Abstract: An echo canceling system, method of attenuating echo, and a bit pump and transceiver employing the system and method. The echo canceling system is couplable between a transmit and receive path of the bit pump and receives and attenuates the echo in a receive signal propagating along the receive path. In one embodiment, the echo canceling system includes a slave echo canceling stage that employs a filter coefficient to attenuate the echo. The echo canceling system also includes a separation circuit, coupled to the slave echo canceling stage, that generates data representing a residual echo substantially exclusive of the receive signal. The echo canceling system still further includes a master echo canceling stage, coupled to the separation circuit, that receives the data and modifies the filter coefficient based thereon.

Abstract: A separation circuit, method of determining a residual level of an echo, and an echo canceling system, bit pump and transceiver employing the circuit and method. The echo canceling system employing the separation circuit is couplable between a transmit and receive path of the bit pump and generates an echo canceling signal. In one embodiment, the separation circuit includes a symbol determination circuit that accepts a receive signal, propagating along the receive path, substantially free of an echo and determines a symbol associated with the receive signal. The separation circuit also includes an estimator stage, coupled to the symbol determination circuit, that receives the symbol and provides an estimated receive signal. The separation circuit generates data representing a residual level of the echo as a function of the estimated receive signal and the echo canceling signal.

Abstract: An adaptive filter is provided which has fixed point or floating point data stored in a data RAM (74) and block scale floating point coefficients stored in a coefficient RAM (84). The data and coefficients are utilized in a filter algorithm which utilizes a multiplier and an accumulator to provide a convolution result. Coefficients are updated by adding the multiplied result of the data RAM value and the error value to the old value of the coefficient. This is done for all the coefficient values in the coefficient RAM. The error value indicates the difference between the filter output and the sampled near-end signal that is the echo. These new coefficients are examined and if any have a value above or all have a value below a predetermined threshold, then the mantissas of all the coefficients are shifted and the exponent adjusted in the next filter cycle.

Abstract: A double-talk detector for an echo canceller includes power estimators (60) and (62) which are utilized to measure the ERLE value in a calculator (64). This ERLE is stored in a register (70) when it is the largest value generated. This register (70) is updated whenever a new and better ERLE occurs. A fraction of the value in register (70) is utilized as an input to a comparator (88), and then compared to the current ERIE value. If the current ERLE differs from the SERLE in register (70) an inhibit signal is generated for blocking the updates of an adaptive filter (40). The value stored in the register (70) is periodically decremented to reduce the value thereof. This decrement operation is performed in response to detection of an utterance from the far-end. A half-Duplex operation is provided with two attentuators (352) and (354) to provide a switching operation and allow only one side access to the communication path.

Abstract: A variable gain echo suppressor is provided that utilizes two variable attenuators (410) and (412) that are disposed in the receive and transmit paths, respectively, of a communication system. An echo suppressor (414) receives the input from the far end and transmits the output from the near end and controls the two attenuators to set a variable gain therein. The echo suppressor utilizes a normalized power level which is normalized with respect to the background noise at the respective end and then takes the ratio of this normalized power and the normalized power at the opposite end to define an associated power ratio. This power ratio value is utilized to determine the attenuation for the associated end. When the power ratio is high, this indicates that a stronger signal is being received from that end and a small amount of attenuation is associated in the transmit path from that end. When they aye equal, this will result in both systems having approximately the same attenuation, a mid-level attenuation.