Abstract: A digital subscriber line (DSL) communication system that utilizes the high frequency band of a standard telephone line does not require the use of a plain old telephone service (POTS) splitter in the resident's home, which provided isolation between the POTS frequency band (0 to 4 kHz) and the DSL frequency band. A digital subscriber line modem utilizes either constant envelope modulation or quadrature amplitude modulation for outputting DSL signals upstream to a central office. When a telephone in the resident's home is detected as being off-hook, then the constant envelope modulation is used by the DSL modem in order to lessen the intermodulation product distortion that results in audible noise heard by a user of the telephone. When the telephone is on-hook, then another type of modulation, such as QAM, is used to maximize the upstream data rate capability in the DSL frequency band, since any noise generated by the QAM is not a problem due to the non-use of the POTS frequency band.

Abstract: A system of and method for reducing or eliminating any unwanted sideband component in a signal derived from the output of a quadrature modulator. An unwanted sideband detector detects the unwanted sideband in the output of the quadrature modulator, and responsive thereto, a correction circuit corrects a baseband signal prior to inputting it to the quadrature modulator. In one embodiment, the unwanted sideband detector is an envelope detector.

Abstract: A system of and method for reducing or eliminating any unwanted sideband component in the output of a transmitter comprising a quadrature modulator followed by a translational loop. In one implementation, a value representative of the unwanted sideband is derived from a low frequency signal generated within or by the translational loop. In this implementation, the low frequency signal is taken from an input to a VCO within the translational loop.

Abstract: A digital subscriber line (DSL) communication system that utilizes the high frequency band of a standard telephone line does not require the use of a plain old telephone service (POTS) splitter in the resident's home, which provided isolation between the POTS frequency band (0 to 4 kHz) and the DSL frequency band. Digital signal processing techniques are utilized to adapt to varying subscriber line conditions due to POTS telephone equipment. The digital signal processing techniques eliminate the need for a splitter by reducing susceptibility to distortion due to varying subscriber line characteristics. The digital subscriber line modem utilizes constant envelope modulated signals and frequency division multiplexing, where the constant envelope modulations lessens the intermodulation distortion products due to DSL signals that are transmitted by the modem and which may result in audible noise at the POTS telephone equipment due to non-linearities of the POTS telephone equipment.

Abstract: A digital subscriber line (DSL) communication system that utilizes the high frequency band of a standard telephone line does not require the use of a plain old telephone service (POTS) splitter in the resident's home, which provided isolation between the POTS frequency band (0 to 4 kHz) and the DSL frequency band. A digital subscriber line modem utilizes either constant envelope modulation or quadrature amplitude modulation for outputting DSL signals upstream to a central office. When a telephone in the resident's home is detected as being off-hook, then the constant envelope modulation is used by the DSL modem in order to lessen the intermodulation product distortion that results in audible noise heard by a user of the telephone. When the telephone is on-hook, then another type of modulation, such as QAM, is used to maximize the upstream data rate capability in the DSL frequency band, since any noise generated by the QAM is not a problem due to the non-use of the POTS frequency band.

Abstract: A circuit for resetting an electronic system based on voltage fluctuations in the power supply is disclosed. The circuit comprises a diode means for generating a first voltage being offset from the supply voltage, a first inverter having its input connected to the diode and powered by a reference voltage source, a second inverter having its input connected to the same reference voltage source and powered by the power supply; and an OR- or NOR- gate having its inputs from the outputs of the first and second inverters, such that its output, when asserted, resets the electronic system.

Abstract: A differential amplifier with improved offset cancellation is disclosed. The differential amplifier has a floating current source coupled to the drain terminals of the differential pair for providing complementary currents to cancel the offset voltage. In this way, the tail current in the differential pair is not affected by the offset cancellation and remains constant, while the common-mode offset is not worsened by the injected current.

Abstract: A converter for converting a single-ended input V.sub.IN to a differential output signal V.sub.OUT through positive and negative output terminals is disclosed. The converter comprises a fully differential amplifier with one of its input terminals coupled to the single-ended input and its other input terminal coupled to a fixed voltage. The converter also has a first resistor ("R.sub.1 ") coupled between the single-ended input and the positive input terminal of the fully differential amplifier, a second resistor ("R.sub.2 ") coupled between the fixed voltage and the negative input terminal of the fully differential amplifier, a third resistor ("R.sub.3 ") coupled between the positive input terminal and the negative output terminal of the fully differential amplifier, and a fourth resistor ("R.sub.