How to Properly and Carefully Use Oscilloscope Average and
High Resolution Mode
Author: Roger Lee
Product Marketing Department
Digital oscilloscopes provide many acquisition modes to meet the needs of general and special applications. These acquisition modes include sample mode, average mode, and peak detection mode. Mid-level and advanced digital oscilloscopes (such as GW Instek's GDS-3000A series oscilloscopes) are equipped with the high-resolution mode to augment the average mode.
How to make good use of average and high-resolution acquisition modes?
Random noise can be eliminated and measurement resolution can be improved through average and high-resolution modes (an odd-numbered measurement result and an even-numbered measurement result can be averaged to increase the resolution). Hence, users can make good use of these two acquisition modes when they have the above-mentioned application requirements.
However, what is the difference between high-resolution mode and average mode applications? (Please refer to the sampling figures below)
The main difference is that the average mode is suitable for continuous, repetitive and stable signals. The number of averages can be selected to perform multiple sampling averages. The more averages are selected, the slower the waveform update rate will be. From the above constraints, the average mode is not suitable for single shot, because there is only one shot and no next shot can be used for averaging. The high-resolution mode averages on a waveform, so even a single shot or unstable signals can still be averaged.
The analog-to-digital converter (A/D) must slowdown in the middle (ms/us div) and low speed time base ranges (roll mode) of the oscilloscope, otherwise the waveform memory will be used up after converting partial waveforms. The peak detect mode and high-resolution mode use the characteristics of digital oscilloscope to slowdown in the middle and low speed time base ranges, and check the peak value (reserve maximum or minimum) or take average at sampling points without slowing down in the sampling intervals.
Therefore, these two modes are only valid in the middle and low speed time base ranges. These two modes of most digital oscilloscopes will fail when the sampling rate is higher than 200MS/s, so they must be used with caution. If your test report is to evaluate noise please don't fool yourself with the average mode or the high resolution mode.
Figure 1: Schematic diagram of the calculation method of the average mode
Figure 2: Schematic diagram of the calculation method of the high-resolution mode
The following three comparison diagrams are provided for reference:
- Measurement resolution comparison: In the high resolution mode, the measurement resolution will have one more decimal point.
Figure 3: Sample mode waveform and measurement results - Measurement comparison when the waveform is not triggered: if the average mode is selected, the waveform will be distorted and the measurement results will be invalid for reference.
Figure 4: High-resolution mode waveform and measurement results
Figure 5: The sample mode does not meet the trigger conditions, and the waveform is unstable, which is correct.
Figure 6: High-resolution mode does not meet the trigger conditions, and the waveform is unstable, which is correct.
Figure 7: Average mode does not meet the trigger conditions, average unstable waveforms, and wrong results appear. - Test single shot noise signal comparison.
Figure 8: Waveform of single shot noise in the sample mode.
Figure 9: Results of average single shot noise in the hi-resolution mode
Summary:
|
High resolution mode |
Average mode | |
|
Acquisition mode |
One-time waveform averaging, less affected by waveform updates, but still slower than sampling mode | Multiple waveform averaging, the more average times, the slower the waveform update rate |
|
Suitable signal |
Ideal for average single shot or unstable signals | Suitable for averaging repetitive and stable signals |
|
Application restrictions |
Only middle and low speed time base ranges are applicable | No time base range limit |
The above elaboration is to enable users to make good use of these acquisition modes and use them carefully to complete test and measurement tasks.
For more oscilloscope product information:www.gwinstek.com/en-global/products/detail/GDS-3000A
Contact us:
Overseas Sales Department
Good Will Instrument Co., Ltd
No. 7-1, Jhongsing Road, Tucheng Dist.,
New Taipei City 23678, Taiwan R.O.C
Email: marketing@goodwill.com.tw