System and method for echo cancellation in a communication system

An echo canceller for reducing an echo component in an analog output signal caused by cross coupling of an incoming received signal received at a communication unit with the analog output signal, the echo canceller comprising:

• a digital echo canceller for digitally processing the analog output signal after being converted to digital form to reduce the cross coupling echo component before transmission from the communication unit;
• an analog echo canceller connected between the communication unit output and the digital echo canceller for analog reduction of the cross coupling echo component in the analog output signal when in analog form before digital processing by the digital echo canceller, wherein the analog echo canceller includes:
• means for generating an analog cancellation signal which is substantially the same as the acoustic coupling echo component in the analog output signal before digital processing by the digital echo canceller;
• and
• means for combining the analog echo cancellation signal with the analog output signal to reduce the cross coupling echo component before digital processing by the digital echo canceller, wherein the combining means produces an echo reduced analog output signal and includes means interposed between the combining means and the digital echo canceller to automatically amplify the echo reduced analog output signal to a level for substantially maximum resolution digitization of the echo reduced analog output signal;
• wherein said automatically amplifying means includes:
• a variable gain amplifier,
• means for setting the amplifier gain at a level below a digitization saturation level,
• means for training the analog echo canceller until substantially maximum echo reduction is achieved, and
• means for increasing the gain of the variable gain amplifier after training is completed to obtain maximum digital resolution during conversion.

An echo canceller for reducing an echo component in an analog output signal caused by cross coupling of an incoming received signal received at a communication unit with the analog output signal, the echo canceller comprising:

• a digital echo canceller for digitally processing the analog output signal after being converted to digital form to reduce the cross coupling echo component before transmission from the communication unit;
• an analog echo canceller connected between the communication unit output and the digital echo canceller for analog reduction of the cross coupling echo component in the analog output signal when in analog form before digital processing by the digital echo canceller, wherein the analog echo canceller includes:
• means for generating an analog cancellation signal which is substantially the same as the acoustic coupling echo component in the analog output signal before digital processing by the digital echo canceller, and
• means for combining the analog echo cancellation signal with the analog output signal to reduce the cross coupling echo component before digital processing by the digital echo canceller;
• wherein the combining means produces an echo reduced analog output signal, and includes means interposed between the combining means and the digital echo canceller to automatically amplify the echo reduced analog output signal to a level for substantially maximum resolution digitization of the echo reduced analog output signal;
• means for training the analog echo canceller until substantially maximum echo reduction is achieved;
• another means for amplifying the echo reduced analog output signal at an output terminal of the digital echo canceller after both analog and digital reduction of the cross coupling echo component;
• and
• means for controlling the gain of the other amplifying means to compensate for changes in gain of the automatically amplifying means to maintain a substantially uniform total gain from both the other amplifying means and the automatically amplifying means.

An echo cancelling method for reducing an echo component in an analog output signal at a communication unit caused by cross coupling of an incoming received signal at the communication unit with the analog output signal, the method comprising the steps of:

• reducing with an analog echo canceller the cross coupling echo component in the analog output signal to produce an echo reduced analog output signal, wherein the step of reducing with an analog echo canceller includes the steps of:
• generating an analog cancellation signal which is substantially the same as the cross coupling echo component in the analog output signal before digital processing by a digital echo canceller;
• and
• combining the analog echo cancellation signal with the analog output signal to reduce the acoustic coupling echo component before digital processing by the digital echo canceller, wherein the step of combining results in production of the echo reduced analog output signal;
• digitally processing the echo reduced analog output signal to reduce the acoustic coupling echo component before transmission;
• and
• automatically amplifying the echo reduced analog output signal to a level for substantially maximum resolution digitization of the echo reduced analog output signal with an amplifier interposed between combining means and the digital echo canceller, wherein said step of automatically amplifying the echo reduced analog output signal is performed with a variable gain amplifier, and includes the steps of:
• setting the amplifier gain at a level below a digitization saturation level,
• training the analog echo canceller until substantially maximum echo reduction is achieved, and
• after training is completed, automatically increasing the gain of the amplifier to obtain substantially maximum digital resolution during conversion of the echo reduced analog output signal.