QUESTIONS FOR CKT DEBUGGING TEST

SEMICONDUCTOR THEORY AND DEVICES

1. Why is Silicon not used as a substrate in Light emitting diodes?a. Si is tetravalent in nature.b. Si has high temperature and mechanical stability.c. Si is a direct band gap semiconductor, with momentum commensurate between

valence band and conduction band.d. Si is an indirect band gap semiconductor involving a metastable energy state that causes

its electrons to produce heat energy while transition to valence band from the conduction band.

2. Design an analog circuit using diodes and DC sources ONLY, to convert a sine wave of peak amplitude 20V to a square wave of peak amplitude 15V. Assume the diodes are ideal, need of protective resistance can be neglected and suitable approximation in the output waveform shape is allowed.

3. A semiconductor diode starts to conduct exponentially in forward bias condition when the input DC bias exceeds its cut in voltage because

a. A small voltage is present inherently in the semiconductor material of the diode.b. With high DC input bias, the holes and electrons gain kinetic energy and large current is

initiatedc. The barrier potential due to the depletion region is overcome by the increasing input

bias voltage, resultig in huge current flowing in the diode.d. None of these

4. A zener diode regulator in figure, is to be designed to meet the specifications: IL =10mA, V0 = 10 volts, and Vin varies from 30 volts to 50 volts. The zener diode has Vz = 10 volts, and Izk (knee current) = 1mA.

For satisfactory operation,

a. R ≤ 1800 ohmsb. 2000 ohms ≤ R ≤ 2200 ohmsc. 3700 ohms ≤ R ≤ 4000 ohmsd. R > 4000 ohms

5. For a sinoidal input of 50V amplitude, the circuit shown in the following fig can be used as

a. Regulated DC power supplyb. Square wave generatorc. Half wave rectifierd. Full wave rectifier

ANALOG ELECTRONICS

1. In the circuit shown below, voltage at the point A is: (assume β = 100)

a. 0Vb. 2Vc. 3.1Vd. 3.9V

2. Introducing a resistor in the emitter of a common amplifier stabilizes the DC operating point against variations in

a. Only the temperatureb. Only the β of the transistorc. Both temperature and βd. None of the above

3. Which of the following regions of operation are mainly responsible for transistor heating when working as a switch?I. Saturation region II. Cut off regionIII. Transition from saturation to cut offIV. Transition from cut off to saturation

a. I and IIb. II, III and IVc. I and IIId. I, III and IV

4. In the case of BJT amplifier, bias stability is achieved bya. Keeping the bias current constantb. Changing the bias current in order to keep IC and VCE constantc. Keeping the temperature constantd. Keep the temperature and bias current constant

5. The gain of a transistor amplifier falls at high frequencies due toa. Internal capacitances of the device plus stray wiring capacitancesb. Coupling capacitors at input, output and feedback pathsc. Skin effectd. None of these

6. The circuit shown below implements what kind of filter? (assume opamp is ideal)

a. Low pass filterb. High pass filterc. Band pass filterd. Band elimination filter

7. Consider the following statements regarding a common emitter transistor amplifier. It can be converted into an oscillator by:

I. providing adequate positive feedbackII. phase shifting the output by 180 degrees and feedbacking

III. using only a series tuned circuit as a load on the amplifierIV. using a negative resistance device as a load on the amplifier

Which of the above statements are correct?a. I, II, III and IVb. I and IIc. I, III, and IVd. III and IV

8. A circuit is shown in the following fig. The largest value of RLthat can be used, is

a. 100 ohmsb. 400 ohmsc. 2 kilo ohmsd. 20 kilo ohms

9. An opamp isa. A direct coupled amplifierb. An indirect coupled amplifierc. RC coupled amplifierd. Transformer coupled amplifier

10. Consider the Schmidt trigger circuit shown below. A triangular wave which goes from -12V to 12V is applied to the inverting input of the opamp. Assume that the output of the opamp swings from +15V to -15V. The voltage at the non-inverting input, swings between

a. -12V and +12Vb. -7.5V and +7.5Vc. -5V and +5Vd. 0V and 5V

11. The input resistance of the circuit shown in the fig, assuming an ideal opamp, is

a. R/3b. 2R/3c. R

d. 4R/3

DIGITAL ELECTRONICS12. Draw the analog circuit of 2-input 1-output NAND gate using BJTs and resistors only.

13. The initial output of the following circuit is 1. If we apply 010101 at input A (first bit is zero), then bit pattern generated at the output Y is,

a. 010101b. 101010c. remains at 0d. remains at 1

14. In the fig, the LED

a. emits light when both S1 and S2 are closedb. emits light when both S1 and S2 are openc. emits light when only S1 or S2 are closedd. Does not emit light, irrespective of the switch positions

15. All the logic gates in the circuit shown below have finite propagation delay. The circuit can be used as a clock generator, if

a. X=0b. X=1c. X=0 or 1d. X=Y

16. If X1 and X2 are the inputs to the circuit shown in the fig, the output Q is

a. (X1+X2)'b. (X1*X2)'

c. (X1)' * X2d. X1 * (X2)'

17. The figure of merit of a logic family is given bya. Gain bandwidth productb. Propagation delay and Power dissipation productc. Fan out and Propagation delay productd. Noise margin and Power Disspation product

18. Majority of digital voltmeters are built with a Dual-slope ADC because they area. less complex than other types of ADCsb. faster than other ADCsc. Can be designed to be insensitive to noise and interferenced. provide BCD outputs

COMMUNICATIONS1. An AM signal and a narrowband FM signal with identical carriers, modulating signals and

modulation indices of 0.1 are added together. The resultant signal can be closely approximated by

a. Broadband FMb. SSB with carrierc. DSB-SCd. SSB without carrier

2. A fully charged mobile phone with a 12 volt battery is good for a 10 min talktime. Assume that, during the talk-time, the battery delivers a constant current of 2A and its voltage drops linearly from 12V to 10V. How much energy does the battery deliver during this talktime?

a. 220Jb. 12kJc. 13.2kJd. 14.4J

3. Four independent messages have bandwidths of 100Hz, 100Hz, 200Hz and 400Hz, respectively. Each is sampled at the Nyquist rate, and the samples are time division multiplexed and transmitted. The transmitted sample rate(samples/sec) is

a. 1600b. 800c. 400d. 200

4. Consider a signal x(t) of bandwidth 7kHz in the range 7 to 14kHz. Then the signal x3(t) will not contain which of the following frequencies

a. 15kHzb. 25kHzc. 30kHzd. 40kHz

5. H(z) is a discrete rational transfer function. To ensure that both H(z) and its inverse are stable, itsa. Poles must be inside the unit circle and zero must be outside the unit circleb. poles and zeros must be inside the unit circlec. poles and zeros must be outside the unit circled. poles must be outside the unit circle and zeros must be inside the unit circle