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Oscillator

(UJT As a Relaxation Oscill.)

10.04.2019

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Oscillator Circuit- By- Ratnesh k Pandey

Oscillator is an electronic circuit which converts dc signal into ac signal.

Oscillator एक इलेक्ट्रॉनिक सर्कि ट है जो DC ससग्िल को AC ससग्िल में परिवनतित किता है

Oscillator is basically a positive feedback amplifier with unity loop gain.

ऑस्ककलेटि मूल रूप से एक सकािात्मक एम्पलीफायि है जो unity loop लाभ के साथ है।

For an inverting amplifier- feedback network provides a phase shift of 180°

while for non-inverting amplifier- feedback network provides a phase shift of 0°

to get positive feedback

If A β =1 then Vo =infinite

Positive Feedback

When input and feedback signal both are in same phase, It is called a positive

feedback.

जब इिपुट औि फीडबैक ससग्िल दोिों एक ही phase में होते हैं, तो इसे सकािात्मक feedback कहा जाता है

Positive feedback is used in analog and digital systems.

Positive feedback का उपयोग एिालॉग औि डडस्जटल ससकटम में र्कया जाता है

A primary use of +ve feedback is in the production of oscillators.

+ Ve feedback का एक प्राथसमक उपयोग ऑससलेटि के उत्पादि में है .

Vo = AVi = A( Vs +Vf ) and Vf = βV

Principle of Oscillators

'Active device' either Transistor or Op Amp is used as an amplifier.

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'एस्क्ट्टव डडवाइस' या तो राांस्जकटि या Op एम्प का उपयोग एम्पलीफायि के रूप में र्कया जाता है। Feedback circuit' with passive components such as R-C or L-C combinations .

To start the oscillation with the constant amplitude, positive feedback is not the

only sufficient condition. Oscillator circuit must satisfy the following two conditions

known as Barkhausen conditions:

The first condition is that the magnitude of the loop gain (Aβ) must be unity.

This means the product of gain of amplifier 'A' and the gain of feedback

network 'β' has to be unity.

The second condition is that the phase shift around the loop must be 360° or 0°.

This means, the phase shift through the amplifier and feedback network has to

be 360° or 0°.

Types of oscillators

1. RC oscillators

Wien Bridge

Phase-Shift

2. LC oscillators

Hartley

Colpitts

Crystal

3. Unijunction / relaxation oscillators

RC Oscillators

Adjusting R to zero is impractical because it would lead to no voltage across R,

thus in a RC circuit, phase shift is always 90 degree and it is a function of

frequency.

Hence to get 180o phase shift from the feedback network, we need 3 RC circuits

RC oscillators build by using inverting amplifier and 3 RC circuits is known as

phase shift oscillator.

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Difference between Amplifiers and Oscillator

Amplifier

Oscillators

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Amplifier is an electronic circuit

which gives output as amplified form

of input.

Oscillator is an electronic circuit

which gives output without

application of input.

The amplifier does not generate any

periodic signal.

The oscillator is generating of the

periodic electronic signal.

Amplifier uses negative feedback.

Oscillator uses positive feedback.

Amplifier operates as a multiplier.

Oscillator operates as a source

Amplifiers do nothing till input signal

is fed to the input.

Oscillators produce signals from the

moment of powered.

Difference between RC phase shift oscillator & Wein bridge oscillator

RC phase shift oscillator

Wein bridge oscillator

This oscillator is used for low

frequency range.

This oscillator is used for low

frequency range since both are RC

oscillator.

Feedback network provide 180° phase

shift.

Feedback network do not provide

180° phase shift.

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Op-Amp is used in inverting mode.

Op-amp is used in non-inverting

mode.

Op-Amp introduces 180° phase shift.

Op-amp does not introduce 180°

phase shift.

Amplifier gain |A| >=29

Amplifier gain |A| >= 3

3RC section in feedback.

Low frequency range since both is RC

oscillator.

Difficult to adjust frequency

variation.

Easy adjustment of frequency by

varying both capacitors.

Oscillator type Frequency range

Audio frequency (AF) Oscillators Few Hz --------------- 20 kHz.

Radio Frequency (RF) Oscillators 20 kHz –-------------- 30 MHz.

Very High Frequency (VHF) Oscillators 30 MHz –----------- 300 MHz.

Ultra High Frequency (UHF) Oscillators 300 MHz –---------- 3 GHz.

Microwave Oscillators Above 3 GHz.

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1.

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The most suitable oscillator circuit for 2 kHz frequency is

2 kHz आवतृ्ति के लिए सबसे उपयकु्ि oscillator सर्कि ट है

a) Tuned collector oscillator

b) Wein bridge oscillator

c) Colpitt’s oscillator

d) Hartley oscillator.

2.

The frequency of oscillation will be stable in which of the following oscillators?

दोिन की आवतृ्ति ननम्न में से र्कस दोिक में त्थिर होगी?

a) Wein bridge

b) Colpitt’s

c) Crystal

d) Hartley.

3.

For generating 1 kHz frequency which of the following oscillators will be suitable?

1 र्किोहर्ट्ि़ आवतृ्ति उतपन्न करने के लिए ननम्नलिखिि में से कौन सा ऑलसिेटर उपयुक्ि होगा?

a) Tuned collector oscillator

b) Colpitts oscillator

c) Wein bridge oscillator

d) Hartley

4.

The mostly used piezoelectric material in RF crystal oscillators is-

आरएफ र्िथटि oscillators में ज्यादािर इथिमेाि पीजोइिेत्क्िक सामग्री है

a) Setellite

b) Quartz

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c) Tourmaline

d) Rochelle salt.

5.

______ oscillator is the most stable oscillator.

______ ऑलसिेटर सबसे त्थिर ऑलसिेटर है।

a) Crystal controlled

b) Hartley

c) Colpitts

d) Wein bridge.

6.

Which of the following oscillators uses a capacitive voltage divider to provide feedback?

ननम्नलिखिि में से कौन सा ऑलसिटेसि feedback प्रदान करने के लिए एक कैपेलसटटव वोल्टेज ववभक्ि का उपयोग करिा है?

a) Colpitts

b) Armstrong

c) Hartley

d) Wein bridge.

7.

The oscillator that uses a taped coil in its tank circuit is

Oscillator जो अपने टैंक सर्कि ट में एक टैप र्कए गए कॉइि का उपयोग करिा है

a) Hartley

b) Tuned base

c) Pierce oscillator

d) Colpitts.

8.

Which of the following piezoelectric materials can be used for very high frequencies?

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ननम्न में से कौन सी पीजोइिेत्क्िक सामग्री बहुि उच्च आवतृ्तियों के लिए उपयोग की जा सकिी है?

a) Tourmaline

b) Rochelle salt

c) Quartz

d) All of the above.

9.

In a Wein bridge oscillator the RC elements of the bridge provide a

एक वेन ब्रिज ऑलसिेटर में bridge के आरसी ितव प्रदान करि ेहैं a) No feed back

b) Negative feedback

c) Negative feedback at low frequency

d) Positive feedback

10.

Which of the following is non-sinusoidal oscillator?

ननम्न में से कौन सा गरै - साइनसोइडि ऑलसिेटर है?

a) Relaxation oscillator using UJT

b) Multivibrator

c) Relaxation oscillator using tunnel diode

d) Any of the above.

11.

In a Hartley oscillator feedback is provided through a _____and in a Colpits oscillator

through a _________.

हाटििे ऑलसिेटर में एक _____ और कोिवपर्ट्स ऑलसिेटर में _________ के माध्यम से प्रनिर्िया प्रदान की जािी है । a) Coil, Capacitor

b) Capacitor, Coil

c) Resistor, Coil

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d) Capacitor, Resistor.

12.

Oscillator with best frequency stability is

सबसे अच्छा आवतृ्ति त्थिरिा के साि Oscillator है

a) Crystal oscillator

b) Hartley oscillator

c) Clapp oscillator

d) Phase shift oscillator.

13.

The crystal oscillator frequency is very stable due to ___ of the crystal.

र्िथटि के ___ के कारण र्िथटि oscillator आवतृ्ति बहुि त्थिर है। a) Vibration

b) High Q

c) Rigidity

d) None of above.

14.

A CE phase shift oscillator has three RC legs. The phase shift per leg must be

a) 400

b) 600

c) 800

d) 1800

15.

In phase shift RC network the basic amplifier used is

a) CC

b) CB

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c) CE

d) Any of the above.

17.

Phase shift oscillator consists of a number of _______ circuits.

फेज लिफ्ट ऑलसिेटर में कई _______ सर्कि ट होि ेहैं। a) LC

b) RL

c) RC

d) RLC.

18.

The basic amplifier in Wein bridge oscillator consists of

वेन ब्रिज ऑलसिटेर में मिू एम्पिीफायर होि ेहैं a) CE stage followed by CC

b) CC stage followed by CE

c) CB stage followed by CE

d) CE stage followed by CB.

19.

Rochelle salts

a) Exhibit the greatest piezoelectric activity

b) Break easily

c) Are mechanically weak

d) All of the above.

20.

The tuned base oscillator is also known as

र्ट्यनू्ड बेस oscillator के रूप में भी जाना जािा है

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a) Tickler oscillator

b) Nyquist oscillator

c) Pierce oscillator

d) None of these

21.

The gain of an ideal oscillator is

एक आदिि oscillator का िाभ है

a) Unity

b) Zero

c) Infinity

d) Slightly more than unity.

22.

RC oscillator can be used upto

RC oscillator िक इथिमेाि र्कया जा सकिा है

a) 5 kHz

b) 20 kHz

c) 60 kHz

d) 10 kHz

23.

Which one of the following oscillators is well suited for the generation of wide range audio

– frequency sine wave.

a) R-C phase-shift oscillator.

b) Wien-bridge oscillator.

c) Colpitts oscillator.

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d) Hartley oscillator.

24.

An oscillator of the L-C type that has a split capacitor in the tank circuit is

a) Hartley oscillator.

b) Colpitts oscillator.

c) Wien bridge oscillator.

d) Hartley oscillator.

25.

Which one of the following oscillators is used for the generation of high frequencies?

ननम्नलिखिि में से कौन सा दोिक उच्च आवतृ्तियों की पीढी के लिए उपयोग र्कया जािा है?

a) R-C phase shift oscillator.

b) Wien bridge oscillator.

c) L-C oscillator.

26.

Consider the following statements:

1. Wien bridge oscillator is suitable for generating 1 kHz.

2. Colpitts oscillator is suitable for generating 1 MHz.

Which of the statements given above is / are correct?

ननम्नलिखिि किनों पर ववचार करें: 1. वीन ब्रिज ऑलसिटेर 1 kHz उतपन्न करने के लिए उपयकु्ि है। 2. Colpitts oscillator 1 मेगाहर्ट्िज उतपन्न करने के लिए उपयकु्ि है । ऊपर टदए गए किनों में से कौन सा सही है / हैं

a) 1 Only.

b) 2 Only.

c) Both 1 and 2

d) Neither 1 nor 2.

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27.

In a Wien bridge oscillator. If the resistance in the positive feedback circuit are decreased

,the frequency-

एक वेन ब्रिज ऑलसिेटर में। यटद सकारातमक प्रनिर्िया सर्कि ट में प्रनिरोध कम हो , आवतृ्ति हो जािी है। a) Decreases.

b) Increases.

c) Remains the same.

d) None

28.

In a wien bridge oscillator, the positive feedback attenuation is

एक wien ब्रिज ऑलसिटेर में, सकारातमक प्रनिर्िया क्षीणन है-

a) 1

3

b) 1

29

c) -29

d) 3

29.

The frequency of oscillation of Wien bridge oscillator is given by

Wien bridge oscillator के दोिन की आवतृ्ति द्वारा टदया जािा है -

a) 𝑓𝑎 = 1

2𝜋𝑅𝐶

b) 𝑓𝑎 = 1

2𝜋√𝑅𝐶

c) 𝑓𝑎 = 1

𝜋𝑅𝐶

d) 𝑓𝑎 = 1

𝜋√𝑅𝐶

30.

For a R-C phase shift oscillator, R = 220 kΩ ad C = pF. Frequency of oscillation is

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a) 295 Hz

b) 1,180 Hz

c) 590Hz

d) 250 Hz

31.

An R-C phase shift oscillator will not produce any oscillation until and unless the voltage

gain of its internal amplifier is

R-C phase shift oscillator िब िक कोई दोिन पदैा नहीीं करेगा जब िक र्क उसके आींिररक एम्पिीफायर का वोल्टेज

िाभ न हो a) Unity.

b) Less than unity.

c) Around 3.

d) More than 29.

32.

Consider the following statements regarding an R-C phase-shift oscillator.

R-C phase -लिफ्ट ऑलसिटेर के बारे में ननम्नलिखिि किनों पर ववचार करें। 1. The amplifier gain is positive. ‘

2. The amplifier gain is negative.

3. The phase shift introduced by the feedback network is 1800

4. The phase shift introduced by the feedback network is 3600

a) 1 and 3 are correct.

b) 2 and 3 are correct.

c) 2 and 4 are correct.

d) 1 and 4 are correct.

33.

[17 ]

In three R-C combinations of a phase-shift oscillator, each R-C gives a phase shift of

फेज-लिफ्ट ऑलसिेटर के िीन आरसी सींयोजनों में, प्रतयेक आरसी एक फेज लिफ्ट देिा है

a) 600

b) 900

c) 300

d) 450

34.

In an R-C phase shift oscillator, the minimum number of R-C networks to be connected in

cascade will be –

आरसी चरण लिफ्ट ऑलसिेटर में, कैथकेड में जोडा जाने वािा आरसी नेटवकि की न्यनूिम सींख्या होगी a) One.

b) Two.

d) Three.

e) Four.

35.

The highest frequency stability is achieved by using an oscillator of type:

उच्चिम आवतृ्ति त्थिरिा प्रकार के एक oscillator का उपयोग करके प्राप्ि की जािी है:

a) Colpitts.

b) Crystal controlled

c) Hartley.

d) RC oscillator.

36.

RC network shown in the given figure can provide a maximum theoretical phase shift of

[18 ]

a) 900

b) 1800

c) 2700

d) 3600

37.

Crystal oscillators are superior to tuned LC oscillators mainly because of their.

र्िथटि ऑलसिेटसि र्ट्यनू र्कए गए एिसी ऑलसिटेसि से बेहिर होि ेहैं क्योंर्क मखु्य रूप से उनके। a) High degree of frequency stability.

b) Size of crystal.

c) High value of Q.

d) Availability of crystal.

38.

Crystal oscillators are normally for high frequency within the range of

र्िथटि ऑलसिेटसि की सीमा के भीिर उच्च आवतृ्ति के लिए सामान्य रूप से होि ेहैं a) 100 MHz - 500 MHz.

b) 10 kHz – 100 kHz.

c) 10 MHz – 100 MHz.

d) 100 kHz – 10 MHz

39.

A crystal oscillator is frequently used in digital circuits for timing purposes because of its

एक र्िथटि oscillator अक्सर इसकी वजह से समय के प्रयोजनों के लिए डडत्जटि सर्कि ट में उपयोग र्कया जािा है

a) Low cost

b) High frequency stability.

[19 ]

c) Simple circuitry.

d) Ability to set the frequency at the desired value.

40.

The primary advantage of a crystal oscillator is that

एक र्िथटि oscillator का प्रािलमक िाभ यह है र्क

a) It can oscillate at any frequency.

b) It gives a high output voltage.

c) Its frequency of oscillation remains almost constant.

d) It operates on a very low dc supply voltage

41.

A Hartley oscillator is used for generation of

a) Very low frequency oscillation,.

b) Radio frequency oscillation.

c) Microwave oscillation.

d) Audio-frequency oscillation.

42.

The frequency of oscillation of a Hartley oscillator is

a) 𝜔 =1

𝐿𝐶

b) 𝜔 =1

√𝐿𝐶

c) 𝜔 = 2𝜋𝐿𝐶

d) 𝜔 =2𝜋

√𝐿𝐶

43.

In connection with oscillators

[20 ]

a) In every oscillator the loop gain is slightly larger than unity.

b) Oscillations will sustain if product of transfer gain of amplifier and magnitude of

feedback gain at the oscillator frequency is less than unity.

c) In Hartley oscillators, two capacitors connected in parallel with an inductor.

d) None of these

44.

In colpit’s oscillator C1 = 0.2𝜇𝐹, C2 = 0.02𝜇𝐹 . If the frequency of oscillation is 10kHz.

The value of inductor needed is

a) 15mH.

b) 13mH.

c) 10mH.

d) 130mH.

45.

The Barkhausen criterion for sustained oscillations is given by

a) A𝛽 = 1

b) |A𝛽| ≥ 1

c) |A𝛽| < 1

d) ∠ A𝛽 = 1800

46.

The basic conditions for generating sinusoidal voltage in a feedback type oscillator is are

a) Total loop gain should be ‘1’.

b) Total phase shift should be ‘3600’

c) Either (a) or (b)

d) Both (a) and (b)

[21 ]

47.

Oscillators use following feedback-

Oscillators ननम्नलिखिि प्रनिर्िया का उपयोग करि े

a) Negative.

b) Positive

c) Both negative and positive

d) None

48.

The frequency band from 30 MHz to 300 MHz is of

a) Audio-frequency oscillator.

b) Radio-frequency oscillator.

c) Video-frequency oscillator.

d) Very high frequency

49.

A UJT has ……………….

a) Two pn junctions

b) One pn junction

c) Three pn junctions

d) None of the above

50.

In a UJT, the p-type emitter is ……………. doped

a) Lightly

b) Heavily

c) Moderately

d) None of the above

[22 ]

51.

When the emitter terminal of a UJT is open, the resistance between the base terminal is

generally………………..

जब UJT का एलमटर टलमिनि िुिा हो, बेस टलमिनि के बीच प्रनिरोध आम िौर पर ……………… .. होिा है।

a) High

b) Low

c) Extremely low

d) None of the above

52.

When a UJT is turned ON, the resistance between emitter terminal and lower base terminal

…………….

जब एक UJT चाि ूहोिा है, िो प्रनिरोध एलमटर टलमिनि और िोअर बेस टलमिनि ……………।

a) Remains the same

b) Is decreased

c) Is increased

d) None of the above

53.

To turn on UJT, the forward bias on the emitter diode should be …………… the peak point

voltage

UJT को चाि ूकरने के लिए, उतसजिक डायोड पर आग ेका पवूािग्रह पीक पॉइींट वोल्टेज होना चाटहए

a) Less than

b) Equal to

c) More than

d) None of the above

[23 ]

54.

A UJT is sometimes called …………. Diode

एक UJT को कभी-कभी ………… कहा जािा है

a) Low resistance

b) High resistance

c) Single-base

d) Double-base

55.

When the temperature increases, the inter-base resistance (RBB) of a UJT ………….

जब िापमान बढिा है, िो इींटर-बेस UJT का प्रनिरोध (RBB) ………।

a) Increases

b) Decreases

c) Remains the same

d) None of the above

56.

Between the peak point and the valley point of UJT emitter characteristics we have

………….. region.

यजूेटी के लििर ब्रब ींद ुऔर घाटी ब्रब ींद ुके बीच एलमटर वविषेिाओीं……… .. क्षेत्र ।

a) Saturation

b) Negative resistance

c) Cut-off

d) None of the above

57.

The device that exhibits negative resistance region is ………………..

डडवाइस जो नकारातमक प्रनिरोध क्षेत्र प्रदलििि करिा है

[24 ]

a) Diac

b) Triac

c) Transistor

d) UJT

58.

The UJT may be used as ……………….

UJT का उपयोग ……………… के रूप में र्कया जा सकिा है

a) Am amplifier

b) A sawtooth generator

c) A rectifier

d) None of the above

[25 ]

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