Abstract: A terminal apparatus for full duplex transmission of digital data comprising an echo canceler having FIR and IIR type filters and also comprising a filter convergence controller. The filter convergence controller performs its converging operation over both filters in a first duration of a communication starting sequence from the start of transmission from a local terminal to a remote terminal to the detection of the convergence of the echo canceller to a certain extent, stops the converging operation of the IIR type filter in a second duration of the communication starting sequence from the detection of the convergence to the detection of synchronization with the remote terminal, and again performs the converging operation of the both filters in a third duration after the detection of the synchronization.

Abstract: A sending data buffer for holding sending data temporarily and transmitting the data to an echo canceler section is installed between a sending section and an echo canceler section of an echo canceler integrated circuit included in a subscriber line circuit of an integrated service digital network. The sending data buffer is operated in a shift register mode during a sending training mode, and operated in FIFO (first in-first out) mode during a sending/receiving training mode. Also, an adjustment function of the delay amount corresponding to the use setting is added.

Abstract: A signal processing method and system in a receiving apparatus including a receiving equalizer circuit are provided for extracting transmission data from a received signal inputted via a transmission path every transmission frame having a predetermined synchronization pattern and transmission data. A phase error is detected from the received signal extracted in synchronism with a sampling signal in the receiving equalizer circuit. The frequency of the sampling signal is controlled until the phase error becomes minimum. In parallel, it is detected whether the frame synchronization pattern is present in the received signal in a predetermined interval or not. When the presence of the frame synchronization pattern is not detected after the phase has been stabilized by frequency control of the sampling signal, the sampling phase of the received signal is judged to be in the quasi-convergence state. Then the frequency of the sampling signal is forcibly changed largely.

Abstract: A method for cancelling an echo in a network termination (NT) of a transmission system and an apparatus therefor are disclosed. The method comprises the steps of detecting an end of transmission of a specific data train in an up-going signal when the phase of the received clock is to be shifted for synchronization during the transmission of the up-going signal from the NT, shifting the phase of the receiving clock when the end of transmission is detected, sampling a residual echo signal of the echo of the specific data train not cancelled by the adaptive filter, determining a correction value for the output of the adaptive filter and storing the correction value and adding a sign corresponding to the direction of the phase shift to the correction value after the phase shift and adding the result to the output of the adaptive filter to cancel the echo of the specific data train.

Abstract: A method for cancelling an echo in a network termination (NT) of a transmission system and an apparatus therefor are disclosed. The method comprises the steps of detecting an end of transmission of a specific data train in an up-going signal when the phase of the received clock is to be shifted for synchronization during the transmission of the up-going signal from the NT, shifting the phase of the receiving clock when the end of transmission is detected, sampling a residual echo signal of the echo of the specific data train not cancelled by the adaptive filter, determining a correction value for the output of the adaptive filter and storing the correction value and adding a sign corresponding to the direction of the phase shift to the correction value after the phase shift and adding the result to the output of the adaptive filter to cancel the echo of the specific data train.

Abstract: A CODEC including a coder and decoder to construct the subscriber's circuit of a digital telephone switching system or the like, wherein an analogue balancing circuit is provided between the output terminal of a post-filter and the input terminal of a pre-filter in order to effectively eliminate a return signal in the case of two-wire/four-wire conversion, and return signals not eliminated by the analogue balancing circuit are further eliminated by a digital balancing circuit.Especially in the present invention, the analogue balancing circuit is so constructed that its characteristics are independent of frequencies, and hence, the analogue balancing circuit and the digital balancing circuit are readily implemented as an LSI.

Abstract: Disclosed is an interpolative A/D converter for converting an over-sampled analog signal into a digital signal without the occurrence of over slope distortions, wherein the difference between the analog input signal and an analog feedback signal derived from the converter output through D/A conversion is integrated, the integrated output is compared with several reference voltages and, after being converted into a digital signal, the comparison result is integrated in a digital manner to complete a digital output signal of the A/D converter.

Abstract: An oversampling type digital-to-analog converter which has a light gradient overload and a high signal-to-noise ratio in spite of a comparatively low sampling frequency.In a digital-to-analog converter wherein the difference between an oversampled digital input signal and a feedback signal is taken, such differences are integrated, the integral value is quantized to obtain the feedback signal, and part of the feedback signal is used as an analog output signal; a circuit for the quantization is constructed of a circuit which converts the integral value into a digital signal smaller in the number of bits than the digital input signal, and the feedback signal is obtained by integrating the outputs of the quantization circuit by means of a digital integral circuit.