Terminal apparatus for full-duplex data transmission having an echo canceller

A full duplex data transmission terminal apparatus having a hybrid circuit connecting transmitting and receiving lines to a 2-wire transmission line for performing data communication with a remote terminal on a full duplex transmission basis, comprising:

• a sampler for sampling the signal on the receiving line, thereby providing a sampled signal;
• an echo canceler for canceling an echo generated on the receiving line by a first digital signal applied on the transmitting line, said echo canceler including an FIR type filter for receiving the signal from the transmitting line to generate a first component replica of said echo, an IIR type filter for receiving one tap output of said FIR type filter to generate a second component replica of said echo, and coupling means for subtracting the output first and second component replicas of said echo of said FIR type and IIR type filters, respectively, from the signal on the receiving line;
• slicer means connected to an output of said coupling means for discriminating a second digital signal transmitted from said remote terminal and receiving at said receiving line;
• a phase locked loop circuit for controlling a sampling phase of said coupling means and said slicer means;
• filter converging means for converging said FIR and IIR type filters on the basis of an error signal obtained from the output of said coupling means;
• data communication starting step detection means, having received the outputs of said coupling means and said slicer means, for monitoring whether or not convergence of said echo canceler is attained relative to a threshold value and whether or not a synchronization pattern is present in an output signal train of said slicer means;
• and
• control means for setting a duration from start of transmission of said first digital signal to detection of the convergence, a duration until detection of said synchronization pattern and a duration after the detection of said synchronization pattern to be first, second and third durations respectively, and for further enabling the converging operation of both said FIR and IIR type filters by said filter converging means in said first and third durations, for stopping the converging operation in at least said IIR type filter in said second duration, and for stopping said phase locked loop circuit or making a loop gain of said locked loop circuit smaller than that of the second duration and that of the third duration.

A full duplex data transmission terminal apparatus having a hybrid circuit connecting transmitting and receiving lines to a 2-wire transmission line for performing data communication with a remote terminal on a full duplex transmission basis, comprising:

• an echo canceler for canceling an echo generated on the receiving line by a first digital signal applied on the transmitting line, said echo canceler including an FIR type filter for receiving the signal from the transmitting line to generate a first component replica of said echo, an IIR type filter for receiving one tap output of said FIR type filter to generate a second component replica of said echo, and coupling means for subtracting the output first and second component replicas of said echo of said FIR type and IIR type filters, respectively, from the signal on the receiving line;
• slicer means connected to an output of said coupling means for discriminating a second digital signal transmitted from said remote terminal and receiving at said receiving line;
• error correction means for creating an estimated value of a far end signal based on an output of said slicer means and for correcting a first error signal issued from an output of said coupling means to form a second error signal;
• data communication starting step detection means, having received the outputs of said coupling means and said slicer means, for monitoring whether or not convergence of said echo canceler is attained relative to a threshold value and whether or not a synchronization pattern is present in an output signal train of said slicer means;
• and
• filter convergence control means for setting a duration from start of transmission of said first digital signal to detection of the convergence, a duration until detection of said synchronization pattern and a duration after the detection of said synchronization pattern to be first, second and third durations respectively and for converging both of said FIR and IIR type filters according to said first error signal in said first duration, for stopping the convergence of at least said IIR type filter in said second duration, and for converging both FIR and IIR type filters according to said second error signal in said third duration.