OPAMP step response

[Sambhav_1]

Hi All,

In 12.3, when the step is applied to the feedback circuit 12.2(b), why the vout starts from Hight voltage?

Also,

When our minimum supply is zero and both v- and V+ are 0 then will the 12.2b circuit should be considered in feedback?

because acc. to what we have studied, When the opamp output is at max or min supply then virtual ground concept is not applicable.

Thankyou

 

[FvM]

The quote from Razavi, Chap. 12 Introduction to Switched-Capacitor Circuits abstracts from supply voltage limits, finite gain or bandwidth. Sufficient supply voltage and gain is simply presumed. Power supply effects are discussed in chapter 9 Operational Amplifiers.

In 12.3, when the step is applied to the feedback circuit 12.2(b), why the vout starts from Hight voltage?

Don't jump into conclusions. The drawing shows two traces without absolute voltage reference. Just assume that Vout starts at zero.

Notice that the Vin and Vout waveform are idealized and won't be observed exactly so with real OPs. It's the first step to introduce switched capacitor circuits, no discussion of exact OP behavior.

 

[KlausST]

Hi,

It has been answered in your precious post: https://www.edaboard.com/threads/finding-the-response-of-the-opamp.400535/post-1724739

Again:
A step response is no suitable test signal for an OPAMP circuit with capacitor as input.
An OPAMP can not supply an infinite high ouput current.

Thus the cacluations with C2 and Rf are useless.

When our minimum supply is zero and both v- and V+ are 0 then

Then the OPAMP simply can´t work at all. What happens then is determined be the OPAMP´s inner circuit.
In worst case the OPAMP may get killed.



Klaus