hi there! i have implemented plulse amplitude modualtion circuit that running correctly. In the circuit description , there is a dc shift in the modulating signal but by observing the modulated signal the waveform negative half doesnt cutoff. My question is why we use dcshift in our circuit and by switching off the dcpowersupply after giving dc shift we are getting right result otherwise the required waveform amplitude is cuttingoff when powersupply is on !
kindly help me out !
thanks !

 

You need to post schematics and waveforms.