Parametric Sweep—Inverter Switching Speed

When designing digital circuits we are concerned with how different circuit elements affect the operation of the circuit. In this section we will look at switching speed. First, we will look at a basic BJT inverter and observe its operation. Wire the circuit below  

We would like to run a Transient Analysis because we are looking at waveforms versus time. Select PS pice and then New Simulation Profile from the Capture menus, enter a name for the profile, and then click the Create button. By default, the 77/716 DO/IWln (TTHflSlGfTt) AlWtYSlS type is selected. Fill in the parameters as shown in the Time Domain dialog box below  

Click the OK button when you have made the changes to return to the schematic. The input to the inverter will be a short 1 ps pulse. The attributes of the pulsed voltage source are Period = 50u, rise time = In, fall time = In, Pulse width = lu, initial.voltage = 0, Pulsed voltage = 5, delay.time = lu. Double-click the LEFT mouse button on the pulsed voltage source graphic to obtain the spreadsheet for the source  

Fill in the specified parameters and then type CTRL-F4 to close the spreadsheet and return to the schematic. 

We see that the pulse width is 1 pis and the period is 50 pis long to let the capacitor come into steady state after the pulse. Note that we are simulating the circuit for only one period. We could have used the PWL source, but the pulsed voltage source is easier to set up. Run the simulation and then run Probe. We will first look at the input to see if the pulse is correct Add the trace V (VIN)  

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