A fundamental component of wireless communications systems is the power amplifier (PA). Such wireless communications systems include a variety of broadband and multimedia services. In such systems, the power amplifier is supported by a wireless RF transmitter. The power efficiency of the PA is an important aspect of the operational efficiency of the system as a whole. For a long time, the linearity and efficiency of power amplifiers have been two of the most difficult issues faced by wireless system designers and users. These problems are closely related to both the power spectrum efficiency and the power efficiency of power amplifiers.
Prior art predistortion technologies used to linearize the PA in wireless communication systems mainly use analog predistortion approaches. Some have also used a digital adjustment component implemented by means of an analog feed-forward approach and a digital predistortion approach employing a base-band digital signal processing (DSP) technique.
The traditional analog predistortion technologies are based on the principle of error subtraction and a power match to linearize the PA. These approaches must use an auxiliary power amplifier to match exactly the non-linearity of the main PA and, at the same time, overcome the signal time-delay that is a variable with frequency and environmental temperature. As a result, it is difficult for this approach to meet the requirement of the advanced wireless communication systems.
Prior art DSP-based predistortion methods generally require that the predistortion sub-system and circuit design rely on the I and Q signal of the base band in the base station, and therefore have to embed the predistortion processing into the base band circuits of the base station. This requires that the existing base band circuit in the base station must be modified, which is an inconvenient high-cost solution for wireless carriers and equipment makers. Also, the typical DSP-based predistortion technology is not suitable to linearization of the PA when multi-modulation schemes and multi-carrier signals go through a PA.