Abstract: Components of a radio-frequency (RF) apparatus including transceiver circuitry and frequency modification circuitry of a crystal oscillator circuit that generates a reference signal with adjustable frequency may be partitioned in a variety of ways, for example, as one or more separate integrated circuits. The frequency modification circuitry may be implemented as part of a crystal oscillator circuit that includes digitally controlled crystal oscillator (“DCXO”) circuitry and a crystal. The frequency modification circuitry may include at least one variable capacitance device and may be employed to generate a reference signal with adjustable frequency. The adjustable reference signal may be provided to other components of the RF apparatus and/or the RF apparatus may be configured to provide the adjustable reference signal to baseband processor circuitry.

Abstract: A digital capacitive isolation barrier system is provided that is suitable for use in a telephone or modem where the locally powered circuits must be effectively isolated from the public telephone system, while permitting data transfer across the barrier. In particular, an automatic ADC offset calibration system is provided for determining the magnitude of the ADC offset signal required in the system during a calibration operation, and for providing the ADC offset signal during normal operation of the isolation barrier system. Fixed bias signals are also provided for the ADC and for a DAC in the system. In a preferred embodiment, the ADC is located on the isolated side of the isolation barrier, while the integrator and register that determine and hold the offset signal are located on the powered side of the isolation barrier.

Abstract: In a vertical-cavity surface-emitting laser (VCSEL) with an active region, and first and second mirror stacks forming a resonant cavity, the VCSEL having a radial electrode configuration with a first electrode disposed around the base of the first mirror stack near one side of the active region, a second electrode on the other side of the active region with a first contacting region and a second contacting region on each side of the active region in contact with the respective electrodes, each of the contacting regions providing a current path for distributed current through the active region, the improvement wherein there is a nonlinear grading of resistivity in at least one of the contacting regions between at least one of the electrodes and the active region.

Abstract: A surface-normal cavity, AlGaAs, Distributed-Bragg Reflector laser. The laser is constructed on a GaAs substrate. There is a nipinipi . . . gain-producing active section comprised of a plurality of gain-producing i-segments disposed at periodic intervals with respect to the wavelength of an intended operating frequency of the laser is stacked vertically with respect to the surface of the substrate. A pair of Distributed-Bragg-Reflector stacks are disposed at the respective ends of the nipinipi . . . active section. A pair of electrodes are formed on either side of and operably connected to the nipinipi . . . active section in electrical contact therewith for applying a driving current to the nipinipi . . . active section in parallel. In one embodiment, the nipinipi . . . active section has interfaces between p+ and n+ sections thereof positioned at standing wave maxima of the intended operating frequency of the laser. In another, the nipinipi . . .