# GATE Questions & Answers of Analog Circuits Electronics and Communication Engg

#### Analog Circuits 108 Question(s) | Weightage 13 (Marks)

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 ________

Consider the oscillator circuit shown in the figure. The function of the network (shown in dotted lines) consisting of the 100 kΩ resistor in series with the two diodes connected back-to-back is to:

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 ________

Resistor R1 in the circuit below has been adjusted so that I1 = 1 mA. The bipolar transistors Q1 and Q2 are perfectly matched and have very high current gain, so their base currents are negligible. The supply voltage Vcc is 6 V. The thermal voltage kT/q is 26 mV.

The value of R2 (in Ω) for which I2=100 μA is ________

Which one of the following statements is correct about an ac-coupled common-emitter amplifier operating in the mid-band region?

The switch S in the circuit shown has been closed for a long time. It is opened at time = 0 and remains open after that. Assume that the diode has zero reverse current and zero forward voltage drop.

The steady state magnitude of the capacitor voltage VC (in volts) is ______

The figure shows a half-wave rectifier with a 475 $\mu$F filter capacitor. The load draws a constant current IO=1 A from the rectifier. The figure also shows the input voltage Vi, the output voltage VC and the peak-to-peak voltage ripple u on VC. The input voltage Vi is a triangle-wave with an amplitude of 10 V and a period of 1 ms.

The value of the ripple u (in volts) 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 ________

The diodes D1 and D2 in the figure are ideal and the capacitors are identical. The product RC is very large compared to the time period of the ac voltage. Assuming that the diodes do not breakdown in the reverse bias, the output voltage VO (in volt) at the steady state is __________

Consider the circuit shown in the figure. Assuming VBE1 = VEB2 = 0.7 volt, the value of the dc voltage VC2 (in volt) is __________

In the astable multivibrator circuit shown in the figure, the frequency of oscillation (in kHz) at the output pin 3 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 in the figure, the channel length modulation of all transistors is non-zero $\left(\lambda \ne 0\right)$. Also, all transistors operate in saturation and have negligible body effect. The ac small signal voltage gain (Vo/Vin) of the circuit is

In the circuit shown in the figure, transistor M1 is in saturation and has transconductance gm = 0.01 siemens. Ignoring internal parasitic capacitances and assuming the channel length modulation $\lambda$ to be zero, the small signal input pole frequency (in kHz) is __________

For the circuit with ideal diodes shown in the figure, the shape of the output (Vout) for the given sine wave input (Vin) will be

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

The circuit shown in the figure has an ideal opamp. The oscillation frequency and the condition to sustain the oscillations, respectively, are

In the circuit shown, I1 = 80 mA and I2 = 4 mA. Transistors T1 and T2 are identical. Assume that the thermal voltage VT is 26 mV at 27 oC. At 50 oC, the value of the voltage V12 = V1V2 (in mV) is _____.

If the circuit shown has to function as a clamping circuit, then which one of the following conditions should be satisfied for the sinusoidal signal of period $T$ ?

In the circuit shown, $V_0=V_A$ for switch SW in position $A$ and $V_0=V_B$ for SW in position $B$. Assume that the opamp is ideal. The value of $\frac{{V}_{OB}}{{V}_{OA}}$ 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 _________

The diode in the circuit given below has VON = 0.7 V but is ideal otherwise. The current (in mA) in the 4 kΩ resistor 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 ac equivalent circuit shown, the two BJTs are biased in active region and have identical parameters with β > > 1. The open circuit small signal voltage gain is approximately _____.

In the circuit shown in the figure, the BJT has a current gain ($\beta$) of 50. For an emitter-base voltage VEB = 600 mV, the emitter-collector voltage VEC (in Volts) is _____.

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

In the circuit shown, assume that diodes D1 and D2 are ideal. In the steady state condition, the average voltage Vab (in Volts) across the 0.5μF capacitor 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 circuit shown, both the enhancement mode NMOS transistors have the following characteristics: ${k}_{n}={\mu }_{n}{C}_{ox}\left(W/L\right)=1mA/{V}^{2};{V}_{TN}=1V$. Assume that the channel length modulation parameter $\lambda$ is zero and body is shorted to source. The minimum supply voltage VDD (in volts) needed to ensure that transistor M1 operates in saturation mode of operation is _____.

In the circuit shown, assume that the diodes D1 and D2 are ideal. The average value of voltage Vab (in Volts), across terminals ‘a’ and ‘b’ is ______.

A good current buffer has

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 following circuit employing pass transistor logic, all NMOS transistors are identical with a threshold voltage of 1 V.  Ignoring the body-effect, the output voltages at P, Q and R are,

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

For the amplifier shown in the figure, the BJT parameters are VBE = 0.7 V, β  = 200, and thermal voltage VT  = 25 mV. The voltage gain (vo/vi) of the amplifier 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

In the circuit shown, the PNP transistor has $\left|{V}_{BE}\right|=0.7\mathrm{V and}$ $\mathrm{\beta }=50$ Assume that For V0 to be 5 V, the value of RC (in K$\Omega$) is _______

The figure shows a half-wave rectifier. The diode D is ideal. The average steady-state current (in Amperes) through the diode is approximately ____________.

In the circuit shown, the silicon BJT has β = 50. Assume VBE =0.7 V and VCE(sat)= 0.2 V. Which one of the following statements is correct?

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

If the emitter resistance in a common-emitter voltage amplifier is not bypassed, it will

Two silicon diodes, with a forward voltage drop of 0.7 V, are used in the circuit shown in the figure. The range of input voltage V for which the output voltage Vo=Vi, is

The circuit shown represents

Consider the common-collector amplifier in the figure (bias circuitry ensures that the transistor operates in forward active region, but has been omitted for simplicity). Let IC be the collector current, VBE be the base-emitter voltage and VT be the thermal voltage. Also, gm and ro are the small-signal transconductance and output resistance of the transistor, respectively. Which one of the following conditions ensures a nearly constant small signal voltage gain for a wide range of values of RE?

For the common collector amplifier shown in the figure, the BJT has high β, negligible VCE(sat), and VBE = 0.7 V. The maximum undistorted peak-to-peak output voltage vo (in Volts) is _______.

In the circuit shown below what is the output voltage (Vout) if a silicon transistor Q and an ideal op-amp are used?

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

In a MOSFET operating in the saturation region, the channel length modulation effect causes

In the circuit shown below, the knee current of the ideal Zener diode is 10 mA. To maintain 5 V across RL, the minimum value of RL in $\Omega$ and the minimum power rating of the Zener diode in mW, respectively, are

The small-signal resistance (i.e., dVB/dID) in k $\Omega$ offered by the n-channel MOSFET M shown in the figure below, at a bias point of VB = 2 V is (device data for M: device transconductance parameter kN = ${\mu }_{n}{C}_{ox}^{\text{'}}\left(W/L\right)=40\mu A{V}^{2}$, threshold voltage VTN = 1 V, and neglect body effect and channel length modulation effects)

The ac schematic of an NMOS common-source stage is shown in the figure below, where part of the biasing circuits has been omitted for simplicity. For the n -channel MOSFET M, the transconductance gm = 1 mA/V, and body effect and channel length modulation effect are to be neglected. The lower cutoff frequency in Hz of the circuit is approximately at

In the circuit shown below the op-amps are ideal. Then Vout in Volts is

A voltage 1000 Volts is applied across YZ. Assuming ideal diodes, the voltage measured across WX in Volts, is

In the circuit shown below, the silicon npn transistor Q has a very high value of $\beta$ . The required value of R2 in k$\Omega$ to produce IC = 1 mA is

The current ib through the base of a silicon npn transistor is 1+0.1 cos(10000$\pi t$) mA. At 300 K, the r$\pi$ in the small signal model of the transistor is

The diodes and capacitors in the circuit shown are ideal. The voltage v(t) across the diode D1 is

In the CMOS circuit shown, electron and hole mobilities are equal, and M1 and M2 are equally sized. The device M1 is in the linear region if

The voltage gain ${A}_{V}$ of the circuit shown below is