Using Automated Assistants in Filter DesignGuide

This chapter describes the Automated Assistants available in this DesignGuide.

Filter Assistant


The Filter Assistant is used to generate and update the design contained within a single SmartComponent from the given specifications. The Filter Assistant is accessed using the Filter DesignGuide Control window. From the Control window, full design control is enabled from the Filter Assistant tab. Component design operations can also be accomplished using the Control window menu and toolbar. Any parameter change made from the Filter Assistant tab is reflected on the SmartComponent in the schematic.

To view a SmartComponent, select the SmartComponent from the SmartComponent drop-down list box in the upper right corner of the Control window. The SmartComponent parameters are shown inside the Filter Assistant tab.

Impedances

Order

The filter order is automatically calculated depending upon the parameters specified for all the response types except Bessel-Thomson and Gaussian. For these two responses a filter order must be input manually using the Order (N) text box.

Design Information

Design Information is not editable, but rather shows information about the filter.

Response Type

Six filter response types can be used for designing: Maximally Flat (Butterworth), Chebyshev, Elliptical, Inverse-Chebyshev, Bessel-Thomson, and Gaussian. A plot of the filter response is show below the Response Type drop-down list box. Pressing the Redraw button automatically scales and redraws the response plot.

Frequency

Frequency settings can be changed by either moving the vertical frequency slide bars on the response plot or by changing the values in the frequency text boxes. The frequency text box captions dynamically change depending on the SmartComponent being used. For any lowpass or highpass network:

For any bandpass of bandstop network:

Attenuation

Attenuation settings can be changed by either moving the horizontal attenuation slide bars on the response plot or by changing the values in the attenuation text boxes.

Zooming in/out of the response plot is possible using the dB/square spin-box.

Realizations

These parameters tell the Filter DesignGuide how many networks to show after designing. If View All is not checked only one network is synthesized. If View All is checked the number of shown networks can be specified in the Max # text box.

Design

The design is accomplished using one of the these methods.

If multiple realizations for the filter network were found, a dialog box appears.

All networks can be viewed using the Component List spin box. Each network can be viewed in two places:

Simulation Assistant


The Simulation Assistant is used to analyze the design contained within a SmartComponent. The Simulation Assistant creates a simulation circuit around the SmartComponent, then automatically performs the appropriate simulation. If set, the tool displays the simulation results automatically.
The Simulation Assistant is accessed using the Filter DesignGuide Control window, where full simulation control is enabled from the Simulation Assistant tab. Also, basic simulation can be accomplished using the Control window menu and toolbar.

For all simulation operations, the selected SmartComponent is designed if necessary, a simulation schematic is created, the simulation is performed, and the results are displayed. The simulation frequency sweep must be specified on the Simulation Assistant tab in the Control window as described in detail in section Simulation Frequency Sweep.

Simulation Frequency Sweep

The simulation frequency sweep is specified on the Filter DesignGuide Control window. While performing the simulation from the Control window, select the Simulation Assistant tab and specify the sweep by entering the start frequency, stop frequency, and either frequency step size or number of points. The values entered are stored in the selected SmartComponent (as displayed in the SmartComponent drop-down list box) and is recalled each time this SmartComponent is selected.

Automatically Display Results

If the Automatically Display Results box on the Simulation Assistant tab is selected, the simulation results are automatically displayed upon completion of the analysis.

Starting the Simulation

The simulation can accomplished using one of the these methods.

Simulation Templates

In some cases, you can simulate the SmartComponent manually. To generate a simulation schematic around the selected SmartComponent, press the Create Template button on the Control window Simulation Assistant tab. You can examine or modify the simulation schematic, then manually start the simulation by selecting Simulate > Simulate from the Schematic window. When you are finished, pressing the Update from Template button on the Simulation Assistant tab transfers any changes you have made to the SmartComponent on the simulation schematic to the original SmartComponent and redesigns if necessary. You can close the simulation schematic manually using File > Close Design from the Schematic window menu, although this results in loss of any changes you have made to the SmartComponent.

Yield Assistant


The Yield Assistant is used to analyze the design sensitivities contained within a SmartComponent. The Yield Assistant creates a yield analysis circuit containing the SmartComponent, then performs a simulation. By sweeping the component values for a selected set of components in the network, this analysis generates a probability density function of the performance given statistical variations of the component values. The probability that the performance remains within the specified bounds is the yield of the network.

The Yield Assistant is accessed using the Filter DesignGuide Control window, where full control is enabled from the Yield Assistant tab. Also, basic yield analysis can be accomplished using the Control window menu and toolbar.

The selected SmartComponent must be designed before yield analysis can be performed. The analysis proceeds by statistically sweeping the value of each selected component and analyzing the impact of this component value variation on the frequency response of the network.

Simulation Frequency Sweep

The simulation frequency sweep is specified on the Yield Assistant tab of the Filter DesignGuide Control window. From this tab, specify the sweep by entering the start frequency, stop frequency, and either frequency step size or number of points. The values entered are stored in the selected SmartComponent (as displayed in the SmartComponent drop-down list box) and are recalled each time this SmartComponent is selected.

Statistical Components

The Statistical Components list-box displays all components that are statistically varied during simulation.
Clicking View Components opens a dialog box that shows the yield status of the components in the network.
Clicking Modify Statistics/Optimization opens the Modify Component Parameters dialog to simplify the process of selecting components. The filter network is displayed in the schematic with the currently-selected component highlighted.

To sweep this component value statistically during the analysis, select Enabled in the Statistics Status box. Then specify the parameters of the statistical sweep.

After you have specified all parameters for a component, pressing Next proceeds to the next component in the network. You can select a maximum of 4 components at one time. After you have finished specification, press Done .

Click View Statistical Components to view a summary of the statistical parameters for each selected component. Click Modify Statistics/Optimization to open the Modify Component Parameters dialog from this summary dialog to facilitate editing of the statistical sweep parameters.

The # Simulations parameter specifies the number of Monte Carlo simulations that are used to estimate the statistical behavior of the network. Increasing the number of simulations increases the statistical sample size and therefore provides a better estimate of the performance at the expense of increased computational time.

Yield Optimization

The network component values can also be optimized so that the performance is less sensitive to component value variations. This can be accomplished by selecting the Yield Optimization check box. The simulation uses the ADS engine to optimize the selected component values.

Specifying an appropriate set of Yield/Optimization Goals is a critical step in ensuring this optimization yields acceptable results. The # Iterations parameter available for Yield Optimization specifies the maximum number of optimization iterations that the simulation performs to try to find the appropriate network component values.

Yield/Optimization Goals

Yield and Yield Optimization simulations require that a set of performance (yield) goals be specified for the network. The yield is defined as the probability that the network frequency response satisfies these performance specifications given the statistical properties of the individual components.
Yield simulations use these goals to determine the percentage of networks that satisfies the specifications given tolerances of the components. Yield Optimization simulations use the goals in determining suitable component values that maximize the yield.
Each component has a default set of goals depending on the type of response (lowpass, bandpass, etc.). You can modify these goals, including adding or deleting goals, by clicking Set Yield Spec/Goals on the Yield Assistant tab to display the dialog.

Each goal specifies the insertion loss performance of the network in dB and can represent a specification that the value stay above or below the stated level. The specification can be at a single point, or over a given frequency band.

Automatically Display Results

If the Automatically Display Results box on the Control window Yield Assistant tab is selected, the simulation results are displayed automatically after completion of the analysis.

Starting the Simulation

The yield analysis can accomplished using one of these methods.

Yield Results

For each component (up to a maximum of 4) chosen for yield analysis, a yield sensitivity histogram is displayed. The yield definition can be changed on the first page of the display by setting passband frequencies Fp_1 and Fp_2 as well as the maximum insertion loss at these frequencies, and stopband frequencies Fs_1 and Fs_2 as well as the minimum insertion loss at these frequencies. Other pages in the display show the overall statistics of the yield as well as the frequency response for each of the Monte Carlo simulations.

Yield Templates

In some cases, you can simulate the SmartComponent manually. To generate a simulation schematic around the selected SmartComponent, click Create Template on the Control window Yield Assistant tab. You can examine or modify the simulation schematic, then manually start the simulation by selecting Simulate > Simulate from the Schematic window. When you are finished, clicking Close Template on the Yield Assistant tab returns you to the original design. You can close the simulation schematic manually using File > Close Design from the Schematic window menu.

Display Assistant


The Display Assistant is used to easily and quickly display the performance of a SmartComponent. The display templates are preconfigured display files that provide a comprehensive look at the performance of the component. You can create your own displays or modify the included display templates using the built in features of Advanced Design System, but in most situations, the included display templates provide all the information you need.

The Display Assistant is accessed using the Filter DesignGuide Control window, where full display control is enabled from the Display Assistant tab. Basic display selection can also be accomplished using the Control window menu and toolbar.

Display Template Features

The display templates opened by the Display Assistant have common features that are discussed here. For features unique to the display templates of some SmartComponents, refer to the chapter SmartComponent Reference.

Basic Layout

Basic Layout of Display Template shows the basic layout of the display templates. Area one of the display template contains a graph of the most important parameters of the SmartComponent. Area two contains several graphs that give a comprehensive look at the component's performance. Area three contains a table listing the basic specifications and performance of the component.

Basic Layout of Display Template

Typical Area One Graph

Typical Graphs from Area One shows a typical graph from area one of a display template. The frequency range of the graph is determined by the Simulation Assistant. As you change the frequency range in the Simulation Assistant, this graph updates appropriately. The markers A and B are used to define the frequency range of the graphs in area two. This feature is used to zero in on the region of interest and obtain a comprehensive look at the component's performance. The marker M1 can be moved by dragging the marker with the mouse. The performance at the frequency given by M1 is shown in the table in area three.


Typical Graphs from Area One

Typical Area Two Graphs

Typical graphs from area 2 of a display template are shown in Typical Graphs from Area Two. These graphs provide a quick, comprehensive look at the component's performance. Their frequency range is determined by the location of the "A" and "B" markers found in the main graph. Any markers such as M2 shown here can be moved by dragging them with the mouse. Performance criteria at the marker frequency is displayed in the table in area three.


Typical Graphs from Area Two

Typical Area Three Templates

A typical table from area three of a display template is shown in Typical Table from Area Three. The white rows show the specifications and important performance criteria for the component. The gray rows give the performance criteria at the user defined marker frequencies. The box below the table provides explanatory information for the table.


Typical Table from Area Three

Display Assistant Operation

Before using the Display Assistant, a valid dataset from a simulation of the selected SmartComponent must exist in the current project data directory. This simulation can be conveniently accomplished using the Simulation Assistant. Refer to the Simulation Assistant chapter for details on this step.

Opening a Display

To display results from a SmartComponent simulation using the Control window, select the SmartComponent from the SmartComponent drop-down list box in the upper right corner of the Control window. The display is launched using one of the these methods.

If no valid dataset exists for the selected SmartComponent, the Display button on the Display Assistant tab is insensitive. If the toolbar or menu are used to try to display the results, a message appears, indicating that no dataset exists.

Display Templates

In some cases, you can use one of the display templates provided with the DesignGuide for other applications. To gain access to one of these templates, select the template from the Available Templates field and click Open Display Template on the Control window Display Assistant tab. Insert a dataset of your choice using the dataset pull-down list box in the upper left corner of the display. If you find that some parameters in the display template are not defined in the selected dataset, you can make appropriate modifications to the display. You can save these changes by using the commands in the display File menu.

Transformation Assistant


After a Filter DesignGuide SmartComponent has been designed, the lumped inductors and capacitors can be transformed into equivalent distributed element counterparts using the Transformation Assistant. This feature enables you to quickly and easily transform an ideal filter topology to a form that is realizable for high-frequency systems.

The Transformation Assistant is opened from the Filter DesignGuide Control window, either by selecting Tools > Distributed Element Transformations from the Control window menu or from the Toolbar.
When the Transformation Assistant is opened, the SmartComponent subnetwork appears in the schematic window and a dialog box is opened. The transformations are then accomplished using the controls on the dialog.

Selecting a Transformation Type

The type of transformation to be applied is selected from three options:

After a transform has been selected, the graphical area displays the components that can be transformed using the current selection. Black components represent elements included in the original circuit available for transformation, while gray components represent elements not included in the original circuit.

From this graphical area, use the left mouse button to select one of the available component types. The graphical area changes to reveal the different distributed element equivalents available for substitution. Transformations Available for a Series Inductor Circuit shows the transformations available when a series inductor circuit has been selected.

Transformations Available for a Series Inductor Circuit

From this point, the type of equivalent network can be selected using the left mouse button from the available structures at the right of the graphics area. A box highlights the currently selected structure. Text at the bottom of the window changes as different selections are made, providing help for the particular transform selected.

Component Selection

After the type of circuit component to be transformed is selected, the actual circuit elements to apply the transform to can be selected using the Component Selection tools. As the left and right arrows within this area are pushed, valid components within the original circuit are highlighted, and their instance names (i.e. L1, C4) appears in the text box on the Transformation Assistant dialog. The three buttons are used to select the specific components that should be subjected to the current transformation:

Transformation Buttons

The buttons across the bottom of the dialog box are used to accomplish the transformation on the selected components.

Changing Component Type

After all transformations have been made on a specific component type (such as series inductor), performing a left mouse click the red return arrow in the upper left hand corner of the graphic area (or performing a right mouse click anywhere on the graphic area) can be used to return to the main component selection page. Another component type can then be selected, and the transformation steps can be repeated for this new selection.

Transmission Line Types

Five basic transmission line elements can be produced using the Transformation Assistant. These are identified as:
.

Additional Transformation Functions

Unit Element

For certain transformations, either the electrical length or characteristic impedance of the resulting transmission line must be specified by the user. If the Unit Element box is checked, the resulting transmission line has an electrical length of 45 degrees and the characteristic impedance is computed appropriately. If the Unit Element box is unchecked, then the Characteristic Impedance (Z0) box becomes active and the computation uses this characteristic impedance to compute the appropriate length.

Characteristic Impedance

The Characteristic Impedance (Z0) box is used to specify the transmission line characteristic impedance for certain transformations. In cases where either the electrical length or the characteristic impedance can be specified, this box works in conjunction with the Unit Element box as discussed above. In certain other cases, this Characteristic Impedance (Z0) box is used alone. For example, when adding lines to the front or end of a network as part of Kuroda's identities, the characteristic impedance of the transformation can be specified using this box.

Add Transmission Lines

As part of the TLine to TLine transformation, unit element (45 degree electrical length) transmission lines can be added to the front or end of the network. The characteristic impedance of these lines is specified using the Characteristic Impedance (Z0) box. Such lines can be added as needed during the transformation process.

Note
Addition of these lines changes the phase response and, if the characteristic impedance is not equal to the network terminal impedance, the magnitude response of the network.

Microstrip Substrate

When performing LC, TLine to MLine transformations, the microstrip substrate thickness (h) and relative permittivity (Er) must be specified. All microstrip elements within a design must share the same substrate parameters. The substrate parameters used in the final design are the values that appear in the boxes after the final transformation step.

TLine to TLine Transforms (Kuroda Identities)

The TLine to TLine transforms are typically used to transform series short-circuited stubs to parallel open circuited stubs in preparation for implementation in planar transmission line technologies. However, these operations only work on Unit Element lines with electrical lengths of 45 degrees. Therefore, when performing lumped to ideal distributed transformations, you must perform substitutions that conform to this Unit Element specification. Preferred stubs (highlighted in blue on the graphical area) as well as series transmission lines (transformed with the Unit Element box checked) can be transformed in this way. When adding transmission line elements before or after the network, the electrical length is 45 degrees and only the characteristic impedance must be specified.

Microstrip Transforms

Note
This set of transforms is only available if a valid license for the Passive Circuit DesignGuide exists.

The LC, TLine to MLine transformations form a somewhat unique class of operations. This set of transformations takes lumped inductor/capacitor combinations as well as ideal series transmission lines and shunt transmission line stubs (obtained from the LC to TLine transformations), and converts them to microstrip. Note that series stubs cannot be used in this transformation since series stubs cannot be realized in microstrip.
In addition to the standard transmission line topologies, certain lumped elements can be replaced with SmartComponents from the Passive Circuit DesignGuide. The available SmartComponents are:

When making such substitutions, the design capabilities of the Passive Circuit DesignGuide are used to realize the topologies. In this case, however, the design procedure is approximate, and some tuning of the elements can be required before the substituted device offers the correct performance. In such cases, after completion of the transformation, push into the SmartComponent on the schematic window and open the Passive Circuit DesignGuide Control window. The Simulation and Optimization Assistants in the Passive Circuit DesignGuide SmartComponent can then be used to quickly and efficiently tune the performance of each individual element.

 

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