Troubleshooting RF System Budget Analysis

Here are some typical budget simulation problems and remedies to resolve them.

Using Components with Three or More Pins

Only two-port, two-pin components are supported by the budget simulation in the top-level schematic, except for these components: AGC_Amp, AGC_PwrControl, S2P, PathSelect2, and R with pin 2 tied to ground. The simulation will generate an error if any other unsupported components have three or more pins.

Using Unsupported Networks

If the topology in the design is not a simple two-port, two-pin cascaded network, an error is generated indicating more than three components pins are connected to the same node in the network. Only two-port, two-pin cascaded RF system designs can be used with the Budget controller. For example designs, see Performing Budget Simulations.

Using Unsupported Components

If your design contains components in the top-level schematic that are not supported in a budget analysis, an error is generated. The component may not be supported for one of the following reasons:

• The component does not have an S-parameter representation.
• The component cannot be used with the ADS P2D analysis controller. This is one of the limitations of the Budget controller, since it relies on P2D analysis to determine the nonlinear characteristics of RF system components.

Unfortunately, no workaround exists for these components. They are simply not supported in the top-level schematic for a budget simulation. However, these components can be used in subnetworks to create circuit designs that are used as two-port, two-pin subnetworks in top-level schematics.

Enabling Other Simulation Controllers in a Design

When performing a budget analysis, no other analysis can be enabled in a simulation. If other analyses are included, an error is generated indicating that the design contains an instance of another ADS simulation controller, such as Harmonic Balance, DC, S_Param, etc., or an ADS parent controller, such as Sweep, Optim, Yield, etc., that does not sweep or optimize the budget analysis instance. The Budget controller can only be used in isolation, except where parent controllers are used to sweep or optimize the budget analysis. Remove or deactivate any instances of these other ADS simulation controllers to proceed.

Instance Name Conflict in Subnetworks

The Budget analysis simulation reports an error when a top-level subnetwork reference designator (or instance name) is the same as the reference designator of a component inside the subnetwork. Use a different reference designator for one of the two instances.

Setting the CmpMaxPin Parameter

If the value for the maximum component input power parameter ( CmpMaxPin ) is set too low, the analysis cannot characterize nonlinearity. Increase the value of the Budget controller parameter CmpMaxPin and try again. For information about how CmpMaxPin is used with nonlinear models, see Characterization of Component Nonlinearities.

Using 1 dB Power Compression Measurements

When using the 1 dB power compression measurements, the simulator may detect conditions requiring you to consider modifying the design or changing how the measurement is set up. The following topics discuss these conditions and ways you might resolve them:

• The system nonlinear analysis may not converge while calculating 1 dBm compression points after a certain number of iterations. This means that one or more components in the system cascade have S-parameters that do not allow for the Budget iterative large signal algorithm to converge.
  • Provide more isolation between nonlinear stages by resetting one or more component S12 values to zero.
  • Look at the component P2D file in the project data directory for irregular power or S-parameter values. Test the component with a separate P2D analysis and look for irregular power or S-parameter values. Irregular S-parameters include S21 that decreases at a rate much greater than 1 dB per input power change. Irregular power values include P2 power levels that suddenly drop in level.
  • Turn off all P1dB measurements.
• A particular component has a power input in dBm that is greater than the component nonlinearity definition during analysis. This means that a component has large signal S-parameters that conflict with analysis power levels incident at its port 1 or port 2.
  • Look at the component P2D file in the project data directory for irregular power or S-parameter values. Test the component with a separate P2D analysis and look for irregular power or S-parameter values. Irregular S-parameters include S21 that decreases at a rate much greater than 1 dB per input power change. Irregular power values include P2 power levels that suddenly drop in level.
  • Turn off all P1dB measurements.
• A system nonlinear analysis error occurs because the overall system gain is less than -200 dB. This indicates that one or more components in the system cascade has a loss that is too large for the nonlinear analysis to proceed successfully.
  • Look for one or more components with excessive loss and reduce its loss.
  • Turn off all P1dB measurements.
• A system nonlinear analysis error occurs because the gain for a particular component output is less than -200 dB. This indicates that the component has a loss that is too large for the nonlinear analysis to proceed successfully.
  • Change the component to reduce its loss.
  • Turn off all P1dB measurements.

Error Messages During Large Signal Analysis

During large-signal analysis, the simulator may detect conditions requiring you to consider modifying the design. The following topics discuss these conditions and ways you might resolve them:

• The system small signal gain to a component output has gain that is less than -200 dB. This indicates that one or more components in the system cascade has a loss that is too large for the small signal analysis to proceed successfully.
  • Look for one or more components with excessive loss and reduce its loss.
• The system nonlinear analysis did not converge, indicating that the budget nonlinear analysis did not converge.
  • Provide more isolation between nonlinear stages by resetting one or more component S12 values to zero.
  • Look at the component P2D file in the project data directory for irregular power or S-parameter values. Test the component with a separate P2D analysis and look for irregular power or S-parameter values. Irregular S-parameters include S21 that decreases at a rate much greater than 1 dB per input power change. Irregular power values include P2 power levels that suddenly drop in level.
• There is a system nonlinear analysis error, indicating that an undocumented error has occurred in the budget nonlinear analysis.
  • Insufficient information is known to provide a resolution. Please contact Agilent EEsof Technical Support for further investigation. You may be asked to send the design to Agilent.

Internal Errors

If a fatal internal error occurs, please report the problem to Agilent EEsof Technical Support. Also, keep the design that is causing the error available for evaluation by Agilent EEsof.