Differential and Push-pull power amplifier

[yearn]

Hi, can anyone give me some comments about differential and push-pull power amplifier?

1.What’s the difference between the differential power amplifier and push-pull power amplifier?
In my opinion, differential means that two transistors are both working at the same time while the output signal of them are out of phase. For push-pull, only one transistor is working at one time and another transistor is off at the same time. That means the push-pull operation will always be related to Class B operation.
Am I right?

2.It was said in some paper that the push-pull power amplifier can output more power than single-ended PA. I think for push-pull class B operation, the signal swing at the output is only Vdd while for differential the signal swing will be 2Vdd, then the output power of differential operation will be higher than the push-pull operation.
How to explain this?

Any reply is welcomed. Thank you.

 

[flatulent]

Differential is usually a term for small signal amplifiers and it applies to the input or output or both.

Push pull usually means two transistors combined with transformers and only one conducting at a time although they can be class A in rare cases.

 

[bobytronic]

You can build a push pull amplifier in CLASS A , CLASS B , CLASS AB, CLASS C etc ...
The best compromise for a good linearity and good efficency is the CLASS B. The bias point is equal to the threshold voltage.
The maximum output voltage swing is (VDD-VDSon).
In HF band, you can't use a complementary pair of transistor (N canal and P canal) or (NPN, PNP) but you must use 2 N canal or 2 NPN transistors.

A differential strucure isn't an output stage of an amplifier but it's the input stage.

 

[guamak_menanak]

Differential Amp is better that Push-pull Amp because Diff Amp can have higher gain(Av). Futermore, Diff Amp is good in rejecting noise as it's reject the common-mode signal! Diff Amp have a better signal handling than Push-Pull because Diff Amp differentiate the input signal from 2 input signal to get better input signal.

I don't have a good knowledge on PA, can't explained or give opinion on that matter

 

[saumi]

Differential PAs have, as apparent from the name itself, differentail inputs and outputs.
The differential outputs are fed to a balun to finally deliver single ended power to the
antenna. A good paper describing design of differential class E PA:

K.C. Tsai and P.R. Gray "A 1.9GHz 1-W CMOS Class E Power Amplifier for Wireless Communications", IEEE J. Solid State Circuits, July 1999