Abstract: A radio frequency tuner comprises one or more tracking filters ahead of at least one frequency changer. A controller has a filter alignment mode and a reception mode. Each filter has one or more resonant networks comprising an inductance and a switched capacitor network which is digitally controlled for selecting the network resonant frequency. In the alignment mode, the controller determines the difference between the nominal and actual capacitances of the network for achieving a known resonant frequency in order to determine a correction factor for the capacitor network. The correction factor is then used during normal reception by the tuner.

Abstract: A variable signal delaying circuit comprising an analog delay line having a control input for controlling the variable delay. A phase detector compares the input and output signals of the delaying circuit and supplies an output signal to a charge pump and integrator. A pulse stream generating arrangement produces pulse streams of different pulse widths and pulse control logic controls a selector for selecting any one of the pulse streams. In a first mode of operation, the control logic monitors the charge pump/filter output and selects the pulse stream which minimizes change in the output. The selection is fixed and the output of the charge pump/filter is then supplied as a correction signal to the control input of the analog delay line. Such an arrangement may be used to maintain minimum phase imbalance in I and Q signal paths of a quadrature frequency converter.

Abstract: A method is provided for reducing imbalance in a quadrature frequency converter. A test tone generator controlled by an alignment controller supplies a test signal to the input of the frequency converter. A starting point is selected in a solution space addressed by I and Q corrections. The starting point comprises in-phase (I) and quadrature (Q) phase correction values. A test is then performed to determine the best direction of movement in the I/Q phase correction plane in order to reduce phase imbalance. The I and Q phase correction values are then moved in that direction towards a phase imbalance minimum.

Abstract: A radio frequency tuner includes a first quadrature frequency changer, I and Q filters which are electronically adjustable, and a second quadrature frequency changer. During alignment of the filters, an alignment controller connects a test tone generator to the input of the frequency converter and the generator supplies a sequence of test tones of different accurately known frequencies. The amplitude of the resulting signals at the output of one of the filters is measured by a level detector. The controller compares the measured levels with a desired frequency response and adjusts the filter accordingly. The controller then causes the generator to supply a sequence of two test tones of different frequencies and a differential phase detector measures the phase difference between the output signals of the mixers of the second frequency changer.

Abstract: A radio frequency tuner comprises one or more tracking filters ahead of at least one frequency changer. A controller has a filter alignment mode and a reception mode. Each filter has one or more resonant networks comprising an inductance and a switched capacitor network which is digitally controlled for selecting the network resonant frequency. In the alignment mode, the controller determines the difference between the nominal and actual capacitances of the network for achieving a known resonant frequency in order to determine a correction factor for the capacitor network. The correction factor is then used during normal reception by the tuner.

Abstract: A frequency changer arrangement is provided for a radio frequency tuner. The arrangement comprises a first quadrature frequency changer for converting a desired input channel to zero or near-zero intermediate frequency in-phase and quadrature signals. These signals are filtered by low pass filters, whose turnover frequencies may be varied so as to vary the intermediate frequency bandwidth. A second quadrature frequency changer upconverts the filtered signals and supplies these to a summer. The resulting output intermediate frequency is determined by the frequency of commutation signals in the second frequency changer so that the output intermediate frequency may be continuously varied to allow any desired frequency to be selected.

Abstract: A method is provided for reducing imbalance in a quadrature frequency converter. A test tone generator controlled by an alignment controller supplies a test signal to the input of the frequency converter. A starting point is selected in a solution space addressed by I and Q corrections. The starting point comprises in-phase (I) and quadrature (Q) phase correction values. A test is then performed to determine the best direction of movement in the I/Q phase correction plane in order to reduce phase imbalance. The I and Q phase correction values are then moved in that direction towards a phase imbalance minimum.

Abstract: A radio frequency tuner includes a first quadrature frequency changer, I and Q filters which are electronically adjustable, and a second quadrature frequency changer. During alignment of the filters, an alignment controller connects a test tone generator to the input of the frequency converter and the generator supplies a sequence of test tones of different accurately known frequencies. The amplitude of the resulting signals at the output of one of the filters is measured by a level detector. The controller compares the measured levels with a desired frequency response and adjusts the filter accordingly. The controller then causes the generator to supply a sequence of two test tones of different frequencies and a differential phase detector measures the phase difference between the output signals of the mixers of the second frequency changer.

Abstract: A variable signal delaying circuit comprising an analog delay line having a control input for controlling the variable delay. A phase detector compares the input and output signals of the delaying circuit and supplies an output signal to a charge pump and integrator. A pulse stream generating arrangement produces pulse streams of different pulse widths and pulse control logic controls a selector for selecting any one of the pulse streams. In a first mode of operation, the control logic monitors the charge pump/filter output and selects the pulse stream which minimizes change in the output. The selection is fixed and the output of the charge pump/filter is then supplied as a correction signal to the control input of the analog delay line. Such an arrangement may be used to maintain minimum phase imbalance in I and Q signal paths of a quadrature frequency converter.