Solving difference amplifier with capacitor with equations

[Bjtpower]

Hi,
I would like to learn Difference amplifier and its equation when capacitors are connected in Feedback like below
My intension understand capacitor impact and its equation for learning purpose.

 

[barry]

Do you know how to do analysis of the circuit WITHOUT the capacitors? If so, then the capacitors are just impedances: 1/sC (or, 1/jwC). Sorry, reactances are messier than plain resistors.

If you don't know how to analyze an opamp circuit, then I can just tell you the capacitors act add some low-pass filtering. In your circuit they're pretty small, so they're probably just there for noise reduction.

 

[D.A.(Tony)Stewart]

The differential inputs are unbalanced for impedance and gain.
The inverting input gain is -44 dB with a breakpoint at 0.5MHz due to C7 and around 15 MHz from C8.
The VAC- input (neutral) has less attenuation -17 dB. and a similar breakpoint at 0.5MHz.

You can plot each input separately.


What specs would you like for attenuation, impulse rejection and noise filtering?

 

[danadakk]

All those caps. 4.7 pF, seem to be stray C representations, eg. layout
generated C and package C......? Except for C7

"Normally" one uses LaPlace s plane analysis on this, but the # components
would make the algebra challenging.

Consider using signal flow graph analysis to get to T(s) (transfer Function).

Signal Flow Graph Solver

Regards, Dana.

 

[Bjtpower]

Do you know how to do analysis of the circuit WITHOUT the capacitors? If so, then the capacitors are just impedances: 1/sC (or, 1/jwC). Sorry, reactances are messier than plain resistors.

If you don't know how to analyze an opamp circuit, then I can just tell you the capacitors act add some low-pass filtering. In your circuit they're pretty small, so they're probably just there for noise reduction.

Hi,

I would be happy if you help with me some equations, how they play roles? No matter if they are smaller or higher values.

 

[danadakk]

Basic OpAmp differential analysis :

https://www.ti.com/lit/an/slyt157/slyt157.pdf

One way of doing this is create a diagram where you replace
a series RC or parallel RC with a symbol, say Z1, Z2, .... Then you
write node and loop equations and solve. Then sub back into
your analysis the values for Z1.

A parallel Rc Z1 = (R x 1/sC) / ( R = 1/sC)

Good luck, can be very tedious if a large number of passives involved.

Reason for using signal flow graph analysis with a utility.

Signal Flow Graph for electrical circuits

I am a student and my question is about finding the signal flow graph for a simple circuit. I found the above formula for a \$k\$ node having \$U_k\$ potential. In the book it is said that this is a

electronics.stackexchange.com

https://web.mit.edu/6.101/www/reference/op_amps_everyone.pdf

Are you a student with an assignment ?


Regards, Dana.

 

[albbg]

Here is my analysis. It should be valid as far as the op-amp can be considered (almost) ideal. If the frequency increases and the input capacitance (between inverting and non-inverting pin) starts to play a role this quite simple math loose validity. How much can be high the frequency depends from the used op-amp.