Abstract A digital tone signal detector having N-path filters eliminates the need for a variable-frequency active filter and makes possible the use of integrated circuits in paging receivers, transceivers, mobile radio equipment and so forth. The tone signal detector comprises a clock pulse generator, an N-path filter (where N is an integer equal to or greater than 2), a low-pass filter, a wave shaping circuit, a gate circuit, a counter and detection circuitry. The clock pulse generator generates clock pulses of a predetermined frequency Fc equal to N times the frequency fo of tone signals. The N-path filter samples and selects the tone signal of the frequency fo according to the output of the clock pulse generator. The low-pass filter converts the sampled tone signal including the clock frequency component into a form close to sine wave to eliminate the clock frequency component. The wave shaping circuit shapes the output of the low-pass filter to produce pulses, and the gate circuit passes the clock pulses in accordance with the output of the wave shaping circuit. The counter is connected to the output of said gate circuit to count the number of the output pulses of the gate circuit. The detection circuitry is connected to the counter to detect whether or not the received tone signals are the designated tone signals by the count accumulated by the counter in a prescribed period of time.
A tone signal detector for receiving and detecting tone signals comprising: a clock signal generator for generating clock pulses of a frequency equal to N times the frequency of said tone signals, where N is an integer equal to or greater than 2; an N-path filter for sampling and selecting said tone signals according to the output signals of said clock signal generator; a low-pass filter connected to said N-path filter for eliminating the component of the frequency of said cook pulses included in the sampled tone signals; a wave shaping circuit for shaping the signals having passed said low-pass filter to produce pulses; a gate circuit for controlling the passing of said clock pulses in accordance with the output pulses of said wave shaping circuit; a counter for counting the number of the output pulses of said gate circuit; and means responsive to said clock pulses and the output of said counter for detecting whether or not said tone signals are the designated signals by the count of said counter in a prescribed period of time.
Claim 2
Dependent Claim
177 words
A tone signal detector for receiving and detecting tone signals comprising: a clock signal generator for generating clock pulses of a frequency equal to N times the frequency of said tone signals, where N is an integer equal to or greater than 2; an N-path filter for sampling and selecting said tone signals according to the output signals of said clock signal generator; a low-pass filter connected to said N-path filter for eliminating the component of the frequency of said cook pulses included in the sampled tone signals; a wave shaping circuit for shaping the signals having passed said low-pass filter to produce pulses; a gate circuit for controlling the passing of said clock pulses in accordance with the output pulses of said wave shaping circuit; a counter for counting the number of the output pulses of said gate circuit; and means responsive to said clock pulses and the output of said counter for detecting whether or not said tone signals are the designated signals by the count of said counter in a prescribed period of time.
Claim 3
Dependent Claim
30 words
A tone signal detector as claimed in claim 1 wherein said integration means comprises means capable of varying said preset number in accordance with the frequency of said tone signals.
Claim 4
Dependent Claim
109 words
A tone signal detector as claimed in claim 1 wherein said means for detecting comprises: frequency decision means connected to the output of said counter and controlled thereby to count said clock pulses and produce an output if the number n of clock pulses counted during the output period of said first counter satisfies the relation N-α≦n≦N+α, where α is a predetermined constant less than N; and integration means connected to the output of said frequency decision means and controlled thereby to count said clock pulses and produce an output if a preset number of outputs are produced by said frequency decision means within said prescribed period of time.