In this simple circuit..You can clearly understand how input signal is converted in PAM wave...
Lets talk little bit deeper... In digital communication system, it is necessary to convert voice signal in to digital signal before transmission on digital communication channel.. so we are parting doing same thing here... But only in first step... We are converting voice frequency signal(Here represented by 100Hz input signal ... Voice frequency can be 0.3 to 3kHz but only understanding purpose we are taken here 100 Hz) in to sampled signal i.e. PAM signal...
Here we have used two Op-Amp with non inverting configuration.. so there is no phase shift error would be there... For converting to PAM signal we have put one One MOSFET in series with first Op-Amp.. ideally any channel(either p or n) would be work for this purpose... The MOSFET will allow to pass signal only when its channel is on.. and the channel is not always on.. we are producing sampled output by controlling gate signal frequency.. if gate signal frequency is increased then sample frequency is increased and more accurate sampled pulses we can get at 2nd Op-Amp output Here we have used 500Hz (five times then input signal frequency) frequency signal for samping purpose...
Here capacitor is used ony for holding purpose....
Here we used gain of first Op-Amp is 3 and gain of 2nd Op-Amp is 1... Just to show that it is not necessary to provide gain to PAM sampled signals.. although one can set gain according to need of system design...
In digital communication system.. these PAM wave is further processed and converted in to digital signal and that will pass through digital channel...
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