Advanced Micro Devices Corporation

Herbert M Chen

Alan F Hendrickson

Dale E Gulick

Carlin D Cabler

Rajiv M Hattangadi

V Vijayakumaran Nair

A DECT Base Station Unit for canceling hybrid echoes and suppressing network echoes. The DECT Base Station Unit includes a hybrid that connects a two-wire loop to a four-wire loop, an adaptive balance filter that receives a near-end transmit signal over two wires of the four-wire loop and receives a residual error signal over another two wires of the four-wire loop. The adaptive balance filter outputs an hybrid echo negating signal to a adder. The adder also receives an output from the hybrid that includes a transmit far-end signal and a reflected portion of the near-end transmit signal, and the adder outputs a residual error signal. The DECT Base Station Unit further includes an echo suppressor, an echo suppressor controller for controlling an attenuation level of the echo suppressor, and a decorrelation controller for sending enable/disable signals to the echo suppressor controller and the adaptive balance filter based on a level of correlation between the near-end transmit signal and the residual error signal.

Adaptive echo cancellation used with echo suppression to reduce short

A ring generator circuit is included in a subscriber line interface circuit (SLIC) for providing a high voltage ring signal to a plurality of ringers at the same time. The ring generator circuit includes an adder and divider circuit connected to receive a DC offset and an AC reference signal from the SLIC. The adder and divider circuit outputs a fractionalized summed signal. That signal is supplied to a full-wave rectifier, which rectifies the fractionalized summed signal so that it is always a positive voltage. The rectified signal is supplied to a switch control circuit, a first amplifier and a second amplifier. The first and second amplifiers have the same gain, but with opposite signs or polarities. The outputs of the first and second amplifiers are sent to a commutating switch, which is controlled by an output of the switch control circuit. The output of the switch control circuit is used to force the commutating switch to output a ring signal that has either a same or a reversed polarity with respect to the summed signal.

Ring-signal generation in a SLIC

A ring generator circuit that produces a ring output for a plurality of telephones simultaneously. The ring generator circuit includes a switch that receives an oscillating signal in response to an on condition of an on/off signal. The on/off signal is related to whether an incoming phone call is directed to one of the plurality of telephones or not. The ring generator circuit also includes a DC offset circuit that receives a DC input potential, an amplifier stage for providing a ring output, and a feedback circuit connected between the ring output of the amplifier stage and the switch output.

On-board ring signal generator

A sign-based decorrelation detection and adaptive control arrangement includes structure for detecting cross-correlation between a far-end signal and an echo residual following a balance filter. During the adaptive process, if the detected correlation value is below a certain threshold, indicating that the two signals are decorrelated, the adaptation of the balancing filter is stopped. At such a point, proper echo cancellation has been achieved. Conversely, when the detected correlation value exceeds a threshold, the adaptation is ,continued until the correlation value falls below the threshold again. In any event, such decorrelation controllers are able to detect signal decorrelation and to control adaptation even in the presence of a double-talker condition.

Decorrelation controller for an adaptive echo cancellor

An improved sigma-delta analog-to-digital converter (ADC) is disclosed herein. The digital converter includes a dither circuit fabricated within the package of the ADC. The circuit is configured to apply a dither current to the analog input of the ADC. The frequency of the dither current is selected based upon the bandwidth of the analog signals for which the ADC is designed to sample and convert to digital signals. Application of the dither current to the input of the ADC reduces quantization noises produced as a result of certain ranges of DC offset voltages found within analog signals applied to the ADC.

Analog-to-digital converter with multi-level dither current input

A single integrated circuit forms a hands-free telephone unit for use in a digital telephone network and in association with an external keypad, an external microprocessor, an external microphone, and an external speaker. The integrated circuit includes a keypad monitor arranged to provide digital key code signals, an audio processor for supporting hands-free operation, and a digital interface to provide a digital interface between the integrated circuit and the digital network and the external microprocessor.

Fully-integrated telephone unit

The preferred embodiment of the apparatus comprises a first signal level detector which receives the communications signal as an input and generates a detection signal as an output, a second signal level detector which receives the detection signal as an input and generates a noise detection signal as an output, and a comparing circuit which compares the detection signal and the noise detection signal and produces a speech burst detection signal. Each of the signal level detectors comprises a digital low pass filter having an input and an output which employs a comparator for comparing current samples of signals at the input with previous samples of signals at the output and generating a representative comparator output. Each low pass filter includes circuitry for establishing an attack time and a decay time, in response to the comparator output. The attack time and the decay time in the first signal level detector being established as a fast attack time and a slow decay time relative to the attack time and the decay time in the second signal level detector.

Apparatus for discriminating information signals from noise signals in a

An apparatus for effecting echo suppression facilitating communications between an analog device and a digital device comprising a transmit circuit for processing outgoing signals, a receive circuit for processing incoming signals, and a control circuit for controlling the transmit circuit and the receive circuit. The transmit circuit includes transmit attenuators for attenuating the outgoing signals as they pass through the transmit circuit, and an analog-to-digital conversion circuit for converting analog signals to digital signals. The receive circuit includes receive attenuators for attenuating the incoming signals as they pass through the receive circuit and a digital-to-analog conversion circuit for converting digital signals to analog signals. Each of the transmit attenuators and the receive attenuators is digitally adjustable by the control circuit. The control circuit receives sensed outgoing signals from the transmit circuit and sensed incoming signals from the receive circuit and effects a comparison of the sensed outgoing and incoming signals to determine whether the apparatus is transmitting or receiving. The control circuit digitally adjusts the transmit attenuators and the receive attenuators to distribute a predetermined maximum loss among incoming signals and outgoing signals appropriately to increase signal attenuation in the receive circuit and reduce signal attenuation in the transmit circuit when the apparatus is transmitting, and to increase signal attenuation in the transmit circuit and decrease signal attenuation in the receive circuit when the apparatus is receiving.

Echo suppression with both digital and analog variable attenuators

A method for operating an apparatus for facilitating communications between an analog device and a digital device, which apparatus includes a plurality of signal processing circuits and a control circuit for controlling the signal processing circuits. Each of the signal processing circuits includes signal attenuators and signal burst discrimination circuitry. The apparatus is operable in a plurality of stable states, preferably in an idle stable state, a transmit stable state, and a receive stable state. The apparatus also is operable in a plurality of transitional states, including up-transition states and down-transition states. The method includes the steps of evaluating each of the signal processing circuits by the signal burst discrimination circuitry, responding to detection of a burst indicator by setting a state indicator to an appropriate up-transition state, incrementally adjusting the attenuators in the signal processing circuits to enhance performance of the apparatus until the attenuators are at predetermined settings, periodically checking for presence of the burst indicator, on detection of cessation of the burst indicator, setting the state indicator to an appropriate down-transition state, incrementally adjusting the attenuators to redistribute attenuation losses among the signal processing circuits, if no burst indicator is detected, continuing such redistribution until the apparatus returns to the idle stable state.

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Austin, TX, United States of America

Herbert M Chen