Abstract: The present invention provides a solution that eliminates both the voltage-controlled oscillator (“VXCO” 105) and its associated D/A converter (120) from the timing recovery scheme, thereby significantly reducing manufacturing costs for modems, such as asymmetric digital subscriber loop (“ADSL”) modems. The present invention also enables tracking of a wider frequency offset. The present invention provides this with a novel timing recovery scheme implemented entirely in the digital domain. The present invention includes a free running clock (205) as the sampling clock for the A/D (110) and D/A (115) converters, and interpolators (210, 220, 615 and 635) to correct timing errors for both the receive and transmit samples. The desired sample can be obtained based on its timing offset and its neighboring samples.

Abstract: Alignment methods and apparatus for I/Q phase and amplitude error correction and image rejection improvement that may be used at the time of circuit fabrication or on chip for use during operation. The alignment method may be used to improve the I/Q phase and amplitude accuracy of a direct conversion transceiver or to improve image rejection in an up or downconversion mixer. For alignment purposes, a pilot tone of a selected frequency is used to provide a calibration reference, with adjustments being made in phase and amplitude to drive the I and Q phase and amplitude mismatch toward a minimum.

Abstract: A DMT modem (40) is disclosed, in which a combined time domain equalizer and per-tone equalizer is applied to a received DMT signal. The combined equalizer includes a first FFT function (44) that is applied to a set of samples in a time-domain signal after the application of a time domain equalizer (42). The first FFT function (44) produces an initial FFT result, that is accumulated with a sliding FFT (46) performed upon difference values in the time domain samples. The sliding FFT results are applied to a per-ton equalizer (48) which applies a set of complex coefficients determined in training of the modem. A simple 1-tap FEQ (50) then can recover the signal. The combined equalizer enables per-tone equalization, in a manner that is compatible with conventional DSL training standards. According to a second embodiment, the per-tone equalization is performed only on selected tones of the multitone signal.

Abstract: Precision inphase/quadrature up-down converter structures generally neither requiring trimming at the time of fabrication nor calibration during use. The converters use four mixers arranged to down convert to provide Q, I, {overscore (I)}and Q baseband signals (or up convert Q, I, {overscore (I)} and Q baseband signals), the combination of which signals has a very substantially reduced unwanted image frequency content. The use of an increased number of mixers in effect shifts the primary errors from absolute gain and phase errors, to gain and phase error mismatches between elements in replicated circuits, which mismatches can be held to a minimum in circuits replicated in a single integrated circuit.

Abstract: Alignment methods and apparatus for I/Q phase and amplitude error correction and image rejection improvement that may be used at the time of circuit fabrication or on chip for use during operation. The alignment method may be used to improve the I/Q phase and amplitude accuracy of a direct conversion transceiver or to improve image rejection in an up or downconversion mixer. For alignment purposes, a pilot tone of a selected frequency is used to provide a calibration reference, with adjustments being made in phase and amplitude to drive the I and Q phase and amplitude mismatch toward a minimum.

Abstract: A microwave broadside coupled balun integral in a multi-layer printed wiring board formed by broadside coupled conductors embedded in the multi-layer printed wiring board. The balun may be used to form components which are integrated into the multi-layer printed wiring board, such as a microwave mixer formed by two of said broadside coupled baluns embedded in a multi-layer printed wiring board and connected to a diode ring quad.

Abstract: A compensated mixer including a radio frequency (RF) balun through which RF signals are transferred, and a local oscillator (LO) balun for receiving an LO signal. In an exemplary implementation the mixer further includes a diode ring quad circuit for mixing RF signals received by the RF balun with the LO signal received by the LO balun. During operation the diode ring quad circuit develops, between first and second nodes therein, a capacitive reactance arising from switching at the LO frequency. The mixer further includes a compensation inductor, connected between the first and second nodes, for cancelling the effect of the capacitive reactance at the LO signal frequency.

Abstract: A unbalanced mixer capable of operation in the absence of DC bias is disclosed herein. The mixer includes an input or local oscillator (LO) port for receiving an input signal. A first transistor has a control terminal coupled to the mixer input port, and an output terminal coupled to a first signal port of the mixer. The mixer further includes a resonator circuit, connected between the transistor control and output terminals, for providing signal isolation between the mixer input port and the first signal port. In a preferred implementation the resonator circuit comprises an inductive element in parallel with a first intrinsic capacitance of the transistor. The mixer may also include a diplexer circuit for coupling signal energy of a first frequency between the output terminal and the first signal port, and for coupling signal energy of a second frequency between the output terminal and a second signal port.