| This paper describes a wide band high linearity power amplifier for digital communication system. Feed forward techniques are applied and by selecting suitable power amplifiers, power splitters and controllable AM shifter, the power amplifier's IMD3 is less than -60dBc. Band width is 25MHz and the maximum output power is 30dBm. Power amplifiers must have the correct band, DC, output power and efficiency. The main power amplifier is C class amplifier and the second power amplifier is A class amplifier. Because the main amplifier must has high efficiency, and the second power amplifier has high linearity. The band width of the second power amplifier must larger than that of the main power amplifier, so it can amplify the IMD3 correctly.As the growing of wireless communication, the using of power amplifier is more frequently. But there are problems about the inter-modulation products (IMD) and adjacent channel power ratio (ACPR). They are caused by the non-linear character of power amplifier. So, it is very important to do some research to linearize the power amplifier.In fact, it is easy to design a power amplifier only with high linearity. But other performance factors such as wide band, high efficiency of a power amplifier are required very well except linearity in the communication systems. Especially when the input power is high, it is very difficult to design high linearity power amplifier with wide band and high efficiency.There are many different methods to design high-linearity power amplifier, such as feed forward, pre-distortion and feedback. Each method has its own advantages and disadvantages. In this paper, the feed forward power amplifier is the main part. Other methods are touched also. |
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