Circuit Budget Functions

This chapter describes the circuit budget functions in detail. The functions are listed in alphabetical order.

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B

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bud_freq()
bud_gain()
bud_gain_comp()
bud_gamma()
bud_ip3_deg()
bud_nf()
bud_nf_deg()
bud_noise_pwr()
bud_pwr()
bud_pwr_inc()
bud_pwr_refl()
bud_snr()
bud_tn()
bud_vswr()

Note The circuit budget functions are not directly available in RF Design Environment (RFDE) since they are generally intended for use in Advanced Design System. If you have a need to use circuit budget functions in RFDE, please consult your Agilent Technologies sales representative or technical support to request help from solution services.

Budget Measurement Analysis

Budget analysis determines the signal and noise performance for elements in the top-level design. Therefore, it is a key element of system analysis. Budget measurements show performance at the input and output pins of the top-level system elements. This enables the designer to adjust, for example, the gains at various components, to reduce nonlinearities. These measurements can also indicate the degree to which a given component can degrade overall system performance.

Budget measurements are performed upon data generated during a special mode of circuit simulation. AC and HB simulations are used in budget mode depending upon if linear or nonlinear analysis is needed for a system design. The controllers for these simulations have a flag called, OutputBudgetIV which must be set to " yes " for the generation of budget data. Alternatively, the flag can be set by editing the AC or HB simulation component and selecting the Perform Budget simulation button on the Parameters tab.

Budget data contains signal voltages and currents, and noise voltages at every node in the top level design. Budget measurements are functions that operate upon this data to characterize system performance parameters including gain, power, and noise figure. These functions use a constant reference impedance for all nodes for calculations. By default this impedance is 50 Ohms. The available source power at the input network port is assumed to equal the incident power at that port.

Budget measurements are available in the schematic and the data display windows. The budget functions can be evaluated by placing the budget components from Simulation-AC or Simulation-HB palettes on the schematic. The results of the budget measurements at the terminal(s) are sorted in ascending order of the component names. The component names are attached to the budget data as additional dependent variables. To use one of these measurements in the data display window, first reference the appropriate data in the default dataset, and then use the equation component to write the budget function. For more detailed information about Budget Measurement Analysis, see "Budget Analysis" in the chapter "Using Circuit Simulators for RF System Analysis" in the Using Circuit Simulators documentation.

Note The budget function can refer only to the default dataset, that is, the dataset selected in the data display window.

Frequency Plan

A frequency plan of the network is determined for budget mode AC and HB simulations. This plan tracks the reference carrier frequency at each node in a network. When performing HB budget, there may be more than one frequency plan in a given network. This is the case when double side band mixers are used. Using this plan information, budget measurements are performed upon selected reference frequencies, which can differ at each node. When mixers are used in an AC simulation, be sure to set the Enable AC frequency conversion option on the controller, to generate the correct plan.

The budget measurements can be performed on arbitrary networks with multiple signal paths between the input and output ports. As a result, the measurements can be affected by reflection and noise generated by components placed between the terminal of interest and the output port on the same signal path or by components on different signal paths.

and Backward-Traveling Wave Effects

Reflection and Backward-Traveling Wave Effects

The effects of reflections and backward-traveling signal and noise waves generated by components along the signal path can be avoided by inserting a forward-traveling wave sampler between the components. A forward-traveling wave sampler is an ideal, frequency-independent directional coupler that allows sampling of forward-traveling voltage and current waves
This sampler can be constructed using the equation-based linear three-port S-parameter component. To do this, set the elements of the scattering matrix as follows: S12 = S21 = S31 = 1 , and all other Sij = 0 . The temperature parameter is set to -273.16 deg C to make the component noiseless. A noiseless shunt resistor is attached to port 3 to sample the forward-traveling waves.