RF Input Subsystem
- Updated2023-03-22
- 2 minute(s) read
RF Input Subsystem
The PXIe-5645 has two configurable RF paths. The following high-level block diagram represents the PXIe-5645 RF input path.
The vector signal analyzer (VSA) portion of the PXIe-5645 consists of a single-stage, direct-conversion (I/Q) downconverter. The PXIe-5645 downconverts the RF signal from the configured LO frequency to DC, where the PXIe-5645 can digitize the baseband signal for processing. This architecture allows for wide instantaneous bandwidth with high residual sideband image suppression and minimal residual LO power. Residual sideband images and residual LO power performance are achieved by wideband quadrature correction. The PXIe-5645 RF input path is optimized for use as a VSA for wideband demodulation.
The PXIe-5645 RF input path includes several solid-state attenuators that provide more than 80 dB of attenuation, variable in 1 dB steps. The RF input is AC-coupled. Three switchable gain amplifiers and a preamplifier extend dynamic range and improve noise figure.
A low phase noise LO is supplied internally on the PXIe-5645 RF input channel, which is shown at the lower part of the preceding figure. You can use the PXIe-5645 RF input path LO signal to connect multiple downconverters with a single LO source. Using the same LO source is useful for phase-coherent signal acquisition applications, such as multiple-input, multiple-output (MIMO) systems. When using this configuration, every PXIe-5645 RF channel sharing the common LO tunes to the same RF frequency.
The downconverted baseband signal is digitized by the internal ADC channels of the PXIe-5645 as shown in the right part of the preceding figure. The 16-bit ADC channels digitize the baseband analog signal at 120 MS/s and perform the following actions to the signal depending on your configuration:
- Route the resulting signal to the onboard FPGA for further processing
- Transfer the signal to the host or to other devices in the chassis through Peer-To-Peer DMA
- Retransmisson the signal on the PXIe-5645 RF output channel
Related Information
- RF IN Signal Gain and Attenuation
The RF IN signal path chooses gain and attenuation settings based on the requested reference level.
- 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.