OSP Decimation Range

[Alann]

Hey,

I want to change the OSP Decimation Range of NI-5142 digitizer. How do we do that?

[Speedy_Badger]

Hello Marry,

The OSP decimation of the 5142 is based on integer resampling. As a result, your IQ rate will be coerced based on the following defintions as seen in the specifications documented below:

1, 2, 4, 6, 8, 10
12 to 4,096 (Multiples of 4)
4,096 to 8,192 (Multiples of 😎
8,192 to 16,384 (Multiples of 16)

This can be referenced on page 24 of the PCI/PXI 5142 specifications document: https://www.ni.com/docs/en-US/bundle/pci-5142-specs/page/specs.html

The integer decimation value of the OSP as seen above will be dependent on the IQ rate chosen, relative to the max ADC sample rate of 100 MS/s.

Best Regards,

[Alann]

and what is actually meant by Programmable IF bandwidth? Does that relate to span?

[Speedy_Badger]

Hi Marry,

The term Programmable IF Bandwidth  refers to the programmable IQ rate of the Digitial Downconverter (DDC) present on the 5142 digitizer. The Digitizer itself will acquire at 100 MS/s on its ADC. DDC however will have a specific bandwidth however based on another rate, IQ rate, that you can choose. This allows us to downconvert a bandwidth of information to baseband. The hard limit of this bandwidth is based on a FIR filter and is defined as 0.4 x Real Sample rate or 0.8 x Complex Sample rate. For instance, if we have a complex (IQ) rate of 50 MS/s and multiply it by 0.8 we will have our upper limit, which is 40 MHz bandwidth. As you decrease your IQ rate, you will narrow the IF bandwidth that is digitally downconverted. This is all described in detail in the 5142 specifications manual, under the OSP section, found here.

This does correlate directly to the idea of span. For instance, the PXI-5661 RF Vector Analyzer uses the PXI-5142 along with the PXI-5600 downconverter. The PXI-5600 has a real-time bandwidth of 20 MHz around the center frequency, which is then downconverted to 15 MHz IF frequency. The 5142 is then used to acquire the analog waveform and digitally downconvert a certain IF bandwidth or span around that 15 MHz IF frequency.

In regards to the previous question -

You could customize your decimation range by using an external clock instead of the onboard sample lock. The integer values I listed above are used to divide down the clock, which if different than the internal sample clock, will yield different decimation values that you will be coerced to.

Also, this forum is geared towards the IF-RIO product which is somewhat different than the 5142 digitizer. For the best support on your product of interest I would recommend taking a look at this forum: High-Speed Digitizers

Hope that helps!

Best Regards,

[Alann]

Thanks a lot Chris!