Signal level expansion apparatus as for a telecommunications system
First Claim
1. A signal level expansion system comprising:
- means for applying an input signal;
variable attenuator means, coupled to receive said input signal and responsive to a control signal, for providing an output signal representing a reduced-amplitude version of said input signal;
amplifier means, coupled to said variable attenuator means for amplifying the signal provided thereby;
signal detection means, coupled to said amplifier means and responsive to the amplitude of the signals provided thereby for generating said control signal including;
a switch, coupled to said amplifier means, to a source of operating potential and to a source of reference potential and biased to establish a conduction path between said source of operating potential and said source of reference potential, wherein said switch is responsive to the amplitude of the signal provided by said amplifier means being above a threshold value for increasing the impedance of the conduction path between the source of operating potential and the source of reference potential; and
means, coupled to said switch, for generating said control signal, said generated control signal being in a state which acts to decrease the level of attenuation provided by the variable attenuation means when the switch exhibits said increased impedance.
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Abstract
A signal level expansion system for use in a telephone device is described which includes a level expansion circuit and an optional microphone enclosure. The circuit includes a voltage divider circuit which is used as a variable attenuator. The voltage divider has a junction field effect transistor (JFET) in its takeoff leg. The signal provided by the voltage divider is applied to an amplifier and then fed to a switch which detects voice signals. When a voice signal is detected having a level above a predetermined threshold, a timing circuit is energized. The timing circuit is connected to the JFET and, when energized, tends to increase the resistance in the takeoff leg of the voltage divider, increasing the signal level applied to the amplifier. The microphone enclosure surrounds the sides of the microphone with layers of rigid and resilient materials. These materials tend to attenuate all sound signals except those incident on the top of the microphone, which is positioned to receive speech signals from a user.
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Citations
13 Claims
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1. A signal level expansion system comprising:
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means for applying an input signal; variable attenuator means, coupled to receive said input signal and responsive to a control signal, for providing an output signal representing a reduced-amplitude version of said input signal; amplifier means, coupled to said variable attenuator means for amplifying the signal provided thereby; signal detection means, coupled to said amplifier means and responsive to the amplitude of the signals provided thereby for generating said control signal including; a switch, coupled to said amplifier means, to a source of operating potential and to a source of reference potential and biased to establish a conduction path between said source of operating potential and said source of reference potential, wherein said switch is responsive to the amplitude of the signal provided by said amplifier means being above a threshold value for increasing the impedance of the conduction path between the source of operating potential and the source of reference potential; and means, coupled to said switch, for generating said control signal, said generated control signal being in a state which acts to decrease the level of attenuation provided by the variable attenuation means when the switch exhibits said increased impedance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A signal level expansion system comprising:
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means for applying an input signal; variable attenuator means, coupled to receive said input signal and responsive to a control signal, for providing an output signal representing a reduced-amplitude version of said input signal, said variable attenuator means including; resistance means, having first and second terminals and coupled to receive said input signal at said first terminal; and variable conduction means having a principle conduction path between first and second electrodes the conductivity of said principle conduction path being controlled in response to said control signal applied to a third electrode, said first electrode being coupled to the second terminal of said resistance means and said second electrode being coupled to a source of reference potential; wherein the output signal of said variable attenuator means is taken between the first electrode of said variable conduction means and said source of reference potential; and amplifier means, coupled to said variable attenuator means for amplifying the signal provided thereby; signal detection means, coupled to said amplifier means and responsive to the amplitude of the signals provided thereby for generating said control signal which acts to decrease the level of attenuation provided by the variable attenuator means in response to an increase in the amplitude of the signal provided by the amplifier means, said signal detection means including; switch means, coupled to receive the signal provided by said amplifier means, for generating said control signal that is in a first state and a second state when the amplitude of the signal provided by said amplifier is respectively less than and greater than a threshold value; and timing means, coupled to said switch means for holding said control signal in said second state for a predetermined time interval; and feature switching means, coupled between a source of operating potential and said timing means for forcing said control signal to be in said second state to selectively disable said variable attenuation means.
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13. A signal level expansion system comprising:
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means for applying an input signal; variable attenuator means, coupled to receive said input signal and responsive to a control signal, for providing an output signal representing a reduced-amplitude version of said input signal, said variable attenuator means including; first and second resistance means, each having first and second terminals, said first resistance means coupled to receive said input signal at said first terminal; variable conduction means having a principle conduction path between first and second electrodes the conductivity of said principle conduction path being controlled in response to said control signal applied to a third electrode, said first electrode being coupled to the second terminal of said first resistance means and said second electrode being coupled to the first electrode of said second resistance means, wherein the second electrode of said second resistance is coupled to a source of reference potential; and attenuation control switching means having a first terminal coupled to the second terminal of said variable conduction means and a second terminal coupled to said source of reference potential, said attenuation control switching means being operable to change the level of attenuation provided by said variable attenuator means in response to said control signal; wherein the output signal of said variable attenuator means is taken between the first electrode of said variable conduction means and said source of reference potential; and amplifier means, coupled to said variable attenuator means for amplifying the signal provided thereby; signal detection means, coupled to said amplifier means and responsive to the amplitude of the signals provided thereby for generating said control signal which acts to decrease the level of attenuation provided by the variable attenuator means in response to an increase in the amplitude of the signal provided by the amplifier means, said signal detection means including switch means, coupled to receive the single provided by said amplifier means, for generating said control signal that is in a first state and a second state when the amplitude of the signal provided by the amplifier is respectively less than and greater than a threshold value.
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Specification