Amplitude Shift Keying demodulation Using Multisim

This is the circuit used to Demodulate the ASK modulated signal.

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  ASK or Amplitude Shift keying is the digital modulation technique.And it is simpler over other Digital modulation techniques. similar to other digital modulation techniques ASK is also effected by the atmospheric noise and distortion.ASK technique is used to transmit digital data over an optical fiber.in this technique frequency and phase of the carrier remains constant.this technique is also called on-off keying and is used at radio frequencies to transmit Morse code . ASK needs high SNR i.e. high signal to noise ratio to recover the digital data.the band width is also very high for this type of shift keying technique.if we are using only one or zero to transmit digital data then this type of ASK is called BASK i.e. binary amplitude shift keying.the problem associated with ask is it does not have constant envelop this imposes a restrictions on the power amplification of ask signal because power amplification requires linearity but at the same time the demodulation is we can implement demodulation by using simple envelop detector.Amplitude shift  keying (ASK) is  a  simple   and   elementary form   of  digital modulation in which the amplitude of a carrier sinusoid is modified in a discrete manner depending on the value of a modulating   symbol.This is a narrowband modulation scheme and we assume that a large number of carrier   cycles   are   sent   within  a   symbol interval.obvious that the information is embedded only in the peak amplitude of the modulated signal.this is described as a one type of digital amplitude modulation technique. BASK has only one basis function so this can be described as a one dimensional modulation scheme.this technique is used for telegraph services.on-off keying is not a spectrally not efficeint scheme becuse as the amplitude of the carrier changes abruptly when the data bit changes. for this reason this technique is used for transmission of data at low or moderate data rates..the ask demodulation is done in two steps in first step the band limited bit stream is recovered and in second step regeneration if digital bit stream is done.There are so many other Digital modulation techniques like Frequency shift keying, Phase shift keying, M- array shift keying & combination of Shift keying known as hybrid shift keying. in hybrid shift keying we can combine the two or more shift keying. In all these methods ASK is the easy implementable Shift keying process.
The circuit used here is the asynchronous ASK detector. When the signal passes through a rectifier we get positive half wave signal. by using low pass filter we can detect the envelop of the signal.in the circuit first op-amp acts as the amplifier in inverting configuration to amplify the incoming signal. Diode acts as the rectifier which converts the signal to a half wave signal. resistor and the capacitor combinely forms the low pass filter and acts as envelop detector. Second op-amp with the combination of pot, resistor,diode,capacitor forms a comparator. the entire process can be represented with a simple block diagram.