Let’s have a look at the circuit diagram and basic operation of class A amplifier: In this class, the transistor remains in active mode all the time which leads to excessive heat generation thus causing a reduction in the efficiency. Throughout the input signal, the transistor remains in forward bias mode. This class is used when we simply want a distortion-free output. Here, the maximum possible efficiency is of 50%. It only operates on the linear region of the load as the operating point is so selected which gives us exact output as that of input. In this class of power amplifiers, the output current flows for overall i.e., 360﮲ of the input cycle. Power amplifiers are classified as different classes which shows the variation of the output signal with respect to the applied input signal. Stage 3: Output stage: This stage essentially consists of power amplifiers and is responsible to transfer maximum power to the output device.
Stage 2: Driver stage: The amplified voltage obtained from the voltage amplifier is fed to the driver stage to provide maximum power gain and to facilitate impedance matching.
Here, we have used two stages of voltage amplifier so as to amplify the low-value input to the desired level. Stage 1: Voltage amplification stage: As the input signal developed by the transducer is of very low value and a higher value signal is needed at the output so input signal is amplified at the very first stage of power amplifiers. To provide the necessary power amplification, Power amplifiers consist of the following three stages as shown below: It is always suggested to have a distortionless output.
How large PAPR effects the power amplifier In LTE system, OFDM signal PAPR is approx. This ratio of the peak to average power value is termed as Peak-to-Average Power Ratio. When all the points achieve the maximum value simultaneously this will cause the output envelope to suddenly shoot up which causes a ‘peak’ in the output envelope.ĭue to presence of large number of independently modulated subcarriers in an OFDM system, the peak value of the system can be very high as compared to the average of the whole system. At each instant they are different with respect to each other at different phase values. PAPR occurs when in a multicarrier system the different sub-carriers are out of phase with each other. The PAPR is the relation between the maximum power of a sample in a given OFDM transmit symbol divided by the average power of that OFDM symbol. In simple terms, PAPR is the ratio of peak power to the average power of a signal.