Provided is a transmission circuit (1) which accurately compensates offset characteristics of an amplitude modulating section (15) and operates at low distortion and high efficiency over a wide output power range. A signal generating section (11) outputs an amplitude signal and an angle modulation signal. An amplitude amplifying section (14) supplies the amplitude modulating section (15) of a voltage corresponding to the magnitude of the inputted amplitude signal. The amplitude modulating section (15) modulates the amplitude of an angle modulation signal by the voltage supplied from the amplitude amplifying section (14), and outputting it as a modulation signal. A temperature measuring section measures the temperature of the amplitude modulating section (15). An offset compensating section (12) calculates an offset compensation value based on the temperature change of the amplitude modulating section (15) from from an initial status, and adds the calculated offset compensation value to the amplitude signal.

In a polar modulation system, there is disclosed a polar-modulation transmission device, which can be dispensed with an isolator thereby to suppress a circuit scale and the heat loss of a power amplifier. In this device, a current detecting unit (130) detects a current value (Icc) to flow from a power source voltage transforming unit (120) to a power amplifier (180), and a power control unit (140) inputs a power control signal (S30) and outputs a control signal (S31) to a power applying unit (150) on the basis of the current value (Icc). The power applying unit (150) multiplies a baseband amplitude modulation signal (S11) by the control signal (S31) thereby to produce an amplitude modulation signal (S13). A regulator (160) feeds a power source voltage (S22), which is changed from a power source voltage (S21) by the amplitude modulation signal (S13), to a power amplifier (180). This power amplifier (180) amplifies the power of a phase modulation high-frequency signal (S14) by using the power source voltage (S22) as a power source, thereby to acquire an RF transmission signal (S15).

An RF transmitter, comprising: signal generation means operable to generate first and second digital RF signals in dependence upon data to be transmitted, the first digital signal being a pre-distorted version of the second digital signal; first DAC means operable to convert the first digital RF signal into a first analogue RF signal; second DAC means operable to convert the second digital RF signal into a second analogue RF signal; an amplifier, operatively connected to the first DAC means, for producing an amplified transmission signal in dependence upon the first analogue RF signal; an antenna operatively connected to said amplifier for transmitting said amplified transmission signal; and an error-signal generator, operatively connected to the antenna and the second DAC means, for producing an error signal in dependence upon a difference between the transmission signal and the second analogue RF signal; wherein said signal generation means is operatively connected to the error-signal generator to control generation of said first digital RF signal in dependence upon said error signal so as to tend to reduce said difference.

Aspects of a method and system for digital tracking in direct and polar modulation are presented. Aspects of the system may include at least one circuit within a phase locked loop (PLL) circuit that enables adaptive and digital control of an analog fractional N (Frac N) PLL during direct modulation of a signal or polar modulation of the signal.

A transmitter includes a first limiter (104) for performing a first clipping in which an amplitude part at a level higher than an amplitude level based on a first clipping level (CR1) is cut out from an input signal to be subjected to power amplification, a second limiter (105) for performing a second clipping in which an amplitude part at a level lower than the amplitude level based on a second clipping level (CR2) is cut out from a first signal that has undergone the first clipping, a separation section (106) for separating a second signal that has undergone the second clipping into an amplitude modulated part and a constant amplitude part, a first amplifier (111) for amplifying the amplitude modulated part, a second amplifier (112) for amplifying the constant amplitude part, and a combiner (113) for outputting a third signal obtained by combining the amplitude part amplified by the first amplifier (111) and the constant amplitude part amplified by the second amplifier (112).

A timing adjusting method detects a phase error between a main signal path (41) from which a transmitting signal (Tx) is obtained and a control signal path (42) from which a voltage control signal (v) is obtained, based on a to-be-amplified signal that is to be amplified and represents an amplitude or a power of the transmitting signal (Tx) prior to amplification and a feedback signal (Fb) that represents an amplitude or a power of the transmitting signal (Tx) after the amplification, adjusts an amount of delay of at least one of the main signal path (41) and the control signal path (42) so as to mutually cancel the phase error, and amplifies the transmitting signal (Tx) from the main signal path (41) depending on the voltage control signal (v) from the control signal path (42). The detecting the phase error may include detecting polarity transition points of a slope of a waveform of the to-be-amplified signal or the feedback signal (Fb), and measuring the phase error using the detected polarity transition points.