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Repetitive Sampling

Last Modified: November 26, 2019

Repetitive sampling increases the sample rate of the Oscilloscope by shifting the acquisition time for different acquisition cycles and interleaving multiple acquisition results.

The following figure explains how the Oscilloscope achieves a repetitive sampling rate that is four times the configured sample rate.

Multiple Acquisition Cycles

When you set the sample rate to 100 MS/s, the Oscilloscope samples the signal every 10 ns, known as the sample interval.

To achieve a repetitive sampling rate of 400 MS/s, the Oscilloscope divides the sample interval into four bins, and ensures that each bin is filled with a sample data point. To do so, the Oscilloscope starts sampling at a different time during each acquisition by inserting a time lapse, known as acquisition offset, between when the trigger occurs and when the Oscilloscope starts sampling. The acquisition offset ranges from 0 to 10 ns.

To ensure that each bin is filled with a sample date point, at least four acquisition cycles are needed because of the randomness of the acquisition offset. The previous figure shows an ideal situation with just four acquisition cycles.

High Sample Rate Waveform

When all four bins are filled with sample data points, the Oscilloscope interleaves the sample data sets to form a single, high sample rate waveform.

The high sample rate waveform in the previous figure illustrates the concept of ideal repetitive waveform acquisition. In the actual case, the Oscilloscope samples for at least 16 acquisition cycles to generate a high sample rate waveform. The generated data points, which are uniformly distributed in each bin, are averages of four sample data points in the corresponding bin.

Limitations

Because the Oscilloscope creates the waveform from multiple samples acquired at different times with respect to the trigger, the repetitive sampling method has certain limitations. The input signal must be periodic and low-noise.


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