How to observe the ripple of the power supply by Siglent digital storage oscilloscope

Now, the technology of the power module and supply is  update  very quickly. The engineers have to face a challenge: How to select the power supply instruments more efficiently and accurately, which meets the requirements. And the measurement&test companies must offer the solution to test the ripple with the digital storage oscilloscope.

1.Measuring method

Many engineers find the ripple is hundreds of units mv tested by the digital storage oscilloscope. That is an error caused by the wrong test method dozens of times as large as the description in the specifications. We would like to introduce the correct steps of using SDS1000 as following as below:

1.1 Active the function of limiting bandwidth and set 20MHz, or open low-pass filter to adjust the max value of the bandwidth; The purpose of this setting is preventing from the high frequency noise in digital circuit to keep the accuration.

1.2 Choose AC coupling: in order to avoid DC signal is too strong to being captured by SDS1000. (using small voltage range to observe ripple)

1.3 Keep the ground cable of the probe be as short as possible. For example: remove the probe’s ground cable, and use a short ground cable to tie with the core of the probe. That will keep the length of ground cable be less 1cm. (It is very important to reduce the noises from other devices. Because the ripple signal is very weak)

1.4 Digital storage oscilloscope must be floating, except the ground junction between the probe and signal. Do not adopt other methods to connect the instrument with the ground to avoid other noise.

Comparison of measuring the ripple:

2.  Requirements

Digital storage oscilloscope

Have the function of bandwidth limitation or digital filtering, for example SDS1000 series.


There is a short metal wire in the accessories of Siglent probe. Use them together, or make a short ground line by yourself; Take off the original ground line from the probe, then make a short one with moderate CAT5 copper wire, Tin wire, or Aluminum wire.

Choose 1X(non-attenuation): reduce the jam from the high frequency noise by the passive probe with 1X in 6MHz/10MHz. Using 10X will weaken the ripple signal to raise the difficulty of the observation, let alone filter.

3.Comparison of measuring the ripple with different probes

Use normal probe to test the ripple:

Image 3.1  ripple test of Power supply output 0.18V(2mv/div sensitivity SIGLENT runs bandwidth limitation automatically)

Use the proceeded short probe to test the ripple:

Image 3.2 after the ground cable of the probe cut down


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