# Op Amp Circuit Weird Characteristics

• Engineering
• Marcin H
In summary: The ideal OP amp approximation is a simplification of the real world, but it is a good starting point for analysis.
Marcin H

V=IR
KCL/KVL

## The Attempt at a Solution

I have a similair problem to this one in my notes and I know how to solve this circuit, but I am confused on some parts of it. First, at V1 why can we say the voltage there is 0V? Is it because it is connected to the ground (-) of the op amp and we can say that the potential is 0V at that point? Also, why is the op amp drawn like that? Why is the (+) on the bottom go to ground? What does that mean exactly?

And V2 is also equal to 0 but I am not sure why. Is it for the same reason I said above?

Marcin H said:
First, at V1 why can we say the voltage there is 0V?
We just approximate it to zero volts, because in comparison with the level of other voltages in the circuit it must be very much smaller. We know it is not exactly zero volts, but we know it will be very small so for the purpose of easy analysis we can regard it as approximately zero. This is based on the principle of the virtual Earth at the ideal OP-AMP's inverting input, and google will help you with this.

Last edited:
Can you state "the ideal op amp approximation"? This will probably answer your questions. If you don't know it, it is probably in your notes or your textbook.

NascentOxygen said:
We just approximate it to zero volts, because in comparison with the level of other voltages in the circuit it must be very small. We know it is not exactly zero volts, but we know it will be very small so for the purpose of easy analysis we can regard it as approximately zero. This is based on the principle of the virtual Earth at the ideal OP-AMP's inverting input, and google will help you with this.
Hmm ok. I'll do some googling later then.
phyzguy said:
Can you state "the ideal op amp approximation"? This will probably answer your questions. If you don't know it, it is probably in your notes or your textbook.
It is not unfortunately. So are allthe things I mentioned in my posts just givens about ideal op amps? Things we can assume at the start of the problem?

Not really givens but rather the consequences of the properties of an ideal op amp. For example if the gain is very very large then for the output to be in a linear region the difference between + and - input must be very small, virtually zero. For example if the circuit is powered by 5v rails and the gain is 1,000,000 then the input must not differ by more than 5/1,000,000v. Otherwise the output will be limited by the supply rail and hence not operating in a linear mode.

Marcin H

## 1. What are some common weird characteristics of op amp circuits?

Some common weird characteristics of op amp circuits include offset voltage, input bias current, input offset current, slew rate limitation, and input impedance.

## 2. How do offset voltage and input bias current affect op amp circuits?

Offset voltage is a small DC voltage that appears at the output of an op amp when both inputs are grounded. Input bias current is the small current that flows into the input terminals of an op amp. These characteristics can cause errors and distortions in the output signal of an op amp circuit.

## 3. What is the input impedance of an op amp circuit?

The input impedance of an op amp circuit is the resistance that the op amp presents to the input signal. It is typically very high, in the range of millions of ohms, which helps reduce the loading effect on the input signal.

## 4. What is slew rate limitation in op amp circuits?

Slew rate limitation is the maximum rate at which an op amp can change its output voltage. This can cause distortion in the output signal if the input signal changes too quickly for the op amp to keep up.

## 5. How can I minimize the effects of these weird characteristics in an op amp circuit?

To minimize the effects of weird characteristics in an op amp circuit, you can use external components such as resistors and capacitors to compensate for offset voltage and bias current. You can also select an op amp with a higher slew rate and carefully choose the values of resistors and capacitors in the circuit to optimize its performance.

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