Feed-forward amplifier

Abstract

The present invention provides a feedforward amplifier capable of obtaining a sufficient distortion compensation effect by a predistortion circuit even when the ambient temperature changes. This feed-forward amplifier is provided with a variable attenuator (4) to control the attenuation of the signal input to the main amplifier (6), and the attenuation is controlled in order to prevent deterioration of distortion compensation due to changes in the ambient temperature of the main amplifier (6). A variable attenuator (21), a variable attenuator (12) for controlling the attenuation of the signal input to the sub-amplifier (14), in order to prevent distortion compensation caused by changes in the ambient temperature of the sub-amplifier (14) The variable attenuator (22) that degrades and controls the attenuation, controls the variable attenuator (4,12) with the control circuit (19) so that the gain drop with the main amplifier (6) and the gain of the auxiliary amplifier (14) The amount of drop decreases the attenuation accordingly, and the control circuit (23) controls the variable attenuators (21, 22) so as to become the optimum temperature corresponding to the ambient temperature of the main amplifier (6) and the ambient temperature of the sub-amplifier (14). good attenuation.

Description

technical field [0001] The present invention relates to a feed-forward amplifier having a pre-distortion circuit (pre-distortion compensator), and more particularly to a feed-forward amplifier capable of obtaining a distortion compensation effect by the pre-distortion circuit even when the ambient temperature changes. Background technique [0002] In recent years, various developments have been made regarding feedforward amplifiers. [0003] In a feedforward amplifier, when amplifying a modulated wave signal with a high peak-to-average power ratio, the linearity deteriorates and large distortion occurs when the compensation of the amplifier is reduced in order to improve efficiency ( distortion). Conversely, when the compensation is increased in order to improve linearity, the efficiency will deteriorate. [0004] [Existing Example 1: Figure 2] [0005] For example, as a method of compensating nonlinear distortion (nonlinear distortion) caused by small compensation, there...

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Problems solved by technology

[0037] The second problem is that when the gain of the sub-amplifier 107 changes due to changes in ambient temperature, etc., the compensation amount of the pre-distortion circuit 102B changes, and the distortion of the sub-amplifier 107 cannot be compensated.

[0062] When the ambient temperature of the power amplifier used in the sub-amplifier 14 changes, generally, as shown in FIG. 6(a), the gain decreases at high temperatures.

In addition, the generated distortion also depends on the output power more than the ambient temperature, and as shown in Fig. 6(b), the higher the output level, the larger the distortion

[0063] In the feedforward amplifier of the conventional example 5 shown in FIG. 7, when considering the increase in the ambient temperature, the gain of the auxiliary amplifier 14 decreases as shown in FIG. 6(a) due to the increase in the ambient temperature. However, in this state, the amplitudes of the signal line c and the signal line d are not the same amplitude, so after the synthesizer 9 is synthesized, the injected pilot signal cannot be completely eliminated, and the output from the synthesizer 9 is

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