Frequency discriminating circuit
AssigneeHitachi, Ltd.
InventorTakayuki Furumoto
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Abstract
The frequency of an input signal is converted to a corresponding digital quantity and the digital quantity is then compared with preset reference values thereby to discriminate the frequency of the input signal.
Claims8
A frequency discriminating circuit for determining whether a received input signal has a predetermined frequency wherein the input signal is converted to a digital signal and the digital-converted input signal is gate-controlled for a given period of time by a count enable signal, and further wherein a count value of a counter which counts the number of pulses of the gate-controlled digital input signal is compared in a comparator with respective reference values representing predetermined frequencies generated by a reference value generator to determine if the input signal corresponds to one of said predetermined frequencies.
A frequency discriminating circuit for determining whether a received tone signal has a predetermined frequency comprising a tone signal receiving circuit for receiving said tone signal and for delivering a first signal indicating the presence of said tone signal and a second signal of a digital-converted version of said tone signal;
- a control circuit for delivering a count enable signal in response to said first signal;
- an AND gate for producing a count signal from said second signal and said count enable signal;
- a counter for counting the count signal from the output of said AND gate;
- and a comparator for comparing the count value of said counter with predetermined reference values representing predetermined frequencies to determine if the frequency of said tone signal corresponds to one of said predetermined frequencies.
Dependencies are inferred from the claim text.