Patent ID: 8379838

Claim:
A tone detector comprising: a comparator configured to connect to an input, the input intermittently receiving a tone signal, such that the comparator generates a square wave output signal in response to the tone signal; one or more edge detectors configured to detect an edge of the square wave signal and responsive to detection of an edge, generate a reset signal; a counter configured to generate a counter output signal unless reset by receipt of the reset signal prior to reaching a maximum counter value; a maximum value detector configured to receive the counter output signal and generate a maximum value signal; a logic element configured to receive the maximum value signal and an output from the one or more edge detectors and responsive thereto, generate a flip flop clocking signal; and a flip flop configured to receive the square wave signal and the maximum value signal such that in response to the maximum value signal and the square wave signal the flip flop outputs a first signal when a tone signal is not present at the input and a second signal when a tone signal is present at the input.