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The AWR Design Environment platform Visual System Simulator (VSS) software models the behavioral characteristics of RF systems such as communications links and radar. Prior to the current AWR V16 software, accounting for PCB trace effects including loss, impedance mismatch, delay and coupling between traces was a tedious process when creating system diagrams and generating the appropriate models for the PCB traces. AWR V16 software introduced the INTRCONN element that provides an efficient method of modeling the effects of PCB traces at the system level. The INTRCONN element facilitates a design flow methodology starting from early estimates of trace losses to full characterization of the completed design.
The design flow aspects of the INTRCONN element can be demonstrated with two integrated circuits (ICs) connected with PCB traces.
Not only might there be losses and impedance mismatch effects associated with these traces, more critically, coupling between the various traces may exist. In the system diagram associated with this layout, INTRCONN elements representing the PCB traces are inserted as shown.
The INTERCONN element supports five different modes of operation via its TYPE parameter options.
The order of the different INTRCONN operating modes outlines a progression in the design of the system. In the beginning of the design process, before physical traces are routed, only an estimate of the trace losses may be known. At this stage of the design process, the INTRCONN Attenuator mode is selected. Further refinement may be to model an individual PCB trace as a Microstrip or Transmission Line, enabling line length or delay to be modeled in the system. As the design progresses, trace discontinuities due to steps in line width or bends in the meandering traces are included in the analysis. At this point, INTRCONN Linear co-simulation mode is selected. Each trace is designed as a Microwave Office circuit, and co-simulation between VSS and Microwave Office software brings these more sophisticated aspects of the trace design into the system simulation.
The final step in the design process is to model the actual layout of the design. The PCB layout is first imported into the AWR Design Environment, then the traces are extracted into an EM document.
After an EM simulation of this structure, the INTRCONN Coupling co-simulation mode is selected to link the results of the EM simulation to the INTRCONN elements in the system design. Not only is coupling between traces introduced into the system analysis, but EM simulation provides more accurate trace loss and impedance results.
Why is it so important to model PCB trace effects at the system level? PCB traces that are not perfectly impedance matched and have line length introduce ripple in the frequency response. Unaccounted for ripple can lead to unexpected power loss, low power added efficiency, low bit-error-rate, and more. Modeling the coupling aspects of the PCB traces can show effects of leakage around filters, that is, stopband signals bypassing the filters due to PCB trace coupling. Other effects of coupling include unwanted spurious signals in systems containing up or down converters.
By: Brian AvenellSr. Principal Product EngineerCadence AWR R&D - U.S.
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