RF Output Subsystem
- Updated2025-04-22
- 3 minute(s) read
The PXIe-5841 has two configurable RF paths comprised of an independent vector signal analyzer (RF input) path and vector signal generator (RF output) path. The following high-level block diagram represents the PXIe-5841 RF output path.
The PXIe-5841 RF output path is AC coupled and covers a frequency range of 9 kHz to 6,000 MHz center frequency. For frequencies below 120 MHz (low frequency), RF output signals are directly generated via digital-to-analog (DAC) conversion. Frequencies greater than 120 MHz (high frequency) are translated from baseband I and Q signals to the specified RF frequency via a single stage direct conversion (I/Q) upconverter, allowing for a wide instantaneous bandwidth.
High Frequency RF Output Path
The high frequency subsystem of the RF output path consists of a wideband direct conversion upconverter and a front end signal path with programmable RF filtering and gain stages. I and Q baseband signals generated by the DAC are mixed and combined to create an RF signal with up to 1,000 MHz of complex equalized bandwidth centered at the specified RF center frequency. This signal can then be conditioned for both bandwidth and level.
Greater than 80 dB of RF attenuation can be configured nominally through the combination of switchable fixed attenuation and programmable step attenuators. RF attenuation is automatically chosen in conjunction with amplification to provide optimal reference levels over the support range of the device. There are two switchable amplifiers and one switchable high power amplifier.
The switchable high power amplifier is used for generating signals significantly larger than 0 dBm. This amplification stage is automatically selected based on output power level setting and extends the available peak power range to +20 dBm, calibrated. Additional power may be achieved above +20 dBm, however it is not guaranteed to meet absolute or relative accuracy specifications.
Low Frequency RF Output Path
The low frequency subsystem of the RF output path is used to directly generate the requested RF output signals below 120 MHz from the DAC. The RF signal is generated from the DAC through programmable gain stages and transmitted from the RF OUT front panel connector through a frequency selective diplexer. This allows for a seamless transition from low frequency to high frequency paths. Refer to the RF Path Transitions topic for more information about using the low frequency path.
The low frequency path programmable gain stages consist of a 31 dB step attenuator with 1 dB resolution and a switchable amplification stage. The off state of the switchable amplifier has additional fixed attenuation integrated into it. This provides a nominal gain range of +5 dB to -40 dB. Additional attenuation is possible with the DAC full scale configuration settings as well as digital waveform scaling.
Related Information
- RF Path Transitions
The PXIe-5841 supports acquisition and generation of RF signals from 9 kHZ to 6 GHz. For both the RF Input and RF Output channels, the transition from low frequency to high frequency is implemented with a passive diplexer scheme. This passes RF energy below 120 MHz to the low frequency path and RF energy above 120 MHz to the high frequency path. Because the diplexer has a frequency response of its own, it is possible to extend RF frequency coverage above or below 120 MHz in both paths.