hi
Power Amplifier can be categories, depending on whether they’re broadband or narrow band , and whether they for non-constant envelop or constant envelop operation.If it is non-constant envelop operation, a linear amplifier required (class A or AB) is required. If the signal has a constant amplitude, nonlinear amplifiers like class C or D switching amplifiers are more efficient. The most important trade-off in PA design is between efficiency and linearity. There are two basic ways to define PA efficiency drain efficiency and power added efficiency. Drain efficiency is the ratio of the RF output power to the dc consumed power. Power added efficiency (PAE) is the ratio of the difference between the RF output power and the RF input power to the dc consumed power. The PAE is a more practical measure as it accounts for the power gain of the amplifier. As the power gain decreases, more stages will be required. Since each stage will consume a certain amount of power, the overall power consumption will increase, thus decreasing the overall efficiency.Another key issue in the design of PA`s is the issue of linearity. In the nonconstant-envelope case, there is symbol information contained in the transmitted signal, so the PA must accurately amplify the amplitude of the signal that it is driven with. Non-linearity in the PA can cause the transmitted signal to contain the incorrect information, corrupting the communications link.
regards,
selvaraja