ADS Tutorial Transient Simulation C. E. Saavedra 1. Start ADS 2. Go to the Devices BJT library 3. Select the BJT M box and place it in the window. This box allows you to set the different

model parameters of the transistor. Every transistor that is manufactured has a different set of model parameters.

4. In this case we are going to use the NPN 2N3904 transistor. Input the following parameters: Is = 6.734e-15, Bf = 416, NF = 1, Vaf = 74, Ikf = 0.0668, Ise = 6.73e-15, Ne = 1.259, Nr = 1, Rb = 10, Rc = 1, Eg = 1.11, Cjc = 3.8e-12, Cje = 4.5e-12, Tr = 239e-9. The data sheet has some, but not all, of the parameters that are present in the ADS device model. This is not a problem. If you leave one of the parameters blank, then ADS will just use the default values.

5. From the component library choose BJTNPN and place it in the window. 6. Layout the circuit shown in Figure 1 below. The DC Voltage source can be found in the

Sources Time Domain library. Set the DC voltage to 10 V. The sinusoidal voltage source can also be found in this library and it is appropriately called Sine. Set the frequency to 1 MHz, and the amplitude to 0.01 V.

7. You will need to label the input and output wires in the schematic so that you can plot them in the results window. To label the wires click on the icon on the top part of the Schematic window labeled Name. Then input a name like Vin and then click on the wire that connects the source to the input capacitor. Repeat this process and label the wire connected to the output load resistor (2 kW). Call the output wire Vout

Figure 1 Circuit Schematic

8. Next you will set up the simulation. Go to the Simulation-Transient library. 9. Click on the Trans icon and place it in the schematic window. 10. Double-click on the Transient component in the schematic window. Set the start time to 0.0

(default value), set the Stop time to 5 sec, and set the Max timestep to 50 nsec. Click Apply and then OK.

11. Now you are ready to simulate. Click on the simulation icon, or else press the F7 key. 12. The results window will pop-up automatically. Choose a rectangular coordinate graph and

place it in the window. A dialog box will pop-up. From the left-hand column select Vin and then click Add. Next select Vout and click Add again. Both Vin and Vout should appear under the Traces column. Click OK. You will now see your input and your output voltage and it will should look like figure 2.

Figure 2 Results Window

13. Notice that indeed you have gain because the amplitude of the output signal (blue) is much

bigger than the amplitude of the input signal (red). 14. The output signal is not centered about 0 V, as expected. This is because there are some

transient effects at the beginning. If you would simulate for long enough (> 100 sec) the signal will certainly be centered about 0V.