WALSH FUNCTION MIXER AND TONE DETECTOR

摘要

WALSH FUNCTION MIXER AND TONE DETECTOR A mixer stage having particular application to digital detectors. The mixer stage includes first and second sets of transmission gates and a Walsh function generator. The first set of transmission gates is driven by sine function coefficient signals from the Walsh function generator so as to open and close individual gates of the set so as to effectively multiply an input signal by the sine of a tone reference frequency to be tone detected. Similarly, the second set of transmission gates driven by cosine coefficient signals from the Walsh function generator so as to open and close individual gates of the second set to effectively multiply the input signal by the cosine of the reference frequency to be tone detected. To form a complete digital tone detector, the sine and cosine multiplied outputs of the mixer stage are each filtered and squared and are then summed and further filtered to provide a "detect" signal when the input signal includes the reference frequency.