Transfer functions in op amps

[edosqclbe699]

I have a question regarding finding the transfer functions when dealing with op amps. I do not understand the steps towards going from a general op amp circuit towards getting an the transfer function where you can draw the bode plots for magnitude and phase. Could anyone give me a general step by step tutorial for finding this function or give me a website where they go in depth with these types of problems.

 

[rbj]

first you need to confirm that the op-amp is configured to have negative feedback (that they didn't wire it up backwards), so it's a linear circuit.

then, define the current going into the "+" and "-" terminals is zero (because of the extremely high input impedance) and define that the voltage difference between the "+" and "-" terminals is zero (because of the extremely high gain of the op-amp).

then you apply either the Loop-Current method or Node-Voltage method of circuit analysis, along with the known volt-amp characteristics of every other component in the circuit. this can also be done with the frequency-domain volt-amp characteristics, which is what you want to do if you are seeking frequency-domain behavior (which is what the transfer function is) instead of time-domain behavior (which is what the impulse response or step response are).

 

[piercas]

Sure, I'd be happy to help you understand the process for finding transfer functions in op amps. First, it's important to understand that transfer functions describe the relationship between the input and output signals of a system. In the case of op amps, the transfer function is used to determine how the input voltage is amplified or attenuated to produce the output voltage.

To find the transfer function for an op amp circuit, you will need to follow these steps:

1. Identify the input and output signals of the op amp circuit. This will help you determine the appropriate transfer function to use.

2. Draw a circuit diagram of the op amp circuit and label all components, including resistors, capacitors, and the op amp itself.

3. Apply Kirchhoff's laws to the circuit to determine the input-output relationship. This will involve using Ohm's law and the op amp's ideal characteristics, such as infinite input impedance and zero output impedance.

4. Use algebraic manipulation to rearrange the equation in terms of the output voltage over the input voltage. This will give you the transfer function in a general form.

5. To plot the bode plots for magnitude and phase, you will need to convert the transfer function to its frequency domain representation using Laplace transforms. This will involve replacing s (the Laplace variable) with jω (where ω is the angular frequency) and simplifying the equation.

6. Once you have the frequency domain transfer function, you can plot the bode plots by varying the frequency and calculating the magnitude and phase using the transfer function.

There are many online resources and tutorials available that can help you better understand the process of finding transfer functions in op amps. Some recommended websites include All About Circuits and Electronics Tutorials. Additionally, many textbooks on circuit analysis and op amps also provide detailed explanations and examples of finding transfer functions. I hope this helps you understand the process better.