What does Linearity of an RF/Microwave amplifier mean?
It is one of the essential jobs of the amplifier. It is used to increase the power level of the input signal without having to alter the content of the incoming signal. This term ‘linearity’ is derived from the linear relationship between the input and output power. In an ideal amplifier, this would be related to the gain made by the amplifier.
However, it is not as easy as it sounds. It involves matching complex matching circuits to facilitate the flow from a low impedance of solid state to a higher impedance. But still, most amplifiers will have to suffer again roll off at the higher frequencies inevitably. In order to get high amplifier linearity, you will have to sacrifice on efficiency.
What deprives an amplifier of its linearity?
Amplifiers are not the ideal devices to have transfer characteristics, because they can generate harmonic signals multiple times the fundamental input signal. The intermodulation distortion also gets amplified along with it.
Non-linearity can also occur due to time. These non-linarites occur due to memory effects. It can happen when an input signal stresses the power supply voltage which results in creating input signal dependent non-linarites which are also known as the memory effects.
If anyone wants to extend transistor life and maintain good linearity, it is crucial to have thermal management for the microwave amplifier. It is because the linearity is dependent upon the temperature as cold or hot transistors exhibit different functions.
Raditek microwave amplifiers can be seen at http://raditek.com/AMPLIFIERS/Microwave-Amplifiers.htm