Adaptive transmit amplifier

• US 6,671,371 B1
• Filed: 08/30/1999
• Issued: 12/30/2003
• Est. Priority Date: 08/30/1999
• Status: Expired due to Term

• Current Assignee: Plantronics, Inc.
• Original Assignee: Plantronics, Inc.
• Inventors: Khamashta, Robert M., McNeill, Iain J
• Primary Examiner(s): TIEU, BINH KIEN
• Application Number:
  US09/385,824
• Time in Patent Office: 1,583 Days
• Field of Search: 395/395, 395/387.01, 395/387.02, 381/111, 381/112, 381/113, 381/114, 381/94.2, 379/388.03, 379/390.03, 379/394, 379/398, 379/399.01, 379/419, 379/424, 379/428.02
• US Class Current: 379/387.01
• CPC Class Codes: H04M 1/6008 in the transmitter circuit
• CPC Class Codes: H04M 1/6033 for providing handsfree use or a loudspeaker mode in telephone sets arrangements for preventing acoustic echo H04M9/08

Abstract

An adaptive transmit amplifier for automatically adjusting the transmit output characteristics of a headset adapter output stage includes a detector adapted to detect a value of a bias current in a host microphone transmit circuit. The adaptive transmit amplifier further includes a switching stage coupled to the detector and adapted to select a gain level and impedance level of the headset adapter output stage based upon the bias current value. The adaptive transmit amplifier may further include a logic/timing block coupled to the detector and to the switching stage. The logic/timing block is adapted to control a sequence of detection of the bias current and selection of the gain level and impedance level of the headset adapter output stage. A method of automatically selecting the output characteristics of a headset adapter output stage includes detecting a value of a bias current in a host microphone transmit circuit, and selecting a gain level and impedance level of the headset adapter output stage in response to the value of the bias current.

Claims

1. An adaptive transmit amplifier for automatically adjusting the transmit output characteristics of a headset adapter output stage, the adaptive transmit amplifier comprising:

a detector adapted to detect a value of a bias current in a host telephone transmit circuit; and

a switching stage coupled to the detector and adapted to select a gain level and impedance level of the headset adapter output stage based upon the bias current value.

2. The adaptive transmit amplifier of claim 1 further comprising:

a logic/timing block coupled to the detector and to the switching stage and adapted to control a sequence of detection of the bias current and selection of the gain level and impedance level of the headset adapter output stage.

3. The adaptive transmit amplifier of claim 2 wherein the logic/timing block comprises a window comparator adapted to generate output control signals responsive to the bias current value.

4. The adaptive transmit amplifier of claim 2 wherein the logic/timing block comprises a microcontroller adapted to generate output control signals responsive to the bias current value.

5. The adaptive transmit amplifier of claim 2 wherein the logic/timing block comprises a digital signal processor adapted to monitor the bias current value and adapted to generate output control signals responsive to the bias current value.

6. The adaptive transmit amplifier of claim 1 wherein the detector comprises an opto-coupler responsive to the bias current value.

7. The adaptive transmit amplifier of claim 6 wherein the opto-coupler comprises:

a diode adapted to emit a light signal in response to current; and

a light-sensitive solid-state relay responsive to the light signal emitted from the diode.

8. The adaptive transmit amplifier of claim 1 wherein the detector comprises:

a headset/handset relay adapted to generate impulse signals by switching of the bias current;

a transformer coupled to the headset/handset relay and adapted to generate voltage pulses in response to the impulse signals;

a pulse shaping network coupled to the transformer and adapted to filter the voltage pulses generated by the transformer; and

an integrated detector coupled to the pulse shaping network and adapted to generate an output control signal dependent on the bias current value.

9. The adaptive transmit amplifier of claim 1 wherein the detector comprises:

a Hall Effect sensor coupled to a transmit transformer in the headset adapter output stage and adapted to generate an output control signal dependent on the bias current value.

10. The adaptive transmit amplifier of claim 1 wherein the detector comprises:

a current sensing resistor adapted to generate a voltage signal dependent on the bias current value;

a multiplexer coupled to the current sensing resistor and adapted to transmit the voltage signal from the current sensing resistor; and

an analog-to-digital converter coupled to the multiplexer and adapted to convert the voltage signal into a digital code representing the bias current value.

11. The adaptive transit amplifier of claim 1 wherein the switching stage comprises a gain switching stage.

12. The adaptive transmit amplifier of claim 11 wherein the gain switching stage comprises:

a resistor divider for defining voltage levels based upon an initial voltage level generated in the headset adapter output stage; and

a plurality of analog switches coupled to the resistor divider and adapted to select a gain level from the resistor divider based upon the bias current value.

13. The adaptive transmit amplifier of claim 1 wherein the switching stage further comprises an impedance switching stage.

14. The adaptive transmit amplifier of claim 13 wherein the impedance switching stage comprises:

a second diode for emitting a light signal in response to a threshold value of the bias current; and

a light-sensitive solid-state relay responsive to the light signal emitted from the second diode and adapted to select a load resistor for adjustment of the impedance level of the headset adapter output stage.

15. An adaptive transmit amplifier for automatically adjusting the output characteristics of a headset adapter output stage, the adaptive transmit amplifier comprising:

a first circuit adapted to receive a bias current conducting in a host telephone transmit circuit, the first circuit including;

a first diode adapted to conduct the bias current;

a first resistor stage coupled to the first diode and adapted to receive the bias current conducting through the first diode, the first resistor defining a turn-on voltage level in response to the bias current rising to a defined threshold value;

a plurality of transistors coupled together in a Darlington pair configuration and coupled to the first resistor stage, and adapted to activate in response to the turn-on voltage level;

a second diode coupled to the plurality of transistors and adapted to emit a light signal in response to the activation of the plurality of transistors; and

a light-sensitive solid state relay adapted to generate an output signal for setting an output gain level of the headset adapter output stage in response to the light sign al from the second diode.

16. The adaptive transmit amplifier of claim 15 further comprising:

a second resistor stage coupled to the second diode, the first and second resistor stages defining an output impedance level of the headset adapter output stage if the bias current is at least equal to the defined threshold value, the first resistor stage defining the output impedance level if the bias current is below the defined threshold value.

17. The adaptive transmit amplifier of claim 15 further comprising:

a second circuit coupled to the first circuit and adapted to receive the bias current in the host telephone transmit circuit and select the output gain level and output impedance level of the headset adapter output stage in response to a value of the bias current.

18. An apparatus for selecting the output characteristics of a headset adapter output stage, the apparatus comprising:

a detector configured to generate an output signal that depends on a value of a bias current conducting in a host telephone transmit circuit; and

a switching stage coupled to the detector and configured to select a transmit output characteristic of the headset adapter output stage in response to the output signal from the detector.

19. The apparatus of claim 18 wherein the transmit output characteristic includes an output gain level of the headset adapter output stage.

20. The apparatus of claim 18 wherein the transmit output characteristic includes an output impedance level of the headset adapter output stage.

21. The apparatus of claim 18 further comprising:

a logic/timing block coupled to the detector and to the switching stage and configured to control a sequence of detection of the bias current and selection of the transmit output characteristic of the headset adapter output stage.

22. The apparatus of claim 21 wherein the logic/timing block comprises a window comparator configured to generate an output control signal responsive to the bias current value.

23. The apparatus of claim 21 wherein the logic/timing block comprises a microcontroller configured to generate an output control signal responsive to the bias current value.

24. The apparatus of claim 21 wherein the logic/timing block comprises a digital signal processor configured to monitor the bias current value and configured to generate an output control signal responsive to the bias current value.

25. The apparatus of claim 18 wherein the detector comprises an opto-coupler responsive to the bias current value.

26. The apparatus of claim 25 wherein the opto-couplcr comprises:

a diode configured to emit a light signal in response to current; and

a light-sensitive solid-state relay responsive to the light signal emitted from the diode.

27. The apparatus of claim 18 wherein the detector comprises:

a headset/handset relay configured to generate an impulse signal by switching of the bias current;

a transformer coupled to the headset/handset relay and configured to generate a voltage pulse in response to the impulse signal;

a pulse shaping network coupled to the transformer and configured to filter the voltage pulse generated by the transformer; and

an integrated detector coupled to the pulse shaping network and configured to generate an output control signal dependent on the bias current value.

28. The apparatus of claim 18 wherein the detector comprises:

a Hall Effect sensor coupled to a transmit transformer in the headset adapter output stage and configured to generate an output control signal dependent on the bias current value.

29. The apparatus of claim 18 wherein the detector comprises:

a current sensing resistor configured to generate a voltage signal dependent on the bias current value;

a multiplexer coupled to the current sensing resistor and adapted to transmit the voltage signal from the current sensing resistor; and

an analog-to-digital converter coupled to the multiplexer and adapted to convert the voltage signal into a digital code representing the bias current value.

30. The apparatus of claim 18 wherein the switching stage comprises a gain switching stage.

31. The apparatus of claim 30 wherein the gain switching stage comprises:

a resistor divider for defining voltage levels based upon an initial voltage level generated in the headset adapter output stage; and

a plurality of analog switches coupled to the resistor divider and configured to select a gain level from the resistor divider based upon the bias current value.

32. The apparatus of claim 18 wherein the switching stage further comprises an impedance switching stage.

33. The apparatus of claim 32 wherein the impedance switching stage comprises:

a second diode for emitting a light signal in response to a threshold value of the bias current; and

a light-sensitive solid-state relay responsive to the light signal emitted from the second diode and adapted to select a load resistor for adjustment of the impedance level of the headset adapter output stage.

34. A method of automatically selecting the output characteristics of a headset adapter output stage, the method comprising:

detecting a value of a bias currant in a host telephone transmit circuit; and

selecting a gain level and impedance level of the headset adapter output stage in response to the value of the bias current.

35. An apparatus for selecting the output characteristics of a headset adapter output stage, the adaptive transmit amplifier comprising:

means for detecting a value of a bias current in a host telephone transmit circuit; and

coupled to the detecting means, means for selecting a gain level and impedance level of the headset adapter output stage in response to the value of the bias current.

36. A method of selecting the output characteristics of a headset adapter output stage, the method comprising:

generating an output control signal dependent on a value of a bias current in a host telephone transmit circuit; and

setting an output characteristic of the headset adapter output stage in response to the output control signal.

37. The method of claim 36 wherein the step of setting an output characteristic comprises:

setting an output gain level of the headset adapter in response to the output control signal.

38. The method of claim 36 wherein the step of setting an output characteristic further comprises:

setting an output impedance level of the headset adapter in response to the output control signal.

39. An apparatus for selecting the output characteristics of a headset adapter output stage, the apparatus comprising:

means for generating an output control signal dependent on a value of a bias current in a host telephone transmit circuit; and

coupled to the generating means, means for setting an output characteristic of the headset adapter output stage in response to the output control signal.

40. The apparatus of claim 39 wherein the setting means comprises:

means for setting an output gain level of the headset adapter in response to the output control signal.

41. The apparatus of claim 39 wherein the setting means further comprises:

means for setting an output impedance level of the headset adapter in response to the output control signal.

42. An adaptive transmit amplifier for adjusting the transmit output characteristics of a headset adapter output stage, the adaptive transmit amplifier comprising:

a detector configured to detect a value of a bias current in a host telephone transmit circuit; and

a switching stage coupled to the detector and configured to select an output characteristic of the headset adapter output stage based upon the bias current value.

43. The apparatus of claim 42 wherein the output characteristic includes an output gain level.

44. The apparatus of claim 42 wherein the output characteristic includes output impedance level.

45. The adaptive transmit amplifier of claim 42 further comprising:

a logic/timing block coupled to the detector and to the switching stage and configured to control a sequence of detection of the bias current and selection of an output characteristic of the headset adapter output stage.

46. A telephone and headset system, comprising:

a host telephone having a host telephone transmit circuit;

a headset having a headset adapter output stage; and

an apparatus for selecting a transmit output characteristic of the headset adapter output stage, the apparatus including;

a detector configured to generate an output signal that depends on a value of a bias current conducting in the host telephone transmit circuit, and

a switching stage coupled to the detector and configured to select the transmit output characteristic of the headset adapter output stage in response to the output signal from the detector.