Tone detection
First Claim
1. A tone detector comprising:
- a power detector for detecting power of an input signal;
a sinusoidal signal eliminator responsive to the input signal to eliminate any sinusoidal signal therein independently of its frequency within a bandwidth of the input signal;
a power detector for detecting power of an output of the sinusoidal signal eliminator; and
a comparator responsive to the powers detected by the power detectors to provide an indication of the presence or absence of a tone in the input signal;
wherein the input signal comprises a sampled signal having successive samples x(k), and the sinusoidal signal eliminator comprises apparatus for producing at its output samples substantially equal to {x(k)+x(k-2)}x(k-2)-{x(k-1)+x(k-3)}x(k-3).
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Accused Products
Abstract
AMPS (Advanced Mobile Phone System) ST (signalling tone) is detected by a tone detector in which samples of a demodulated signal are amplitude limited to remove click energy, and the limited signal is bandpass filtered, using a notch filter and summer, to limit it to the range of possible ST frequency. Power of the bandpass filtered signal is detected, and compared with detected power of a version of the bandpass filtered signal from which any sinusoidal signal has been eliminated, independent of frequency, to provide for ST detection. A function [x(k)+x(k-2)]x(k-2)-[x(k-1)+x(k-3)]x(k-3) for successive samples x(k) of the bandpass filtered signal is used for the sinusoidal signal elimination. The invention can also be used to detect other tones.
28 Citations
12 Claims
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1. A tone detector comprising:
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a power detector for detecting power of an input signal; a sinusoidal signal eliminator responsive to the input signal to eliminate any sinusoidal signal therein independently of its frequency within a bandwidth of the input signal; a power detector for detecting power of an output of the sinusoidal signal eliminator; and a comparator responsive to the powers detected by the power detectors to provide an indication of the presence or absence of a tone in the input signal; wherein the input signal comprises a sampled signal having successive samples x(k), and the sinusoidal signal eliminator comprises apparatus for producing at its output samples substantially equal to {x(k)+x(k-2)}x(k-2)-{x(k-1)+x(k-3)}x(k-3). - View Dependent Claims (2, 3, 4, 5)
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6. A detector for detecting a signalling tone in a wireless communications system using frequency modulation, comprising:
an amplitude limiter responsive to samples of a demodulated signal for producing a limited signal; a bandpass filter for filtering the limited signal to produce a filtered signal having a bandwidth corresponding to a possible frequency range of the signalling tone; a sinusoidal signal eliminator responsive to the filtered signal to eliminate any sinusoidal signal therein independently of its frequency within said bandwidth; power detectors for determining powers of the filtered signal and an output of the sinusoidal signal eliminator; and a comparator responsive to the powers determined by the power detectors to determine the presence or absence of the signalling tone; wherein the sinusoidal signal eliminator is arranged to produce at its output, in response to successive samples x(k) of the filtered signal, samples substantially equal to {x(k)+x(k-2)}x(k-2)-{x(k-1)+x(k-3)}x(k-3). - View Dependent Claims (7)
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8. A method of tone detection comprising the steps of:
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eliminating any sinusoidal signal from an input signal which may contain a tone to be detected, said step of eliminating any sinusoidal signal from the input signal comprising producing output samples substantially equal to {x(k)+x(k-2)}x(k-2)-{x(k-1)+x(k-3)}x(k-3) from successive samples x(k) of the input signal; and comparing powers of the input signal before and after the sinusoidal signal elimination to detect the tone. - View Dependent Claims (9, 10, 11, 12)
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Specification