# Help with LTSpice Op-Amp Modelling

#### noobeestudent

##### Junior Member level 3
Hello guys, I'm in need of urgent help.

For my assignment, I was required to model an Op-Amp using a Behavioral Voltage Source using LTSpice.
The input resistance of the Op-Amp is 70MΩ and output resistance is 30Ω. The open loop voltage gain is 80k and the supply voltages is +-15V. I'm having problems with the behavioral voltage source. This is what I got so far.
Can anyone help me? Thank you in advance.

#### FvM

##### Super Moderator
Staff member
E.g. :

By the way, did you study the behavioral OP models shipped with LTspice, ipamp, opamp2 and universalopamp2?

#### noobeestudent

##### Junior Member level 3
Thanks for the help.
By the way, did you study the behavioral OP models shipped with LTspice, ipamp, opamp2 and universalopamp2?
I did learn to use those but I was asked to use the behavioral voltage to model the op-amp in this assignment

#### noobeestudent

##### Junior Member level 3
I need help again. I am supposed to use the above op-amp model to create a non-inverting amplifier with a gain of 40.

This is what I have now. But the syntax for the behavioural voltage source does not work. What does it need to be?

Edit: Ive figured it out, changed it to "V=limit((V(Vi)-V(Vx))*80k,-15,15)" and it worked.

Last edited:

#### FvM

##### Super Moderator
Staff member

Wrong node voltage syntax, write either V(Vi,Vx) or (V(Vi)-V(Vx)).

#### noobeestudent

##### Junior Member level 3
Using this op-amp model , i have to integrate these extra conditions
• Unity gain bandwidth = 10MHz
• Frequency response roll-off rate = 20 dB/dec

Does anyone knows how to implement those into the op amp model?
Any help is very much appreciated. Thanks a lot.