US 4,021,653 A · Digital programmable tone detector

Abstract

An improved detection arrangement for detecting the presence of a given tone in a received input signal. A reference generator, in the form of a reference clock and a programmable divider, produces a first reference frequency, equal to the frequency of the tone, and at an arbitrary phase angle thereto. A second generator output is in quadrature to the first. Each reference signal is product detected with the input signal via exclusive OR gates. A unique digital low pass filter, operating in a time multiplex mode, receives the gate outputs, removes all high frequency components therefrom, and produces pairs of output binary number encoded signals, each of which is representative of a vector component of a detected tone. Threshold detector circuitry monitors the outputs indicating an above threshold condition at its output in response to predetermined combinations of the binary numbers. The combinations represent all input vectors whose resultant absolute magnitude exceeds a chosen threshold. A second detector samples the threshold detector output, recording the number of samples over threshold during a given interval. If the number exceeds a selected minimum an output signal is produced which indicates the presence of a received tone.

Claims26

Dependent claims

An improved digital detector arrangement for detecting the presence of a tone of a given frequency f comprising in combination:

reference signal generating means having first and second outputs, the first output producing a signal of frequency f at a first phase reference, the second output producing a signal of frequency f at a second phase reference predeterminedly related to the first phase reference;
a first mixer means for mixing the input signal with the reference generator first output;
a second mixer means for mixing the input signal with the reference generator second output;
means times multiplexing the first and second mixer outputs through a digital low pass filter, said filter producing first and second digital outputs, each digital output representative of a vector component of the amplitude of the input tone;
and
processing means for processing the filter digital outputs and producing a tone detect signal in response to the presence of predetermined first and second vector components, the processing means including means for determining the resultant vector of said first and second vector components and further comprising means for generating said tone detect signal in response to the amplitude of said resultant vector exceeding a given threshold level.

3 more elements

A digital detector which detects the presence of a tone of a given frequency f in an incoming signal, having a

reference signal generating means having a first and a second output, the first output producing a signal of frequency f at a first phase reference, the second output producing a signal having a second phase reference in quadrature with the first phase reference;
a first mixer for multiplying the reference signal generator first output and the input signal, a second mixer multiplying the reference signal generator second output and the input signal, the improvement comprising:
a digital low pass filter means for processing the first and second mixer outputs, said filter means producing first and second digital outputs, each digital output representative of a vector component of the amplitude of the input tone;
and
processing means for producing the filter digital outputs and producing a tone detect signal in response to the presence of predetermined first and second vector components, the processing means including means for determining the resultant vector of said first and second vector components and further comprising means for generating said tone detect signal in response to the amplitude of said resultant vector exceeding a given threshold level.

2 more elements

Dependencies are inferred from the claim text.

Digital programmable tone detector

Life of this patent

Digital programmable tone detector

Life of this patent

Abstract

Claims26