Topic 4

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Topic 4:

Momentum Techniques

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Objectives

Utilize different Momentum port typesMesh curved structures efficientlyControl various layout settingsSimulate from schematic: layout look-alike component Embed a Thin Film Resistor for simulation

Here is an example circuit...

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Example: 3dB microstrip 6 GHz splitterADS schematic components generated into layout, resulting in a structure solved in Momentum with expected results:

5 ports

Microstrip artwork generated into layout for solution in Momentum.

First, how to meshthe curved structure...

TECHNIQUES REQUIRED:

Mesh - arbitrary geometry with curves.Ports - different port types (single & internal). Creating a look-alikecomponent for ADS simulator.

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Mesh for curved structures: 3 examples

Simulation time is directly proportional to Mesh density but NOTdirectly proportional to accuracy. Meshing curved structures

requires experience and technique - the answer is in the lab exercise!

45 degrees10 cells / l

20 degrees30 cells / l

10 degrees30 cells / l

QUESTION: Which Arc Facet Angle (degrees) and Density (cells per wavelength) is accurate but does not take too long to solve?

Simulation Time

Next, port types...

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Port types: single and internal

Ports 1, 2, 3 are Single. But ports 4 and 5 are too close back-to-back for Momentum port calibration. The half-wavelength extension would overlap the geometry. Therefore, ports 4 and 5 must become Internal ports!

Exploded view ports 4 & 5

Next, internal port excitation...

P1

P3

P2 P4

P5I

Single port is calibrated:

1/2 l extension at port boundaryfor all simulation frequencies.

No room for single port calibration extension.

Calibration extension.

P4

P5

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Internal port excitation: edge or surface

Direct excitation at surface point

Define the port as internal.Then place the port at any point on the metal surface.

Direct excitation at edge point

Momentum automatically recognizes internal ports...

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Momentum automatically converts port typesAt Momentum simulation time, the single ports (default) are converted to Internal ports , if they cannot be calibrated.

When this happens, a warning message appears.

Next, simulation...

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Simulation set up and results...

Sweep from 1 to 10 GHz: Simulation results show about 6dB loss for splitter at ports 2 and 3.The structure will become a 3dB splitter after ports 4 and 5 have a resistor connected between them.

All five port impedances set to 50 ohms (default for single and internal ports).

Next, using Momentum data in an ADS circuit simulation...

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Using Momentum solutions in ADS schematics

Dataset assigned to an SNP:

SNP is a black-box and requires a Touchstone, CITIFILE or dataset. You set everything up!

Creating a look-alike layout component...

Look-alike component:

2 different ways to do it!

Look-alike is a scaled version of the layout drawing. It is created in Momentum and available in the ADS library as a component! It can also be simulated with measured data like and SNP.

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Creating a layout look-alike component & model

3

Create dialog = set up the look-alike.Symbol : a scaled copy of the layout shape is created. Set min or max pin-pin distance, or layout units.

Model: these parameters will be available in schematic. They are a subset of the Momentum simulation setup.

modelDB: this is where the Momentum solution data is stored as a citifile.

Click OK and the entries will be passed to the look-alike.

Be sure to check this box to have the citifile created from the last Momentum simulation!

Next, go to schematic and insert the look-alike...

modelDB:

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Using the look-alike splitter component in schematic

The layout look-alike component can be inserted from the library:

Ref: The reference pin is created as a voltage reference for all the other pins of the component.. Connect the Ref to ground or use to simulate floating ground.

Also, push / pop if schematic exists!

Simulation in schematic...

Double click:

Component dialog = view or set up the simulation parameters.

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S-parameter simulation setup with look-alike

Use any other ADS simulator: AC, HB, Transient, etc. Or, use an SNP ...

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Momentum data assigned to an SNP

To begin, set up the SNP:File = dataset name.dsType = Dataset

S-Parameter N-port

is a file basedcomponent that allows S-parameter data to be simulated.

S5PSNP1File="splitter_a.ds"

Next, set up the Simulation...

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SNP simulation setup and resultsTFR at ports 4 & 5

Splitter is S5P

S5P File = mom dataset.

S-parameter circuit simulator requires Terms (ports).

TFR is a standard ADS microstrip component.

3 dB insertion loss at 6 GHz for ports 2 and 3 with very good isolation. Output Z is about 50 Ohms

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Now, it is time to do the lab exercise!

Here is an overview...

You are here

Lab 1: Momentum Basics: Microstrip Meander Line

Lab 2: Momentum RF Mode: RFIC Launch

Lab 3: Designing with Momentum: Via-fed Patch Antenna

Lab 4: Momentum Techniques: 3 dB Splitter

Lab 5: Optimization: 3 GHz Band-Reject Filter

Lab 6: Optional Advanced Topics: Coplanar Waveguide

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Lab 4: 3dB Splitter Open the splitter microstrip designVerify schematic component mapping to layout layersChange Momentum port arrow attributesVerify the internal portsModify layout layer settings and textMesh curved surfaces with variationsCreate a look-alike componentSimulate the splitter from schematic

Generate the layout.

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Lab 4 continued: 3dB Splitter

Try 3 different meshes for curves:

Set preference and layer settings for ports, text, and drawing layers:

Internal ports

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Lab 4 continued: 3dB SplitterSchematic with layout look-alike component for simulation :

Create the look-alike, simulate from schematic, plot the results, check the database.

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Lab 4 continued: OPTIONAL STEP

Start the lab now!

MSub

EqnVar

DESIGN: splitter_wtfr - generated into layout for Momentum simulation:

Layout drawing layers cond (splitter) and resi (TFR) are both mapped to the same substrate layer: Alumina. Also, embedded layout TFR gives better match but less isolation than circuit simulator results.