3.1 Schematic capture and simulation with Xscheme and NGSpice

This section demonstrates the usage of Xschem and NGSpice opensource tools.

1. Run Xscheme

• Open a Ubuntu 22.04 terminal and run the following commands (assuming that you already installed the tools):

$ source $HOME/unic-cass/env.sh
$ xschem

• The window pops up successfully as follows.

Source

• Xscheme Tutorial.

Schematic capture - Create instances

Draw a RLC circuit in Xscheme:

• Create a new instance by selecting Tools » Insert Symbol (Shift + i)

• Create a resistor by xscheme_library/devices » res.sym » OK » Click on the schematic windows

• Create an inductor (ind.sym)

• Create a capacitor (capa.sym)

• Create an arithmetic source (vsource_arith.sym)

3. Schematic capture - Change the paramters

Change the capacitance to 50nF and the inductance to 10mH

• Click on the capacitor and press q; change the value of C1 to 50nF then press OK

• Click on the inductor and press q; change the value of L1 to 10mH then press OK

Set the voltage source

• Click on the voltage source and press q; change the value of E1 to " '3*cos(time*time*time*1e11)' " then press OK (note the single and doulbe quotes)

Final view

4. Schematic capture - Wiring

To connect the wire, press w then use the left-mouse click to create multiple wire segments

• 1. Put the cursor to the red point, then press w
• 1. Move the cursor here and left-mouse click, then press w again
• 1. Move the cursor here and left-mouse click, then press w again
• 1. Move the cursor here and left-mouse click on the red point to finish wiring

• 1. Put the cursor to the red point, then press w
• 1. Move the cursor to the red point, then left-mouse click

5. Schematic capture - Create lab pins

To view the waveform and name the net, insert a lab_pin symbol, and change its name

• Create a lab_pin by xscheme_library/devices » lab_pin.sym » OK » Click on the net for the lab_pin

• Select the lab_pin symbol and then press q to rename it into A

• Similary create the lab pin B, C, and 0 (ground)

Note

• You can copy the lab pin A by selecting it and press c, then move it to the correct net

• Rotate can be done by pressing Shift+r

6. Schematic capture - Set up a simulation

To set up the simulation, insert a code symbol and enter the simulation commands

• Create a code symbol by xscheme_library/devices » code.sym » OK » Click on the schematic to place it

• Select the code symbol and press q; change the name into STIMULI and value to:

".tran 10n 2000u uic
.save all"

Note

• The double quote is required

7. Simulate the design using NGSpice

• Xscheme uses NGSpice as the default simulator

• To create the design’s netlist, click Netlist button to generate the spice file

• To view the netlist, select Simulation » Edit netlist

• To simulate, click Simulate button to run the simulation

8. Plot the waveform in NGSpice

• Plot the waveform in NGSpice by enter plot a b c in NGSpice terminal