ADS Tutorial 2

In tutorial 1, we learnt the basics of using ADS. In this tutorial we are going

to design Amplifier using BJT. This simulates the S-parameters and noise

parameters of the device, versus bias voltage and current, at a single

frequency. You specify the collector voltage sweep range and the base

current sweep range, and the single frequency for S-parameter and noise

analysis. The circuit diagram that we are going to consider is shown in

figure-1.

Figure 1

Procedures1. First of all open a new project and a new schematic window. (the

procedure to create a new project is described in tutorial 1).2. Place the BJT_NPN on the schematic from

Insert>Components>Components Library. 3. Place the BJT_Model on the schematic from

Insert>Components>Components Library. Double click on the BJT_Model, you will see a window as shown in figure 2.

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Islamic University of TechnologyElectrical Engineering Department

Advanced Design System (ADS) Software

Figure 2

4. Insert following parameters in “Select parameter” box shown in figure 2.

5. From Lumped Components Palette Place 2 inductor (L1,L2), 2 capacitor (C1,C2) and insert their value 1mH, 1mH, 1uF and 1uF respectively. This can be done simply by double clicking on the each component.

6. From the Probe Components palette, select I_Probe and name it “IC” by double clicking on the probe. Again from Insert>

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Components> Components Library, place two terminator component named as “Term”. Give their value Z=Z0 (figure 1).

7. From the Library List select Sources-Freq Domain palette, place I_DC. Edit this component and define Idc = IBB, rather than a numerical value, Click “Apply”, then “OK”.

8. Now connect the components using “wire” tool as shown in figure 1.9. Choose the Data Items palette; select Var eqn (Variables and

equations). Place this component on the schematic and enter the

following equations (as shown in figure 3):Figure 3

10. Select another Var eqn (Variables and equations). Place this component on the schematic and enter the following equations (as shown in figure 4):

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Figure 4

11. Choose Simulation-DC palette, select Prm Swp (ParamSweep). Place two “Prm Swp” named as “sweep 1” and “sweep 2” and edit these as follows:

Sweep 1

On the Sweep tab (Figure 5):

Parameter to sweep = IBB

o Start = IBBmino Stop = IBBmaxo Step = IBBstep

On the Simulations tab:

o Simulation 1 = Sweep2o Simulation 2 = DC1

Click OK to accept changes and close the dialog box.

Figure 5

Sweep 2

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On the Sweep tab (Figure 6):

Parameter to sweep = VCE

o Start = VCEmino Stop = VCEmaxo Step = VCEstep

On the Simulations tab:

o Simulation 1 = SP1

Click OK to accept changes and close the dialog box.

Figure 6

12. Choose Simulation-S Param palette, select S P (S-parameters). Place it in the schematic and edit it as follows:

On the Frequency tab (Figure 7):

Sweep type = single point

On the Noise tab: Mark “Calculate noise”

Then on the “Output” tab:

o Mark Measurement equationo Insert maximum depth= 2

Then click add/remove in the same window. From the next window select and Z0. Click OK to accept changes and close the dialog box.

13. From Simulation-DC palette, select D C, Place it in the schematic and edit it as follows:

Parameter to sweep = VCE. This appears as SweepVar on the schematic if this parameter is displayed on the schematic. Select “Linear” from sweep type, (Figure 8) and

o Start = VCEmin

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Figure 7

o Stop = VCEmaxo Step = VCEstep

14. From Simulation-DC palette, select Options, Place it in the schematic and edit it as follows:

In MISC tab insert

o Simulation temperature= 16.85 Celsiuso Model temperature= 25 Celsius

15. That is all for constructing the circuit. The whole schematic will look like as shown in figure 9.

16. Now press “simulate” to start simulation.

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Figure 8

Figure 9

Plotting the output:

In this tutorial we are going to go for a bit detail to plot different parameters.

1. First of all in data display window; place rectangular plot. Then write “NFmin[0]” in equation box (Figure 10) then press >>Add>> . This will give an output of minimum noise figure versus IBB and VCE (figure 11).

2. Next, similarly using rectangular plot, plot db(S2,1) versus IBB and VCE inserting “db(S(2,1)[0])” in equation editor.(figure 11).

3. The Collector Current versus IBB and VCE is plotted simply plotting “IC.i” using rectangular plot. (figure 12). Now we will put markers in these figures (figure 11 and 12). This can be done selecting “insert new marker” from the toolbar and just clicking on the plot where we want to put the marker. These markers are visible in figure 11 and 12 (m1,m2,m3).

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4. Now we will use some equations to get our desired plot. This will be done opening a new page in data display window. Go to Page>new page from the menu bar. Give a new name for the page. A new page will open.

Figure 10

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Figure 11

Figure 12

5. Next Available Gain & Noise Circles, Stability Circle, Source Gamma, Corresponding Load Gamma will be plotted in the smith chart. To do so, we need to introduce some equations.

ICindex2 is the index for the collector current, IC, corresponding to marker m3’s y-axis location. IC is dependent on both swept variables, IBB and VCE. The [VCEindex2] syntax is equivalent to [VCEindex2] and forces a search of all collector currents corresponding to one collector voltage.

Set step sizes and number of circles, here.

GAcircles are the available gain circles at the frequency specified by marker m3. GAstep_size and num_GAcircles are variables you set to change the number of circles and their spacing.

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Source_stabcir is the source stability circle at the m3 bias point.

Noise_circleMin generates a circle at the source reflection coefficient that will produce the minimum noise figure. Noise_circles generates num_NFcircles noise circles, spaced at NFstep_size dBs. The circles are both at the frequency specified by marker mBiasPt.

GPcircles are the power gain circles at the frequency specified by marker m3. GPstep_size and num_GPcircles are variables you set to change the number of circles and their spacing.

Load_stabcir is the Load stability circle at the m3 bias point.

Ploting Stability Circles, Available Gain circles and Noise circles:

1. In “data display window” select smith chart and place. In the equation editor (shown in figure 13) write “Source_stabcir” then click add.

2. Similarly place “GAcirles” and “Noise_cirles” and click add.3. Click OK. The Available Gain & Noise Circles, Source Stability Circle will

be plotted. (figure 14)

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Figure 13

Figure 14 Figure 15

4. To plot load stability place another smith chart, and type “Load_stabcir” in equation editor. (the process is exactly similar to point 1)

5. Similarly place “GPcirles” and click add.6. Click OK. Load Stability Circle will be plotted. (figure 15)

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Finding S-parameters:

S-parameters at the bias point specified by marker m3.

Now from the data display window, select “list” from left palette and place it. Then in the equation editor type “db(S_11)” then “add”. Similarly add “db(S_22)”, “db(S_12)” and “db(S_21)” . Click “OK” (figure 16).

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Figure 16

The output will be as follow:

Calculating Noise Figure:To calculate noise figure at particular stable region, first we need to generate spiral on the smith chart to locate arbitrary point. The following equations generate a spiral on the Smith Chart, and allow you to move the GammaS marker nearly anywhere on the chart. tindex is a vector of

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numbers 0,1,2,3,...,2000. rhos are 2001 complex reflection coefficients. Their magnitude varies slowly as tindex increases from 0 to 2000. Their phase varies rapidly for tindex small, but varies more and more slowly as tindex increases.

Plot this “rhos” in the same smith chart where the source stability circle was plotted. Then place a marker on the smith chart and name it “GammaS” (Figure 17) shows the smith chart with spiral points.

Figure 17

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The following equations compute the noise figure if the source reflection coefficient is at marker GammaS.

Now from the data display window, select “list” from left palette and place it. Then in the equation editor type “NF_at_GammaS” then “add”. Click “OK”. The output will display the Noise Figure (dB) at marker GammaS (Figure 18). If you change the marker “GammaS” the Noise Figure value will be changed automatically.

Figure 18

To see the minimum noise figure at bias point “m3” we need to type “NFmin[ICindex2,VCEindex2,0]” in the equation Editor (figure 19).

Figure 19

THE END

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