摘要:
A PCM coder and decoder circuit for use in a subscriber line interface circuit of a telephone communication system has a digital balancing network for removing any echo signal. The digital balancing network is formed by series-connecting a first balancing circuit having characteristics corresponding to the fixed characteristics of a coder, decoder, etc. and a second balancing circuit having characteristics corresponding to variable characteristics of an external circuit including two-wire transmission line which is connected to the coder and decoder circuit. Thus, a replica of an echo signal is precisely produced, and the circuit configuration is simplified.
摘要:
Disclosed is a PCM coder-decoder having a construction such that a digital filter contained originally in the PCM coder-decoder is utilized on the time division basis in order to fold back a digital reception signal to a digital signal transmission side and thus to accomplish interruption, communication exchange between three parties, gain control, fold-over test of the PCM signal, and so forth, in addition to the coding and decoding functions inherent to the PCM coder-decoder.
摘要:
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.
摘要:
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.
摘要:
A PCM decoder for converting to an analog voice signal an 8-bit PCM signal the first bit of which is a polarity specifying bit, the PCM decoder comprising a capacitor array having binary-weighted capacitors and a resistor string circuit having plural resistors for dividing a reference voltage to obtain different tap voltages, wherein the tap voltages corresponding to the four lower bits of the PCM signal are derived from the resistor string circuit and the combination of the reference voltage and each of the tap voltages, made according to the contents of the second, third and fourth bits of the PCM signal is applied to the corresponding one of the capacitors in the capacitor array circuit whereby the capacitor array circuit delivers an analog voltage signal corresponding to the received signal, the resistor string circuit having two groups of intermediate taps so that the conversion characteristic for obtaining voltages in the signalling frame may be different from that in the non-signalling frame.
摘要:
A demodulation circuit comprises: a phase detection circuit for determining an absolute value of a phase difference between an input signal to be demodulated and a reference signal; a binary phase detection circuit for converting a phase lead or lag between the input signal and the reference signal into a sign of phase difference; and a phase demodulation circuit for calculating, from the absolute value and the sign of phase difference, a phase difference quantity between the input signal and the reference signal and for performing a delay detection on the phase difference quantity; wherein the binary phase detection circuit includes a delay circuit which generates a delay time corresponding to the operation delay of the phase detection circuit; and wherein the phase detection circuit includes a level limiter circuit to limit an internal signal voltage and a reference voltage adjust circuit to correct deviations in the internal signal voltage.
摘要:
An over-sampling analog-to-digital converter using a current switching circuit 102 as a local digital-to-analog converter, wherein a difference between the output currents Isig and Iq of a voltage-to-current converter circuit 101 and a current switching circuit is integrated by a capacitor 105 of which the one end is grounded to a dc potential VB. Further, the current switching circuit 102 has many bits to decrease the difference current between the signal current Isig and the feedback current signal Iq. Moreover, the level-shifting function of the voltage-to-current converter circuit 101 makes it possible to apparently subtract the dc component from the input analog signal Vsig which is produced based on an internally generated dc voltage as a dc bias voltage, and to decrease a change in the voltage between the electrodes of a capacitor caused by the integration of current.
摘要:
Herein disclosed is an oversampling type A/D converter, wherein there are connected in multiple stages units interpolation type A/D conversion circuits each including: an analog integration circuit for integrating the difference between an analog input signal and a feedback signal; a voltage comparison circuit for adding the integrated signal and said difference to produce a digital signal on the basis of the added value; a digital integration circuit for integrating the digital signal coming from the voltage comparison circuit; a feedback load D/A conversion circuit for producing a feedback signal from the output of the digital integration circuit; and an addition circuit for adding the output and input of said digital integration circuit.
摘要:
A non-uniform weighting circuitry which is effective for enhancing speed and accuracy in the operations of encoders and decoders comprises in a cascade connection a constant current switch, a variable attenuator, a polarity changing circuit and a uniform weighting circuit. An impedance converting means is provided to make at least one of input and output terminals of the variable attenuator to be of low impedance, whereby spike-like noises generated by a switching element constituting a part of the variable attenuator is reduced.
摘要:
An AD converter which uses no buffer for receiving the input signals or uses the buffer having relaxed requirements concerning the range of input signals and the output impedance. Voltage at the connection points of a resistor ladder in which a plurality of resistor elements are connected in series, are compared with a reference voltage by a plurality of voltage comparators, a first current circuit is provided on the high potential side of the resistor ladder, a second current circuit is provided on the low potential side thereof, and analog input voltages are fed by providing an input terminal at any place of the resistor ladder except both ends thereof.