Abstract: In a digital demodulator for phase modulated signals, logical values of a waveform-shaped phase-modulated signal are sampled based on a clock signal having a period that stands in integer ratio relationship to a carrier period of the modulated signal and thereafter subjected to serial/parallel conversion for each predetermined interval, whereby a logical pattern of a digital code train subjected to the serial/parallel conversion is analyzed. As a result, phase information required to demodulate digital data can be logically detected.

Abstract: In a semiconductor integrated circuit having a plurality of electronic circuits each provided with interfaces used for effecting signal transmission, and supplied with operating voltages from a plurality of independent power supply terminals, protective elements each having high threshold voltages at which the elements are off in the ordinary state of power supply are provided, and a resistor and a diode both for preventing electrostatic breakdown are connected to the gate of an input MOSFET of the interface for carrying out signal transmission between the electronic circuits. Even when a high voltage due to static electricity is applied to each power supply terminal while the semiconductor integrated circuit is handled, electrostatic breakdown of the interface can be prevented by the protective element or the electrostatic breakdown preventive circuit comprising a resistor and a diode.

Abstract: A Gm-controllable amplifier is used in an OTA-C filter. Specifically, the amplifier is one in which a constant voltage from a bias circuit is applied to the gates of load MOSFETs connected to the drains of input differential MOSFETs of a differential amplifier to allow the load MOSFETs to operate as constant current sources and the inverted output terminals of the circuit are connected to the input terminals. The load MOSFETs of the input differential MOSFETs are made to operate as the constant current sources, so that the drain voltages of the input differential MOSFETs become independent of the threshold voltage of the load MOSFETs. Even if the supply voltage is set to as low as about 1.5 V, the input differential MOSFETs can be prevented from being unsaturated when the input signals rise.

Abstract: The number of current sources and switches necessary for a plurality of unit D/A converters using equal reference currents, are drastically reduced to reduce the parasitic capacitance coupled to current output lines, by converting a plurality of digital signals of a predetermined bit, which are divided from an input digital signal, into an analog current unit D/A converters and by converting the analog current in a manner to correspond to the weights of the corresponding input digital signals, thereby to synthesize the currents. The fixed reference digital signal is inputted to the D/A converter for cancelling offsets. The offsets of a plurality of analog output signals in positive and opposite phases obtained by branching the output of the D/A converter are individually detected. After this, the DC offset values of the individual analog outputs are used as offset adjusted negative feedback signals for a desired value.

Abstract: The difference between the output current of a voltage-current converter circuit and the output current of a local D/A converter circuit 2, whose output current is controlled by a feedback signal, is integrated by an analog circuit of which one end is connected to a DC potential point, and the voltage obtained by the integration thereof is quantized by a quantizing circuit. The result is integrated by a digital integrating circuit and is fed to a feedback correcting circuit 6 and, further, the result of A/D conversion is output. The feedback correcting circuit outputs a temporary feedback signal while the digital integration is being operated based on the output of the quantizing circuit. After the digital integrating operation completes the digital integration operation, a corrected feedback signal is generated instead of the temporary feedback signal. The signals inputted into the analog circuit 3 are continuously sampled even while the digital integration operation is being carried out.

Abstract: 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.