Abstract: The invention relates to a calibration method and a calibration arrangement for an active filter intended to be used especially in portable radio apparatus. The filter (100) according to the invention is an active RC filter and it is integrated except for one or more of its capacitances or one or more of its resistances. Advantageously the highest capacitance or the highest resistance is left unintegrated. When using an external capacitance, the principle of the calibration is as follows: The integrated resistances are corrected using a common coefficient such that the external capacitance together with the integrated resistances produces the correct time constants (1). Then the integrated capacitances are corrected using a common coefficient such that they together with the internal resistances that were corrected in the previous phase produce the correct time constants (2). If the filter comprises multiple circuit stages, the two-phase calibration process described above is repeated for each circuit stage.

Abstract: The object of the invention is a transceiver for transmitting and receiving an RF signal on at least two operating frequency ranges. One idea of the invention is to use a transceiver based on the direct transform and where the mixing frequency is generated with the aid of the same synthesiser. This is preferably realised so that when operating on frequency ranges far from each other the output signal of the synthesiser is divided with different divisors in order to generate the mixing frequency (211, 231, 261, 281). When operating on frequency ranges which are close to each other the divisor (P) used in the feedback of the synthesiser is advantageously changed (248). With the aid of the invention two mixing signals with a mutual phase difference of 90 degrees can be generated in connection with the division of the synthesiser frequency, whereby no RC phase shifters are required in the signal line, and a good phase accuracy is obtained which is independent of the frequency.

Abstract: The invention relates to a method and radio receiver for attenuating spurious signals when receiving (6 to 12) radio signals, when radio signals are mixed (10) to a second frequency, which may be the baseband frequency, for example. Spurious signals are caused by balance errors in the mixer (10) which result from component value fluctuations within tolerance limits. According to the invention, mixing is balanced by setting (12) variable-level bias voltages and/or currents to transistors in the mixer circuit (10). An advantage of the invention is that even-order spurious signals caused by balance errors in the mixing of a signal to a second frequency are considerably attenuated. The invention finds particular utility in a mobile communications device, for example.

Abstract: A modulator having a high signal-to-noise ratio. The modulator comprises a switching arrangement and a driver arrangement coupled to the switching arrangement, said driver arrangement comprising driver components and among the driver components a low-pass filter arrangement. The modulator can be used, for example, in the transmitters of dual-band mobile stations without separate filters for each frequency band.

Abstract: The invention relates to a calibration method and a calibration arrangement for an active filter intended to be used especially in portable radio apparatus. The filter (100) according to the invention is an active RC filter and it is integrated except for one or more of its capacitances or one or more of its resistances. Advantageously the highest capacitance or the highest resistance is left unintegrated. When using an external capacitance, the principle of the calibration is as follows: The integrated resistances are corrected using a common coefficient such that the external capacitance together with the integrated resistances produces the correct time constants (1). Then the integrated capacitances are corrected using a common coefficient such that they together with the internal resistances that were corrected in the previous phase produce the correct time constants (2). If the filter comprises multiple circuit stages, the two-phase calibration process described above is repeated for each circuit stage.

Abstract: A digital phase comparator comprises a first signal input (VCO) and second signal input (REF) as well as a first output (UP+) and second output (DOWN+). It is arranged so as to produce an output pulse (503, 504) to the first output and second output per each of the cycles of the periodic signals (501, 502) brought to the first signal input and second signal input. The duration of the output pulse produced to the first output is longer than the duration of the output pulse produced to the second output when the phase of the periodic signal brought to the first signal input is lagging with respect to the phase of the periodic signal brought to the second signal input. Correspondingly, the duration of the output pulse produced to the first output is shorter than the duration of the output pulse produced to the second output when the phase of the periodic signal brought to the first signal input is leading with respect to the phase of the periodic signal brought to the second signal input.