Analyzing the circuit using EDSpice simulator

This is a Class AB amplifier and a scaled down BJT version of the popular Crescendo. This example demonstrates Small signal AC analysis and transient analysis with default parameters. These values could be changed for experimentation purpose. The steps followed for this simulation exercise is:

1. From the drop down list of the File menu of Project Explorer, select Open Project and select a project. Load the project SPICDEMO.EPB from \JOB directory.

2. We will observe that preprocessing of the circuit takes place. Preprocessing involves analyzing the schematic and checking for the Spice element. It is also used to establish the degree to which the circuit is ready for simulation. The results of preprocessing are displayed in the Info window.

3. First of all, you must ensure that the schematic components, in the project, are recognized as SPICE circuit elements, which are capable of being simulated by EDSpice.

Note: In this project we have placed the components (diodes and transistors) having a Simulation function attached to it. The simulation reference serves as a link between a part in the library to the corresponding model in the model library. This link makes the simulator acknowledge the component as an EDSpice element. If the captured part has a simulation reference then at the time of preprocessing, the model parameters corresponding to that part will get automatically loaded into the project from the Spice model parameter library (*.Sparam). The simulation reference for the loaded part may be viewed from the preprocessing window. You will have to assign the model/instance parameters for the symbols that do not have any simulation reference assigned to them.

4. Click the CLOSE button to close this dialog box.

5. The input stage is a double differential amplifier comprising T1/T2 and T3/T4 with current sources T5 and T6. T7 and T8 are drivers for the output stage. The output stage comprises of super transistors NPN (T11+T13+T15) and PNP (T12+T14+T16).

6. We will first define parameters to the circuit elements. Right click and select the tool Set Parameters/ Models and click on each component and enter values except for those components having simulation references assigned to them.

7. Click on the AC source to pop up the Instance Parameter window in which values are to be defined. Scroll down the window to get the instance parameter Source function. Click on row corresponding to Source Function (last row of this dialog box) to get another window of Source function where you may select the source function and define the function parameters for the selected one. Select “Sin ” from the list and specify the following parameter values.

Frequency 500Hz

Amplitude 1V

8. Click ACCEPT to get the Instance Parameter window.

9. Next select the capacitor C1 which is a basic circuit element and edit the values in the text box as shown below:

10. Repeat the above steps for all basic circuit elements like capacitors and resistors. You may either enter the value in the column or copy the parameters used for another component from the list box. To do this, click on the drop down Copy instance params from that shows all the components of the same category and select any one from the list. The parameters is filled in the column and ACCEPT the values.

11. Next select transistor T1 and you will get a window as shown below

12. Basic circuit elements like Capacitor, Resistor and voltage sources do not have any special model parameters and hence they are not modeled. More complicated circuit elements like transistors, diodes etc are modeled in EDSpice. Here all the transistor models have simulation references assigned to them. Hence it is not required to enter the parameter values here. The type of the model (model code) permits the simulator to accurately interpret the characteristics of the element.

13. If the model parameter value has to be changed, then click on the row showing the model code inorder to define model parameters. This will pops a Model parameter window with all the parameters listed.

14. You may either load the parameters from the library or enter values from the scratch. You may also copy the model parameters entered for another element belonging to the same category. For this, you have to select any of the components from the drop down list Copy parameters from and the values get filled in the corresponding rows. Click on ACCEPT to return to the previous window. If you have changed the values for any parameter, the current project will get effected unless it is not saved to the library by overwriting the existing parameter library. Proceed the above method for all elements.

15. The next step is to set the waveform contents for analysis. The vectors, of those variables, whose values are to be calculated by the simulator, are included in the netlist. First place the markers by selecting the tool Voltage TP from the function tool Testpoints and click on the node of voltage source. The marker gets tagged to the cursor. Next click on the node of T15 that would be the output node for analysis.

16. Click on the Analysis menu to pop up a window. Select Analysis/ Transient Analysis/ Waveform Viewer from the tree view on the left side of the window. You will observe that the two nets corresponding to the marked nodes get filled in the rows (UN39 for input and UN30 for output). After analysis, the outputs of these two nets get displayed on the waveform viewer.

17. These are the preliminary steps to be done before analyzing the circuit. The simulation process is initiated by selecting one of the available analysis, setting up the required parameters, and starting its execution.

18. Two type of analysis may be performed with this project, Transient and Small signal AC analysis.