Two-way communications device having a single transducer

• US 7,881,483 B2
• Filed: 11/10/2004
• Issued: 02/01/2011
• Est. Priority Date: 11/11/2003
• Status: Active Grant

• Current Assignee: Soundec Co., Ltd.
• Original Assignee: Matech Inc .
• Inventors: Kume, Yasuhiro, Masuda, Masahisa
• Primary Examiner(s): Jamal; Alexander
• Application Number:
  US10/595,757
• Publication Number:
  US 20070133442A1
• Time in Patent Office: 2,274 Days
• Field of Search: 381/163, 379/406.08
• US Class Current: 381/163
• CPC Class Codes: H04B 3/20 Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other
• CPC Class Codes: H04M 1/6058 involving the use of a headset accessory device connected to the portable telephone
• CPC Class Codes: H04M 9/082 using echo cancellers echo cancellers per se H04B3/23

Abstract

Embodiments of the invention provide a small and economical two-way communications device that has both an excellent echo-cancellation function that substantially suppresses echoes over the entire frequency range and an excellent voice-operated exchange function that provides natural switching of conversation sounds while protecting against unnatural disconnection or echoes during conversation, even when a reception signal and a transmission signal are superimposed in a single transducer.

Claims

1. A two-way communication device comprising:

an analog signal processor configured to insert in or close to an ear canal and having a first analog input for receiving a reception signal containing electrical audio signals, a second analog output for outputting a transmission signal containing electrical audio signals, the analog signal processor further comprising a bridge circuit configured to provide a first echo cancellation operation and including a transducer configured to convert the reception signal at the first analog input into acoustic wave vibrations in the ear canal and further configured to convert acoustic wave vibrations received from the ear canal into the transmission signal at the second analog output; and

a digital signal processor (DSP) having a first digital output coupled to the first analog input of the analog signal processor and a second digital input coupled to the second analog output of the analog signal processor, the DSP configured to measure operating characteristics of an electronic signal path through the transducer and the bridge circuit in the analog signal processor by comparing the reception signal input into the transducer by the DSP through the first analog input with the transmission signal output by the same transducer from the second analog output responsive to the reception signal, the DSP further configured to use the measured operating characteristics to provide a second echo cancellation operation to filter reception signal echo from the transmission signal not filtered by the first echo cancellation operation provided by the analog signal processor.

2. The device of claim 1 wherein the bridge circuit further comprises:

a first node coupled to the first analog input of the analog signal processor and coupled to a first end of a first resistor;

a second node coupled to a first end of the transducer, a second end of the first resister, and a first input of a differential amplifier; and

a third node coupled to a second end of the transducer through a second resistor and coupled to a second input of the differential amplifier.

3. The device according to claim 2 wherein the digital signal processor includes a filter that applies filter coefficients generated by a filter coefficient calculator to the reception signal to generate a filter output signal, the digital signal processor further including an adder coupled at a first end to the ouput of the differential amplifier and coupled at a second end to the filter and configured to apply the filter output signal to the transmission signal output from the differential amplifier.

4. The device according to claim 2 wherein the bridge circuit further comprises a first resistor-capacitor filter coupled between the first and third nodes and a second resistor-capacitor filter coupled between the second and third nodes.

5. The device according to claim 1 wherein the digital signal processor monitors the operating characteristics of the transducer while the transducer is located in an external ear canal.

6. The device according to claim 1 wherein the digital signal processor periodically measures the operating characteristics of the transducer while in operation and uses the periodic measurements to continuously adjust the filtering of the reception signal echo from the transmission signal.

7. The device according to claim 1 wherein the digital signal processor includes a voice operated exchanger (VOX) controlling attenuation of the reception signal and the transmission signal according to predetermined gain values.

8. The device according to claim 7 including:

a first analog to digital converter (A/D) converting the reception signal received by the VOX;

a first low pass filter filtering the A/D converted reception signal;

a first attenuator attenuating the reception signal; and

a power controller controlling attenuation of the reception signal by the attenuator according to the filtered A/D converted reception signal.

9. The device according to claim 8 including a second attenuator attenuating the transmission signal output from the analog signal processor according to the power controller.

10. The device according to claim 9 including a second low pass filter receiving the transmission signal from the analog signal processor and sending a filtered transmission signal to the second attenuator, the power controller controlling attenuation of the filtered transmission output signal according to a power level of the filtered transmission signal or power level of the filtered reception signal.

11. The device according to claim 7 wherein the digital signal processor further includes an echo canceller (EC) receiving the reception signal from the VOX and outputting the transmission signal with reception signal echo cancellation to the VOX.

12. The device according to claim 11 including:

a first analog to digital converter (A/D) operating between a reception terminal and the VOX;

a first digital to analog converter (D/A) operating between the reception signal output from the EC and the analog signal processor;

a second A/D converter operating between the transmission signal output from the analog signal processor and the EC; and

a second D/A converter operating between the transmission signal output from the VOX and a transmission terminal.

13. The device of claim 12 wherein the echo canceller includes:

a first buffer with an output coupled to both an input of the first D/A converter and an input of a compensation filter;

a second buffer with an input coupled to an output of the second A/D converter, wherein the compensation filter is configured to simulate transmission characteristics along a signal path starting at the input of the first D/A converter, passing through the transducer in the analog signal processor, passing out from the same transducer through the second A/D converter, and ending at an output of the second buffer; and

an adder configured to subtract an output of the compensation filter from the output of the second buffer.

14. A device according to claim 13 including:

a first switch configured to selectively provide an input of the first buffer to either the voice-operated exchanger or a test signal generator;

a parameter calculator receiving the outputs of the first and second buffers and configured to set the parameters of the compensation filter by processing a signal from the second buffer and a test signal from the first buffer; and

a second switch configured to selectively provide an output of the adder to either the voice-operated exchanger or to a ground.

15. The device of claim 7 wherein the analog signal processor includes a four-sided bridge circuit having a first node coupled to the reception signal output from the digital signal processor and coupled to a first end of the transducer through a first resistor, and having a second node coupled to a second end of the transducer through a second resistor and outputting the transmission signal to the digital signal processor.

16. The device according to claim 15 wherein the analog signal processor includes a first amplifier coupled between the first node and the reception signal output from the DSP and a second differential amplifier coupled to the first and second nodes of the bridge circuit and outputs the transmission signal to the DSP.

17. The device of claim 15 wherein the bridge circuit includes:

a first side having a third resistor coupled in series with a first capacitor and both coupled in parallel with the transducer;

a second side having the first resistor;

a third side having a fourth resistor connected in parallel with a second capacitor; and

a fourth side having the second resistor.

18. The device according to claim 7 wherein the analog signal processor includes a variable resistor having a first end coupled to the reception signal output from the digital signal processor and a second end coupled to the transmission signal output to the digital signal processor and a center tap coupled to the VOX, the center tap moved toward the first end or second end by the VOX according to a selected reception mode or selected transmission mode.

19. In a two-way communication device comprising a digital signal processor and an analog signal processor with a transducer that is designed to be inserted into an ear canal, a method comprising:

configuring a first filter in the digital signal processor to simulate a input voltage generated by the analog signal processor with a large amplitude;

configuring a second filter in the digital signal processor to simulate an input voltage generated by the analog signal processor with a small amplitude, wherein the second filter further simulates a signal path through the analog signal processor for determining characteristics in the signal path between an input and output of a same transducer by comparing a first electrical audio test signal input into the transducer with a second electrical audio test signal output from the same transducer responsive to the first electrical audio signal; and

subtracting an output of the second filter from an output of the analog signal processor to substantially cancel an echo component present in the output of the analog signal processor.

20. The method of claim 19, further comprising:

configuring the first and second filter in the digital signal processor to simulate the different signal paths through the analog signal processor comprising;

generating a test signal;

propagating the test signal through the different signal paths while the transducer is placed in an external ear canal; and

setting parameters of the first and second filter based on characteristics of the propagated test signals through the different signal paths.

21. The method of claim 20, wherein generating the test signal comprises:

generating a test signal chosen from the group consisting of a digital signal that corresponds to any one of the following;

an impulse, an actual voice during conversation, a natural voice, a reception sound, or a musical sound;

a diffusion code signal, and a tone sweep signal.

22. The method of claim 19 including reconfiguring the first and second filter after a predetermined amount of time to compensate for a variation of the acoustic conditions of the ear canal.

23. In a two-way communication device comprising a digital signal processor and an analog signal processor, the analog signal processor including a transducer that is designed to be inserted into an ear canal, a method comprising:

transmitting a first test signal through a first signal path in the analog signal processor;

generating a first set of filter coefficients from the first test signal that simulate signal transmission characteristics through the first signal path;

transmitting a second test signal through a second signal path in the analog signal processor;

generating a second set of filter coefficients from the second test signal that simulate signal transmission characteristics through the second signal path;

combining the first set of coefficients with the second set of coefficients in a first filter in the digital signal processor to simulate a response of a large amplitude signal through the first signal path and the second signal path through the analog signal processor;

transmitting a third test signal through the first signal path and through a third signal path, wherein the third signal path includes the first filter and the second signal path;

generating a third set of coefficients from the third test signal;

using the third set of coefficients in a second filter located in the digital signal processor to simulate a response of a small amplitude signal through the analog signal processor;

transmitting a receive signal through the first signal path and the third signal path; and

subtracting an output of the second filter from an output of the analog signal processor to substantially cancel an echo component present in the output of the analog signal processor.

24. The method of claim 23 including

a differential amplifier having a first input coupled to the first signal path, a second input coupled to the second signal path, and an output comprising the output of the analog signal processor.

25. The method of claim 24 including:

propagating the first test signal through the first signal path while an input to the second signal path is grounded, wherein the first signal path includes a first amplifier, the transducer, a first resistor, and the first input of the differential amplifier;

propagating the test signal through the second signal path while an input to the first signal path is grounded, wherein the second signal path includes a third amplifier, second and third resistors, and the second input of the differential amplifier; and

setting parameters of the first filter based on characteristics of the propagated first and second test signals and wherein the first filter simulates an input voltage at the second amplifier with a the large amplitude and the second filter simulates the input voltage at the second amplifier with the small amplitude.

26. The method of claim 24 including generating the test signals from a group consisting of a digital signal that corresponds to any one of the following:

an impulse, an actual voice during conversation, a natural voice, a reception sound, or a musical sound;

a diffusion code signal, and a tone sweep signal.

27. The method of claim 23 including:

inserting the transducer into the ear canal;

periodicially transmitting each of the first, second, and third test signals through the analog signal processor while the transducer is inserted into the ear canal;

periodically generating new first and second sets of coefficients for the first filter responsive to the periodically transmitted first and second test signals; and

periodically generating new third sets of coefficients for the second filter responsive to the periodically transmitted third test signal.

28. A two-way communications device comprising:

a piezoelectric transducer, wherein the piezoelectric transducer is configured to detect vibrations of an eardrum membrane caused by sound waves, and wherein the piezoelectric transducer is also configured to transmit a sound wave to the eardrum membrane;

a housing shaped like an earplug that is configured to contain the piezoelectric transducer; and

an echo-canceller configured to model the variable acoustic characteristics of the piezoelectric transducer caused by the eardrum membrane and an ear canal associated with the eardrum membrane, wherein the echo-canceller comprises;

a first buffer with an output coupled to both an input of a first D/A converter and an input of a first compensation filter;

a second buffer with an input coupled to an output of a second A/D converter, wherein the compensation filter is configured to simulate transmission characteristics along a signal path starting at the input of the first D/A converter, passing through the piezoelectric transducer, passing out from the same piezoelectric transducer through the second A/D converter, and ending at an output of the second buffer; and

an adder configured to subtract an output of the compensation filter from the output of the second buffer.