Tone detector system

Claim 2

A tone detector system for communications receiving equipment for detecting a tone signal transmitted by communications transmitting equipment comprising: circuit means for supplying audio signals received from the transmitting equipment and detected by the receiving equipment; frequency selective amplifier circuit means coupled to the audio signal supply circuit means and selectively responsive to signal components at the tone frequency of the tone signal for producing an amplified tone signal; peak detector circuit means responsive to the amplified tone signal for producing output pulses coincident with the peak portions of a given polarity of each cycle of the tone signal which exceed a predetermined level; pulse generator circuit means responsive to each peak detector output pulse for producing a pulse of fixed minimum duration; time constant circuit means responsive to the pulses produced by the pulse generator circuit means for producing an output signal which does not exceed a predetermined level so long as the time interval between successive pulse generator pulses does not exceed a predetermined value; and level sensitive bistable circuit means coupled to the output of the time constant circuit means for producing a distinctive and non-varying output signal during the occurrence of said tone signal.

Claim 3

A tone detector system in accordance with claim 1 wherein the frequency selective amplifier circuit means includes: direct-coupled amplifier circuit means having an input circuit coupled to the audio signal supply circuit means; resistor-capacitor filter circuit means coupled between an input and an output circuit of the direct-coupled amplifier circuit means for providing a negative feedback path therebetween, such filter circuit means being constructed to have a substantial dip in its signal transfer characteristic at the tone frequency of the tone signal; and circuit means for coupling the output of the direct-coupled amplifier circuit means to the input of the peak detector circuit means.

Claim 4

A tone detector system in accordance with claim 2 wherein the resistor-capacitor filter circuit means is a twin-T filter circuit consisting solely of resistors and capacitors.

Claim 5

A tone detector system in accordance with claim 2 wherein the resistor-capacitor filter circuit means comprises a twin-T filter circuit wherein one T section is a low pass filter for passing signal components at frequencies less than the tone frequency of the tone signal and the other T section is a high pass filter for passing signal components at frequencies greater than the tone frequency of the tone signal.

Claim 6

A tone-to-digital converter comprising: circuit means for supplying a tone signal; peak detector circuit means responsive to the tone signal for producing output pulses coincident with the peak portions of a given polarity of each cycle of the tone signal which exceed a predetermined level; pulse generator circuit means responsive to each peak detector output pulse for producing a pulse of fixed minimum duration; time constant circuit means responsive to the pulses produced by the pulse generator circuit means for producing an output signal which does not exceed a predetermined level so long as the time interval between successive pulse generator pulses does not exceed a predetermined value; and level sensitive bistable circuit means coupled to the output of the timE constant circuit means for producing a distinctive and non-varying output signal during the occurrence of said tone signal.

Claim 7

A tone-to-digital converter comprising: circuit means for supplying a tone signal; peak detector circuit means responsive to the tone signal for producing output pulses coincident with the peak portions of a given polarity of each cycle of the tone signal which exceed a predetermined level; pulse generator circuit means responsive to each peak detector output pulse for producing a pulse of fixed minimum duration; time constant circuit means responsive to the pulses produced by the pulse generator circuit means for producing an output signal which does not exceed a predetermined level so long as the time interval between successive pulse generator pulses does not exceed a predetermined value; and level sensitive bistable circuit means coupled to the output of the timE constant circuit means for producing a distinctive and non-varying output signal during the occurrence of said tone signal.

Claim 8

A tone-to-digital converter in accordance with claim 5 wherein the peak detector circuit means includes: a grounded emitter transistor circuit having its collector circuit coupled to the input of the pulse generator circuit means; and Zener diode means coupled in series between the tone signal supply circuit means and the base electrode circuit of the transistor circuit for passing thereto signal components of a first polarity which exceed a predetermined amplitude level.

Claim 9

A tone-to-digital converter in accordance with claim 5 wherein the time constant circuit means includes capacitor means and the pulse generator circuit means is constructed to produce pulses of fixed minimum duration, which minimum duration is sufficient to discharge the capacitor means.

Claim 10

A tone-to-digital converter in accordance with claim 5 wherein the pulse generator circuit means is a monostable multivibrator circuit.

Claim 11

A tone-to-digital converter in accordance with claim 5 wherein the pulse generator circuit means includes: NOR circuit means having a first input coupled to the output of the peak detector circuit means; NAND circuit means having a first input coupled to the output of the NOR circuit means and having an output coupled to a second input of the NOR circuit means; capacitor means coupled to a second input of the NAND circuit means; inverter circuit means having an input coupled to the output of the NOR circuit means; impedance means coupled between the output of the inverter circuit means and the second input of the NAND circuit means for charging and discharging the capacitor means; and circuit means for supplying the signal appearing at the output of one of the NOR and NAND circuit means to the time constant circuit means.

Claim 12

A tone-to-digital converter in accordance with claim 5 wherein the time constant circuit means includes: capacitor means; resistive charging circuit means for charging the capacitor means; transistor means coupled to the capacitor means and responsive to the pulses produced by the pulse generator circuit means for maintaining the capacitor means discharged during the occurrence of the pulse generator pulses; and circuit means for supplying the signal across the capacitor means to the input of the level sensitive bistable circuit means.

Claim 13

A tone-to-digital converter in accordance with claim 5 wherein the level sensitive bistable circuit means is a Schmitt trigger circuit.

Claim 14

A tone-to-digital converter in accordance with claim 5 wherein the level sensitive bistable circuit means is a digital logic type Schmitt trigger circuit and includes: a plural input coincidence type logic circuit having one input coupled to the output of the time constant circuit means; and circuit means for supplying a steady enabling signal to the other input of the coincidence type logic circuit means.

Claim 15

A tone detector system for a radio telephone mobile unit for detecting first and second audio-frequency tone signals transmitted by a base station comprising: circuit means for supplying audio signals received from the base station and detected by the mobile unit; first tuned amplifier circuit means coupled to the audio signal supply circuit means for selectively amplifying signal components of the first audio frequency tone of one of two signal pairs, each signal pair having first and second audio frequency tones, such first tuned amplifier circuit means including first and second filter circuit means, said first filter circuit means of said first tuned amplifier circuit generating an output in response to the frequency of the first tone signal of the first signal pair, and said second filter circuit means of said first tuned amplifier circuit generating an output in response to the frequency of the first tone signal of tHe second signal pair; second tuned amplifier circuit means coupled to the audio signal supply circuit means for selectively amplifying signal components of the second audio frequency tone of one of two signal pairs, each signal pair having first and second audio frequency tones, such second tuned amplifier circuit means including first and second filter circuit means, said first filter circuit means of said second tuned amplifier circuit generating an output in response to the frequency of the second tone signal of the first signal pair and said second filter circuit means of said second tuned amplifier circuit generating an output in response to the frequency of the second tone signal of the second signal pair; a mode selector switch for signifying selection of a particular one of two operating modes for the mobile unit; and control circuit means coupled to the mode selector switch and to the filter circuit means in the first and second tuned amplifier circuit means for enabling the first filter circuit means in each tuned amplifier circuit means and disabling the second filter circuit means in each tuned amplifier circuit means in one mobile unit operating mode and for enabling the second filter circuit means and disabling the first filter circuit means in the other mobile unit operating mode.

Claim 16

A tone detector system for a radio telephone mobile unit for detecting first and second audio-frequency tone signals transmitted by a base station comprising: circuit means for supplying audio signals received from the base station and detected by the mobile unit; first tuned amplifier circuit means coupled to the audio signal supply circuit means for selectively amplifying signal components of the first audio frequency tone of one of two signal pairs, each signal pair having first and second audio frequency tones, such first tuned amplifier circuit means including first and second filter circuit means, said first filter circuit means of said first tuned amplifier circuit generating an output in response to the frequency of the first tone signal of the first signal pair, and said second filter circuit means of said first tuned amplifier circuit generating an output in response to the frequency of the first tone signal of tHe second signal pair; second tuned amplifier circuit means coupled to the audio signal supply circuit means for selectively amplifying signal components of the second audio frequency tone of one of two signal pairs, each signal pair having first and second audio frequency tones, such second tuned amplifier circuit means including first and second filter circuit means, said first filter circuit means of said second tuned amplifier circuit generating an output in response to the frequency of the second tone signal of the first signal pair and said second filter circuit means of said second tuned amplifier circuit generating an output in response to the frequency of the second tone signal of the second signal pair; a mode selector switch for signifying selection of a particular one of two operating modes for the mobile unit; and control circuit means coupled to the mode selector switch and to the filter circuit means in the first and second tuned amplifier circuit means for enabling the first filter circuit means in each tuned amplifier circuit means and disabling the second filter circuit means in each tuned amplifier circuit means in one mobile unit operating mode and for enabling the second filter circuit means and disabling the first filter circuit means in the other mobile unit operating mode.

Claim 17

A tone detector system in accordance with claim 13 wherein: the first tuned amplifier circuit means includes first direct-coupled amplifier circuit means having an input circuit coupled to the audio signal supply circuit means and the first and second filter circuit means are first and second resistor-capacitor filter circuit means coupled between an input and an output circuit of the first direct-coupled amplifier circuit means for providing negative feedback paths therebetween, said first filter circuit means of said first tuned amplifier being constructed to have a substantial dip in its signal transfer characteristic at the frequency of the first audio tone of the first signal pair, and said second filter circuit means of the first tuned amplifier being constructed to have a substantial dip in its signal transfer characteristic at the frequency of the first audio tone of the second signal pair; and the second tuned amplifier circuit means includes second direct-coupled amplifier circuit means having an input circuit coupled to the audio signal supply circuit means and the first and second filter circuit means are first and second resistor-capacitor filter circuit means coupled between an input and an output circuit of the second direct-coupled amplifier circuit means for providing negative feedback paths therebetween, said first filter circuit means of said second tuned amplifier being constructed to have a substantial dip in its signal transfer characteristic at the frequency of the second audio tone of the first signal pair, and said second filter circuit means of said second tuned amplifier being constructed to have a substantial dip in its signal transfer characteristic at the frequency of the second audio tone of the second signal pair.

Claim 18

A tone detector system in accordance with claim 14 wherein each of the resistor-capacitor filter circuit means in each of the tuned amplifier circuit means is a twin-T filter circuit.

Claim 19

A tone detector system in accordance with claim 14 wherein the control circuit means includes: four coupling diodes individually connected in series between the output of a different one of the resistor-capacitor filter circuit means and the input of its direct-coupled amplifier circuit means; first digital logic circuit means for disabling the coupling diodes associated with the two first filter circuit means when the mode selector switch is in one of its positions; and second digital logic circuit means for disabling the coupling diodes associated with the two second filter circuit means when the mode selector switch is in the other of its positions.

Claim 20

A tone detector system for a radiO telephone mobile unit for detecting first and second audiofrequency tone signals transmitted by a base station comprising: circuit means for supplying audio signals received from the base station and detected by the mobile unit; first tuned amplifier circuit means coupled to the audio signal supply circuit means for selectively amplifying signal components of the first audio frequency tone of one of two signal pairs, each signal pair having first and second audio frequency tones, such first tuned amplifier circuit means including first and second filter circuit means, said first filter circuit means of said first tuned amplifier circuit having a distinctive effect at the frequency of the first tone signal of the first signal pair, and said second filter circuit means of said first tuned amplifier circuit having a distinctive effect at the frequency of the first tone signal of the second signal pair; second tuned amplifier circuit means coupled to the audio signal supply circuit means for selectively amplifying signal components of the second audio frequency tone of one of two signal pairs, each signal pair having first and second audio frequency tones, such second tuned amplifier circuit means including first and second filter circuit means, said first filter circuit means of said second tuned amplifier circuit having a distinctive effect at the frequency of the second tone signal of the first signal pair and said second filter circuit means of said second tuned amplifier circuit having a distinctive effect at the frequency of the second tone signal of the second signal pair; a mode selector switch for signifying selection of a particular one of two operating modes for the mobile unit, said selection including choosing between two signal pairs; control circuit means coupled to the mode selector switch and to the filter circuit means in the first and second tuned amplifier circuit means for enabling the first filter circuit means in each tuned amplifier circuit means and disabling the second filter circuit means in each tuned amplifier circuit means in one mobile unit operating mode and for enabling the second filter circuit means and disabling the first filter circuit means in the other mobile unit operating mode; first tone-to-digital converter circuit means coupled to said first tuned amplifier circuit means for producing a tone signal indicative digital output signal during the occurrence of the first tone signal of the signal pair selected by said mode selector switch; first digital logic circuit means coupled to the output of the first tone-to-digital converter circuit means for producing a tone signal indicative digital output signal during the occurrence of the first tone signal of the signal pair selected by said mode selector switch; second tone-to-digital converter circuit means coupled to said second tuned amplifier circuit means for producing a tone signal indicative digital output signal during the occurrence of the second tone signal of the signal pair selected by said mode selector switch; second digital logic circuit means coupled to the output of the second tone to digital converter circuit means for producing a tone signal indicative digital output signal during the occurrence of the second tone signal of the signal pair selected by said mode selector switch; and circuit means cross-coupling the inputs and outputs of the first and second digital logic circuit means for causing a tone signal indicative digital output signal to appear at the output of only one of the digital logic circuit means at any given instant.

Claim 21

A tone detector system for a radiO telephone mobile unit for detecting first and second audiofrequency tone signals transmitted by a base station comprising: circuit means for supplying audio signals received from the base station and detected by the mobile unit; first tuned amplifier circuit means coupled to the audio signal supply circuit means for selectively amplifying signal components of the first audio frequency tone of one of two signal pairs, each signal pair having first and second audio frequency tones, such first tuned amplifier circuit means including first and second filter circuit means, said first filter circuit means of said first tuned amplifier circuit having a distinctive effect at the frequency of the first tone signal of the first signal pair, and said second filter circuit means of said first tuned amplifier circuit having a distinctive effect at the frequency of the first tone signal of the second signal pair; second tuned amplifier circuit means coupled to the audio signal supply circuit means for selectively amplifying signal components of the second audio frequency tone of one of two signal pairs, each signal pair having first and second audio frequency tones, such second tuned amplifier circuit means including first and second filter circuit means, said first filter circuit means of said second tuned amplifier circuit having a distinctive effect at the frequency of the second tone signal of the first signal pair and said second filter circuit means of said second tuned amplifier circuit having a distinctive effect at the frequency of the second tone signal of the second signal pair; a mode selector switch for signifying selection of a particular one of two operating modes for the mobile unit, said selection including choosing between two signal pairs; control circuit means coupled to the mode selector switch and to the filter circuit means in the first and second tuned amplifier circuit means for enabling the first filter circuit means in each tuned amplifier circuit means and disabling the second filter circuit means in each tuned amplifier circuit means in one mobile unit operating mode and for enabling the second filter circuit means and disabling the first filter circuit means in the other mobile unit operating mode; first tone-to-digital converter circuit means coupled to said first tuned amplifier circuit means for producing a tone signal indicative digital output signal during the occurrence of the first tone signal of the signal pair selected by said mode selector switch; first digital logic circuit means coupled to the output of the first tone-to-digital converter circuit means for producing a tone signal indicative digital output signal during the occurrence of the first tone signal of the signal pair selected by said mode selector switch; second tone-to-digital converter circuit means coupled to said second tuned amplifier circuit means for producing a tone signal indicative digital output signal during the occurrence of the second tone signal of the signal pair selected by said mode selector switch; second digital logic circuit means coupled to the output of the second tone to digital converter circuit means for producing a tone signal indicative digital output signal during the occurrence of the second tone signal of the signal pair selected by said mode selector switch; and circuit means cross-coupling the inputs and outputs of the first and second digital logic circuit means for causing a tone signal indicative digital output signal to appear at the output of only one of the digital logic circuit means at any given instant.