# GATE Questions & Answers of BJT and MOSFET Amplifiers: Multi-stage, Differential, Feedback, Power and Operational

## What is the Weightage of BJT and MOSFET Amplifiers: Multi-stage, Differential, Feedback, Power and Operational in GATE Exam?

Total 37 Questions have been asked from BJT and MOSFET Amplifiers: Multi-stage, Differential, Feedback, Power and Operational topic of Analog Circuits subject in previous GATE papers. Average marks 1.59.

For the operational amplifier circuit shown, the output saturation voltages are ±15V. The upper and lower threshold voltages for the circuit are, respectively,

A good transconductance amplifier should have

The amplifier circuit shown in the figure is implemented using a compensated operation amplifier (op-amp), and has an open-loop voltage gain, A0=105 V/V and an open-loop cut-off frequency, fc=8 Hz. The voltage gain of the amplifier at 15 kHz, in V/V is_____________.

In the voltage reference circuit shown in the figure, the op-amp is ideal and the transistors Q1, Q2...., Q32 are identical in all respects and have infinitely large values of common-emitter current gain ($\beta$). The collector current (Ic) of the transistors is related to their base-emitter voltage (VBE) by the relation Ic = Is exp (VBE / VT), where Is is the saturation current. Assume that the voltage VP shown in the figure is 0.7 V and the thermal voltage VT = 26 mV.

The output voltage Vout (in volts) is__________

Consider the constant current source shown in the figure below. Let $\beta$ represent the current gain of the transistor.

The load current I0 through RL is

The following signal Vi of peak voltage 8 V is applied to the non-inverting terminal of an ideal opamp. The transistor has $V_{BE}=0.7\;\mathrm V,\;\beta=100,\;V_{LED}=1.5\;\mathrm V,\;V_{CC}=10\;\mathrm V$ and $-V_{CC}=-10\;\mathrm V$ .

The number of times the LED glows is ________

An ideal opamp has voltage sources V1, V3, V5,...., VN-1 connected to the non-inverting input and V2,V4, V6,.....,VN connected to the inverting input as shown in the figure below (+VCC=15 volt,-VCC=-15 volt) The voltages V1, V2, V3, V4, V5, V6,… are 1, − 1/2, 1/3, −1/4, 1/5, −1/6, … volt, respectively. As N approaches infinity, the output voltage (in volt) is ___________

A p-i-n photodiode of responsivity 0.8A/W is connected to the inverting input of an ideal opamp as shown in the figure, +Vcc = 15 V, −Vcc = −15V, Load resistor RL = 10 kΩ. If 10 μW of power is incident on the photodiode, then the value of the photocurrent (in μA) through the load is ________

In the opamp circuit shown, the Zener diodes Z1 and Z2 clamp the output voltage V0 to +5 V or −5 V. The switch S is initially closed and is opened at time t=0.

The time t=t1 (in seconds) at which V0 changes state is ________

An opamp has a finite open loop voltage gain of 100. Its input offset voltage Vios (= +5mV) is modeled as shown in the circuit below. The amplifier is ideal in all other respects. Vinput is 25 mV.

The output voltage (in millivolts) is ________

For the circuit shown in the figure, R1 = R2 = R3 = 1 Ω, L = 1 μH and C = 1 μF. If the input Vin = cos(106t) , then the overall voltage gain (Vout /Vin) of the circuit is __________

In the circuit shown, assume that the opamp is ideal. The bridge output voltage V0 (in mV) for $\delta$ = 0.05 is ____.

In the bistable circuit shown, the ideal opamp has saturation levels of $±$V. The value of R1(in kΩ) that gives a hysteresis width of 500 mV is _________

Assuming that the opamp in the circuit shown below is ideal, the output voltage V0 (in volts)

For the voltage regulator circuit shown, the input voltage (Vin) is 20 ± 20% and the regulated output voltage (Vout) is 10 V. Assume the opamp to be ideal. For a load RL drawing 200 mA, the maximum power dissipation in Q1 (in Watts) is __________.

In the circuit shown using an ideal opamp, the 3-dB cut-off frequency (in Hz) is _____.

In the circuit shown, assume that the opamp is ideal. If the gain (Vo/Vin) is –12, the value of R (in kΩ) is ____.

In the ac equivalent circuit shown in the figure, if iin  is the input current and RF  is very large, the type of feedback is

In the low-pass filter shown in the figure, for a cut-off frequency of 5 kHz , the value of R2 (in kΩ) is _____________.

In the voltage regulator circuit shown in the figure, the op-amp is ideal. The BJT has VBE = 0.7 V and β  = 100, and the zener voltage is 4.7 V. For a regulated output of 9 V, the value of R (in Ω) is _______.

In the circuit shown, the op-amp has finite input impedance, infinite voltage gain and zero input offset voltage. The output voltage VOUT is

The feedback topology in the amplifier circuit ( the base bias circuit is not shown for simplicity) in the figure is

In the differential amplifier shown in the figure, the magnitudes of the common-mode and differential-mode gains are Acm and Ad, respectively. If the resistance RE is increased, then

The desirable characteristics of a transconductance amplifier are

Assuming that the Op-amp in the circuit shown is ideal, Vo is given by

The circuit shown represents

In a voltage-voltage feedback as shown below, which one of the following statements is TRUE if the gain k is increased?

Assuming the OP-AMP to be ideal, the voltage gain of the amplifier shown below is

The transfer characteristic for the precision rectifier circuit shown below is (assume ideal OP-AMP and practical diodes)

In the circuit shown below, the op-amp is ideal, the transistor has VBE = 0.6 V and β = 150. Decide whether the feedback in the circuit is positive or negative and determine the voltage V at the output of the op-amp

Consider the following circuit using an ideal OPAMP. The I-V characteristics of the diode is described by the relation $I={I}_{o}\left({e}^{\frac{v}{{v}_{r}}}-1\right)$ where VT = 25mV, Io = 1$\mu$A and V is the voltage across the diode (taken as positive for forward bias).

For an input voltage Vi = -1V, the output voltage Vo is

The OPAMP circuit shown above represents a

In a transconductance amplifier, it is desirable to have

For the Op-Amp circuit shown in the figure, Vo is

In the Op-Amp circuit shown, assume that the diode current follows the equation I = IS exp(V/VT). For Vi = 2 V, Vo = Vo1 and for Vi = 4 V, Vo = Vo2. The relationship between Vo1 and Vo2 is

Consider the Op-Amp circuit shown in the figure.

The transfer function V0(s)/Vi(s) is

If ${V}_{i}={V}_{1}\mathrm{sin}\left(\omega t\right)$ and $V_o=V_2\sin\left(\omega t+\phi\right)$, then the minimum and maximum values of $\phi$ (in radians) are respectively