# Questions & Answers of Analog Circuits

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

Question No. 23

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

Question No. 24

The following signal Vi of peak voltage 8 V is applied to the non-inverting terminal of an ideal opamp. The transistor has .

The number of times the LED glows is ________

Question No. 25

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:

Question No. 50

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 ___________

Question No. 51

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 ________

Question No. 124

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 ________

Question No. 125

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

Question No. 144

The switch S in the circuit shown has been closed for a long time. It is opened at time t=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 ______

Question No. 149

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 ________

Question No. 150

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 ________

Question No. 151

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 ________

Question No. 223

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 __________

Question No. 224

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

Question No. 225

In the astable multivibrator circuit shown in the figure, the frequency of oscillation (in kHz) at the output pin 3 is __________

Question No. 250

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 __________

Question No. 251

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

Question No. 252

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 __________

Question No. 21

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

Question No. 50

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

Question No. 51

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

Question No. 52

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

Question No. 121

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 ?

Question No. 122

In the circuit shown, VO=VOA for switch SW in position A and V0=VOB for SW in position B. Assume that the opamp is ideal. The value of $\frac{{V}_{OB}}{{V}_{OA}}$ is ___________.

Question No. 123

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 _________

Question No. 149

The diode in the circuit given below has VON = 0.7 V but is ideal otherwise. The current (in mA) in the 4 k Ω resistor is

Question No. 150

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

Question No. 151

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 __________.

Question No. 152

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 _____.

Question No. 221

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 _____.

Question No. 222

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

Question No. 223

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 _____.

Question No. 249

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

Question No. 250

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 _____.

Question No. 251

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 ______.

Question No. 21

A good current buffer has

Question No. 22

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

Question No. 23

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

Question No. 24

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,

Question No. 47

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 _______.

Question No. 48

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

Question No. 49

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 _______

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Question No. 121

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

Question No. 122

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

Question No. 221

The desirable characteristics of a transconductance amplifier are

Question No. 222

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 _______

Question No. 223

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

Question No. 247

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?

Question No. 248

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

Question No. 321

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

Question No. 322

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

Question No. 323

The circuit shown represents

Question No. 347

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?

Question No. 349

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 _______.

Question No. 10

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

Question No. 15

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

Question No. 17

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

Question No. 30

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

Question No. 34

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)

Question No. 35

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

Question No. 41

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

Question No. 43

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

Question No. 46

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

Question No. 1

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

Question No. 13

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

Question No. 37

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