ASK Modulation Simulation in Multisim

 What is ASK modulation?

Amplitude shift keying refer to a type of amplitude modulation in which the amplitude of carrier sinusoidal is modified according to binary input data.  

Design of ASK modulation  

Transistor is need to be operate as a switch hence choose saturation values from data sheet 

i.e V_CE(sat) = 200mV V_BE(on) = 700mV   h_FE = β = 50, Ic=10mA and assuming that Ic=I_E.

  

  

Calculation of RE	Calculation of RB
Vpeak = Vcc=VCE + IERE  5V= 200m + 10m RE     RE= R2=480 Ω	VB=IBRB + VBE + IERE 10= (10m /50) RB + 700m + 10m X 480  RB = R2 = 22.5KΩ

               

• Like Amplitude modulation, an ASK is also linear and sensitive to atmospheric noise, distortions,propagation conditions on different routes in PSTN, etc.
• The ASK technique is also commonly used to transmit digital data over optical fiber. For LED transmitters, binary 1 is represented by a short pulse of light and binary 0 by the absence of light.
• In case of Laser transmitters normally have a fixed "bias" current that causes the device to emit a low light level. This low level represents binary 0, while a higher-amplitude light wave represents binary 1.
• The ASK operates as a switch, using the presence of a carrier wave as a binary one and its absence/-ve to indicate a binary zero. This type of modulation is called on-off keying (OOK), and is used at radio frequencies to transmit Morse code

Design of Demodulation

The demodulator circuit works as a low pass filter, it allows low frequency signal source 500Hz and filter out carrier frequency 5KHz.

Hence assume Xc=R and C=0.1uF  corner frequency fc=500Hz  

  

 

 

                       Original message signals is recovered form demodulator by using opamp.