Amplitude Shift Keying Sunny Babu

IntroductionDigital data, more specifically, the binary data changes the properties of the carrier signal

• Amplitude • Frequency• Phase

Digital modulation• In digital modulation, an analog carrier signal is modulated by a discrete signal

Changing amplitude, frequency or phase in proportional to the binary data, produces digital modulated signal called

• Amplitude Shift Keying (ASK)• Frequency Shift Keying (FSK)• Phase Shift Keying (PSK)

ASK – Amplitude shift keying • Amplitude-shift keying (ASK) is a form of modulation that represents

digital data as variations in the amplitude of a carrier wave.

• The amplitude of an analog carrier signal varies in accordance with the bit stream (modulating signal), keeping frequency and phase constant.

• The level of amplitude can be used to represent binary logic 0s and 1s.

Binary ASK(BASK) or On-Off Keying (OOK)• Although we can have several levels (kinds) of signal elements,

each with a different amplitude, ASK is normally implemented using only two levels. This is referred to as binary amplitude shift keying.

•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 OOK.

OOK

MSK – Multiple shift keying• The above discussion uses only two amplitude levels. We can have

multilevel ASK in which there are more than two levels. We can use 4,8, 16, or more different amplitudes for the signal and modulate the data using 2, 3, 4, or more bits at a time.

ASK Generation

Demodulator Or Detector • The demodulator determines the amplitude of the received signal

and maps it back to the symbol it represents, thus recovering the original data.

Pros and ConsPros:• ASK transmitter and receiver are simple to design.• ASK needs less bandwidth than FSK.

Cons:• ASK transmission can be easily corrupted by noise

Application:• early telephone modem(AFSK)• ASK is used to transmit digital data over optical fibre.