NI 5441 Quadrature Upconversion

NI Signal Generator

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NI 5441
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 or download a custom set of FIR filter coefficients.
  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 Pre-Filter Gain I and Q to attenuate your data and prevent clipping.

With Signal Impairments

Signal Impairments can be added to a quadrature upconverted signal on the fly. IQ Gain Imbalance impairments can be simulated by changing the I or Q Pre-Filter Gain. The following formula converts from IQ Gain Imbalance (dB, must be negative) to Pre-Filter Gain (only the I or Q Pre-Filter Gain should be changed).

Note   When simulating an IQ gain imbalance, only the I or Q pre-filter gain should be changed.

Pre-Filter Gain = 10(IQ Gain Imbalance / 20)

I/Q DC Offset impairments can be simulated by changing the I and Q Pre-Filter Offset. The following formula converts from I/Q DC Offset (%) to I/Q Pre-Filter Offset.

Pre-Filter Offset = (DcOffset / 100) × PreFilterGain

Quadrature Skew impairments can be simulated 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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