# Pspice: derivative function in probe

• ram0001
In summary, the speaker is asking for help with obtaining parameters for noise margin in MOSFET inverters using Pspice. They have tried using the probe function 'd()' at 'V(2)' but it is not working. They are using the 9.1 Student Demo version and have referred to the user manual. They would appreciate any assistance.

#### ram0001

Hi Guys,
I am stuck at a point and needs help.
The thing is I am doing MOSFET inverters using Pspice.
I am getting its VTC (voltage characteristic Curve) But I don't know how to get derivative of this curve in order to obtain some parameters required for Noise margin.
Here is the file:

.model NMOD NMOS (LEVEL=1, VTO=0.6 GAMMA=0 LAMBDA=0 KP=60U)
.model PMOD PMOS (LEVEL=1, VTO=-0.8 GAMMA=0 LAMBDA=0 KP=20U)

***********
* CIRCUIT *
***********

VDD 3 0 DC 3
VGS 1 0 DC 3
M1 2 1 0 0 NMOD L=0.8U W=2U
M2 2 1 3 3 PMOD L=0.8U W=10U
.OP
.DC LIN VGS 0 3 0.1
.PLOT DC V(2)
.PROBE
.END

I have 9.1 Student ,Demo version. I referred to user manual... and it says I used use probe function 'd()' to get derivative but that's not working. It says invalid expressions.
I am taking 'd()' at 'V(2)'.
I would really appreciate if some one can help me out.
Thanks,

I got it.
thanks

Hi there,

Thank you for reaching out for help with your Pspice project. It sounds like you are trying to obtain the derivative of your VTC curve in order to calculate the noise margin for your MOSFET inverter.

To get the derivative of a curve in Pspice, you can use the 'd()' function in the Probe window. However, it looks like you may be using it incorrectly. The 'd()' function takes in two arguments - the variable you want to take the derivative of and the variable you want to differentiate with respect to.

In your case, you want to take the derivative of the voltage at node 2 (V(2)) with respect to the gate-source voltage (VGS). Therefore, the correct syntax for the 'd()' function would be 'd(V(2),VGS)'. This should give you the derivative of your VTC curve at each point.

I hope this helps you with your project. If you continue to have trouble, please don't hesitate to reach out for further assistance. Best of luck!

## What is Pspice and how does it work?

Pspice is a computer software program used for simulating and analyzing electronic circuits. It uses mathematical models to simulate the behavior of electrical components and allows users to predict circuit performance.

## What is a derivative function in Pspice?

A derivative function in Pspice is a mathematical function that calculates the rate of change of a signal with respect to time. In other words, it calculates how fast the signal is changing at a specific point in time.

## How can I use the derivative function in Pspice?

The derivative function in Pspice can be used to analyze the transient response of a circuit. It can help identify the peak values, rise and fall times, and other important parameters of a signal.

## What are the benefits of using the derivative function in Pspice?

The derivative function in Pspice can provide valuable information about the behavior of a circuit, such as stability, bandwidth, and distortion. It can also help identify potential issues and improve the overall design of the circuit.

## Are there any limitations to using the derivative function in Pspice?

While the derivative function in Pspice can provide useful insights, it is important to note that it is based on mathematical models and may not always accurately reflect the behavior of a real circuit. It is always recommended to validate the results with physical measurements.