Dsc Communications Corporation

Kishan Shenoi

Helena S Ho

Patrick L Hanagan

Frank I Yu

Terrence G Sopira

Thomas T Oshidari

David J Wetle

Paul P Yang

An echo canceler (10) is controlled and operated during hangover time between a double talk condition and a single talk condition for a more natural residual echo cancellation. The adaptive gain and the residual suppression threshold necessary for controlling an adaptive filter and a residual echo suppressor, respectively, are computed such that their respective values increase gradually and smoothly from predetermined minimum values to predetermined maximum values during the hangover time.

Apparatus and method for controlling an echo canceler

An N:1 data compression system for compressing data on N DS1 trunks carrying 4N channels is disclosed. Waveform encoding circuitry is coupled to the N DS1 trunks for compressing the DS1 data into x bits and producing both encoded data and control parameters, where x.ltoreq.8. The system further includes circuitry coupled to the waveform encoding circuitry for receiving the encoded data and control parameters, performing digital speech interpolation and producing data packets which may include encoded data and control parameters that are transmittable on a single DS1 trunk.

N:1 bit compression apparatus and method

A circuit is provided for detecting out-of-lock condition in a phase lock loop. The phase lock loop receives a first signal having a first frequency and a voltage controlled oscillator of the phase lock loop produces a second signal having a second frequency. The circuit comprises a first data flip-flop coupled to the phase lock loop for receiving the first signal and clocked by the second signal. The first flip-flop produces an inverted output of the first signal. A second flip-flop is coupled to the phase lock loop for receiving the second signal clocked by the first signal, and produces a non-inverted output of the second signal. Additionally, an EXCLUSIVE-OR gate is coupled to the first and second flip-flops for receiving the inverted and non-inverted output thereof and producing a signal indicative of an out-of-lock condition.

Apparatus and method for detecting out-of-lock condition in a phase lock

Apparatus for packing and unpacking DS1 trunks comprises a packing circuitry for receiving compressed data from a plurality of DS1 trunks, packing the compressed data into the space of one DS1 trunk, and providing a serial output of data for the packed DS1 trunk. An unpacking circuitry is further provided for receiving data from a packed DS1 trunk, unpacking the data into the space of a plurality of DS1 trunks, and providing an output thereof.

DS1 trunk packing and unpacking apparatus and method

An integrated echo canceling multiplexor is provided which comprises an echo canceler for receiving DS1 signals for canceling echo in the DS1 signal and producing an echo-free digital logic signal. A first performance monitor is coupled to the echo canceler for receiving the echo-free digital logic signal and determining the quality of the signal. A multiplexor-demultiplexor is further coupled to the echo canceler for receiving the echo-free digital logic signal and producing a DS3 signal. Additionally, a second performance monitor is coupled to the multiplexor-demultiplexor and receives the DS3 signal and determines the quality of the signal.

Integrated echo canceling multiplexor

Rudimentary digital speech interpolation apparatus for compressing data on a plurality of channels is disclosed, which includes circuitry for receiving data bits and control bits for each channel. The presence of silence on each channel is determined in response to the received data bits and zero bits are allocated for any silent channel in a frame structure. In addition, circuitry also allocates x bits per channel for the data bits in an non-silent channel in the frame. At least six bits per channel are also allocated for the control bits in the frame. 4N such frames are grouped to form a multi-frame.

Rudimentary digital speech interpolation apparatus and method

An apparatus for controlling the operational status of echo canceling in an echo canceler is disclosed. A digital signal processor (DSP) module (52) is configured to provide two bandlimited filters (66, 68). A CAT filter (66) detects the exclusive presence of a continuity assurance. Test (CAT) tone, and a disable filter (68) detects the exclusive presence of an echo canceling disable tone. Outputs from the DSP module (52) couple to a controller module (64), and a control output from the controller module (64) couples to an echo canceler module (54). The control output causes the echo canceler module (54) either to provide echo canceling or to bypass echo canceling. Upon detection of the CAT tone (106), the control module (64) enables echo canceling (88). After the CAT tone disappears (90), the control module (64) monitors the disable filter (68) to determine whether the disable tone is being transmitted (94). If the disable tone is detected, the control module (64) disables echo canceling (100). After the disable tone disappears (102), the control module (64) monitors the CAT filter (66) to determine whether the CAT tone is being transmitted (106).

Operational status controller for echo canceling

A method and apparatus for generating low level noise signals are provided. Two random numbers X.sub.1 and Y.sub.1 are first generated and bits 0-4 of the first random number X.sub.1 are extracted to produce a number X.sub.2. A number X.sub.3 is further computed by the formula: X.sub.3 =2.sup.-N (X.sub.2 .multidot.I), where N is a predetermined number and 1.ltoreq.I.gtoreq.2.sup.N -1. Bit 7 of the second random number Y.sub.1 is then extracted and combined as a sign bit with the computed number X.sub.3 to produce a sign-magnitude eight bit number W representing a sample of low level noise encoded in accordance with .mu.-law.

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Milpitas, CA, United States of America

Kishan Shenoi