PULSE PRESENCE DETECTING CIRCUIT

PURPOSE:To detect the presence of a pulse by providing a circuit which compares a signal to be detected with a threshold signal and a circuit which detects the width of the signal. CONSTITUTION:The signal to be detected is inputted to the plus terminal of a comparator 2 and the threshold voltage TH is inputted to the minus terminal. A signal S to be detected desirably and a signal containing a noise N are compared with the threshold value TH to generate a 1st level signal when the signal is larger than the TH or a 2nd level signal when not. A pulse signal PN corresponding to the noise and a pulse signal PS corresponding to the signal to be detected desirably are obtained in the 1st high level signal. Therefore, only a signal P0 corresponding to the PS larger than (t) is outputted through a timer 4. Consequently, even when the noise and the signal to be detected desirably are at nearly the same level, the noise is removed to detect only a desired pulse signal.