This circuit is a pulse amplitude modulation circuit used in signal encoding and sampling.
Using a nMOSFET (with Vt = 0.8 simulating one of the 2N7000's characteristics), and a active dc restorer circuit to give the message signal (sinusoidal wave) a DC level to polarize the MOSFET's Drain.
The carrier signal is a pulse train with 50% duty cycle and 10KHz that provides the signal's sampling.
EDIT1: Fixed some details on the circuit. Now the output signal is a PAM modulated signal. Green is the message and purple is the PAM signal.
EDIT2: Added a diode at the output so the negative spike's at the PAM signal may be removed. Even though not removed entirely, it has been attenuated to its minimum interference. It is noted that the message signal (sinusoid) takes some time to acquire it's DC level. Even though it is a small fraction of time it may be big enough to result in data loss at the beginning of the transmission.
NOTE: this circuit MAY not be a practical application of a PAM modulation, suggestions for improvement are always welcome.
