simulate 741 op amp is spice

[mohadese.nozari]

Hi
yes I want to simiulate the internal circuit of 741 op amp. but I don't know which specifications for transistors shoulde be used?
I use some kinde of transistor which is in pspice simulator, but the bias point of op amp doesn't work properly.for example current mirrror dosen't mirror current properly!!

 

[FvM]

A typical 741 SPICE example uses these models

.model NP NPN(BF=125 Cje=.5p Cjc=.5p Rb=500)
.model PN LPNP(BF=25 Cje=.3p Cjc=1.5p Rb=250)

 

[sky_123]

I take it you don't want the SPICE model of a 741, which you could glean from any simulator (e.g. Multisim allows you to view the
SPICE model of the 741 which is part of it's library). I take it you want a SPICE model of a transistor, so you can build a 741
yourself, transistor-by-transistor, in the simulator?

If so, you're extremely unlikely to find any standard transistor (e.g. 2N2222 or whatever) with the same parameters. So, you'd have
to make your own model of a transistor. But where to find the parameters? I think it may be almost impossible, unless you can
reverse engineer the parameters. They probably didn't even use SPICE parameters to design the 741, since it was available before SPICE.
Maybe it was designed by 'gut instinct' about transistor sizing - who knows ; ) I'd be interested to know more though.

EDIT - I didn't realise the model already contained the transistor information! Sorry : )
EDIT2 - I just checked Multisim, and the transistors in the model are slightly different, but maybe it doesn't make much difference to the
overall opamp model.

 

[FvM]

I didn't realise the model already contained the transistor information

The standard SPICE uA741 model provided by manufacturers is a hybrid model using a differential transistor input stage and behavioral modelling of most OP functions.

It's a common exercise in linear integrated circuits courses to simulate a transistor level uA741 model. It's not difficult to find suitable transistor parameters, because the device is based on a well known IC process that's described in many text books.