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Waveform Generators

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Type of Signal Generators

* RF = Radio Frequency

Working on high-end audio equipment, you'll want an audio oscillator, a low-

distortion sine wave oscillator that can be used as a signal source for checking

total harmonic distortion. These signal generators operate in the audio range,

usually going from around 20 Hz or lower to over 20KHz

Exp; Wien Bridge oscillator and phase-shift oscillator

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Working on communications equipment, you'll need an RF signal generator.

These have a frequency output of anywhere around 50KHz or lower to 50MHz,

500MHz, 1GHz or more, depending upon the model

RFGenerator RFOscillators

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An all-around "signal generator" is the function generatorwhich outputs a sine

wave, triangle wave or square wave.

Most have a frequency range of around 1 Hz or less to over 1MHz. Premium

units can go from 0.001Hz to 40MHz and have all sorts of other bells and

whistles built in. The function generator is probably the best choice for general

electronic experimentation.

Pulse generators produce a rectangular output waveform. The frequency

range is from a fraction of a hertz to several megaherzt.

Sweep-frequency generators provide an RF sine-wave output that can be

varied smoothly and continuously over an entire frequency band.

Type of Signal Generators

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4

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Introduction

Many electronic devices require a source of energy at a specific

frequency which may range from a few Hz to several MHz.

This task is achieved by an electronic device called an oscillator,

which is a circuit that generates an ac output signal without

requiring any externally applied input signal.

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Introduction

Where is this oscillator used or what are its applications?

Electronic equipments like in radio and television receivers.

They are also used to generate high frequency wave ( carrier

wave ) in the tuning stages.

Oscillators are also widely used in radar, electronic computers

and other electronic devices.

Oscillators can produce sinusoidal or non-sinusoidal ( say

square) waves.

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Introduction

What is sinusoidal oscillators?

Sinusoidal oscillators are electronic devices that generates sinusoidal

oscillations of desired frequency.

As an oscillator generates a frequency, it does not create energy, butmerely acts as an energy converter. It receives d.c. energy and

changes it into a.c. energy of desired frequency. The frequency of

oscillations depends upon the constants of the device.

The oscillations are produced without any external signal source.

The only input power to an oscillator is the d.c. power supply.

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Requirement for Oscillation

An electronic device used for the purpose of generating a signal.An amplifier

with positive feedback. The signal regenerate and sustain itself.

Oscillator

s

of

V

V

A

AA

1

Gain for amplifier with positive feedback

where

Af= gain with feedback

A = open-loop gain

= feedback factor =o

f

V

V

A

B

Vs +

-

VoOutput

Signal

Input

Signal

Feedback

Signal

Vf = Vo

Vi = Vs - Vf

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Positive Feedback Amplifier

Oscillator.

A transistor amplifier with proper positive feedback can act as an

oscillator.

A positive feedback amplifier is the one that produces a feedback

voltage, Vfthat is in phase with the original input signal.

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Oscillator.

A phase shift of 180 is produced by the amplifier and a furtherphase shift of 180 is introduced by feedback network. The signal get shifted by 360.

This signal is then fed back to the input. The feedback voltage isin phase with the input signal.

The circuit is producing oscillations in the output.

However, this circuit has an input signal.

But, then this is inconsistent with our definition of an oscillator whichstates that an oscillator is a circuit that produces oscillations without anyexternal signal source.

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Oscillator.

If we open the switch S in the figure, we will get the circuit as shown:

It means that the input signal is removed. However, the feedback voltage isstill applied to the input signal. The amplifier will respond to this signal inthe same way that it did to the input signal and that is the feedback voltagewill be amplified and sent to the output.

The function of the feedback network is to send a portion of the outputback to the input. Therefore, the amplifier receives another input cycle andanother output cycle is produced. This process will continue so long as theamplifier is turned on. Therefore, the amplifier will produce sinusoidal output with no external signal source.

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Oscillator

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Oscillator

RF Oscillator

Audio Oscillator

Wien Bridge Oscillator

Phase Shift Oscillator

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RADIO-FREQUENCY OSCILLATORS- Hartley oscillator

XL = Xc

2fL=(2fC)-1

LC circuit is resonant wheninductive reactance and capacitive

reactance are equal

LCf

2

1

Frequency of oscillation,

Adjust

osc. f

2

1

L

L

Feedback factor, 180o phase

shift across

amplifier

Inverting Amplifier

L1 + L2

(3.2)

(3.3)

(3.4)

(3.5)

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