ENVELOPE DETECTOR INCLUDING SAMPLE-AND-HOLD CIRCUIT CONTROLLED BY PRECEDING CARRIER PULSE PEAK(S)

摘要

An amplitude modulated (AM) signal is applied through a sample and hold circuit including a switch (315) and a capacitor (C3) to a series circuit of an amplifier (340), a low pass filter (350) and a group delay equalizer (360) to produce a detected envelope output. The AM signal is also applied through a phase locked loop (325) and a low pass filter (327) to a comparator (330) in series with a differentiator (335) to produce sample pulses applied to the switch (315). A time constant of the low pass filter (327) is chosen so that the comparator produces pulse edges near the wave peaks of the AM signal. The differentiator (335) contains a delay element (336) which delays each sample pulse to cause the switch (315) to sample the AM signal at or near a wave peak which is subsequent to an earlier wave peak which produced the sample pulse.