hand side of fig2 a the signal is transmitted without noise and has a smooth sinusoidal shape near the center of the figure noise is added to the signal so that the wave form of the signal no longer has a smooth sinusoidal shape at the right hand side of fig2 a the signal again is free of noise and the wave form has a smooth sinusoidal shape the first portion of the circuit included within dotted line 8 generates a series of pulses each of which corresponds to a zero transition of the signal at a a 34 zero transition 34 is a point at which the wave form of the signal a crosses the horizontal axis the analog signal is received by a squarer 10 the output of squarer 10 at point b in fig1 is a square wave shown at fig2 b the square wave has uniform amplitude with substantially sharp transitions between a low value and a high value each transition of the square wave corresponds to a zero transition of the signal at a the output of the squarer 10 is connected to the input of a differentiator 20 the output of the differentiator 20 which is shown at fig1 as occurring at point c is depicted in fig2 c as can be seen by comparing fig2 c with fig2 b for each zero transition in the signal in fig2 b there is a short pulse in the signal in fig2 c positive short pulses correspond to transitions from a low level to a high level negative short pulses correspond to transitions from a high level to a low level it will be seen that these short pulses are of alternate.