CMOS OPAMP Design Using LTspice

Hello Dear Reader,

Here in this post, I will give an idea about how CMOS OPAMP designing using 180nm technology node and using LTspice. from that opamp I have design switched capacitor integrator.

Design Specifications:

Here Design specification may be changed according to the application here my target is to design an active lowpass filter so I have chosen an opamp integrator so in the below I have explained how to design an opamp as well as an integrator in a 180nm technology node in LTspice. So let's start design

First, we need a technology parameter file so that the file we can insert in the LTspice, in my example it is 180nm so mostly it is available from the http://ptm.asu.edu/latest.html and you make one text file using notepad or whatever is fit on your own. Then go to the LTspice and new schematic and then you see .op on the right most upper side click on it and give your text file path after .include as shown in the below images.

Now first of all OPAMP has its own design equation which is given here So I have a design opamp follow by this equation.

I have design two stages unbuffered gate driven operational transconductance amplifier where input is applied from the conventional gate terminal of NMOS transistors M1 and M2. Along with M1 & M2, M3 and M4 acting as current mirror load form the first stage of the operational amplifier. M6 and M7 represent the second gain stage of the amplifier. M5 and M8 comprise biasing circuit and Cc represent the compensating capacitance.

OPAMP Design

Designed OPAMP is compensated so it attenuate higher frequency as shown below,

OPAMP with Compensated Capacitor

Design each and every MOSFET aspect ratio(W/L) from design equation such as M1 and M2 is differential pair so they contribution is GB(gain bandwidth) product. M3 and M4 design from Maximum ICMR (Input common-mode range). M5 design from Minumum ICMR and Slew rate specification. M6 and M7 design from maximum and minimum output voltage swing respectively.

Open-loop Gain

First Pole Location

Gain Bandwidth Product

Design of OPAMP Integrator

Transient Analysis for 1KHz sinusoidal

AC Analysis

Thanks for reading and for those who need any design file for references just comment your email id.