1.5 Signal Generator

License Preparation NepalNEC ELECTRONICS

Full marks: 24 · Questions: 24

01Oscillator Fundamentals

An electronic oscillator converts:

dc power into dc power

dc power into ac power

mechanical power into ac power

none of the above

02Oscillator Fundamentals

In an LC transistor oscillator, the active device providing energy amplification is the:

LC tank circuit

Biasing circuit

Transistor

None of the above

03LC Oscillators

In an LC tuned oscillator, the frequency of oscillation is:

proportional to the square of L or C

directly proportional to L or C

independent of the values of L or C

inversely proportional to the square root of L or C

04Oscillator Fundamentals

A continuous sinusoidal oscillator produces which type of oscillations?

Damped oscillations

Undamped (sustained) oscillations

Modulated oscillations

None of the above

05Oscillator Fundamentals

To maintain sustained oscillations, an oscillator circuit must employ:

Positive feedback

Negative feedback

Neither positive nor negative feedback

Data insufficient

06LC Oscillators

An LC tuned circuit oscillator cannot be practically used to produce:

High radio frequencies

Intermediate frequencies

Very low audio frequencies

Very high frequencies

07LC Oscillators

A Hartley oscillator is commonly used as the local oscillator in:

Radio receivers

Radio transmitters

TV receivers

None of the above

08RC Oscillators

In an RC phase-shift oscillator using an inverting amplifier, the feedback network typically employs how many cascaded RC ladder sections?

Two

Three

Four

None of the above

09RC Oscillators

In an RC phase shift oscillator, the frequency-determining passive components are:

L and C

R, L and C

R and C

None of the above

10RC Oscillators

A Wien bridge oscillator utilizes:

Only positive feedback

Only negative feedback

Both positive and negative feedback

None of the above

11Crystal Oscillators

The piezoelectric effect observed in a quartz crystal is:

A voltage developed across crystal faces due to mechanical stress

A change in electrical resistance caused by temperature

A change in natural frequency caused by temperature

None of the above

12Crystal Oscillators

The oscillation frequency of a crystal oscillator exhibits exceptional frequency stability primarily because of the crystal's:

Rigidity

Vibrations

Low Q factor

Extremely high Q factor

13Crystal Oscillators

The application where precise carrier frequency stability necessitates a crystal oscillator is a:

Radio receiver local stage

Radio transmitter carrier generator

AF sweep generator

None of the above

14Oscillator Fundamentals

An oscillator fundamentally differs from an amplifier because it:

Has higher voltage gain

Requires no external AC input signal to produce an output

Requires no DC operating power supply

Always has identical input and output waveforms

15Barkhausen Criteria

According to the Barkhausen criterion, the phase condition for sustained oscillations requires:

A phase shift around the feedback loop of 180°

A gain around the feedback loop of one-third

A total phase shift around the closed feedback loop of 0° (or 360°)

A loop gain of less than 1

16Barkhausen Criteria

The magnitude condition of the Barkhausen criterion for sustained steady-state oscillations requires:

A loop gain magnitude of exactly 1 (|Aβ| = 1)

Zero loop gain

A feedback attenuation of exactly one-third

A purely reactive feedback network

17Barkhausen Criteria

In an oscillator with amplifier voltage gain Av = 50, what must the feedback attenuation factor β be for sustained steady-state oscillation?

0.1

0.02

18Barkhausen Criteria

For an oscillator to reliably build up oscillations from internal circuit noise at power-on, the initial loop gain must be:

Exactly 1

Greater than 1 (|Aβ| > 1)

Less than 1

Equal to zero

19LC Oscillators

In a Colpitts oscillator, feedback voltage to the active device is tapped from:

Mutual magnetic induction in a coupled coil

The centre tap of split inductors

The centre tap of a capacitive voltage divider (split capacitors)

None of the above

20Crystal Oscillators

The quality factor (Q) of a quartz crystal resonator is typically of the order of:

10 to 50

100 to 500

1,000

More than 10,000 (often up to 100,000)

21Crystal Oscillators

Quartz crystal is predominantly selected for crystal oscillators because:

It possesses superior piezoelectric properties, high Q, and temperature stability

It is easily available everywhere

It is very inexpensive

None of the above

22LC Oscillators

In an LC resonant oscillator, if the tank circuit inductance L is increased by a factor of 4, the oscillation frequency is:

Increased 2 times

Decreased 4 times

Increased 4 times

Decreased by a factor of 2

23Crystal Oscillators

A primary practical limitation of piezoelectric crystal oscillators is:

Low output power capability (cannot handle high drive levels)

Extremely high Q factor

Excessive frequency drift

Excessive output distortion

24RC Oscillators

The standard variable-frequency signal generator widely used for audio-frequency laboratory testing is the:

Wien-bridge oscillator

Hartley oscillator

Crystal oscillator

Colpitts oscillator