Understanding Oscilloscopes (VI): Different Acquisition Modes

1 Different acquisition modes

Assume that the storage depth is 1M, the sampling rate is 1G/s, and the single acquisition time of the oscilloscope (the total time of the horizontal axis on the oscilloscope) is 1ms. At this time, all the data of a single sampling just fills the entire screen. If the single acquisition time is adjusted to 10ms, according to the description of Deep Understanding Oscilloscopes (IV): Oscilloscope Storage Depth and Sampling Rate, the oscilloscope will automatically reduce the sampling rate to 1M/10ms=100M/s. But what will happen if the sampling rate is still 1G/s? The most direct result is that the storage depth exceeds 1M and the oscilloscope's memory overflows. However, there is a dedicated processor in the oscilloscope that can process this data first and then update it to the "memory". Different sampling modes require different processing methods of the dedicated processor.

1.1 Normal (ordinary, default) mode

Sampling is performed at a sampling rate calculated by dividing the storage depth by the single acquisition time. A point on the waveform is sampled only once without any processing.

1.2 Peak Detection Mode

The single sampling time is adjusted to be greater than 1ms, such as 10ms (using the example at the beginning of the article), the sampling rate is limited to 1G/s, and 20 points are sampled each time, and the maximum and minimum values ​​are stored. This is equivalent to storing 10ms1G/s÷202=1M points, and the actual sampling rate is 1G/s÷20x2=100M/s.

This mode makes it easier to check glitches and narrow pulses in the waveform. When using this mode, you need to use the infinite persistence function at the same time. The figure below is the waveform in normal mode.

If we turn on the peak detection mode and the infinite persistence function, we will see the following waveform. This function helps us find the burr!

1.3 Average acquisition mode

In the average acquisition mode, the results of "multiple" acquisitions are averaged to reduce noise. Note that multiple acquisitions (triggers) are performed, and the maximum number of acquisitions is 65536.

The larger n is, the longer it takes to display a waveform and the slower the waveform updates.

1.4 High Resolution Mode

This mode is similar to the peak detection mode. The single sampling time is adjusted to greater than 1ms (using the example at the beginning of the article, it is actually setting a slower Time Div), such as 10ms. The sampling rate is still limited to 1G/s, and 10 points are sampled each time and the average is taken. This is equivalent to storing 10ms*1G/s÷10=1M points, and the actual sampling rate is 1G/s÷10=100M/s. This mode is different from the average mode and does not require repetitive waveforms.

1.5 Package Mode

Similar to peak-to-peak detection, but this mode requires acquiring a waveform multiple times and then adding the peak-to-peak values ​​together.