op amps and capacitors help

Thread Starter


Joined Jan 29, 2008

A) Relate the output voltage, V out ( t ), of the amplifier in the circuit above to the input voltage, V in ( t ), which, as the input voltage, we consider given.

Hint: To begin the solution process, first write 6 equations in terms of the unknown voltages and currents v out ( t ) , v R ( t ) , i R ( t ) , v C ( t ) , i C ( t ) , v - ( t ). (Note that in the particular circuit above, the non-inverting input of the op amp is connected directly to ground so that v + ( t ) is zero.)

Combine these 6 equations to show that:

B) In ideal op amps, the gain A approaches infinity. Take the limit as A approaches infinity to show that, with an ideal op amp in the circuit above, the equation you just found simplifies to:

This does not look that hard I am just confused right now. Can someone please help me with this or take me through it please.


Joined Apr 15, 2008
Did you write the equations? You do know the equations for capacitors, resistors, and the open loop opamp, right?

Now assume that the current into the inverting input of the opamp is 0, so Ic = Ir.

Does this do it for you? I'm wary of going further since I may as well do it for you then.