I/Q Input
- Updated2024-06-18
- 2 minute(s) read
I/Q Input
The following high-level block diagram represents the PXIe-5645 I/Q input path.
Use the I/Q inputs of the PXIe-5645 to digitize analog waveforms for processing. The PXIe-5645 is a dual-channel device with the ability to interface with a differential or single-ended device under test (DUT). The PXIe-5645 supports configurable analog gain and filtering to remove aliasing spurs. Additionally, you can configure 36 different amplitude ranges from 32 mVpk-pk to 2 Vpk-pk to optimize the dynamic range for differential or single-ended applications. Proper analog gain selection can provide the best dynamic range for a measurement without clipping. Digital gain is also configurable in the hardware at the expense of effective bits.
| Terminal Configuration | Maximum Voltage 50 Ω |
|---|---|
| Differential | 2 V pk-pk |
| Single-Ended | 2 V pk-pk |
The baseband ADC samples at a rate of 120 MS/s with 16-bit resolution. An analog filter on the device ensures that frequency content above 80 MHz is not misinterpreted for content in the area of interest below 40 MHz. After digitizing, the I and Q signals are accessible through LabVIEW FPGA I/O nodes or NI-RFSA or NI-RFSG properties and attributes for further processing and transfer to the host computer. The I/Q inputs of the PXIe-5645 are DC-coupled. In differential terminal configuration, the I/Q interface rejects common-mode signals, including DC biasing.
The PXIe-5645 is a calibrated device. Calibration removes the uncertainties of individual device components to achieve higher levels of measurement accuracy. Uncertainties removed by calibration include gain and offset errors at DC and ripples in the filter response. Calibration ensures the voltage appearing at the input connector is interpreted accurately. Calibration accounts for the device input impedance to ensure the voltage at the connector.
The PXIe-5645 device calibration provides wideband matching between the in-phase (I) and quadrature (Q) channels. The PXIe-5645 is ideal for applications with complex downconverters where mismatches between channels result in image frequencies appearing.
Related Information
- Quadrature Mixing (Direct Conversion)
Quadrature mixing (direct conversion) allows for the complex modulation or demodulation of signals as represented by two orthogonal signals, I and Q. Quadrature mixing has the added benefit of an increased complex bandwidth that allows for bandwidths up to the sample rate of the DAC.