Agilent ADS Tutorial (Project 3)

UNC Charlotte Agilent ADS Tutorial (Project 3)

(Approx. 3 weeks)

Overview

The objective of the tutorial is to become familiar with fundamental system design tools of Agilent ADS software.

NOTE: Use the Project Report Template and keep answers to questions on consecutive sheets of paper with all plots at the end.

IN NO CASE may code or files be exchanged between groups, and each group must answer the questions themselves and do their own plots, NO COPYING of any sort!

Only turn in requested plots ( Pxx ) and requested answers to questions ( Qxx ).

Part 1

Start the software:

Download the following tar-file (you may need to hold down the shift key while you click on the link):
tpwp3.tar

Move the tar-file into the apps/agilent/ads (or hpeesof/ads) directory, and de-tar using the command

    tar -xvf tpwp3.tar

You should find a new directory project3 created in apps/agilent/ads (or hpeesof/ads)

Run ADS

Go down through the directory tree to ads/project3/networks/ampoip3.dsn, and double click that design file.

Double-click the schematic in the right half of the window, and the following schematic should appear.

Print the schematic and turn it in. ( P1 )

Double-click the "gear" icon in the upper right of the window to simulate.

The data plotting window and the following plot should appear.

Go to the schematic, double click the Harmonic Balance, and note the frequencies. Reset them to 100 and 101 MHz. Double click the AC sourrce and set the frequencies to the new frequencies. Rerun the simulation, and note the re-plotted data. Drop another plotting box in the visible area, and in the pop-up window:

Select DataSet -> Vout -> Add Vs-> Spectrum dBm -> independent variable freq
PlotOptions -> xaxis -> 95-105 MHz.
Select the trace, then TraceOptions -> TraceType ->Spectral
You should get another OIP3 spectrum.

Print this single plot and turn it in. ( P2 )

What is the OIP3 at 100 MHz? (Q1 )

How does this compare to the OP amp spec?? (Q2 )

Part 2

Start the software:

Go down through the directory tree to ads/project3/networks/ami05T33aDiffAmp2.dsn, and double click that design file.

Double-click the schematic in the right half of the window, and the following schematic should appear.

Print the schematic WITH ANNOTATED DC BIAS POINTS and turn it in. (Use MenuBar::Simulate->AnnotateDCSolutions to get the DC voltages on the schematic.) ( P3 )

Double-click the "gear" icon in the upper right of the window to simulate.

The data plotting window and a plot similar to the following plot should appear.

WARNING.
The dBm reading in these plots are in error.
The value is 3 dB below the true value in dBm.

On the manual page for the dbm() function, it states: ... voltage is assumed to be a peak value. Using the dbm() function with rms will yield a result that is 3 dB too low unless the noise voltage is first converted to peak: noise_power = dbm(vout.noise * sqrt(2)); On the manual page for the vfc() function, it states: ... This measurement gives the RMS voltage value of one frequency-component of a harmonic balance waveform Hence, the three dB error.

To correct your OIP3 plots, you must double-click the dBm(xxx) on the plot, and mutliply by 1.414 (square root of 2). This is illustrated in th e above plot. A more safe method might be to multiply by 1.4.4 on the place in the schematic sheet where the variable is defiled, i.e., Voutlin=1.414*vfc(vout,0,{1,0}).

Print this OIP3 plot and turn it in. ( P4 )

In the schematic, what is purpose of the BSIM3 item? (Q3 )

What is the frequency at which the OIP3 was measured? (Q4 )

What is the gain of the amplifier? (Q5 )

What is the output 1 dB compression point of the amplifier? (Q6 )

What is the the output third order intercept point of the amplifier? (Q7 )

Decreasing the DC current source to 5 mA, re-plot the OIP3 plot. Print this single plot and turn it in. ( P5 )

After decreasing the DC current source to 5 mA, what is the output 1 dB compression point of the amplifier? (Q8)

After decreasing the DC current source to 5 mA, what is the output third order intercept point of the amplifier? (Q9)

After decreasing the DC current source to 5 mA, what is the threshold voltage, Vth, of the transistors in the differential amplifier? (Use MenuBar::Simulate->DataDeviceOpPoint to get the threshold voltage on the transistor.) (Q10)

If the current source is cut in half, how may dB do you expect the output power capability to decrease? (Q11) Hint: is the amplifier voltage or current going to clip first?

Part 3

Run ADS

Go down through the directory tree to project3/networks/receiversweep.dsn, and double click that design file.

Double-click the schematic in the right half of the window, and the following schematic should appear.

Print the schematic and turn it in. ( P6 )

Double-click the "gear" icon in the upper right of the window to simulate.

The data plotting window and 3 plots shown below should appear.

Print the 3 plots on one sheet and turn it in. ( P7 )

Click the "rectangular plot" icon in the left of the window to simulate. Drop a plotting box in the visible area, and in the pop-up window:

Select DataSet -> S(2,1) -> Add Vs-> dB -> freq
You should get another sweep of the receiver.

Double click the plot select "plot options", set the plot x axis to 100 - 105 MHz. Then, go to the schematic, double click the s-parameters, and set the frequency sweep to 100 - 105 MHz. Rerun the simulation, and note the re-plotted data.

Print this single plot and turn it in. ( P8 )

Click the "rectangular plot" icon in the left of the window to simulate. Drop another plotting box in the visible area, and in the pop-up window:

Select DataSet -> S(2,1) -> Add Vs-> dB -> freq
You should get another sweep of the receiver.

Double click the plot select "plot options", set the plot x axis to cover the image frequency +/- approx. 1MHz. Then, go to the schematic, double click the s-parameters, and set the frequency sweep to the image frequency +/- approx. 1MHz. Rerun the simulation, and note the re-plotted data. It should look like the following (use the -50 to + 50 dB scaling).

Print this single plot and turn it in. ( P9 )

What is the image rejection? (Q12 )

How does the image rejection compare to the theoretical value? (Q13 )

What type of filter is the preselector (Cheby, elliptic, butterworth?). (Q14 )
What is the gain, Noise Figure, 1dB copmpression (P1dB), and output intercept pount (OIP3) of the first amplifier? (Q15 )

Use an excel spreadsheet (amp3.xls) to calculate gain, Noise Figure, 1dB copmpression (P1dB), and output intercept pount (OIP3) of the entire radio, and turn in this spreadsheet. (P10 25 points)
The spreadsheet results should match your simulation. If the 1 dB compression point is not given for a component, then use Psat as an approximate 1 dB compreession point.

Save a copy of the schematic in a differently named file. In this new schematic file, delete the back end of the radio (mixer through IF filter) and connect the output "term" to the output of the second preselector. Sweep the "front end of the radio from 50 to 150 MHz and plot S21. Plot this and turn it in. (P11 )

Why does the image frequency response have the same shape as the frequency response of the desired channel? (Q16 )

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NEW Plots & Questions

Return to the original schematic, and retune the radio (by changing the LO frequency) to receive at an input frequency of 90 Mhz.
Plot the radio frequency response from 40-140 MHz with vertical axis from -50 to 100 dB in steps of 10 dB. (P12 )

What is the new LO frequency? (Q17 )

What is the new Image frequency? (Q18 )

Part 4

Start the software:

Download the following tar-file (you may need to hold down the shift key while you click on the link):
tpwCouplers.tar

Move the tar-file into the apps/agilent/ads (or hpeesof/ads) directory, and de-tar using the command

    tar -xvf tpwCouplers.tar

You should find a new directory couplers created in apps/agilent/ads (or hpeesof/ads)

Run ADS

Go down through the directory tree to ads/couplers_prj/networks/wilkinson.dsn, and double click that design file.

Double-click the schematic in the right half of the window, and the following schematic should appear.

Print the schematic and turn it in. This is the Wilkinson power divider in Appendix G of Ludwig and Bretchko. ( P13 )

Double-click the "gear" icon in the upper right of the window to simulate.

Plot the magnitude (in dB) and phase of S21, S31 from 0.1 to 2 GHz. ( P14 )

Plot Smith chart of S11 from 0.1 to 2 GHz. ( P15 )

What is the center frequency? (where the lines are quarter wave) ( Q19 )

What are the magnitude (in dB) and phase of S21 and S31 at the center frequency? ( Q20 )

What is the relative phase of S21 and S31? (i.e., how many degrees does the output phases of the two ports differ?) ( Q21 )

Go down through the directory tree to
ads/couplers_prj/networks/branchline.dsn,
and double click that design file.

Double-click the schematic in the right half of the window, and the following schematic should appear.

The design given in the schematic is wrong!
This is the Branch Line coupler in Appendix G of Ludwig and Bretchko. Fix the transmission line widths so that the design corresponds to figure G4 of Ludwig and Bretchko. Ports 2 and 3 should have the largest output power (S21 and S31 should be -3 dB). Print the schematic after you correct the transmission line widths, and turn it in.
Hint: you will need to adjust the width of the lines to an accuracy of about 1 percent. You will need to experimentally find the correct linewidth using ADS and a sample length of line. ( P16 )

Double-click the "gear" icon in the upper right of the window to simulate.

Plot the magnitude (in dB) and phase of S21, S31, S41 from 0.1 to 2 GHz. ( P17 )

Plot Smith chart of S11 from 0.1 to 2 GHz. ( P18 )

What is the relative phase of the two output ports (S31 and S21)with the largest magnitudes? (i.e., how many degrees does the output phases of the two ports differ?) ( Q22 )

Place a 50 ohm resistor in parallel with the 50 ohm terms at ports 3 and 2. This creates a mismatch and reflections from these points. Re-plot the magnitude and phase of S21, S31, S41 from 0.1 to 2 GHz. ( P19 )

Re-plot Smith chart of S11 from 0.1 to 2 GHz. ( P20 )

Where did all the reflected power go?. ( Q23 )

Part 5

Next, automatically layout your branch line coupler design.

DO NOT USE run Layout-->Generate/UpdateLayout

It might prevent layout problems if you convert all of your dimensions to mils (1 mil = 1/1000 inch), or to meters, for the transmission lines. The mixed use of mils for width and meters for length can cause difficulty in aligning the components in the layout. This can result in "invisible gaps" and strange simulation results.

From the schematic menu bar, use the command Layout-->PlaceComponentsFromSchematic to place the 4 transmission lines individually in the layout.

Accept the defaults in the pop-up pane and click OK

From schematic window run Layout-->ShowUnplacedComponents, and make sure only grounds are in highlight on the schematic.

In the layout window, run the command from the menu bar Schematic-->ShowEquivalentComponent to highlight the corresponding transmission line in the schematic.

Rearrange the transmission lines as illustrated below. as you move the transmission lines, delete the wires. Dashed lines will appear. In the final layout, overlap the blue dots/squares to once again establish connection between the transmission line segments. You may need to use Options-->GridSnap to turn gridsnap off if you have odd-sized lines (leave pin-snap on).

Run Tools-->CheckDesign to make sure you have no unconnected pins (you should get 0 warnings).

Plot the Layout( P21 )

Run Momentum-->Substrate-->UpdateFromSchematic

Momentum is a 2.5D planar electromagnetic (EM) simulator for passive circuit analysis of arbitrary design geometries. It accurately simulates complex electromagnetic effects including coupling and parasitics.

Run Momentum-->Substrate-->CreateModify, and see that the substrate is the same as on the schematic.

Run Momentum-->Substrate-->UpdateFromSchematic

Click the menu bar InsertPort button (hexagon with pin shown below), and add a port to each of the blue square pins in the layout, making sure the ports are numbered the same as in the schematic.

Run Momentum-->Simulation-->Sparameters using adaptive sweep from 1-2 GHz

Plot the s-parameters S21, S31, S41( P22 )

Plot the Smith Chart S11( P23 )

How do the results of the simulation of the layout compare to the results from the schematic? ( Q24 )

Other Tips and notes:

Subcircuits and symbols can be created. First, add ports to your schematic using the InsertPorts button (looks like a hexagon). Then use view->Create/EditSchematicSymbol from the menu bar to create a symbol. To use the symbol in a schematic, ust the menu-bar DisplayComponentLibrary (looks like a bookshelf), navigate to the directory (usually under your project name under sub-networks), highlite the component, and when you move the mouse to the schematic window, the new symbol should appear.

To export ADS files to cadence in iff format, from ADS run File-Export and export as type iff, and check that the options show overwrite iff, and all 3 checkboxes are unchecked, default library name should be the exact same name as your ADS project directory, schematicHeriarchy includes currrent design, projects, and all libraries. After exporting the iff file, it should be somewhere in your ADS directory tree. Copy this file to your cadence/ncsu directory.

Before running cadence icfb to import the iff file, you must first have this at/near bottom of your .cdsinit file:
load("/afs/uncc.edu/coe/unix/opt/ads2006/links/tools/iff/cadence/composer/mdsinit.il")
Then, you should see the IFF->importIff option in the icfb menu-bar (in the icfb text-window not the icfb file window). Click the IFF menu bar button, select the iff file to be imported. Check/activate the three "do not" buttons, and click OK to convert. In the pop-up, attach to existing techfile, attach to the proper library (ami06).

If all goes well, you should be able to open the schematics in Cadence. Manually open schematics and remove the yellow parameter boxes, if you wish. Also remove power supplies and any ADS-specifice items such as variables, harmonic balance boxes, transistor models, power supplies, etc.

Report

Use the Project Report Template (also shown as pdf file)

Write any comments or observations you may have directly on the printouts. Type or clearly handwrite. Do not add extraneous pages or put explanations on separate pages unless specifically directed to do so. The instructor will not read extraneous pages!

Only turn in requested plots ( Pxx ) and requested answers to questions ( Qxx ). All plots must be labeled P1, P2, etc. and all questions must be numbered Q1, Q2, etc.

Turn in a separate sheet with answers to all of the specific questions above.