eec 132 ads momentum tutorial -...

EEC 132

ADS Momentum Tutorial

Huan Liao

Kelvin Yuk

Winter 2009

This is a brief tutorial on the use of ADS Momentum. Please refer to the ADS/Agilent site

http://eesof.tm.agilent.com/products/momentum_main.html for additional information.

Example:

Design a microstrip radial stub low pass filter, with 1 dB corner frequency at 3.2 GHz, and at least

25 dB of attenuation in the range :3.9-6.0 GHz. The lumped circuit design is shown in Figure 1.

Simulate this design and plot its S-parameters.

1. Lumped Circuit Design

S_Param

SP1

Step=0.01 GHz

Stop=10.0 GHz

Start=0.5 GHz

S-PARAMETERS

C

C4

C=1.728 pF

L

L3

R=

L=3.129 nH

C

C3

C=2.624 pF

L

L2

R=

L=3.343 nH

C

C2

C=2.624 pF

L

L1

R=

L=3.129 nH

C

C1

C=1.728 pF

Term

Term2

Z=50 Ohm

Num=2

Term

Term1

Z=50 Ohm

Num=1

Figure 1. Schematic of Lumped Circuit

2. Distributed Circuit Design, using radial stubs. The lumped design has been converted into

microstrip transmission line elements as shown in Figure 2. Transmission lines have been

used in place of the inductors and radial stubs have been used in place of the capacitors.

Fifty-ohm microstrip transmission lines and tapers have been added to each end of the filter.

Simulate this design and compare it with the lumped design.

MSUBMSub1

Rough=0 mil

TanD=0T=0.7 milHu=3.9e+034 milCond=1.0E+50Mur=1Er=4.3H=59 mil

MSub

S_ParamSP1

Step=0.01 GHzStop=10.0 GHzStart=0.5 GHz

S-PARAMETERS

TermTerm2

Z=50 Ohm

Num=2

TermTerm1

Z=50 Ohm

Num=1

MLINTL1

L=300 milW=115 milSubst="MSub1"

MTAPERTaper1

L=97.5 milW2=40 milW1=115 milSubst="MSub1"

MLINTL5

L=300 milW=115 milSubst="MSub1"

MTAPERTaper2

L=97.5 milW2=40 milW1=115 milSubst="MSub1"MBSTUB

Stub4

D=15 milAngle=60Ro=218.7 milW=40 mil

Subst="MSub1"

MLINTL4

L=215 milW=40 milSubst="MSub1"MBSTUB

Stub3

D=15 milAngle=45Ro=276.6 milW=40.0 mil

Subst="MSub1"

MLINTL3

L=225.7 milW=40 milSubst="MSub1"MBSTUB

Stub2

D=15 milAngle=45Ro=276.6 milW=40.0 mil

Subst="MSub1"

MLINTL2

L=215 milW=40 milSubst="MSub1"MBSTUB

Stub1

D=15 milAngle=60Ro=218.7 milW=40 mil

Subst="MSub1"

Figure 2. Schematic of Distributed Circuit

3. Momentum

1) Generate the schematic for Momentum simulation

In order to set up the Momentum simulation, a schematic using microstrip components

must be converted into a layout and the appropriate ports need to be designed. Using the

schematic shown in Figure 2 above, delete the 50-ohm Term components and the

S-Parameter block..

Add two ports to the schematic as shown in Figure 3.

Port

P2Num=2

Port

P1Num=1

MSUB

MSub1

Rough=0 milTanD=0

T=0.7 milHu=3.9e+034 mil

Cond=1.0E+50Mur=1Er=4.3

H=59 mil

MSub

MLIN

TL1

L=300 milW=115 mil

Subst="MSub1"

MTAPER

Taper1

L=97.5 mil

W2=40 milW1=115 mil

Subst="MSub1"

MLIN

TL5

L=300 milW=115 mil

Subst="MSub1"

MTAPER

Taper2

L=97.5 mil

W2=40 milW1=115 mil

Subst="MSub1"MBSTUB

Stub4

D=15 milAngle=60

Ro=218.7 milW=40 mil

Subst="MSub1"

MLIN

TL4

L=215 milW=40 mil

Subst="MSub1"MBSTUB

Stub3

D=15 milAngle=45

Ro=276.6 milW=40.0 mil

Subst="MSub1"

MLIN

TL3

L=225.7 milW=40 mil

Subst="MSub1"MBSTUB

Stub2

D=15 milAngle=45

Ro=276.6 milW=40.0 mil

Subst="MSub1"

MLIN

TL2

L=215 milW=40 mil

Subst="MSub1"MBSTUB

Stub1

D=15 milAngle=60

Ro=218.7 milW=40 mil

Subst="MSub1"

Figure.3. Schematic of Circuit for Momentum Simulation

2) Generate/Update Layout

The schematic is ready for conversion into a layout. Go to the Layout menu, select

Generate/Update Layout. Click OK in the dialog box. The layout shown in Figure 4. will

appear.

Figure 4. Layout of microstrip distributed filter

3) Define and Solve the Substrate

You must instruct Momentum as to how the different metal/slot layers in your drawing are

“mapped” to different layers of your substrate.

This is achieved by either (1) updating the substrate parameters defined in the MSUB

component (recommended) or (2) by defining the substrate parameters within the Momentum

controller.

(1) The first is accomplished by selecting Momentum->Substrate->Update from the menu

bar in the Layout window as shown in Figure 5.

Figure 5. Updating the Momentum substrate information using information from the

MSUB component in your schematic.

(2) The other requires you to set information about the substrate in an additional dialog box

which can be activated by Momentum->Substrate->Create/Modify as shown in Figure 6.

Figure 6. Manual creation of Momentum substrate parameters

In the Substrate Layers Tab shown in Figure 7, enter the Thickness and the Permittivity which are

the same as those in the schematic.

Figure 7. Create/Modify Substrate: Substrate Layers

Click the Layout Layers tab as shown in Figure 8. Highlight and enter the Thickness and

Conductivity of the metal layer which agree with those in the schematic.

Figure 8. Create/Modify Substrate: Layout Layers

In most cases, you can first perform an “Update from schematic” substrate definition,

followed by a check using “Create/modify” option. In this case, the Substrate Layers have been

loaded already; you just need to edit the Metallization Layers.

Click on the Momentum pull-down menu and select Substrate -> Precompute Substrate as

shown in Figure 9.

Figure 9. Precompute Substrate

In this step, Momentum will perform a series of computations that are specific to the

substrate definition only, not the shapes of the objects in the layout. This is useful since you may

be able to use the same substrate for different shapes of microstrip circuits, but you will not have

to re-compute these preliminary functions. A pop-up window appear asking for the minimum

frequency and maximum frequency of substrate computations. Enter a minimum frequency of

0.5 GHz and a maximum frequency of 10 GHz as shown in Figure 10. A status window

displaying details of the computation will appear as shown in Figure 11.

Figure 10. Specifying the frequency range of the substrate computation.

Figure 11. Status window displaying details of the substrate computation

When the substrate calculations are complete, save the substrate computation by clicking on

Momentum -> Substrate -> Save as shown in Figure 12.

Figure 12. Saving the substrate computation results.

4) Mesh Setup

Before the simulation can proceed, we need to define the mesh by opening the mesh

setup dialog box. Click Momemtum->Mesh->Setup… as shown in Figure 13.

Figure 13. Setup the Mesh

A Mesh Setup Controls window will appear as shown in Figure 14. The important

parameter is the mesh frequency which is the highest frequency you want to analyze the

circuit for. In our case, 10 GHz will be good. (the higher the frequency, the finer the mesh will

be and the longer the simulation time.) Enter 10GHz as the Mesh Frequency and click OK

as shown in Figure 14.

Figure. 14. Mesh Setup Controls Dialog Box

Now preview the mesh on your circuit layout by clicking on Momentum -> Mesh ->

Preview… as shown in Figure 15.

Figure 15. Preview the Mesh on your circuit layout.

A Preview Mesh window will pop up as shown in Figure 16.. Enter a Mesh Frequency of 10

GHz and click OK. A status window as shown in Figure 17 will appear.

Figure 16. Mesh Preview pop up window

Figure 17. Status window for Mesh Preview…

Your layout should now resemble Figure 18.

Fig. 18. Layout after Mesh Precompute

5) Simulation

In this step, Momentum uses the substrate, mesh information and the method of

moments to characterize the circuit.

In the layout view, select Momentum->Simulation->S-parameters… as shown in Figure

19.

Figure 19. Momentum S-parameter simulation

A Simulation Control window will appear as shown in Figure 20. We now have to

specify the S-parameter sweep parameters. PLEASE NOTE: DUE TO THE

COMPLEXITY OF THIS OPERATION IT IS IMPORTANT THAT YOU CHOOSE

“Adaptive” SWEEP AND THAT THE SAMPLE POINTS LIMIT IS SET TO THE

MINIMUM THAT IS NECESSARY. THIS OPERATION CAN TAKE UP TO SEVERAL

HOURS OR DAYS IF TOO MANY POINTS ARE SPECIFIED.

In the Simulation Control menu, choose the “Adaptive” Sweep Type. Enter a Start of

0.5GHz and Stop of 10GHz. Enter a Sample Points Limit of 30. Then, click “Add to

Frequency Plan List” or “Update”.

Figure 20. Simulation Control Dialog Box

After the frequency sweep plan has been entered. Click the Simulate button to perform a

simulation on the layout. PLEASE NOTE: THIS SIMULATION MAY TAKE SEVERAL

HOURS TO COMPLETE. A status window as shown in Figure 21 will appear and display

the simulation progress.

Figure 21. Status window for Momentum S-parameter simulation

6) Viewing the Results

When the simulation is complete, a data display window should open automatically and

include separate plots of all four S-parameters. The name of the data set that is created will be

the same as the layout filename, with an “_a” extension. This file will automatically be saved

to the Data subdirectory of your project as a dataset file (.ds file). The automatically

generated plot for S21 is shown in Figure 22.

2 4 6 80 10

-50

-40

-30

-20

-10

-60

0

Frequency

Mag. [dB]

S21

Figure 22. Simulation Results Comparison, S21

The responses of the Lumped, Distributed and Momentum simulations can be compared

on the same plot as shown in Figure 23 and Figure 24.

m1f req=dB(LPF_lumped..S(2,1))=-3.137

3.300GHz

m2f req=dB(LPF_Radial_Stubs_Momentum0..S(2,1))=-3.000

3.380GHz

m3f req=dB(LPF_Radial_Stubs_Momentum_mom_a..S(2,1))=-3.492

3.386GHz

Lumped

Distributed

Momentum

1 2 3 4 5 6 7 8 90 10

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

-110

0

f req, GHz

dB(LPF_lumped..S(2,1))

m1

dB(LPF_Radial_Stubs_Momentum0..S(2,1))

m2

dB(LPF_Radial_Stubs_Momentum_mom_a..S(2,1))

m3

m1f req=dB(LPF_lumped..S(2,1))=-3.137

3.300GHz

m2f req=dB(LPF_Radial_Stubs_Momentum0..S(2,1))=-3.000

3.380GHz

m3f req=dB(LPF_Radial_Stubs_Momentum_mom_a..S(2,1))=-3.492

3.386GHz


Lumped

Distributed

Momentum

m4freq=dB(LPF_lumped..S(1,1))=-2.887

3.300GHz

m5freq=dB(LPF_Radial_Stubs_Momentum0..S(1,1))=-7.179

3.380GHz

m6freq=dB(LPF_Radial_Stubs_Momentum_mom_a..S(1,1))=-2.627

3.386GHz

1 2 3 4 5 6 7 8 90 10

-30

-20

-10

-40

0

freq, GHz

dB(LPF_lumped..S(1,1))

m4

dB(LPF_Radial_Stubs_Momentum0..S(1,1))

m5dB(LPF_Radial_Stubs_Momentum_mom_a..S(1,1))

m6

m4freq=dB(LPF_lumped..S(1,1))=-2.887

3.300GHz

m5freq=dB(LPF_Radial_Stubs_Momentum0..S(1,1))=-7.179

3.380GHz

m6freq=dB(LPF_Radial_Stubs_Momentum_mom_a..S(1,1))=-2.627

3.386GHz


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