Frequency and Bandwidth Configuration

This section describes how to use the NI-RFSA and NI-RFSG drivers to configure the PXIe-5830 instrument for optimal performance by specifying frequency and bandwidth constraints.

The following table shows the equivalencies between NI-RFSA and NI-RFSG properties mentioned throughout the section.

Table 11. NI-RFSA and NI-RFSG Frequency and Bandwidth Configuration Properties
NI-RFSA Property NI-RFSG Property
IQ Carrier Frequency Frequency
Downconverter Center Frequency Upconverter Center Frequency
Downconverter Frequency Offset Upconverter Frequency Offset
LO Frequency LO Frequency
Device Instantaneous Bandwidth Device Instantaneous Bandwidth
Signal Bandwidth Signal Bandwidth
IQ Rate IQ Rate
Downconverter Frequency Offset Mode Upconverter Frequency Offset Mode

The following block diagram represents the PXIe-5830 RF input connectors and the associated NI-RFSA properties.


1378

Note Then names of the input connectors change depending on your instrument configuration.

The following block diagram represents the PXIe-5830 RF output connectors and the associated NI-RFSG properties.


1378

Note The names of the output connectors change depending on your instrument configuration.

Frequency and Bandwidth Configuration Terminology

Refer to the following list of terms when configuring frequency and bandwidth.

  • I/Q Rate—The effective sampling rate of the baseband signal chain. Setting a value lower than the maximum will limit the available passband.
  • I/Q Carrier Frequency—The center frequency of the waveform data acquired or generated.
  • Downconverter Center Frequency— The frequency present at the mixer during downconversion or upconversion. This frequency is derived from the LO frequency through a series of multipliers. The multiplication factor may be 1, 2, 4, or 8, depending on the target frequency. In a direct conversion architecture, the downconverter center frequency contains LO leakage in the I/Q data.
  • LO Frequency— The frequency of the local oscillator as present at the LO IN or LO OUT port. This frequency may or may not be equal to the downconverter center frequency depending on the conversion architecture and any frequency multipliers in the LO path. The signal from the onboard LO or the LO IN port passes through signal conditioning circuits and frequency multipliers or dividers to hit the mixer at the required frequency and power.
  • Device Instantaneous Bandwidth— The total calibrated bandwidth available through the instrument signal path, centered at the downconverter center frequency. For example, if the downconverter center frequency is 6 GHz and the device instantaneous bandwidth is 1 GHz, an acquisition can contain calibrated data from 5.5 GHz to 6.5 GHz.
  • Signal Bandwidth—When performing a signal acquisition, signal bandwidth is the bandwidth of the signal present at the input port, centered at the I/Q carrier frequency. When performing a signal generation, signal bandwidth is the bandwidth of the waveform to be generated, centered at the I/Q carrier frequency.
  • Passband— The bandwidth able to be acquired based on the I/Q rate, centered at the I/Q carrier frequency. This is usually defined at 80% of the I/Q rate. For example, an I/Q rate of 100 MS/s results in a passband of 80 MHz. Note that the passband edge may fall outside of the device instantaneous bandwidth edge and will, therefore, have aliased or uncalibrated data.
  • LO Step Size—The quantum at which the LO frequency can be tuned. You can set the LO Step Size property or, on supported instruments, the VCO Step Size property to control the step size at the mixer or on the onboard LO (before multipliers), respectively, to achieve different hardware performance.

    For example, assume the LO step size for an instrument is 2 MHz and the downconverter center frequency is set to 5,001.5 MHz. The downconverter center frequency will be coerced to 5,002 MHz, and the remaining 500 kHz shift will be applied digitally.

  • LO Power—When using an external LO, the power of the LO is important for maintaining good image and LO leakage performance because the impairments correction is calibrated for a specific LO power at the mixer. Based on the LO IN power, NI-RFSA configures the LO signal path to achieve a mixer power close to the mixer power used during impairment calibration. You can also set the LO OUT power to apply gain to the output signal to avoid power loss when in an LO daisy-chain configuration.