Touch-tone signal generation system

Claim 2

A tone pair generation system including a first tone oscillator for generating a tone at one of a plurality of desired frequencies comprising, a capacitor, a source of direct current voltage for charging said capacitor, a resistance network coupling said source to said capacitor, said resistance network including a first resistor and at least one branch connected in parallel with said first resistor, said one branch including a second resistor and an electronic switch in series, means for applying a switching signal to said electronic switch, and pulse generating means responsiVe to the voltage across said capacitor reaching a predetermined threshold for generating a train of pulses, the frequency of said pulses being a function of the resistance value of said resistance network, having a first value when said switching signal is absent and a second, higher value when said switching signal is present, wherein said pulse generating means comprises voltage threshold detector means connected across said capacitor for providing a triggering signal when the charge on said capacitor reaches said predetermined voltage threshold, one-shot generator means for providing a pulse in response to said triggering signal, and means responsive to said pulse for discharging said capacitor, and wherein the pulse frequency generated by said one-shot generator is twice the desired frequency and said oscillator further comprises means coupling the pulses generated by said one-shot generator to a divide-by-two flip-flop, said flip-flop providing a symmetrical square wave at the desired frequency.

Claim 3

A tone pair generation system including a first tone oscillator for generating a tone at one of a plurality of desired frequencies comprising, a capacitor, a source of direct current voltage for charging said capacitor, a resistance network coupling said source to said capacitor, said resistance network including a first resistor and at least one branch connected in parallel with said first resistor, said one branch including a second resistor and an electronic switch in series, means for applying a switching signal to said electronic switch, and pulse generating means responsive to the voltage across said capacitor reaching a predetermined threshold for generating a train of pulses, the frequency of said pulses being a function of the resistance value of said resistance network, having a first value when said switching signal is absent and a second, higher value when said switching signal is present, a square wave generation means responsive to said train of pulses for generating a symmetrical square wave at said desired frequency, and wherein said oscillator means includes amplitude weighting means for adjusting the amplitude of said square wave as a function of the frequency of said square wave.

Claim 4

A tone pair generation system including a first tone oscillator for generating a tone at one of a plurality of desired frequencies comprising, a capacitor, a source of direct current voltage for charging said capacitor, a resistance network coupling said source to said capacitor, said resistance network including a first resistor and at least one branch connected in parallel with said first resistor, said one branch including a second resistor and an electronic switch in series, means for applying a switching signal to said electronic switch, and pulse generating means responsive to the voltage across said capacitor reaching a predetermined threshold for generating a train of pulses, the frequency of said pulses being a function of the resistance value of said resistance network, having a first value when said switching signal is absent and a second, higher value when said switching signal is present, a square wave generation means responsive to said train of pulses for generating a symmetrical square wave at said desired frequency, and wherein said oscillator means includes amplitude weighting means for adjusting the amplitude of said square wave as a function of the frequency of said square wave.

Claim 5

A tone pair generation system in accordance with claim 2 wherein said amplitude weighting means comprises a source of direct current voltage connected across a first weighting resistor connected in series with a second weighting resistor, said square wave being coupled to the junction between said first and second weighting resistors, a third weighting resistor, and means responsive to said switching signal for effectively connecting said third weighting resistor in shunt with said first weighting resistor to alter the amplitude weighting of said square wave.

Claim 6

A tone pair generation system in accordance with claim 3 wherein said third weighting resistor and a diode are connected in series between said source of direct current voltage and the junction between said first and second weighting resistors and said means responsive to said switching signal maintains the junction between said third weighting resistor and said diode at a relatively low potential in the absence of said switching signal so that said diode effectively isolates said third weighting resistor from said junction between said first and second weighting resistors and, in the presence of said switching signal, maintains said junction between said third weighting resistor and said diode at a relatively high potential so that said diode effectively connects said third weighting resistor to said junction between said first and second weighting resistors.

Claim 7

A tone pair generation system including a first tone oscillator for generating a tone at one of a plurality of desired frequencies comprising, a capacitor, a source of direct current voltage for charging said capacitor, a resistance network coupling said source to said capacitor, said resistance network including a first resistor and at least one branch cOnnected in parallel with said first resistor, said one branch including a second resistor and an electronic switch in series, means for applying a switching signal to said electronic switch, and pulse generating means responsive to the voltage across said capacitor reaching a predetermined threshold for generating a train of pulses, the frequency of said pulses being a function of the resistance value of said resistance network, having a first value when said switching signal is absent and a second, higher value when said switching signal is present, a square wave generation means responsive to said train of pulses for generating a symmetrical square wave at said desired frequency, and wherein said tone oscillator further comprises low pass filter means for attenuating undesired odd harmonics of said square wave, and wherein said low pass filter means provides attenuation which increases with frequency thereby attenuating the fundamental frequency of said square wave and wherein said tone oscillator further comprises amplitude weighting means to compensate for said attenuation of said fundamental frequency.

Claim 8

A tone pair generation system including a first tone oscillator for generating a tone at one of a plurality of desired frequencies comprising, a capacitor, a source of direct current voltage for charging said capacitor, a resistance network coupling said source to said capacitor, said resistance network including a first resistor and at least one branch cOnnected in parallel with said first resistor, said one branch including a second resistor and an electronic switch in series, means for applying a switching signal to said electronic switch, and pulse generating means responsive to the voltage across said capacitor reaching a predetermined threshold for generating a train of pulses, the frequency of said pulses being a function of the resistance value of said resistance network, having a first value when said switching signal is absent and a second, higher value when said switching signal is present, a square wave generation means responsive to said train of pulses for generating a symmetrical square wave at said desired frequency, and wherein said tone oscillator further comprises low pass filter means for attenuating undesired odd harmonics of said square wave, and wherein said low pass filter means provides attenuation which increases with frequency thereby attenuating the fundamental frequency of said square wave and wherein said tone oscillator further comprises amplitude weighting means to compensate for said attenuation of said fundamental frequency.

Claim 9

A tone pair generation system including a first tone oscillator for generating a tone at one of a plurality of desired frequencies comprising, a capacitor, a source of direct current voltage for charging said capacitor, a resistance network coupling said source to said capacitor, said resistance network including a first resistor and at least one branch connected in parallel with said first resistor, said one branch including a second resistor and an electronic switch in series, means for applying a switching signal to said electronic switch, and pulse generating means responsive to the voltage across said capacitor reaching a predetermined threshold for generating a train of pulses, the frequency of said pulses being a function of the resistance value of said resistance network, having a first value when said switching signal is absent and a second, higher value when said switching signal is present, and a second tone oscillator similar to the first-named tone oscillator, one of said tone oscillators being a ''''high'''' group oscillator for providing a selected one of a group of relatively high frequencies, the other of said tone oscillators being a ''''low'''' group oscillator for providing a selected one of a group of relatively low frequencies, and means for combining the outputs of said tone oscillators to provide a tone pair signal having tones at one of said relatively high frequencies and one of said relatively low frequencies, and wherein each of said oscillators comprise a high pass network to block the direct current component of the provided tone, said high pass networks introducing attack transients, each of said oscillators comprising means for determining the phase of said provided tone, the hase of said tone provided by said ''''high'''' group oscillator being opposite to the phase of said tone provided by said ''''low'''' group oscillator, whereby said transients are substantially canceled.

Claim 10

A tone pair generation system including a first tone oscillator for generating a tone at one of a plurality of desired frequencies comprising, a capacitor, a source of direct current voltage for charging said capacitor, a resistance network coupling said source to said capacitor, said resistance network including a first resistor and at least one branch connected in parallel with said first resistor, said one branch including a second resistor and an electronic switch in series, means for applying a switching signal to said electronic switch, and pulse generating means responsive to the voltage across said capacitor reaching a predetermined threshold for generating a train of pulses, the frequency of said pulses being a function of the resistance value of said resistance network, having a first value when said switching signal is absent and a second, higher value when said switching signal is present, and a second tone oscillator similar to the first-named tone oscillator, one of said tone oscillators being a ''''high'''' group oscillator for providing a selected one of a group of relatively high frequencies, the other of said tone oscillators being a ''''low'''' group oscillator for providing a selected one of a group of relatively low frequencies, and means for combining the outputs of said tone oscillators to provide a tone pair signal having tones at one of said relatively high frequencies and one of said relatively low frequencies, and wherein each of said oscillators comprise a high pass network to block the direct current component of the provided tone, said high pass networks introducing attack transients, each of said oscillators comprising means for determining the phase of said provided tone, the hase of said tone provided by said ''''high'''' group oscillator being opposite to the phase of said tone provided by said ''''low'''' group oscillator, whereby said transients are substantially canceled.

Claim 11

A tone pair generation system comprising: a first tone oscillator, a second tone oscillator, each tone oscillator comprising means for generating a selected tone, each tone oscillator comprising a high pass network for blocking the direct current component of the selected tone, said high pass networks introducing attack transients, each of said oscillators comprising means for determining the phase of said provided tone, the phase of said tone provided by said first oscillator being opposite to the phase of said tone provided by said second oscillator, summing means for summing the output from said first and second tone oscillators, whereby said attack transients are substantially canceled.

Claim 12

A tone pair generation system comprising: a first tone oscillator, a second tone oscillator, each tone oscillator comprising means for generating a selected tone, each tone oscillator comprising a high pass network for blocking the direct current component of the selected tone, said high pass networks introducing attack transients, each of said oscillators comprising means for determining the phase of said provided tone, the phase of said tone provided by said first oscillator being opposite to the phase of said tone provided by said second oscillator, summing means for summing the output from said first and second tone oscillators, whereby said attack transients are substantially canceled.

Claim 13

A tone oscillator comprising means for generating a square wave having a selected frequency, low pass filter means for suppressing odd harmonics of said square wave, said low pass filter means providing attenuation which increases with frequency, and amplItude weighting means for compensating for the attenuation of said selected frequency by said filter means, said amplitude weighting means being connected between said square wave generating means and said low pass filter means.

Claim 14

A tone oscillator comprising means for generating a square wave having a selected frequency, low pass filter means for suppressing odd harmonics of said square wave, said low pass filter means providing attenuation which increases with frequency, and amplItude weighting means for compensating for the attenuation of said selected frequency by said filter means, said amplitude weighting means being connected between said square wave generating means and said low pass filter means.

Claim 15

A tone oscillator in accordance with claim 8, wherein said oscillator further comprises means responsive to a logic level signal for selecting said selected frequency and wherein said amplitude weighting means comprises means responsive to said logic level signal for selecting a magnitude of amplitude weighting appropriate for said compensation of the attenuation of said selected frequency.

Claim 16

A tone oscillator in accordance with claim 9, wherein said amplitude weighting means comprises a source of direct current voltage connected across a first weighting resistor connected in series with a second weighting resistor, said square wave being coupled to the junction between said first and second weighting resistors, a third weighting resistor, and means responsive to said logic level signal for effectively connecting said third weighting resistor in shunt with said first weighting resistor to alter the amplitude weighting of said square wave.

Claim 17

A tone oscillator in accordance with claim 10, wherein said third weighting resistor and a diode are connected in series between said source of direct current voltage and the junction between said first and second weighting resistors and said means responsive to said logic level signal maintains the junction between said third weighting resistor and said diode at a relatively low potential in the absence of said logic level signal so that said diode effectively isolates the third weighting resistor from said first and second weighting resistors and, in the presence of said logic level signal, maintains said junction between said third weighting resistor and said diode at a relatively high potential so that said diode effectively connects said third weighting resistor to said junction between said first and second weighting resistors.