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How Do I Configure the NI PXI-515x for Real-Time Sample Rates Over 1 GS/S?

Hardware: PXI/CompactPCI>>Controllers

Problem:
I am trying to configure my NI-SCOPE code to acquire sample rates faster than 1 GS/s using the NI PXI-515x. I have read that I can sample at 2 GS/s with this module, how can I achieve this?

Solution:
You can sample at a rate of 2 GS/s using Time Interleaved Sampling (TIS). TIS uses both ADCs to sample the same input waveform, but at different relative phases. The hardware then interleaves these samples to create a single waveform as if only a single channel is used at twice the sample rate.

Overview of Time Interleaved Sampling

The NI PXI/PCI-5152, 5153 and 5154 incorporate two analog-to-digital converters (ADC) in parallel, with one assigned to each channel. Each ADC is capable of sampling at rates up to 1 GS/s. You can see how these ADCs are incorporated in the overall device in the block diagram shown below.


When TIS is enabled, the process is automatically handled by the driver which performs the following steps:
  1. Offset the sample clocks of the ADCs by 180 degrees.
  2. Sample both channels half the desired sampling rate.
  3. Interleave the resulting data to achieve double the rate of a single ADC
Note: Since both ADC's are used in parallel in TIS mode, only one channel of data can be acquired at 2 GS/s.


Sampling rates are achieved on a single channel through integer division of the clock. Therefore on a single channel you can sample at f/N where f is the maximum sample rate and N is a positive integer. By enabling TIS, you can increase your sample rate to 2f/N. Please see the specifications via the related links below for complete details on valid sampling rates.

Programming - How to Enable TIS
  • LabVIEW
    1. Specify the single channel you wish to acquire on by using the Active Channel NI-SCOPE property.
    2. Set the Enable Time Interleaved Sampling property to TRUE.
Note:The execution of property nodes is order specific. the Active Channel property must be specified before the Enable Time Interleaved Sampling property or the driver will throw an error that says you have not specified a channel on which to enable TIS.
  • C API
    1. Specify the single channel you wish to acquire on by using the NISCOPE_ATTR_CHANNEL_ENABLED attribute.
    2. Set the NISCOPE_ATTR_ENABLE_TIME_INTERLEAVED_SAMPLING attribute.
Example
  1. From LabVIEW open the NI Example Finder and browse to the folder path Hardware Input and Output » Modular Instruments» NI-SCOPE» Demos.
  2. Open niScope EX Configure Acquisition.vi or in CVI open ConfiguredAcquisition.prj
  3. Check the Enable TIS check box on the Front Panel.
It is important to note that if you do not set either of the above properties or attributes correctly an error will be thrown. The errors corresponding to each attribute are listed below:
  • TIS not enabled: -1074118530


  • Channel not specified -1074135024



    • You will also see this second error if you have the order of your LabVIEW properties switched in order so the Enable Time Interleaved Sampling property is first.


Related Links:
Product Page: NI PXI-5152 Digitizer
Product Page: NI PCI-5152 Digitizer
Product Page: NI PXI-5153 Digitizer
Product Page: NI PCI-5153 Digitizer
Product Page: NI PXI-5154 Digitizer
Product Page: NI PCI-5154 Digitizer
Product Manuals: NI PXI/PCI 5152 Specifications (September 2008)
Product Manuals: NI 5153/5154 Specifications (October 2008)
Product Manuals: NI High-Speed Digitizers Help (June 2008)

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Report Date: 10/25/2006
Last Updated: 06/19/2009
Document ID: 42O43RPQ

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