Signal Path:Digitizer Dither Enabled Property

Signal Path:Digitizer Dither Enabled Property

Short Name: Digitizer Dither Enabled

Property of niRFSA

Specifies whether dithering is enabled on the digitizer.

Dithering adds band-limited noise in the analog signal path to help reduce the quantization effects of the A/D converter and improve spectral performance. On the PXIe-5622, this out-of-band noise is added at low frequencies up to approximately 12 MHz.

PXIe-5663/5663E/5665/5667—When you enable dithering, the maximum signal level is reduced by up to 3 dB. This signal level reduction is accounted for in the nominal input ranges of the PXIe-5622. Therefore, you can overrange the input by up to 3 dB with dither disabled. For example, the +4 dBm input range can handle signal levels up to +7 dBm with dither disabled. For wider bandwidth acquisitions, such as 40 MHz, disable dithering to eliminate residual leakage of the dither signal into the lower frequencies of the IF passband, which starts at 12.5 MHz and ends at 62.5 MHz. This leakage can slightly raise the noise floor in the lower frequencies, thus degrading the performance in high-sensitivity applications. When taking spectral measurements, this leakage can also appear as a wide, low-amplitude signal near 12.5MHz and 62.5 MHz. The width and amplitude of the signal depends on your resolution bandwidth and the type of time-domain window you apply to your FFT.

PXIe-5668—When you enable dithering, the maximum signal level is reduced by up to 2 dB. For the PXIe-5624, the maximum input power with dither off is 8 dBm and the maximum input power level with dither on is 6 dBm. When acquiring an 800 MHz bandwidth signal, the I/Q data contains the dither even if the dither signal is not in the displayed spectrum. The dither can affect actions like power level triggering.

Note  For the PXIe-5668, disabling dithering can negatively affect absolute amplitude accuracy.

PXIe-5820/5830/5831/5832/5840/5841/5842: Only Enabled is supported.

Default Value: Enabled

Supported Devices: PXIe-5663/5663E/5665/5667/5668, PXIe-5820/5830/5831/5832/5840/5841/5842

Remarks

The following table lists the characteristics of this property.

Datatype
Permissions	Read/Write
High-level VIs	N/A
Channel-based	No
Resettable	Yes