07. Amplitude Shift Keying

digital data/binary data

This changes the properties of the carrier signal.

modulation

Transforming the information to be transmitted into a format suitable for the used medium.

sine wave

The signals are transmitted as a ____ which has 3 parameters.

amplitude, frequency, phase shift

3 parameters of a transmitted sine wave (HINT: AFP)

data or another modulating signal

These parameters (amplitude, frequency, and phase shift) can be varied in accordance with _____.

analog and digital modulation

2 Types of Modulation

digital modulation

Digital data (0,1) is translated into an analog signal (baseband signal).

analog modulation

The center frequency of the baseband signal generated by digital modulation is shifted up to the radio carrier.

radio carrier

In analog modulation, the center frequency of the baseband signal generated by digital modulation is shifted up to the _____.

digital modulation

It is required if digital data has to be transmitted over a medium that only allows analog transmission (modems in wired networks).

digital signals

They can be sent over wires using voltages.

analog sine waves

wireless must use _____.

shift keying

In digital modulation, ____ is the translation process.

• amplitude shift keying

• frequency shift keying

• phase shift keying

Types of Shift Keying (AFP)

amplitude, frequency, phase

A sine wave is represented by 3 characteristics/parameters (HINT: AFP)

TRUE

[TRUE or FALSE] In digital modulation, we can change one of these characteristics to represent digital data.

• Amplitude Shift Keying (ASK)

• Frequency Shift Keying (FSK)

• Phase Shift Keying (PSK)

3 Types of Digital-to-Analog Conversion

Quadrature Amplitude Modulation

QAM Meaning

carrier signal or carrier frequency

A high frequency signal that acts as a basis for the information signal

digital information

____ then modulates the carrier signal by modifying one or more of its characteristics.

modulation or shift keying, modulated signal

This kind of modification is called ______, and the information signal is called _____.

bit rate

It is the number of bits per second (bps).

baud rate (Nbaud)

It is the number of signal units per second (baud/s).

TRUE

[TRUE or FALSE] A signal unit (one baud) is composed of 1 or more bits.

amplitude shift keying (ASK)

The amplitude of the carrier signal is varied to represent binary 1 or 0.

TRUE

[TRUE or FALSE] In ASK, while the amplitude changes, both frequency and phase remain constant.

constant

In ASK, the peak amplitude of the signal during each bit duration is _____.

bit (0 or 1)

In ASK, the peak amplitude of the signal during each bit duration is constant, and its value depends on the ____.

different amplitudes

In ASK, 0 and 1 are represented by ______.

susceptible to interference

Problem with ASK

TRUE

[TRUE or FALSE] In ASK, constant amplitude is hard to achieve.

optical transmissions

ASK is used for ______ such as infrared and fiber (simple + high performance)

2 levels

Although we can have several levels (kinds) of signal elements, each with a different amplitude, ASK is normally implemented using only _____.

binary amplitude shift keying (BASK)

ASK implemented using only 2 levels.

ON or OFF switch

We can think of a carrier signal as a/an _____.

On Off Keying (OOK)

We can think of a carrier signal as an ON or OFF switch. In the modulated signal, logic 0 is represented by the absence of a carrier, thus giving OFF/ON keying operation and hence the name given _____.

ASK Generation

unipolar binary sequence (message)

One of the main components used in ASK.

demodulator (detector)

It determines the amplitude of the received signal and maps it back to the symbol it represents, thus recovering the original data.

rectifier and low pass filter

main components used in demodulator or detector.

asynchronous ASK detector

It consists of a half-wave rectifier, a low pass filter, and a comparator.

half-wave rectifier

In asynchronous ASK demodulator, the modulated ASK signal is given to the ______, which delivers a positive half output.

positive half output

In asynchronous ASK demodulator, the modulated ASK signal is given to the half-wave rectifier, which delivers a ____.

low pass filter

In asynchronous ASK demodulator, the _____ suppresses the higher frequencies and gives an envelope detected output from which the comparator delivers a digital output.

comparator

In asynchronous ASK demodulator, this delivers a digital output.

synchronous ASK detector

It consists of a square law detector, low pass filter, a comparator, and a voltage limiter.

Square law detector

In synchronous ASK demodulator, the ASK modulated input signal is given to the _____l

Square law detector

It is one whose output voltage is proportional to the square of the amplitude modulated input voltage.

low pass filter

In synchronous ASK demodulator, this minimizes the higher frequencies.

comparator and voltage limiter

In synchronous ASK demodulator, the _____ and _____ help to get a clean digital output.

TRUE

[TRUE or FALSE] ASK transmitter and receiver are simple to design.

TRUE

[TRUE or FALSE] ASK needs less bandwidth than FSK.

TRUE

[TRUE or FALSE] A disadvantage of ASK transmission is it can be easily corrupted by noise.

TRUE

[TRUE or FALSE] One of the applications of ASK is early telephone modem (AFSK).

amplitude shift keing (ASK)

It is used to transmit digital data over optical fiber.