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 active component (400, 500) of a radio device comprises a first transistor (Q1) and a second transistor (Q2). The differential input of the active component comprises a first input line (RF+) and a second input line (RF−), of which the first input line is coupled to the base of the first transistor (Q1) and the second input line is coupled to the base of the second transistor (Q2). In order to match the input impedance there is cross-feedback (Rfb′) between the first transistor (Q1) and the second transistor (Q2).

Abstract: The active component (400, 500) of a radio device comprises a first transistor (Q1) and a second transistor (Q2). The differential input of the active component comprises a first input line (RF+) and a second input line (RF−), of which the first input line is coupled to the base of the first transistor (Q1) and the second input line is coupled to the base of the second transistor (Q2). In order to match the input impedance there is cross-feedback (Rfb′) between the first transistor (Q1) and the second transistor (Q2).

Abstract: The radiotelephone of a time-divided radiotelephone system, i.e. TDMA, has a first mode and a second mode, whereby in the first mode the transmitter (TX) is active and in the second mode the receiver (RX) is active. When the transmitter is on, the TX signal dependent on it controls switching means (V2) in such a way that in the first mode blocking is accomplished of at least one active signal path that is in the other mode. In this way the isolation between the transmitter and the receiver is improved. The switching means can comprise, for example, a transistor (V2), by means of which the collector of the transistor (V1) of the RX amplifier is connected substantially to the earth potential.

Abstract: The useful frequency range of an I/Q diode modulator is increased by adding two capacitors (15, 16) and an inductance (17), or two inductances and one capacitance, as a series-resonant circuit. The capacitors (15, 16) are connected in series and have a zero voltage at their connection point so that the inductance (17) does not influence the oscillator signal. The inductance (17) is chosen so that resonance occurs at the frequency at which leakage across the diodes would otherwise occur, so that the impedance between ground and the diode (4, 5) connection point is very low and, therefore, so is leakage between the mixer outputs. When the diode elements conduct, the voltage at the point between the diodes (4, 5 or 4a, 5a) is connected to both branches of the transformer (8) secondary so that the branches have equal voltages with the same phase. This permits an I/Q modulator or I/Q demodulator for 400 MHz or even 900 MHz frequency to be made with ordinary UHF mixer diodes.

Abstract: The object of the invention is a voltage controlled oscillator with improved tuning linearity, which comprises an oscillating transistor (T, 1), a resonator circuit (C11, C12, 11, 12, 19, 20) formed by a capacitance diode (D, 20) and an inductance (L1, 19), whereby the resonator circuit is connected to one of the transistor's (T, 1) electrodes and defines together with the transistor's internal capacitance and external capacitances the oscillator output frequency provided by the transistor. The output frequency can be changed with an external control voltage (V.sub.cntrl) supplied to the cathode of the capacitance diode (D, 20), the control voltage having minimum and maximum values, whereby the oscillator output frequency (f.sub.vco) is arranged to change within a certain frequency band in accordance with the control voltage (V.sub.cntrl). The resonance circuit (RES) is arranged at the current draining electrode (collector) of the transistor to have an effect on the linearity between the control voltage (V.

Abstract: An active biasing circuit to provide linear operation of an RF power amplifier. A current generator circuit provides a current to the stages of the RF power amplifier. In the final power amplifier stage the current is applied to a bias control amplifier that includes a transistor connected as a diode. The transistor diode is connected through a resistor to the emitter of a bias control transistor, which is in turn connected to and controls the gate of a transistor power amplifier in the final power amplifier stage of the RF power amplifier with a bias current that is the highest current level needed for highest RF power. The transistor diode and the current generator circuit are also connected to bias control transistors in the other stages of the RF power amplifier such that the other stages are likewise controlled with the current from the current generator.

Abstract: An I/Q-modulator or I/Q demodulator circuit in which the modulating signals (2, 3) are input through the output phase transfer branches of the circuit. In relation to the RF-characteristics, a series resistor (16) and a series inductance (20) in the phase transfer circuits are grounded with small capacitors (23, 25). A capacitor (17) having a high impedance at the modulating frequency is located between the branches. Tho modulating signals are not summed through the capacitor (17), and, thus, their phase difference is not weakened.