Tone detector

Claim 2

A tone detector circuit comprising: means for filtering an input signal to produce a first output signal at a first selected frequency, said means for filtering comprising amplifier means including an inverting and a noninverting input lead and an output lead, first feedback means connecting said output lead to said inverting input lead, second feedback means connecting said output lead to said noninverting input lead, means connecting said non-inverting input lead to a first reference potential, means for transmitting said input signal to said inverting input lead, and means electrically connecting said means for transmitting to said output lead; means for detecting said first output signal to produce a second output signal; and means for comparing said second output signal to a reference signal to produce a bilevel output signal, said bilevel output signal having a first level when said first output signal has an amplitude greater than a selected value and Said bilevel output signal having a second level when said first output signal has an amplitude less than said selected value.

Claim 3

A circuit as in claim 1 wherein said first feedback means comprises a resistor; said second feedback means comprises a resistor; said means connecting said non-inverting input lead to said first reference potential comprises a resistor; said means for transmitting comprises a resistive T network connected in series with a first capacitor; and said means electrically connecting said means for transmitting to said output lead comprises a second capacitor connecting the node between said resistive T network and said first capacitor to said output lead.

Claim 4

A circuit as in claim 2 wherein said resistive T network comprises first and second resistors connected in series and a third resistor connected between the node of said first and second resistors and said first reference potential.

Claim 5

A circuit as in claim 3 wherein said first reference potential comprises the common potential of the circuit.

Claim 6

A tone detector circuit comprising: means for filtering an input signal to produce a first output signal at a first selected frequency; means for detecting said first output signal to produce a second output signal, said means for detecting comprising first and second transistors each possessing an emitter, a collector, and a base, means electrically connecting the emitters of said first and second transistors to a first reference potential, means electrically connecting the bases of said first and second transistors to an input lead to said means for detecting, said input lead receiving said first output signal, means electrically connecting the collector of said first transistor to a second reference potential, means electrically connecting the collector of said second transistor to said second reference potential; and means electrically connecting the base of said second transistor to a third reference potential so as to attenuate the AC component of said first output signal; and means for comparing said second output signal to a reference signal to produce a bilevel output signal, said bilevel output signal having a first level when said first output signal has an amplitude greater than a selected value and said bilevel output signal having a second level when said first output signal has an amplitude less than said selected value.

Claim 7

A tone detector circuit comprising: means for filtering an input signal to produce a first output signal at a first selected frequency; means for detecting said first output signal to produce a second output signal, said means for detecting comprising first and second transistors each possessing an emitter, a collector, and a base, means electrically connecting the emitters of said first and second transistors to a first reference potential, means electrically connecting the bases of said first and second transistors to an input lead to said means for detecting, said input lead receiving said first output signal, means electrically connecting the collector of said first transistor to a second reference potential, means electrically connecting the collector of said second transistor to said second reference potential; and means electrically connecting the base of said second transistor to a third reference potential so as to attenuate the AC component of said first output signal; and means for comparing said second output signal to a reference signal to produce a bilevel output signal, said bilevel output signal having a first level when said first output signal has an amplitude greater than a selected value and said bilevel output signal having a second level when said first output signal has an amplitude less than said selected value.

Claim 8

A circuit as in claim 5 wherein said means electrically connecting the emitters of said transistors to a first reference potential comprises first and second resistors connecting said emitters and a third resistor connecting the node between said first and second resistors to said first reference potential.

Claim 9

A circuit as in claim 5 wherein said means electrically connecting the bases of said first and second transistors to an input lead to said means for detecting comprises fourth and fifth resistors, approximately equal in value, connecting the bases of said first and second transistors, respectively, to said input lead to said means for detecting.

Claim 10

A circuit as in claim 5 wherein said means electrically connecting the collector of said first transistor to said second reference potential comprises a sixth resitor; said means electrically connecting the collector of said second transistor to said second reference potential comprises a seventh transistor connected in series with said sixth transistor; and said means electrically connecting the base of said second transistor to said third reference potential comprises a capacitor.

Claim 11

A circuit as in claim 8 wherein said third reference potential comprises the common potential of the circuit.

Claim 12

A tone detector circuit comprising: means for filtering an input signal to produce a first output signal at a first selected frequency; means for detecting said first output signal to produce a second output signal; and means for comparing said second output signAl to a reference signal to produce a bilevel output signal, said bilevel output signal having a first level when said first output signal has an amplitude greater than a selected value and said bilevel output signal having a second level when said first output signal has an amplitude less than said selected value, said means for comparing comprising: means for integrating said second output signal to produce a first integrated signal; comparison means for comparing said first integrated signal to a threshold level and producing a high or low level signal in response thereto; means for producing a high or low level output signal in response to a low or high level signal, respectively, from said comparison means; and means for changing, in response to a low level output signal from said means for producing, the threshold level to which said first integrated signal is compared thereby to lower the level of said second output signal required to maintain a low level signal from said means for comparing.

Claim 13

A tone detector circuit comprising: means for filtering an input signal to produce a first output signal at a first selected frequency; means for detecting said first output signal to produce a second output signal; and means for comparing said second output signAl to a reference signal to produce a bilevel output signal, said bilevel output signal having a first level when said first output signal has an amplitude greater than a selected value and said bilevel output signal having a second level when said first output signal has an amplitude less than said selected value, said means for comparing comprising: means for integrating said second output signal to produce a first integrated signal; comparison means for comparing said first integrated signal to a threshold level and producing a high or low level signal in response thereto; means for producing a high or low level output signal in response to a low or high level signal, respectively, from said comparison means; and means for changing, in response to a low level output signal from said means for producing, the threshold level to which said first integrated signal is compared thereby to lower the level of said second output signal required to maintain a low level signal from said means for comparing.

Claim 14

A tone detector circuit comprising: means for filtering an input signal to produce a first output signal at a first selected frequency; means for detecting said first output signal to produce a second output signal; and means for comparing said second output signal to a threshold level to produce a bilevel output signal, said bilevel output signal having a first level when said first output signal has an amplitude greater than a selected value and said bilevel output signal having a second level when said first output signal has an amplitude less than said selected value, said means for comparing comprising means for integrating said second output signal to produce a first integrated signal; comparison means for comparing said first integrated signal to the threshold level and for producing a high or low level signal in response thereto; means for producing a high or low level output signal in response to a low or high level signal, respectively, from said comparison means; and means for changing, in response to a low level signal from said means for producing, the threshold level to which said first integrated signal is compared thereby to lower the level of said second output signal required to maintain a low level output signal from said means for comparing, said comparison means comprising amplifier means including an inverting and a non-inverting input lead and an output lead; voltage divider means connected between a second reference potential and a third reference potential, said inverting input lead being connected to a selected point on said voltage divider means thereby to generate said threshold level; and means for connecting said non-inverting input lead to said means for integrating thereby enabling said non-inverting input lead to receive said first integrated signal.

Claim 15

A tone detector circuit comprising: means for filtering an input signal to produce a first output signal at a first selected frequency; means for detecting said first output signal to produce a second output signal; and means for comparing said second output signal to a threshold level to produce a bilevel output signal, said bilevel output signal having a first level when said first output signal has an amplitude greater than a selected value and said bilevel output signal having a second level when said first output signal has an amplitude less than said selected value, said means for comparing comprising means for integrating said second output signal to produce a first integrated signal; comparison means for comparing said first integrated signal to the threshold level and for producing a high or low level signal in response thereto; means for producing a high or low level output signal in response to a low or high level signal, respectively, from said comparison means; and means for changing, in response to a low level signal from said means for producing, the threshold level to which said first integrated signal is compared thereby to lower the level of said second output signal required to maintain a low level output signal from said means for comparing, said comparison means comprising amplifier means including an inverting and a non-inverting input lead and an output lead; voltage divider means connected between a second reference potential and a third reference potential, said inverting input lead being connected to a selected point on said voltage divider means thereby to generate said threshold level; and means for connecting said non-inverting input lead to said means for integrating thereby enabling said non-inverting input lead to receive said first integrated signal.

Claim 16

A circuit as in claim 11 wherein said means for producing comprises: a transistor containing a base, a collector, and an emitter; and means for transmitting said low or high level signal from said comparison means to said base thereby to produce on said collector said high or low level output signal produced by said means for producing.

Claim 17

A circuit as in claim 12 wherein said means for changing comprises: resistive means connecting said collector to said selected point, thereby to lower the potential at said selected point and thus said threshold level when said transistor draws collector current.