qpsk amplifier

its urgent !please guide me that what class of power amplifier should i design for the QPSK modulation in S band and the application is on board satellite?and please also mention the reason.

In conventional QPSK the transitions on the I and Q channels goes through zero (e.g. 180° phase transition).
QPSK schemes require linear power amplifiers.

Class A of amplification would be ideal, but for efficiency improvement an optimized Class AB could be used.

Also to improve efficiency can be used some types of linearization as Polar Modulator, Doherty, Feed-Forward, etc.

Class AB will perofrm ok for QPSK modulation

khouly

what if some one using class c and the modulation is QPSK.What will be the drawback?

If Class C is used in QPSK amplifier, this will degrade the EVM and will affect the BER.
The reason is the AM-AM and AM-PM response of the class C amplifier.

I think DPD add doherty is the common method in current time

Hi there,
I would say it requires linear amplification because QPSK contains information in the amplitude, not only because IQ trajectory crosses zero?
GSM/EDGE standard 3pi/8-PSK modulation does not cross zero, yet it does not use saturated PA. Crossing zero sets tougher requirements on linearity performance of PA.
Besides EVM, another difficult parameter to meet in the design of a linear PA is the ACPR spec (power in adjacent channels). Although the use of pre-distortion (analog or DPD) can somehow help, the most common way to get ACP spec is to optimize PA by sacrificing PAE performance (therefore class AB?)
Polar Modulation allows to use a saturated PA to transmit a linear modulation by shifting the linearity problem to the Drain/Collector modulator of the PA...
Mosieur_Oiso