US 4,499,550 AGranted

Walsh function mixer and tone detector

AssigneeGeneral Electric Company

InventorsJohn M. Ray, III, Robert J. Martin

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Abstract

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 is 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.

Claims26

Dependent claims

A mixer stage for multiplying an input signal by the sine and cosine of a reference frequency, comprising:

(a) input means for receiving said input signal;
(b) a first set of transmission gates, each gate having an input means for receiving said input signal, an output, and a control input for receiving a control signal for causing the gate to pass the input signal from the gate input to its output or block the input signal so that it does not pass to the output;
(c) first means associated with said first set of transmission gates for combining the signals at the outputs thereof into a first mixer section output providing a signal defined by the input signal multiplied by the sine of the reference frequency;
(d) first means associated with said first set of transmission gates for weighting the contributions of the signals from each transmission gate to said first combining means;
(e) a second set of transmission gates, each gate having an input means for receiving said input signal, an output and a control input for receiving a control signal for causing the gate to pass the input signal from the gate input to its output or block the input signal so that it does not pass to the output;
(f) second means associated with said second set of transmission gates for combining signals at the outputs thereof into a second mixer section output providing a signal defined by the input signal multiplied by the cosine of the reference frequency;
(g) second means associated with said second set of transmission gates for weighting the contributions of the signals from each transmission gate to said second combining means;
(h) a reference frequency source;
(i) Walsh function generating means, having an input coupled to said reference frequency source, for generating a first set of outputs representing a sine wave synthesis of reference frequency from Walsh function pulse trains, said first set of outputs being coupled to said control inputs of said first set of transmission gates, and for generating a second set of outputs representing a cosine synthesis of said reference frequency from Walsh function pulse trains, said second set of outputs being coupled to said control inputs of said second set of transmission gates.

6 more elements

A digital tone detector for determining the presence or absence of a predetermined reference frequency component in an input signal comprising:

input means for receiving said input signal;
a first Walsh function mixer having a signal input coupled to said input means, a set of control inputs and an output for providing an output signal defined by said input signal multiplied by the sine of said reference frequency;
a second Walsh function mixer having a signal input coupled to said input means, a set of control inputs and an output for providing an output signal defined by said input signal multiplied by the cosine of said reference frequency;
a reference frequency source;
a Walsh function generator having an input coupled to said reference frequency source for generating, at a first set of outputs, signals representing a sine wave synthesis of said reference frequency, said first set of outputs being coupled to said control inputs of said first Walsh function mixer and for generating, at a second set of outputs, signals representing a cosine wave synthess of said reference frequency, said second set of outputs being coupled to said control inputs of said second Walsh function mixer;
a first low pass filter coupled to said output of said Walsh function mixer;
a first squaring circuit coupled to said first low pass filter;
a second low pass filter coupled to said output of said second Walsh function mixer;
a second squaring circuit coupled to said second low pass filter;
means for combining signals from said first and second squaring circuits to provide an output signal whenever said input signal includes, as a component thereof, said reference frequency.

7 more elements

Dependencies are inferred from the claim text.