Question Details

The steady state output (Vout), of the circuit shown below, will

Options

A

saturate to  -VEE

B

saturate to +VDD

C

become equal to -0.1 V

D

become equal to 0.1 V

Show Answer

Correct Answer :

Option A

saturate to  -VEE

Solution :

The correct option is saturate to -VEE.

Let's analyze the given circuit diagram step-by-step:

1. Identify the Circuit Configuration:
The circuit represents an op-amp integrator. The non-inverting terminal (+) is connected to ground through a resistor R2, and a feedback capacitor C1 is connected between the inverting input terminal (-) and the output terminal Vout. The input source of 0.1 V is applied through resistor R1 to the inverting input terminal.

2. Analyze the Terminal Voltages:
Since no current enters the non-inverting input terminal of an ideal operational amplifier, the voltage at the non-inverting terminal is:

V+=0 V

Assuming the op-amp is operating in its linear region initially, we can apply the virtual short concept:

V-=V+=0 V

3. Determine the Current and Output Voltage:
The current entering the node at the inverting terminal through resistor R1 is:

Iin=0.1-V-R1=0.1R1

Because the input impedance of the op-amp is infinite, this current cannot enter the inverting terminal and must flow entirely through the feedback capacitor C1 towards the output:

Ic=Iin=0.1R1

The current through the capacitor is related to the voltage across it by:

Ic=C1d(V--Vout)dt=-C1dVoutdt

Equating the two expressions for current:

-C1dVoutdt=0.1R1

dVoutdt=-0.1R1C1

Integrating both sides with respect to time t:

Vout(t)=Vout(0)-0.1R1C1t

4. Analyze the Steady State Behavior:
The equation shows that the output voltage Vout decreases linearly over time because the input voltage is a constant positive DC value (0.1 V). As time t approaches infinity (t), the output voltage continues to decrease until it hits the negative power supply limit of the op-amp. Since the negative supply voltage rail is -VEE, the output voltage cannot fall below this limit. Therefore, in the steady state, the output will saturate to -VEE.

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