Fundamental frequency detection using peak detectors with frequency-controlled decay time

Abstract

Methods and digital circuits provide frequency correction to frequency synthesizers. Dual switched-capacitor voltage detectors connected to an input signal periodically sample the voltage of the input signal, and then determine a fundamental frequency of the input signal from the output of the dual switched-capacitor voltage detectors. The sample period of the dual switched-capacitor voltage detectors is proportional to a time period between a previous pair of voltage peaks detected in the input signal, thereby eliminating harmonic components in the original signal which might otherwise cause errors in frequency estimation without causing unwanted sluggishness in the transient response of the frequency detection process. The time period between the previous pair of detected voltage peaks is used to create a decay signal that initiates a capacitor decay time for each voltage detector. Two additional digital methods of extracting the fundamental frequency as well as an envelope of an analog audio signal are also described, one utilizing a sliding sample rate, and the other utilizing a fixed sample rate.