Telephonic communications – Subscriber line or transmission line interface – Network interface device
Reexamination Certificate
1998-03-20
2001-04-03
Chan, Wing F. (Department: 2643)
Telephonic communications
Subscriber line or transmission line interface
Network interface device
C379S392000
Reexamination Certificate
active
06212273
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to telecommunication circuits. More specifically, the present invention relates to full-duplex speakerphone control circuits including a control interface.
2. Description of the Related Art
Most modem speakerphones use half-duplex operation which switches transmission between the far-end talker and the near-end speakerphone user. System designers resort to half-duplex operation because the acoustic coupling between the speaker and microphone is much higher in speakerphones than in a handset where the coupling is mechanically suppressed.
Hands-free communication through a microphone and speaker typically results in acoustic feedback or howling because the loop gain of the system exceeds unity when audio amplitudes are adjusted to a reasonable level.
Howling is a condition occurring in fall-duplex operation in which both the microphone and speaker are active at the same time so that, in conjunction with the reflection off the hybrid, a closed loop is created. The signal coupling between the speaker and the microphone causes feedback oscillation or howling when the coupling between the speaker and microphone is strong enough to increase the system closed loop gain above unity.
The solution to the howling problem has typically been half-duplex operation, in which either the transmit channel or the receive channel is active with both channels never active at the same time. Half-duplex operation prevents howling but diminishes the overall communication quality by clipping words and forcing the speaker at each end to wait for the speaker at the other end to stop talking.
In full-duplex conversation, both transmit and receive channels are active simultaneously. Telephone handsets allow full-duplex conversation quality.
A full-duplex communication device, such as a full-duplex speakerphone, includes highly complex and sophisticated control logic that classifies signals into categories including speech, noise, and tones. The fidelity of these classifications determines the performance of the communication device in echo cancellation, noise reduction, and handling of full-duplex communication when multiple parties are speaking. The level of coordination of a large number of mutually interacting control parameters in multiple communication channels that are continually modified, enabled, and disabled determines the stability of the control system, the appropriateness of handling of various conditions including high noise conditions, and communication fidelity.
Typically, the control task of a full-duplex communication system is hindered because various parameters are not available for updating. Some parameters are difficult to access. Often controls for multiple channels are not coordinated so that updating of parameters in one channel destabilizes operations in a different channel.
SUMMARY OF THE INVENTION
In accordance with the present invention, a full-duplex communication circuit including a control interface is provided for full-duplex, hands-free communication. The communication circuit includes a signal path, a half-duplex controller coupled to the signal path, a writable access port, and a controller interface coupled to the access port and coupled to the half-duplex controller. The controller interface includes a writable register having a half-duplex mode enable/disable field. The half-duplex mode enable/disable field controls the half-duplex controller to enable and disable half-duplex mode operation.
In accordance with another aspect of the present invention, a full-duplex communication circuit includes a receive signal path with a receive half-duplex controller coupled to the receive signal path, and a transmit signal path with a transmit half-duplex controller coupled to the transmit signal path. The circuit also includes an echo canceller with an adaptive filter coupled to the transmit signal path and coupled to the receive signal path for accessing a first signal, determining a compensation signal from the first signal, and compensating a second signal using the compensating signal to form a compensated second signal having a loop gain reduction. A controller interface is coupled to a writable access port and to the half-duplex controller. The controller interface includes a writable register having a field for controlling operation of the adaptive filter.
In accordance with still another aspect of the present invention, a full-duplex communication circuit includes a signal path, a suppressor coupled to the signal path, a writable access port, and a controller interface coupled to the access port and the suppressor. The controller interface includes a writable register having suppressor threshold field. The suppressor threshold field controls the suppressor to set a speech detection threshold for disengaging suppression.
REFERENCES:
patent: 5136531 (1992-08-01), McCaslin
patent: 5631900 (1997-05-01), McCaslin et al.
patent: 5668794 (1997-09-01), McCaslin et al.
Hemkumar Nariankadu D.
Wilson Brent W.
Chan Wing F.
Crystal Semiconductor Corporation
Koestner Ken J.
Rutkowski Peter T.
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