Operational Amplifier · Analog Circuits · GATE ECE
Marks 1
An ideal OPAMP circuit with a sinusoidal input is shown in the figure. The 3 dB frequency is the frequency at which the magnitude of the voltage gain decreases by 3 dB from the maximum value. Which of the options is/are correct?



The number of times the LED glows is ______.

The load current I0 through RL is

The value of $${{{V_{OB}}} \over {{V_{OA}}}}$$ is _____

















Marks 2
The opamps in the circuit shown are ideal, but have saturation voltages of ±10 V.

Assume that the initial inductor current is 0 A. The input voltage (Vi) is a triangular signal with peak voltages of ±2 V and time period of 8 μs. Which one of the following statements is true?
In the circuit below, the opamp is ideal.

If the circuit is to show sustained oscillations, the respective values of $R_1$ and the corresponding frequency of oscillation are ____.
The $$\mathrm{{{{V_{OUT}}} \over {{V_{IN}}}}}$$ of the circuit shown below is
A sample and hold circuit is implemented using a resistive switch and a capacitor with a time constant of 1 $$\mu$$s. The time for the sampling switch to stay closed to charge a capacitor adequately to a full scale voltage of 1 V with 12-bit accuracy is ___________ $$\mu$$s (rounded off to two decimal places).
A circuit with an ideal OPAMP is shown. The Bode plot for the magnitude (in dB) of the gain transfer function (Av(j$$\omega$$) = Vout(j$$\omega$$)/Vin(j$$\omega$$)) of the circuit is also provided (here, $$\omega$$ is the angular frequency in rad/s). The values of R and C are __________.


The output voltage Vout (in volts) is _____.

The output voltage (in millivolts) is ________.

The time t = t1 (in seconds) at which Vo changes state is _____.













and V is the voltage across the diode (taken as positive for forward bias). For an input voltage $${V_i}\,\, = \,\, - 1V,$$ the output voltage V0 is



A triangular wave which goes from -12V to 12V is applied to the inverting input of the OP-AMP. Assume that the output of the OP-AMP swings from +15V to -15V. The voltage at the non-inverting input switches between.


If $${V_i} = {V_1}\,\,\sin \left( {\omega \tau + \phi } \right),$$ then the minimum and maximum values of $$\phi $$ (in radians) are respectively
The transfer function $${V_o}\left( s \right)/{V_i}\left( s \right)$$ is



In the figure shown above, the OP-AMP is supplied with $$ \pm $$ 15V.



















Marks 5

(a) Obtain an expression for V0 in terms of Vs, R, and the reverse saturation current Is of the transiostor.
(b) If R = 1$$\Omega $$, Is = 1pA and the thermal voltage VT = 25mV, then what is the value of the output voltage V0 for an input voltage Vs = 1V?
(c) Suppose that the transistor in the feedback path is replaced by a p-n junction diode with a reverse saturation current of Is. The p-side of the diode is connected to node A and the n-side to node B. Then what is the expression for V0 in terms Vs, R and Is ?

The characteristics of the diode are given by the relation I = Is $$\left[ {{e^{{{qV} \over {KT}}}} - 1} \right],$$
Where V is the forward voltage across the diode
(a)Express V0 as a function of Vi assuming Vi> 0.
(b)If R = 100K$$\Omega $$ , Is = 1$$\mu $$A and $${{KT} \over q}\,\, = \,\,25mV$$



when $${R_a}\, = \,{R_b}\, = \,{R_c}\,{R_d}\,$$ ohms.
when $${R_a}\, = \,{R_b}\, = {R_c}\, = 100$$ ohms and $${R_{d\,}}\, = \,120$$ ohms.
