NI 5442 Quadrature Upconversion

NI Signal Generator

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NI 5442
Quadrature Upconversion

The following figure shows the behavior of the OSP block during quadrature upconversion.

In quadrature upconversion, you give the I and Q complex waveform data to the OSP block. This data is then pulse–shaped, interpolated up to a high sample rate, and then upconverted to a programmable carrier frequency. For quadrature upconversion, complete the following steps:

  1. Enable onboard signal processing by setting the OSP Enabled property or the NIFGEN_ATTR_OSP_ENABLED attribute.
  2. Specify the use of complex numbers for the waveform data by setting the Data Processing Mode property or the NIFGEN_ATTR_OSP_DATA_PROCESSING_MODE attribute.
  3. Set the IQ Rate property or the NIFGEN_ATTR_OSP_IQ_RATE attribute.
  4. Set the FIR Filter Type property or the NIFGEN_ATTR_OSP_FIR_FILTER_TYPE attribute.
  5. Set the corresponding filter parameter.
  6. Enable the carrier by setting the Carrier Enabled property or the NIFGEN_ATTR_OSP_CARRIER_ENABLED attribute.
  7. Set the Carrier Frequency property or the NIFGEN_ATTR_OSP_CARRIER_FREQUENCY attribute.
  8. Download the complex waveform data to the signal generator.
Note  If the complex waveform data has transients, use the Prefilter gain I and Q to attenuate your data and prevent clipping.

With Signal Impairments

Signal impairments can be dynamically added to a quadrature upconverted signal. IQ Gain Imbalance impairments can be simulated by changing the I or Q prefilter gain. The following formula converts from IQ Gain Imbalance (dB, must be negative) to prefilter gain.

Note   When simulating an IQ gain imbalance, change only the I or Q prefilter gain.

Prefilter Gain = 10(IQ Gain Imbalance / 20)

I/Q DC offset impairments can be simulated by changing the I and Q prefilter offset. The following formula converts from I/Q DC offset (%) to I/Q prefilter offset.

Prefilter Offset = (DcOffset / 100) × Prefilter gain

You can simulate quadrature skew impairments by changing the I or Q carrier phase. Change the I or Q carrier phase by the required quadrature skew to simulate this impairment.

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