Examples of AC Simulation

This section gives detailed setups to perform an AC simulation for:

• Analyzing a Power Amplifier
• Calculating Linear Noise
• Calculating Port Thermal Noise

The examples show how to simulate a power amplifier and display the amplifier output, how to calculate linear noise, and how to calculate port thermal noise.

Analyzing a Power Amplifier

The first figure below illustrates the setup for an AC simulation of a power amplifier.

Note This design, AC1.dsn, is in the Examples directory under Tutorial/SimModels_prj. The results are in AC1.dds.

In this example, no variables are swept. The output load resistor has been labeled Vout, to represent the AC output voltage.

To perform a basic AC simulation:

1. From the Sources-Freq Domain palette, select V_DC. Place this component on the schematic and edit the component so that Vdc = 5 V.
2. From the Sources-Freq Domain palette, select V_1Tone. Place this component on the schematic and edit the component so that Vac = 1V. You can optionally use a V_AC component.
3. From the Simulation-AC palette, select AC. Place this simulation component on the schematic and edit it to select the Frequency tab. Ensure that Start/Stop is selected, then set the following values:
   • Sweep Type = Linear
   • Start = 1 kHz
   • Stop = 100 MHz
   • Step = 10 MHz
     
     

     Example setup for a basic AC simulation

4. Click OK to accept changes and close the dialog box.
5. Simulate. When the simulation is finished, a Data Display window opens. Plot Vout. The following illustration shows a plot of AC output voltage (Vout), in dB, versus frequency:
   

Calculating Linear Noise

You can simulate linear noise by setting the appropriate options via the Noise tab of the AC Simulation component.

To perform a linear noise analysis:

1. In the circuit to be simulated, ensure that you have named the nodes at which noise data are to be reported (for example, Input and Output).
2. Edit the AC Simulation component and select Noise, then select Calculate Noise.
3. In the Edit field, enter the names of nodes at which you want noise data to be reported.
4. Use the Mode popup menu to obtain the noise contributed by individual noise sources and sort these contributions by name or value. To obtain just the total noise value at the output only, set Mode to Off .
5. Either accept the default for Bandwidth , or edit it as required. The default is often sufficient.
6. Enter a value in the Dynamic range to display field, in dB. The default is often sufficient if Mode is set to On .
7. Click OK to accept changes and close the dialog box.
8. Launch the simulation. To display and plot resulting data, see Data Display.

Calculating Port Thermal Noise

To simulate port thermal noise:

Proceed as in Calculating Linear Noise, with the following additional steps prior to launching the simulation:

• Ensure that you have placed input and output ports in the circuit.
• Select the Include port noise option.

For information on how noise is calculated, see Linear Noise Simulation Description.