PSPICE - simulation of CMOS astable circuit

In summary, the conversation is about simulating a circuit in OrCAD PSPICE. The circuit includes two CMOS inverters, a resistor, and a capacitor. The resistor and capacitor values were chosen for a specific time constant, and the voltage at Va, Vo, and Vi were of interest to the person asking the question. They set V(2) to 5V to start the circuit, but were not seeing any oscillations in the simulation. The other person suggests running the simulation longer and questions the device model being used. They recommend using an actual part number from the PSPICE library.
  • #1
stn0091
7
0

Homework Statement



I'm trying to simulate the following circuit in OrCAD PSPICE.

attachment.php?attachmentid=56542&stc=1&d=1362875259.png


Homework Equations





The Attempt at a Solution



* 8.20

Vdd 1 0 5V

MP1 3 2 1 1 PMOD
MN1 3 2 0 0 NMOD

MP2 4 3 1 1 PMOD
MN2 4 3 0 0 NMOD

R1 3 2 1000
C1 2 4 1uF

.MODEL NMOD NMOS (VTO=2)
.MODEL PMOD PMOS (VTO=-2.0)

.ic v(2)=5

.tran 0.5us 10ms 0 1u uic

.PROBE
.END

Resistor and capacitor values were chosen for some arbitrary time constant. I just wanted to see the waveforms at Va, Vo and Vi.

V(2) corresponds to the gates of the first CMOS and I set that to 5V to "start" the circuit. However, I'm not seeing any oscillations when I simulate the circuit.
 

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  • #2
Give us the voltages at input and output of both inverters. Also your Vcc and Vdd.
 
  • #3
The output plots? Alright. I'm assuming you mean the capacitor voltage when you say Vcc.

V(1) is VDD = 5 V, V(2) is Vi and Vcc (same node), V(3) is the output of the first inverter, V(4) is the output of the second inverter.

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  • #4
Run your simulation longer! It's clear that V3 and V4 are changing.
 
  • #5
How can Vi and Va both be +4.4V?? Are you sure you're running an inverter? What's the part number? Oh, I bet it's your model.

Vi and Va look like the same voltage.

R looks like no current thru it.

I seriously question you model of the device. Pick an actual part number from the list of devices in your PSPICE library. Example: 74HC04.
 

Related to PSPICE - simulation of CMOS astable circuit

1. What is PSPICE and how does it work?

PSPICE is a computer software program used for simulating electronic circuits. It uses mathematical models to predict the behavior of electronic components and circuits. It allows users to create and test circuits virtually, saving time and resources compared to building and testing physical circuits.

2. What is a CMOS astable circuit?

A CMOS astable circuit is a type of electronic oscillator that generates a continuous square wave output. It is made up of two complementary metal-oxide-semiconductor (CMOS) digital logic gates, typically a NOT gate and a NAND gate. It does not require any external input to sustain its oscillation, making it a self-sustaining circuit.

3. How do you simulate a CMOS astable circuit in PSPICE?

To simulate a CMOS astable circuit in PSPICE, you will need to create a schematic diagram of the circuit using the available components and their corresponding models. You can then use the simulation options in PSPICE to run the simulation and analyze the results. It is important to ensure that all components and connections are accurately represented in the schematic for an accurate simulation.

4. What are the advantages of using PSPICE for simulating CMOS astable circuits?

There are several advantages to using PSPICE for simulating CMOS astable circuits. Firstly, it allows for quick and efficient testing of circuit designs without the need for physical components. This saves time and resources compared to building and testing physical circuits. Additionally, PSPICE can provide detailed analysis and visualization of circuit behavior, making it easier to troubleshoot and improve circuit designs.

5. Are there any limitations to using PSPICE for CMOS astable circuit simulation?

While PSPICE is a powerful tool for simulating electronic circuits, it does have some limitations. It relies on accurate modeling of components, so if a component's model is not accurate, the simulation results may not be reliable. Additionally, PSPICE cannot account for external factors such as temperature and noise, which may affect the behavior of a physical circuit. As such, it is important to validate PSPICE simulations with physical testing when possible.

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