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Design Notes

Unified RFB RFI and Time Domain Analysis

This example illustrates how the PORT_SRC and PORT blocks allow VSS to simultaneously perform RFB/RFI and time-domain measurements on the same system diagram.

An RF link is imlemented in the "RF Link" system diagram. A PORT_SRC block is used as the input port and a PORT is used as its output. The PORT_SRC is configured to generate a tone signal with the appropriate frequency and power level for RFB/RFI measurements. The RFB and RFI measurements are set up using this system diagram.

Another system diagram is created to model a modulated signal that passes through the RF link mentioned above. In the "Modulated Signal" system diagram a QAM_SRC is used to create a QAM signal, the "RF Link" system diagram is used as a subcircuit and receiver blocks are used to process the received signal as well as the reference one. Measurements for the time-domain simulation are added to the "Modulated Signal" system diagram. The unique capability of PORT_SRC and PORT blocks is that they are used as signal source and load, respectively, for RFB and RFI measurements, while they act as transparent ports during time-domain simulations. This allows all RFB, RFI and time-domain measurements to be performed simulataneously without requiring any modification of the system diagrams.

In the "RF Link" system diagram we are sweeping the order of the image rejection filter and observe its effect on the noise figure of the RF link as well as the gain at the image frequency, which in this case is at an offset of 400 MHz above the carrier.

System Diagram - Modulated Signal

Graph - RFI

Graph - Cascaded NF

Graph - Cascaded Gain

Graph - Spectral Measurements

Graph - IQ_Constellation