Abstract: The present invention relates to an offset voltage zeroing method of a D/A converter, with the aid of which oscillations of the output voltage of said D/A converter can be radically reduced. An output signal of the converter is carried to a first terminal of a capacitor (5). A second terminal of the capacitor is coupled to a reference voltage (V.sub.ref) with a controllable switch (6) as long as there are no pulses in the output of the converter. As a result, an amended output signal is obtained from the second terminal.

Abstract: The present invention concerns a circuit for forming low power levels in a transmitter of a radio telephone. By a power amplifier (1) of the transmitter is formed the maximum power level and a plurality of lower power levels. As taught by the invention, very low power levels can be produced by controling the power of the RF signal leaking through the power amplifier (1) when said signal is not amplified by the power amplifier. For controlling the leakage power, a PIN diode attenuator (4) connected before the power amplifier (1) is used.

Abstract: The present invention concerns a circuit processes the power signal emitted from an RF power sensor (SK) of a radio telephone to create a detector voltage which is proportional to the power level of the radio telephone transmitter. The circuit comprises a transistor (Q2) acting as an active rectifier, which in the ascending part of the positive half cycle of the power signal charges a capacitor (C3). During the descending part of the power signal the capacitor starts to discharge with a time constant which is remarkably greater than the cycle length of the power signal. The transistor is biassed by means of a transistor (Q1) so that it is conductive even at the lowest power levels.

Abstract: A circuit for forming low power levels in a radio telephone transmitter in which high power levels are produced in a controllable amplifier stage (1), for instance in a class-C power amplifier. According to the procedure, a RF signal is before the amplifier stage (1) divided into two branches in a power divider (4), in one of which the Rf signal is conducted to said amplifier stage (1) for forming high power levels, and in the other branch the RF signal is conducted to an element (5) by which low power levels are produced, and said branches are combined in the output (RFout) of the transmitter. The element (5) may be a PIN diode attenuator.

Abstract: The invention relates to the forming of a control pulse for the transmitter in a GSM radio telephone system. A cos.sup.2 pulse is formed by means of an analog circuit from a rectangular pulse which is first shaped into a triangular pulse which may be somewhat clipped at its peak. The triangular pulse is further shaped into a cos.sup.2 pulse. The circuit also includes the selection of the abruptness of the triangular pulse and, thereby, the abruptness of the cos.sup.2 pulse.