Efficiency and make of a RF amplifier determines the class it belongs to. Class E amplifiers are considered to be the best as they deliver significantly higher quality signals as compared to other class amplifiers. Transistor in Class E amplifiers works as a switch with a similar on/off function. Load network mechanism molds the current voltage and waveforms in a manner so as to avoid high voltage and current occurrences to limit power spread especially when the transistor switches on and off.
When the same transistor at the same frequency and output power is run in Class E, B and C amplifiers, Class E amplifier will operate more efficiently with power loss of less than 2.3 as compared to Class B and C amplifiers. They can be designed to handle frequency operations as large as 225-400 MHz during a fixed tune or narrow band operation. Class B and E amplifiers have same level of harmonic output. One big advantage of Class E amplifier is that they are “designable”, you can say customizable to make it simpler to understand. If you define the frequency variations and component effects in advance when designing Class E amplifiers then they will perform as expected.
To increase the efficiency of RF amplifiers it is important to reduce the power dissipation and still get the preset power output. Consider a RF amplifier and the greatest power dissipation in the entire system happens in the power transistor. Though the transistor has to be designed so as to be able to resist high power voltage and current, its power dissipation can be reduced by ensuring that both high voltage and current do not occur at the same point of time. If this can be attained through changes in the design then the efficiency of RF amplifiers can be increased substantially.
When “On” and the current is really high the transistor switch will work as a low resistance closed switch and the voltage will become zero. When “Off” and the voltage is high the transistor switch will work as an open switch and the current will become zero.
Similarly there are many different alternatives to increase the efficiency of Class E RF amplifier.
0 comments