# How to Calculate the Complex Op Amp in Circuit Diagram

• umair1998
In summary, OP Amps are used in circuit diagrams to reduce noise and amplifying photodiodes. Resistors and capacitors are important in reducing noise. The required speed (i.e. bandwidth) to make a good signal is dependent on the application.

#### umair1998

TL;DR Summary: How to calculate the operational amplifiers in the circuit diagram

Hello Everyone,
I am trying to learn the circuit diagram of one of a device in which I will be doing modifications as a part of my Masters's Research to make it performance better. My background is in Mechanical Engineering and I am looking for a consultation about how to solve this kind of complex Op Amp circuit.

Secondly I want to know what will be the effect of resistors and capacitors on output signals if I increase or decrease the resistor or capacitor values? In short I want to know function of resistors and capacitors in Op Amp and electronics pcb circuits.

You help will be appreciated Thanks

Welcome to PF.

Both those circuits are differential amplifiers, but they are drawn to make it difficult to recognise, and the circuits have asymmetric gain, 12/3 ≠ 3/2.

Where do those circuits come from?
Who put the values on the components?

Thread reopened for now (after moving it to the schoolwork forums).

umair1998 said:
I am looking for a consultation about how to solve this kind of complex Op Amp circuit.

Secondly I want to know what will be the effect of resistors and capacitors on output signals if I increase or decrease the resistor or capacitor values? In short I want to know function of resistors and capacitors in Op Amp and electronics pcb circuits.
This seems like a strange assignment or project for you. You have no circuit design background, but are being asked to understand and optimize these opamp circuits? They are pretty simple, but as Baluncore says, they are drawn awkardly.

Can you say more on what your background is so far in circuit analysis and design? And please explain more about how you were assigned the EE part of this project if you have no EE background yet? Thank you.

berkeman said:
Thread reopened for now (after moving it to the schoolwork forums).This seems like a strange assignment or project for you. You have no circuit design background, but are being asked to understand and optimize these opamp circuits? They are pretty simple, but as Baluncore says, they are drawn awkardly.

Can you say more on what your background is so far in circuit analysis and design? And please explain more about how you were assigned the EE part of this project if you have no EE background yet? Thank you.
Hi Berkeman,
My bachelor's is in mechanical engineering and for my master's, I came abroad, my supervisor's lab is working on mechatronics projects due to this current project modification is in progress, and the professor involves me in it, Professor right now giving me time to learn about electronics and LabVIEW, actually, AFM is a device used to measure the height of mems and other nanodevices, the issue is that microprocessor sometimes doesn't work and when it is working response delay is a lot, so my professor wants to replace the microprocessor of that driver unit with LabVIEW code, almost all code is already built but I want to know the functions of the components on op amp so that I could modify them to reduce noise and get a response faster.

Baluncore said:
Welcome to PF.

Both those circuits are differential amplifiers, but they are drawn to make it difficult to recognise, and the circuits have asymmetric gain, 12/3 ≠ 3/2.

Where do those circuits come from?
Who put the values on the components?
Which of the component help to reduce the noise of the signal? In QPD (Quadrant Photodiode) a lot of complex op-amp are used with resistors and capacitors, QPD purpose is to give us the out put of height/distance by reflecting the laser light back, so how I will make the signal better which shouldn't have noise and if I want the gain larger which component value should I change?

If you are amplifying a photodiode, why is it not shown?
What is the required speed (i.e. bandwidth) to make a good signal?

Graduate work requires research and independent learning. This would be a good problem to start with. OTOH, if you ask a very specific question, I'm sure you'll get an answer from us, but I'm not sure it will actually help you much in the long run.

Honestly, there are too many introductory op-amp web pages to choose one to refer you to, but here are a couple:
https://www.electronics-tutorials.ws/opamp/opamp_8.html
https://www.ti.com/lit/an/sboa092b/sboa092b.pdf

Reducing noise in amplifier circuits is much more difficult than this basic function question. A good place to start would be Sergio Franco's Op-Amp book. It is both good (accurate and appropriate) and easy to read and use.

hutchphd and BvU
umair1998 said:
so how I will make the signal better which shouldn't have noise
Do a search on synchronous modulation/demodulation.

## 1. What is a complex op amp?

A complex op amp is a type of operational amplifier that has both real and imaginary components, meaning it can handle both AC and DC signals. It is commonly used in circuits that require amplification and filtering of complex signals.

## 2. How do I calculate the gain of a complex op amp circuit?

To calculate the gain of a complex op amp circuit, you will need to use the complex gain equation: A = (Zf/Zi) * (1 + Zf/Zg), where Zf is the feedback impedance, Zi is the input impedance, and Zg is the gain impedance. You will also need to take into account the phase shift of the circuit.

## 3. What is the difference between a complex op amp and a standard op amp?

The main difference between a complex op amp and a standard op amp is that a complex op amp can handle both real and imaginary components, while a standard op amp can only handle real components. This means that a complex op amp is better suited for circuits that involve complex signals.

## 4. How do I determine the stability of a complex op amp circuit?

To determine the stability of a complex op amp circuit, you will need to analyze the phase margin and gain margin. Phase margin is the difference between the phase of the feedback signal and the phase of the input signal when the gain is equal to 1. Gain margin is the difference between the gain of the feedback signal and the gain of the input signal when the phase is equal to 180 degrees. A stable circuit will have a positive phase margin and gain margin.

## 5. Can I use a standard op amp in place of a complex op amp?

In most cases, a standard op amp cannot be used in place of a complex op amp. This is because a standard op amp cannot handle imaginary components, which are necessary for amplifying and filtering complex signals. It is important to use the appropriate type of op amp for the specific circuit you are working on.

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