, average acquisition mode, math filter ( filter Vu ), and by filling the screen. These are the common three methods. An oscilloscope is an electronic instrument used for testing electrical circuits. It can display two or more signals graphically in a cycle of time.
Oscilloscope Measurements
Oscilloscopes can display single waveforms or repetitive waveforms. The waveform can be analyzed as alternating current (AC), direct current (DC), frequency in hertz (Hz) or megahertz (MHz), rise time, time interval, and distortion. the graphical display is divided into horizontal division (X division) and vertical division ( Y division). Time is displayed in the horizontal division and voltage is displayed in the vertical division. The upward voltage is positive and the downward voltage is negative.
What Causes Oscilloscope Noise?
Noise in an oscilloscope occurs when you display a wave or while recording it. Noise in the oscilloscope is caused due to power supply ripple or ground bounce, mechanical vibration, movement in the probe tip, input amplifier, and buffer circuits. The probe system and oscilloscope are the primary sources of noise.
Noise from the system:
- Using an attenuator is used to attenuate or amplify the signal using the method of the attenuation (or amplification) ratio according to requirement. It also amplifies the noise.
- After receiving the signal from the probe different sources contribute to distorting the sources which produce noise.
- The non-linear circuit shows the different output for different input and makes it difficult for the oscilloscope to predict and this lead to noise.
How the Common Mode Noise Can Be Reduced From the Oscilloscope Measurements?
Noise is a common problem for oscilloscopes. There are three common ways to reduce noise.
Bandwidth Limit Filter
The bandwidth limit filter is used to control (expand or reduce) the bandwidth. You can adjust the bandwidth according to your need. So, the frequencies higher than the limit will be removed from the trigger path, acquisition, and display path. It will reduce the noise also.
But while using this filter you should know the necessary amount of bandwidth for the signal. If you select the wrong amount then you can’t have the accurate result in the display.
Average Acquisition Mode
In this mode of the oscilloscope, it takes multiple data from the corresponding data points and averages them point to point basis. For using this mode your signal needs to be repetitive. At first, using an oscilloscope shows a fuzzy waveform but after using the mode the waveform gets clean.
Fill the Screen
Noise can be minimized by using the full screen voltage of the oscilloscope. It also gives better accuracy and resolution. It expands the signal to fill the whole screen.
Math Filter
This filter is used to remove a certain frequency of noise from the signal. You can choose the frequency which you want to filter. The Tektronix MSO/DPO2000B oscilloscope has this feature.
How Do You Reduce Signal to Noise Ratio?
An attenuator is used to attenuate and amplify the signal to the right level but it also amplifies the noise. When you are dealing with a bigger signal, it is attenuated to make it small to fit it in the range of the scopes ADC (analog to digital converter). Noise depends on the probe attenuation ratio.
The attenuation ratio of a probe refers to the signal (large or small) you can measure accurately with that probe. If the attenuation ratio of the probe is 1:1, the signal will remain the same. But if you change the probe to a 10:1 attenuation ratio, it will scale your signal 10 times smaller before entering the scope.
A higher attenuation ratio creates more noise because the oscilloscope’s noise gets multiplied when it goes through the ADC and displayed the signal to its original size on the screen. So, the noise is also multiplied by the ratio.
For example, if a probe with an attenuation ratio of 10:1 measures a 1V wave. Then the signal will be scaled to 100 mV before entering the oscilloscope. When it will go through ADC it will be multiplied by 10 and then displayed on the screen back to its form. But the noise will increase.
The same goes for the 100:1 attenuation ratio probe So the signal to noise ratio will be reduced too. It is suitable to use as small an attenuation ratio as possible.
How Do You Remove the 50HZ Signal From an Oscilloscope?
You can use a filter to remove a 50Hz signal from an oscilloscope. You can use a math filter or filter Vu to remove the 50Hz signal. Filter Vu is used to remove a certain frequency of the wave. If you are measuring a wave of 20Hz to 100Hz but the 50Hz wave signal is disturbing your result, you can remove it.
Conclusion
In this article, we have discussed Oscilloscope’s noise and the processes of reduction of noise. Noise can disturb the result of a signal. So it should be prevented to determine the accurate result.
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