Pulse width modulation

Consider a pulse train of repetition rate f and pulse width t. How does the pulse width change in relation to the amplitude of the input signal. I mean whether the pulse width will be less than t for -ve values of message and will it be greater than t for +ve values of messges. Will the no. of pulses /sec (f) will be the same in the original and modulated wave. How do we reconstruct the original message from the PWM signal ?

Please explain


thanx

regards

senthil

senthilpr_in@rediffmail.com