Abstract: The disclosed system for measuring the periodic content of an input signal includes an autocorrelation function generator for generating a sequence of autocorrelation functions. Each of the autocorrelation functions is representative of an autocorrelation function of a portion of the input signal. The system further includes a temporal filter for filtering the autocorrelation functions and thereby generating a lag histogram.In other forms the system may comprise a fetal heart rate monitor for measuring the heart rate of a fetus in vivo. The monitor generates a lag histogram and uses the lag histogram for stabilizing the determination of the fetal heart rate.

Abstract: The invention is a physiological monitor for determining a physiological characteristic of a patient. The monitor is particularly adapted to monitor fetal heart rate, and includes a transducer for receiving a signal from the patient that is indicative of the physiological characteristic and for generating an output signal that is representative of the received signal. The monitor further includes a processor coupled to the transducer for receiving the output signal and generating therefrom a physiological signal that is representative of the physiological characteristic. The physiological signal may further be representative of the signal strength of a signal used to calculate the physiological characteristic. The monitor further includes a display unit fixed to the transducer and coupled to the processor for generating a display representative of the physiological signal.