Telephone headset amplifier with battery saver, receive line noise reduction, and click-free mute switching

• US RE35,536 E
• Filed: 07/18/1995
• Issued: 06/17/1997
• Est. Priority Date: 02/04/1992
• Status: Expired due to Term

• Current Assignee: ACS Wireless Incorporated (Alaska Communications Systems Group Incorporated)
• Original Assignee: ACS Wireless Incorporated (Alaska Communications Systems Group Incorporated)
• Inventors: Irissou, Pierre R., Reid, Kirk A., Lynn, Dwight D., Chen, Shu-Ren
• Primary Examiner(s): Zele, Krista M.
• Assistant Examiner(s): Wolinsky, Scott
• Application Number:
  US08/503,811
• Time in Patent Office: 700 Days
• Field of Search: 379/390, 379/395, 379/387, 379/388, 379/413, 379/421, 379/430, 379/441, 379/442, 330/254, 381/110, 381/106, 381/187, 381/4, 381/5, 381/6
• US Class Current: 379/395
• CPC Class Codes: H04M 1/60 including speech amplifiers
• CPC Class Codes: H04M 1/6016 in the receiver circuit

Abstract

An amplifier for amplifying a signal received on a telephone line and for providing the amplified signal to a telephone headset. The amplifier draws current from a battery. The current drawn is reduced in the absence of activity on the line. The amplifier includes a timer that generates a first control signal after a time-out time. The timer is reset by a second control signal. A threshold circuit generates the second control signal when the signal on the telephone line is above a threshold level. .[.Finally, a.]. .Iadd.A .Iaddend.circuit, responsive to the first control signal, reduces the current drawn from the power supply. The amplifier may additionally or alternatively include receive line muting. The amplifier includes an automatic level control circuit that receives the signal received on the telephone line and controls the level of the amplified signal provided to the headset to a set level in response to a second control signal. .[.Finally, a.]. .Iadd.A .Iaddend.control circuit generates the second control signal in response to the amplified signal provided to the headset and in response to the inverse of the first control signal. The inverse of the first control signal substantially reduces the set level. Finally, the amplifier includes a microphone amplifier with click-free muting.

Claims

1. An amplifier for amplifying a signal received on a telephone line and for providing an amplified signal to a telephone headset, the amplifier drawing current from a battery, and drawing a reduced current from the battery during periods of inactivity on the telephone line, the amplifier comprising:

timer means for generating a first control signal after a time-out time, the timer means being reset by a second control signal, the timer means comprising;

a current source having an output,

a current mirror,

a long-tail pair including a first transistor and a second transistor connected to the current mirror,

a third transistor including;

a collector connected via a first resistor to the output of the current source;

a base being connected via a second resistor to the collector of the first transistor; and

an emitter,

the base of the first transistor being connected to the junction of the current generator and the first resistor,

a fourth transistor including;

a base connected to the collector of the first transistor;

a collector connected to the base of the second transistor; and

an emitter,

a capacitor having two electrodes, the first electrode being connected to the base of the second transistor, the second electrode being connected to the emitters of the third and fourth transistors, and wherein

the second control signal is connected to the collector of the third transistor and pulls the collector voltage of the third transistor close to the emitter voltage of the third transistor to reset the timer means;

threshold means for generating the second control signal when the signal on the telephone line is above a threshold level; and

means responsive to the first control signal, for reducing the current drawn from the battery.

2. The amplifier of claim 1, wherein the threshold means comprises:

a current source;

two transistors in a long-tail pair, each transistor having an emitter coupled to the current source, a base and a collector; and

an unbalanced current mirror; and

wherein

the base of each transistor is differentially coupled to the telephone line,

the collector of each transistor is connected to the unbalanced current mirror, and

the second control signal is taken from the collector of one of the transistors.

3. The amplifier of claim 1, wherein the threshold means comprises:

a current source;

a resistor;

a first transistor;

a second transistor having a collector, an emitter, and a base;

a third transistor having a collector, an emitter, and a base; and

a fourth transistor having a collector, an emitter, and a base;

the first transistor including;

a base coupled to the telephone line,

a collector connected to the collector and base the of third transistor and to the base of the fourth transistor, and

an emitter connected to the emitter of the second transistor and to the current source, and wherein;

the second transistor has

its base coupled to the telephoned line,

its collector connected to the collector of the fourth transistor,

the third transistor has its emitter connected to the emitter of the fourth transistor via the resistor, and

the collector of the second transistor provides the second control signal.

4. The amplifier of claim 3, additionally comprising a fifth transistor, the fifth transistor including:

a collector providing the second control signal;

an emitter connected to the emitter of the third transistor; and

a base connected to the collector of the second transistor.

5. The amplifier of claim 1, wherein the means for reducing the current drawn from the battery comprises:

means for generating a reference voltage from the battery, and

means for reducing the reference voltage in response to the first control signal.

19. The amplifier of claim 1, wherein the time-out time of the timer means is determined by the base current of a transistor charging a capacitor. .Iadd.

6. An amplifier for amplifying a signal received on a telephone line and for providing an amplified signal to a telephone headset, the amplified signal having a level, the amplifier comprising:

threshold means for generating a first control signal when the signal received on the telephone line is below a threshold level;

automatic level control means for receiving the signal received on the telephone line and for controlling the level of the amplified signal provided to the headset to a set level in response to a second control signal;

control circuit means for generating the second control signal, the second control signal being a current, in response to the amplified signal provided to the headset and in response to the first control signal, the first control signal substantially reducing the set level, the control circuit means comprising;

a first current mirror means for receiving an input current at an input and generating an output current at an output, the output current providing the second control signal,

a second current mirror means for receiving an input current at an input and generating an output current at an output, the output being connected to the output of the first current generating means, the output current providing the second control signal,

current generating means for generating a current, and

means for selectably connecting the current generated by the current generating means to the input of the first current mirror or to the input of the second current mirror in response to the first control signal.

7. The amplifier of claim 6, wherein the ratio between the output current and the input current of the first current generating means is less than the ratio between the output current and the input current of the second current generating means.

8. The amplifier of claim 6, wherein:

the amplifier additionally comprises volume control means for adjusting the level of the signal provided to the telephone headset; and

the control circuit means is additionally for generating the second control signal in response to the volume control means.

9. The amplifier of claim 8, wherein the volume control means adjusts the level of the signal provided to the telephone headset by changing the current generated by the current generating means.

10. The amplifier of claim 8, wherein the ratio between the output current and the input current of the first current generating means is less than the ratio between the output current and the input current of the second current generating means.

18. The amplifier of claim 6, wherein the control circuit means further comprises:

amplifying means for amplifying the amplified signal provided to the headset to provide a second amplified signal, the amplifying means having a first gain state and a second gain state, higher than the first gain state, the first control signal selecting the second gain state; and

means for generating the second control signal from the second amplified signal.

11. An amplifier for amplifying a signal from a microphone, and for providing the amplified signal to a telephone line, the amplifier comprising:

attenuator means, having an input and an output, for attenuating the signal from the microphone;

a first transistor, including;

a base coupled to the signal from the microphone,

an emitter, and

a collector connected to a load;

a second transistor, including;

a base coupled to the output of the attenuator means,

an emitter, and

a collector connected to the load;

current generating means for generating a current;

switching means for switching the current from the current generating means to the emitter of the first transistor or to the emitter of the second transistor in response to a control signal; and

means for deriving the amplified signal from the load.

12. The amplifier of claim 11, wherein

the first transistor is coupled to a third transistor in a long-tail pair arrangement, and

the second transistor is coupled to a fourth transistor in a long-tail pair arrangement.

13. The amplifier of claim 11, wherein:

the amplifier additionally comprises threshold means for generating the control signal when the signal from the microphone is above a threshold level, and

the switching means switches the current to the emitter of the first transistor when the signal from the microphone is above the threshold level.

14. The amplifier of claim 11, wherein:

the amplifier additionally comprises mute switch means for generating the control signal, and

the switching means switches the current to the emitter of the second transistor in response to the control signal, and

the attenuating means is for attenuating the signal by more than 40 dB.

15. The amplifier of claim 11, wherein

the switching means is a first switching means,

the control signal is a first control signal, and

the amplifier further comprises:

a third transistor, including;

a base coupled to ground,

an emitter, and

collector connected to the load; and

a second switching means for switching the current generated by the current generator to the emitter of the third transistor, or to the first switching means in response to a second control signal.

16. The amplifier of claim 15, further comprising:

threshold means for generating the first control signal when the signal from the microphone is above a threshold level;

mute switch means for generating the second control signal; and

wherein

the first switching means switches the current to the emitter of the first transistor in response to the first control signal when the signal from the microphone is above the threshold level, and

the second switching means switches the current to the emitter of the third transistor when the mute switch means generates the second control signal.

17. The amplifier of claim 11, wherein the first transistor or the second transistor provides a current to the load, and

the current provided to the load remains substantially constant when the switching means switches the current from the emitter of the first transistor to the emitter of the second transistor in response to the control signal.

20. An amplifier for amplifying a signal received on a telephone line and for feeding an amplified signal to a telephone headset, the amplifier having a first state wherein the amplifier amplifies the received signal and draws a normal current from a power supply, and a second state wherein the amplifier draws a reduced current from the power supply, the amplifier switching from the first state to the second state when the received signal remains below a threshold level for a predetermined time-out period, the amplifier switching from the second state to the first state in response to the received signal exceeding the threshold level, the amplifier comprising:

a timer means functioning to maintain the amplifier in the first state as long as the received signal exceeds the threshold level, and for switching the amplifier into the second state after the received signal drops below the thresold level for the predetermined time-out period, the timer means further functioning to switch the amplifier back to the first state when the received signal exceeds the threshold level, wherein the predetermined time-out period of the timer means is determined by the amount of time required to change the voltage on a capacitor from a first voltage to a second voltage; and

reset means, operating in response to the received signal exceeding the threshold, for fully resetting the timer means to the predetermined time-out period by changing the voltage on the capacitor to the first voltage, regardless of the amount of time for which the received signal exceeds the threshold. .Iaddend..Iadd.

21. The amplifier of claim 20, wherein:

the reset means includes;

line monitoring means for generating a reset signal when the received signal exceeds the threshold level, and

means for fully resetting the timer means in response to the reset signal; and

the timer means includes power control means for selectively switching the amplifier between the first state and the second state, the power control means switching the amplifier back to the first state in response to the reset signal. .Iaddend..Iadd.22. The amplifier of claim 21, wherein the

22. current is the base current of a transistor. .Iaddend..Iadd.23. The amplifier of claim 21, wherein the reset means includes:

holding means, triggered by the reset signal and monitoring the voltage on the capacitor, for generating a holding signal, the holding means, after triggering, generating the holding signal for as long as the voltage on the capacitor is different from the first voltage; and

voltage restoring means, operating in response to the holding signal, for restoring the voltage across the capacitor to the first voltage. .Iaddend..Iadd.24. The amplifier of claim 21, wherein the monitoring means including an unbalanced long-tail pair. .Iaddend..Iadd.25. The amplifier of claim 20, wherein the reset means includes line monitoring means for determining when the received signal exceeds the threshold level. .Iaddend..Iadd.26. The amplifier of claim 25, wherein the reset means resets the timer means to the predetermined time-out period when the line monitoring means determines that the received signal has a peak level

23. exceeding 2 mV. .Iaddend..Iadd.27. An amplifier for amplifying a signal received on a telephone line and for feeding an amplified signal to a telephone headset, the amplifier having an first state wherein the amplifier amplifies the received signal and draws a normal current from a power supply, and a second state wherein the amplifier draws a reduced current from the power supply, the amplifier switching from the first state to the second state when the received signal remains below a threshold level for a predetermined time-out period, the amplifier switching from the second state to the first state in response to the received signal exceeding the threshold level, the amplifier comprising:

control means for switching the amplifier from the first state to the second state in response to a control signal reaching a predetermined level;

timing element means, including a capacitor, for applying the control signal to the control means;

control signal changing means for gradually changing the control signal applied by the timing element means from a starting level towards the predetermined level by operating to selectively supply current to, and to remove current from, the capacitor to change a voltage on the capacitor; and

reset means, operating in response to the received signal exceeding the threshold, for resetting the control signal applied by the timing element means to the starting level regardless of the amount of time for which the received signal exceeds the threshold. .Iaddend..Iadd.28. The amplifier of claim 27, wherein the control means includes a transistor having a base-emitter voltage, the transistor switching the amplifier from the first state to the second state in response to the voltage on the capacitor reaching the base-emitter voltage. .Iaddend..Iadd.29. The amplifier of claim 27, wherein the reset means includes a switching

24. element connected across the capacitor. .Iaddend..Iadd.30. The amplifier of claim 27, wherein:

the amplifier additionally comprises line monitoring means for generating a reset signal when the received signal exceeds the threshold; and

the reset means resets the control signal to the starting level in response to the reset signal. .Iaddend..Iadd.31. The amplifier of claim 30, wherein;

the reset means includes a switching element connected across the capacitor; and

the reset means operates the switching element in response to the reset signal. .Iaddend.