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Why Does My Data Look Noisy when Using Time Interleaved Sampling (TIS)?



Primary Software: Driver Software>>NI-SCOPE
Primary Software Version: 3.5.1
Primary Software Fixed Version: N/A
Secondary Software: N/A

Problem:
I am using an NI 515x High-Speed Digitizer (Scope) in Time Interleaved Sampling (TIS) mode, and it appears that my data (in particular, every other sample) is incorrect. Why is this happening and how can I correct it?

Solution:
There is a known issue when using Time Interleaved Sampling (TIS) mode on the NI 515x digitizer with NI-SCOPE 3.5.2 or earlier. If your channels are configured with two different vertical ranges, incorrect calibration will be applied to the samples digitized by the second channel. For example, if channel 0 is configured with a 100 mV range and enabled for TIS, but channel 1 was last configured with a 1 V range, the interleaved samples acquired by channel 1 will incorrectly use the 1 V coefficients.

Your measured signal may appear to have a triangular pattern in the time domain since every other sample is scaled differently. A spur may be visible in the frequency domain at the Nyquist frequency (half the sample rate) minus the input frequency. For example, when using an NI 5152 to measure a 10 MHz sine wave at 2 GS/s in TIS mode, the signal may show a spur in the frequency domain at 990 MHz (1 GHz minus 10 MHz).

To correct this issue, install NI-SCOPE 3.6 or later. If you are unable to upgrade, the work-around is to ensure that both channels 0 and 1 are configured to use the same vertical range before enabling TIS.

In LabVIEW, simply insert an NI-SCOPE property node, set the active channel to "0,1" and set the vertical range to the desired value as shown below.

If you are using C, use the following function prototype:

ViStatus niScope_SetAttributeViReal64 (ViSession vi, "0,1", NISCOPE_ATTR_VERTICAL_RANGE, ViReal64 range);



Related Links:
KnowledgeBase 42O43RPQ: How Do I Configure the NI PXI-5152 for Real-Time Sample Rates Over 1 GS/s?
Product Manuals: NI High-Speed Digitizers Help (March 2009)
Specifications Explained: NI Oscilloscopes and Digitizers

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Report Date: 06/16/2009
Last Updated: 10/04/2017
Document ID: 4YFD6BLY

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