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

In summary, the transistor characteristics and limitations play a fundamental role in the construction of an ideal op-amp. The ideal op-amp has infinite gain, bandwidth, and input impedance, zero output impedance, and no offsets, while a real transistor has finite values for these characteristics. This makes it impossible to build an ideal op-amp using real transistors. Understanding the inner workings of op-amps, particularly the LM741 op-amp, can provide insight into how the real transistor characteristics affect op-amp performance.
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ZeroFunGame
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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?
 
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  • #2
ZeroFunGame said:
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.
 
  • #3
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.
 
  • #4
ZeroFunGame said:
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
 
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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.
 
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Related to What are the limitations of using real transistors to build an ideal op-amp?

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

The main limitations of using real transistors to build an ideal op-amp include non-ideal characteristics such as finite gain, input and output impedance, and bandwidth limitations. These imperfections can result in errors and distortions in the op-amp's output signal.

2. How does the finite gain of real transistors affect the performance of an ideal op-amp?

The finite gain of real transistors limits the amplification capabilities of an ideal op-amp. This means that the output signal will not be an exact replica of the input signal and will have some level of distortion.

3. What is the impact of input and output impedance limitations on an ideal op-amp?

The input and output impedance limitations of real transistors can cause loading effects, which can affect the accuracy and stability of an ideal op-amp. This can result in errors and distortions in the output signal.

4. How do bandwidth limitations of real transistors affect the performance of an ideal op-amp?

The bandwidth limitations of real transistors can result in a limited frequency response for an ideal op-amp. This means that the op-amp will not be able to accurately amplify signals with frequencies outside of its bandwidth, resulting in distortions and errors in the output signal.

5. Can these limitations be overcome in any way?

While it is not possible to completely eliminate the limitations of using real transistors to build an ideal op-amp, they can be minimized through careful design and selection of components, as well as the use of compensation techniques such as feedback and frequency compensation. Additionally, advancements in semiconductor technology have led to the development of op-amps with improved performance and reduced limitations.

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