About RF System Budget Analysis

The Budget controller enables you to perform an RF system budget analysis to determine the linear and nonlinear characteristics of an RF system comprising a cascade of two-port, two-pin linear or nonlinear components. The RF system may also include automatic gain control (AGC) loops to control gain and set power levels at specific points in the RF system.

RF system budget analysis is achieved by using the Budget controller in an ADS analog/RF schematic. You can use the Budget controller to determine the linear and nonlinear characteristics of an RF system comprising a cascade of two-port, two-pin linear or nonlinear components. The characteristics are derived at the system input, system output (system summary measurements), and at the nodes between the components (system cascade measurements). The system may include such measurements as Power, Third-Order Intercept, Signal-to-Noise Ratio, and others.

RF budget analysis is based on using frequency domain characteristics for each top-level two-port, two-pin component in the RF system design. The components may include mixers and nonlinear amplifiers. The analysis is performed at the single RF tone with specified power from the system input signal source. Each component is characterized for its S-parameter (small-signal and large-signal) and noise parameters. The collection of these parameters for each component in the cascade of two-port, two-pin components composing the RF system design are then used by the Budget controller to calculate the system performance at each node of the system design for the RF budget measurements that you select.

Characteristics of the RF system design on which budget analysis is performed, are:

• The RF system must be a cascade of two-port, two-pin components.
• The components may be any analog/RF two-port, two-pin component that has an S-parameter representation.
• The RF system may include multiple paths of cascaded two-port, two-pin components and use path switching components defined for use with RF budget analysis. The path switch settings must result in only a single cascade two-port path in the RF system design.
• The RF system may also include automatic gain control (AGC) loops to control gain and set power levels at specific points in the RF system. The AGC loops must be achieved using power detectors and voltage-controlled amplifiers defined for use with RF budget analysis.
• No other analog/RF analyses (DC, AC, Harmonic Balance, etc.) can be active in the schematic when the RF budget analysis is performed. When the Budget controller is removed or deactivated, then other analog/RF analyses can be set up with the same RF system design for more detailed circuit analysis.
  See the following topics for details on RF system budget analysis:
• Using the Budget Controller describes when you might use the Budget controller, its benefits, how to begin using it, and the location of an example project.
• Performing Budget Simulations describes application-focused examples including
  • A Simple Budget Design
  • Using Mixers and Multiple Paths
  • Using Two-Port, Two-Pin S-Parameter Files
  • Using AGC Control Loops
  • Using Budget with Sweep
  • Using Budget with Optimization and Yield
• Working with RF System Budget Analysis Results describes how to use the Data Display to view results, and how to export results for post-processing.
• Reference Measurements and Models for RF System Budget Analysis describes measurements used for component inputs and outputs, noise figure, and system performance, in addition to various component models.
• Limitations of RF System Budget Analysis describes the limitations of this frequency domain approach.
• Parameters for RF System Budget Analysis describes details of the dialog box fields and parameters for the Budget controller.
• Theory of Operation for RF System Budget Analysis describes the budget analysis process.
• Troubleshooting RF System Budget Analysis explains how to recover from analysis problems.
• References for RF System Budget Analysis lists information sources that discuss this approach to budget analysis.

Comparison with the Generic Budget Analysis Functions

In addition to using the Budget controller in ADS analog/RF schematics, ADS also offers built-in RF budget MeasEqn function capability. Here are points that compare these two budget analysis approaches:

• Using the Budget controller is in addition to and does not replace the built-in RF budget MeasEqn function capability.
• The Budget controller is separate from and does not rely on the built-in budget MeasEqn function items.

The key advantages of the Budget controller over budget analysis functions are:

• Much easier to use.
• Provides many more built-in budget measurements that you can select.
• Provides improved budget noise measurements.
• Supports tuning, sweeps, optimization, yield, etc.
• Supports AGC loops.
• Supports selection between alternate budget paths.
• Supports export of results in ASCII files for use in third-party tools, including Excel.

The advantages of built-in RF budget MeasEqn function capability are:

• Supports flexible circuit topologies.
• Supports more flexible path selection.
• Supports user-defined subnetworks with frequency conversion.
• Supports more general mixer models.
• Supports concurrent simulation with other analog/RF analyses.

The key Budget controller restrictions are:

• For use primarily with cascaded two-port, two-pin RF systems, though it will also support these multi-pin components:
  • S2P
  • AGC_Amp
  • AGC_PwrControl (for setting up AGC control loops)
  • PathSelect2 (for setting up selectable RF paths)
• Input source must be either _P_1Tone_ or _P_nTone_ and requires Z=50 ohms.
• Output load must be either Term or R and requires Z(R)=50 ohms; with no noise.
• Allows use of only one mixer model: MixerWithLO .
• User-defined circuit subnetworks must be two-port, two-pin networks and no frequency conversion is presumed.
• Does not allow concurrent simulation with other analog/RF analyses.
• Cannot be used with Gradient-like optimization types.