Dial tone detector

Details Dial tone detector Dial tone detector

H - Electricity

04

M

379/73

H04M 1/00 (2006.01) H04M 1/82 (2006.01) H04M 1/2745 (2006.01)

Patent

CA 1259146

DIAL TONE DETECTOR Abstract of the Disclosure A dial tone detector of improved performance is provided by precise definition of a passband. In one example, virtually infinite roll off is achieved in less than 5 hertz. An incoming analog signal of at least a predetermined amplitude is limited to produce square wave pulses which are counted in a first counter over a period of time determined by a periodic RESET signal. A READ signal occuring just before the RESET signal causes either a valid count state or an invalid count state to be stored depending upon the value of the count in the first counter. When a valid count state is in storage, a second counter counts timing pulses while the valid count state persists, whereby in the second counter a count of greater than a predetermined number indicates the presence of dial tone. - i -

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