It is an object of the present invention to provide a transmitter which is inexpensive and small in size and is reduced in power dissipation and besides wherein the output power of a power amplifier can be varied to an arbitrary value. A phase modulator, a variable attenuator, a high power amplifier, a directional coupler, a detector, an error amplifier, a switch and an analog multiplier form an envelope feedback loop. The envelope feedback loop controls an envelope of a modulated wave detected by the detector so that a base band signal and the envelope of the modulated wave may coincide with each other. The circuits mentioned above, a smoothing circuit, another error amplifier, another switch and an adder form an operation point feedback loop. The operation point feedback loop smoothes an error of an output envelope detection signal of the detector and controls so that the smoothed error may be in the minimum.
An attenuation control signal for controlling the power of a transmitted signal is generated as follows: A root-mean-square processor 22, receiving a detected output signal of the transmitted signal from a detector 21, carries out the root-mean-square processing of the detected output signal, and a comparator 8 compares the detected output signal passing through the root-mean-square processing with a reference signal, thereby generating the attenuation control signal.
A radio transmitter in which a power level of a modulated signal that has been amplified by an amplifier is detected, an error component is detected by comparing the detected power level with a theoretical value, an ideal value is calculated by adding the error component to the theoretical value, a reference level is generated by comparing the ideal value with the error component, and the gain of the amplifier is controlled based on a difference between the detected power level and the generated reference level.
Methods in radio communications devices having a transmitter with an integral control loop, and in other integral control systems, including generating a first error signal (210) based upon an amplifier output signal and a corrected reference signal, generating a second error (220) signal based on a closed loop integral control signal applied to a control input of the amplifier and based on an integral control reference signal, and generating the corrected reference signal (230) by correcting a reference signal based upon the first and second error signals.
A modem transmits data between a computer and a telephone line. The modem features a base unit which receives a data signal from the telephone line and which transmits the data signal over a wireless link. A device receives the data signal over the wireless link and outputs an analog data signal that corresponds to the data signal. A modem card receives the analog data signal from the device, digitizes the analog data signal to produce a digital signal, demodulates the digital signal, and provides an output digital data signal to the computer.
A method (200) and device (100) provide an efficient linear power amplifier that generates a variable-envelope radio frequency RF signal. The method includes the steps of: A) using an efficient envelope-following unit to output a supply voltage in accordance with a variable envelope of an input baseband signal, wherein using the efficient envelope-following unit includes: 1) using a bandwidth-limiting mapping unit to determine a reference signal based on the baseband signal; and 2) using an envelope-tracking power converter to output a supply voltage, responsive to the reference signal, to the linear RF power amplifier; B) providing an RF input signal with amplitude and phase information to a linear RF power amplifier; and C) using the linear RF power amplifier to output a power-efficient amplified variable-envelope RF signal with substantially a same amplitude and phase information as the RF input signal.
