Speakerphone using digitally compressed audio to detect acoustic feedback

• US 4,843,621 A
• Filed: 04/18/1988
• Issued: 06/27/1989
• Est. Priority Date: 04/24/1987
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Potratz, Bryan A.
• Primary Examiner(s): Ng, Jin F.
• Assistant Examiner(s): Kim, David H.
• Application Number:
  US07/182,810
• Time in Patent Office: 435 Days
• Field of Search: 379/56, 379/58, 379/61, 379/63, 379/388-390, 370/32, 455/72, 455/79, 333/14, 381/106
• US Class Current: 455/570
• CPC Class Codes: H04M 9/085 using digital techniques H04M9/082 takes precedence

Abstract

A mobile radiotelephone (120) includes a microcomputer (220), speakerphone control circuitry (106) and mobile radio (112). In the transmit voice path, speakerphone control circuitry (106) includes switch (201), variable gain amplifier (202), compressor amplifier (203), switch (204), variable gain amplifier (205), and two registers (212-213). In the receive voice path, speakerphone control circuitry (106) includes variable gain amplifier (232), expander amplifier (233), switch (234), variable gain amplifier (235), switch (236) and two registers (216-217). Speakerphone control circuitry (106) also includes rectifier/filter (224), a companding analog-to-digital (A/D) converter (225), two latches (218-219), rectifier/filter (226) and two registers (214-215). Microcomputer (220) accesses registers (212-217) by means of a data bus (222) including address, control and data lines. Microcomputer (220) utilizes digital samples from A/D converter (225) to dynamically detect acoustic feedback and to continuously generate and store in its memory an envelope signal and a valley signal for the transmit and receive voice paths for controlling voice path gain switching. In order to determine when to switch gain between the voice paths, microcomputer (220) compares the envelope signal to the valley signal to detect the presence of voice signals and, if the voice signals are detected for a pre-selected time, the gain of the path in which voice signals have been detected is increased and the gain of the other path is decreased.

Claims

1. A speakerphone for a radiotelephone for communicating voice signals by way of a radio channel, said radiotelephone including radio means for transmitting a first signal including voice signals on the radio channel and receiving a second signal including voice signals from the radio channel, said speakerphone comprising:

microphone means for producing the first signal;

speaker means for emitting the second signal;

first amplifying means having an input coupled to said microphone means and an output coupled to said radio means and being responsive to first digital control signals for selecting one of a plurality of gain settings and amplifying the first signal;

second amplifying means having an input coupled to said radio means and an output coupled to said speaker means and being responsive to second digital control signals for selecting one of a plurality of gain settings and amplifying the second signal;

converting means for producing first and second digital samples of the output of the first amplifying means and the input of the second amplifying means, respectively; and

processing means coupled to the first and second digital samples of said converting means for detecting voice signals in the first and second signals, respectively, and, in response to detection of voice signals in one of the first and second signals, producing the first and second digital control signals for adjusting the gain settings of said first amplifying means and said second amplifying means such that the gain setting for said one of the first and second signals is increased to a nominal gain and the gain setting of the other of the first and second signals is decreased by a first predetermined gain, and said processing means monitoring a predetermined number of consecutive second digital samples and reducing the first predetermined gain by a second predetermined gain if the predetermined number of consecutive second digital samples have magnitudes differing by less than a third predetermined gain.

2. The speakerphone according to claim 1, wherein said processing means includes microcomputer means.

3. The speakerphone according to claim 1, wherein said first amplifying means includes first register means for storing the first digital control signals, said second amplifying means includes second register means for storing the second digital control signals, and said processing means is coupled to said first and second register means.

4. The speakerphone according to claim 3, wherein said processing means includes microcomputer means.

5. The speakerphone according to claim 1, further including first switch means coupled between the output of said first amplifying means and said radio means and being responsive to a third control signal for substantially muting the first signal, and further including second switch means coupled between the output of said second amplifying means and said speaker means and being responsive to a fourth control signal for substantially mutting the second signal, said processing means coupled to said first and second switch means for producing the third and fourth control signals.

6. A method for detecting acoustic feedback in a speakerphone for a radiotelephone for communicating voice signals by way of a radio channel, said radiotelephone including radio means for transmitting a first signal including voice signals on the radio channel and receiving a second signal including voice signals from the radio channel, said speakerphone including microphone means for producing the first signal, speaker means for emitting the second signal, first amplifying means having an input coupled to said microphone means and an output coupled to said radio means and being responsive to first digital control signals for selecting one of a plurality of gain settings and amplifying the first signal, second amplifying means having an input coupled to said radio means and an output coupled to said speaker means and being responsive to second digital control signals for selecting one of a plurality of gain settings and amplifying the second signal, and processing means coupled to the output of said first amplifying means and the input of the second amplifying means, respectively, and, in response to detection of voice signals in one of the first and second signals, producing the first and second digital control signals for adjusting the gain settings of said first amplifying means and said second amplifying means such that the gain setting for said one of the first and second signals is increased to a nominal gain and the gain setting of the other of the first and second signals is decreased by a first predetermined gain, said method comprising the steps of:

producing first and second digital samples of the output of the first amplifying means and the output the second amplifying means, respectively;

monitoring a predetermined number of consecutive second digital samples; and

reducing the first predetermined gain by a second predetermined gain if the predetermined number of consecutive second digital samples have magnitudes differing by less than a third predetermined gain.

7. The method according to claim 6, wherein the gain settings of said second amplifying means may be changed by the user of said speakerphone, and said monitoring step includes the step of ignoring second digital samples for a predetermined time interval in response to a change in the gain setting of said second amplifying means by the user.

8. A radiotelephone for communicating voice signals by way of a radio channel, comprising:

microphone means for producing a first signal including voice signals;

speaker means for emitting a second signal including voice signals;

radio means for transmitting the first signal on and receiving the second signal from the radio channel;

first amplifying means having an input coupled to said microphone means and an output coupled to said radio means and being responsive to first digital control signals for selecting one of a plurality of gain settings and amplifying the first signal;

second amplifying means having an input coupled to said radio means and an output coupled to said speaker means and being responsive to second digital control signals for selecting one of a plurality of gain settings and amplifying the second signal;

converting means for producing first and second digital samples of the output of the first amplifying means and the input of the second amplifying means, respectively; and

processing means coupled to the first and second digital samples of said converting means for detecting voice signals in the first and second signals, respectively, and, in response to detection of voice signals in one of the first and second signals, producing the first and second digital control signals for adjusting the gain settings of said first amplifying means and said second amplifying means such that the gain setting for said one of the first and second signals is increased to a nominal gain and the gain setting of the other of the first and second signals is decreased by a first predetermined gain, and said processing means monitoring a prederermined number of consecutive second digital samples and reducing the first predetermined gain by a second predetermined gain if the predetermined number of consecutive second digital samples have magnitudes differing by less than a third predetermined gain.

9. The radiotelephone according to claim 8, wherein said processing means includes microcomputer means.

10. The radiotelephone according to claim 8, wherein said first amplifying means includes first register means for storing the first digital control signals, said second amplifying means includes second register means for storing the second digital control signals, and said processing means is coupled to said first and second register means.

11. The radiotelephone according to claim 10, wherein said processing means includes microcomputer means.

12. The radiotelephone according to claim 8, further including first switch means coupled between the output of said first amplifying means and said radio means and being responsive to a third control signal for substantially muting the first signal, and further including second switch means coupled between the output of said second amplifying means and said speaker means and being responsive to a fourth control signal for substantially muting the second signal, said processing means coupled to said first and second switch means for producing the third and fourth control signals.