Abstract: A limiter is connected with the output of a PLL to limit the amplitude of the output from the PLL. The output from limiter is supplied to a voltage-controlled oscillator (VCXO). The limiter determines the difference between the input signal and the output signal. If the difference exceeds a predetermined value, the change in the output from the limiter is limited to the predetermined value. If the difference does not exceed the predetermined value, the change in the output is considered to be a difference value.

Abstract: A PLL circuit that causes an internal oscillation signal to lock to an external input clock signal, and is capable of suppressing jitter. The PLL circuit includes a frequency dividing circuit for frequency-dividing an input clock signal; a voltage-controlled oscillator; a missing-pulse clock signal creation circuit for creating, based on an output signal of the voltage-controlled oscillator, a missing-pulse clock signal having a higher speed than that of an output signal of the frequency dividing circuit and having a periodic missing-pulse portion; a phase comparator circuit for sampling the output signal of the frequency dividing circuit by using the missing-pulse clock signal; a shift register for storing a change in the output signal of the phase comparator circuit; and a digital signal processing circuit for converting a value stored in the shift register into a phase difference, and for controlling the input voltage to the voltage-controlled oscillator based on the phase difference.

Abstract: A transmission system for transmitting a data signal with an analog passband signal through a analog transmission line. The data signal is transformed to a signal representing a descrete data signal point in a vector signal space. The analog passband signal is transformed to a base band signal, and the base band signal is superimposed on the signal representing a descrete data signal point. A signal representing the superimposed data signal point is modulated and transmitted through the analog transmission line. In a receiver, the data signal point is decided from the signal representing the superimposed data signal point, and the superimposed bass band signal is extracted by subtracting the decided result from the signal representing the superimposed data signal point. The base band signal is transformed to the analog passband signal. A portion of information carried by the analog passband signal may be converted to a digital signal, and the digital signal is multiplexed with the data signal.

Abstract: A transmission system for transmitting a data signal with an analog passband signal through a analog transmission line. The data signal is transformed to a signal representing a descrete data signal point in a vector signal space. The analog passband signal is transformed to a base band signal, and the base band signal is superimposed on the signal representing a descrete data signal point. A signal representing the superimposed data signal point is modulated and transmitted through the analog transmission line. In a receiver, the data signal point is decided from the signal representing the superimposed data signal point, and the superimposed base band signal is extracted by subtracting the decided result from the signal representing the superimposed data signal point. The base band signal is transformed to the analog passband signal. A portion of information carried by the analog passband signal may be converted to a digital signal, and the digital signal is multiplexed with the data signal.

Abstract: A limiter is connected with the output of a PLL to limit the amplitude of the output from the PLL. The output from limiter is supplied to a voltage-controlled oscillator (VCXO). The limiter determines the difference between the input signal and the output signal. If the difference exceeds a predetermined value, the change in the output from the limiter is limited to the predetermined value. If the difference does not exceed the predetermined value, the change in the output is considered to be a difference value.

Abstract: A bandpass filter 51 extracts a Nyquist tone signal from an input signal, and a power calculation unit 52 checks the level of the extracted tone signal. A line equalizer control unit 53 controls a line equalizer 42 based on the level of the calculated tone signal. If the level of the tone signal fluctuates beyond a prescribed range, a level adjustment circuit compulsory activation control unit 54 compulsorily activates the line equalizer control unit 53, and if it is judged from the level of the tone signal that the apparatus is in a normal communication state, the level adjustment circuit compulsory activation control unit 54 nullifies the compulsory activation of the line equalizer control unit 53.

Abstract: A transmitter has a power calculation unit for calculating the power of a signal. A maximum value detection circuit determines a maximum value of an output of the power calculation unit, and a floating point transformation circuit changes an output of the maximum value detection circuit into a floating point representation. A significant bit extracting circuit extracts significant bits from an output of the floating point transformation circuit and outputs the significant bits as the transmitting signal.

Abstract: A preceding apparatus for calculating a difference between an inputted signal point and an output signal obtained one timing before and outputting the difference has a position information judging unit for judging which position on a vector plane the output signal obtained one timing before is located in, and a signal point selecting storage for outputting any signal point among a plurality of signal points generated correspondingly to a signal point inputted from the outside with a result of the judgement fed form the position information judging unit nd the signal point inputted from the outside as an address, thereby decreasing the number of cycles required by a DSP process and realizing a precoder process in a degree achieved hitherto.

Abstract: The invention provides a training method for a non-Nyquist transmission system and a training data transmission apparatus for a non-Nyquist transmission system by which initialization processing of a reception section can be performed with certainty even where a non-Nyquist transmission system is employed.

Abstract: The present invention discloses a timing phase control apparatus which is particularly suitable for use in a modem used for very high speed data transmission employing a metallic line. The timing phase control apparatus includes a timing phase extracting portion to extract timing phase information from an input signal, a timing phase control filter portion to make a timing phase control to the input signal depending upon the timing phase information from the timing phase extracting portion through filter processing using a coefficient operation having a preset impulse response characteristic, and a filter processing coefficient determining portion to determine a coefficient used for the filter processing in the timing phase control filter portion depending upon the timing phase information and information about an approximate expression of the impulse response characteristic.

Abstract: A method of controlling a line equalizer such as a modem includes an extracting step of extracting plural tone signals each superimposed on a transmission signal and having a specific frequency component; a judging step of judging levels of the extracted tone signals; and a controlling step of controlling characteristic of a line equalizer which equalizes a receive signal, based on the levels of the judged tone signals. A line equalizer is controlled without performing an exchange of a training signal prior to starting a data transmission and without increasing the amount of hardware of a modem or the like.

Abstract: The invention provides a carrier phase control circuit which can eliminate a phase intercept fluctuation so that, when the carrier phase control circuit is applied to a very high speed modem having a communication speed of, for example, 28.8 kbps, occurrence of a communication error can be suppressed and the modem has an improved characteristic. The carrier phase control circuit is provided on a reception side of a communication apparatus and interposed between an automatic equalizer and a signal decision section. The carrier phase control circuit includes a frequency offset removal section for predicting and removing an offset of a frequency of a transmission signal based on an output of the automatic equalizer, and a phase intercept variation removal section for predicting and removing a phase intercept variation of the transmission signal based on an output of the frequency offset removal section and inputting a resulted signal as an output thereof to the signal decision section.

Abstract: A transmission system includes a transmitter and a receiver and transmits a data signal with an analog passband signal through an analog transmission line. The data signal is transformed to a signal representing a descrete data signal point in a vector signal space. The transmitter includes a data signal point generation unit and a vector signal superimposing unit. The analog passband signal is transformed to a base band signal, and the base band signal is superimposed on the signal representing a descrete data signal point. A signal representing the superimposed data signal point is modulated and transmitted through the analog transmission line. The receiver includes a demodulator unit and a decision unit, wherein the data signal point is decided from the signal representing the superimposed data signal point, and the superimposed base band signal is extracted in a subtracter unit by subtracting the decided result from the signal representing the superimposed data signal point.

Abstract: A transmission synchronizing apparatus and method of a modem, in which a phase difference from a change point of an internal timing signal to a change point of a transmission timing signal is detected as a reference phase difference at the time of pull-in, based on a request to transmit from an external device. After pull-in, in a stationary communicating state, a phase difference is obtained from a change point of the internal timing signal to a change point of the transmission timing signal as a measured phase difference. The measured phase difference is controlled to coincide with the reference phase difference.

Abstract: The invention provides a modulator and demodulator apparatus (modem) which modulates and demodulates a signal in a main channel, for main data, and a secondary channel, for secondary data obtained by frequency division, and which includes a carrier detection unit for detecting a carrier from a demodulation signal and executes a data processing sequence for the demodulation signal in accordance with a result of detection of the carrier detection unit. This apparatus improved in that it can detect a carrier of a low roll-off ratio accurately and stably without a dispersion in detection time and, consequently, data of a demodulation signal can be processed with certainty. The modulator and demodulator apparatus comprises a filter having a characteristic wherein the time axis response is slow and it is provided at a stage preceding the carrier detection unit so that a demodulation signal which has passed through the filter is input to the carrier detection unit.

Abstract: The invention provides a modulator and demodulator apparatus (modem) which modulates and demodulates a signal in a main channel, for main data, and a secondary channel, for secondary data obtained by frequency division, and which includes a carrier detection unit for detecting a carrier from a demodulation signal and executes a data processing sequence for the demodulation signal in accordance with a result of detection by the carrier detection unit. This apparatus can detect a carrier of a low roll-off ratio accurately and stably without a dispersion in detection time and, consequently, data of a demodulation signal can be processed with certainty. The modulator and demodulator apparatus comprises a filter having a characteristic wherein the time axis response is slow and it is provided at a stage preceding the carrier detection unit so that a demodulation signal which has passed through the filter is input to the carrier detection unit.

Abstract: A modulation and demodulation system suitable for use with a modem (modulator and demodulator apparatus) of a first polling type. The system allows reproduction of a signal necessary for initialization of a reception section of a modulator and demodulator apparatus with certainty in a short training time. The modulation and demodulation system is constructed such that, upon transmission of data, training data of a particular pattern are modulated and transmitted prior to transmission of the data, and such training data are demodulated by demodulation means and initialization of a reception section of the modulation and demodulation system is performed using the demodulation training data. The pattern of the training data to be transmitted includes an arrangement of signals wherein signals having phases different by 180.degree. from each other are arranged alternately, and a signal having the same phase as the last signal is arranged intermediately.

Abstract: A backup apparatus in a communication system, functioning such that when an analog dedicated line is working properly, controllers on a host unit side and a terminal unit side control respective switching circuits so as to connect a modem on the host unit side with the analog dedicated line and a modem on the terminal unit side with the analog dedicated line. Thus, data is transmitted and received between the host unit and the terminal unit over the analog dedicated line. When the defect detecting portion of the modem detects occurrence of a line defect, the controller of each backup unit controls the switching circuit and the ISDN interface portion so as to connect the host unit and the terminal unit over the ISDN network. Thereafter, until the analog dedicated line restores from the defect, data communication is made between the host unit and the terminal unit over the ISDN network.

Abstract: In a timing extraction device coupled to a demodulator which derives a real signal component and an imaginary signal component from a signal received via a transmission line, a band-pass filter extracts a 1/2-Nyquist frequency from either the real signal component or the imaginary signal component. The 1/2-Nyquist frequency includes two symmetrical frequency components. A vector conversion unit processes the 1/2-Nyquist frequency so that a vector signal corresponding to one of the two symmetrical frequency components of the 1/2-Nyquist frequency is output from the vector conversion unit. A square multiplier squares the vector signal received from the vector conversion unit and thereby generates a phase error signal indicating timing information concerning the analog signal. The phase error signal has an angle which is double an angle of the vector signal.

Abstract: A modulator receives a main signal synchronizing with a clock and a secondary signal having start and stop bits for each character. The modulator contains a unit for removing the start and stop bits from the secondary signal to generate a clock-synchronizing secondary signal. Then, the clock-synchronizing secondary signal and the main signal are modulated in parallel synchronized with a clock, and modulated signals are frequency division multiplexed. A demodulator receives a frequency division multiplexed modulated signal, and a clock-synchronizing main signal and a clock-synchronizing secondary signal are respectively regenerated by modulation and band separation. The demodulator contains a unit for inserting start and stop bits respectively before and after each character contained in the clock-synchronizing secondary signal to generate a secondary signal in a start-stop system.