Patent ID: 8731112
Filing Date: 2014-05-20
Classification: H04L,H04Q

Abstract:
1. A tone signal circuit comprising: an analog low-pass filter operable to extract a frequency band including at least a tone signal component, from a demodulated signal in a receiver adapted to receive and demodulate a communication signal; an analog-to-digital converter operable to A/D convert an output of the analog low-pass filter from an analog value to digital value and output the digital value as a digital demodulated signal; a Modified Goertzel filter in which a Goertzel filter is modified so that a numerator of transfer function is 1, and that operable to receive an input of the digital demodulated signal; an envelope detector operable to detect an envelope of an output of the Modified Goertzel filter; a differentiator operable to derive a derivative value of the envelope detected by the envelope detector; and a first determination section operable, when the derivative value output from the differentiator is maintained to be equal to or greater than a given first threshold value, to determine that a first prerequisite for existence of the tone signal component is satisfied.