What are the limitations of using real transistors to build an ideal op-amp?

[ZeroFunGame]

TL;DR Summary

What are the transistor characteristics and limitations from building an ideal op-amp?

What are the transistor characteristics and limitations from building an ideal op-amp?

 

[berkeman]

Summary:: What are the transistor characteristics and limitations from building an ideal op-amp?

What are the transistor characteristics and limitations from building an ideal op-amp?

Is this for schoolwork/self-study? Or another thought experiment like your recent CMOS current thread?

In either case, you need to show more effort before we can try to help you with questions like this. What reading have you been doing about this question? Can you post links to that reading, and ask *specific* questions about the parts you are not able to understand? Thanks.

 

[ZeroFunGame]

All my questions are thought experiments for personal understanding. As one goes to higher levels of abstraction, sometimes the connection to the individual components and fundamentals are lost on me. On the current CMOS thread, I'm going through the tutorials to learn to read the circuit in order to answer your question regarding what happens when Ion is close to the leakage (thanks for the great link btw, https://www.tutorialspoint.com/vlsi_design).

This will take some time to go through, but I'll have an answer once I feel comfortable to address your question. On this particular question, it's taking some fundamental circuit, and trying to understand how the individual transistor physics play into IC performance. Most readings I've done discusses the opamp as a unit, without diving into the transistor level. Any recommended reading on how to understand the inner workings would also be much appreciated.

 

[berkeman]

Any recommended reading on how to understand the inner workings would also be much appreciated.

You can start with the introductory article on opamps at Wikipedia:

https://en.wikipedia.org/wiki/Operational_amplifier

The LM741 is a classic basic bipolar opamp, and it's good to understand it in detail before going on to more sophisticated FET-based opamps, IMO:

http://www.physics.utah.edu/~jui/3620-6620/y2009m02d03/741.html

http://pallen.ece.gatech.edu/Academic/ECE_6412/Spring_2003/L210-DCAnalysisof741-2UP.pdf

http://pallen.ece.gatech.edu/Academic/ECE_6412/Spring_2003/L220-ACAnalysisof741-2UP.pdf

 

[eq1]

I don't think knowledge of the inner workings are necessary here. Real transistor characteristics are the logical inverse of the characteristics of an ideal opamp.

An ideal opamp has: 1) infinite gain, 2) infinite bandwidth, 3) infinite input impedance, 4) zero output impedance, 5) no offsets

A real transistor has: 1) finite gain, 2) finite bandwidth, 3) finite input impedance, 4) nonzero output impedance, 5) never perfectly matches other transistors

It should be clear why one cannot construct an ideal opamp from real transistors.