Hi Stefan,

yes, a single ended class E amplifier would give the same power with
both FETs in parallel but, due to symmetry, the push-pull design has the
advantage of cancelling all even order harmonics by design. 3f is the
first harmonic to worry about so the lowpass filter can be made simpler.
The added complexity of push-pull is minimal - one more capacitor and
one more DC feeding choke. And, yes, an output transformer in case you
didn't already use one for impedance matching in the single ended case.

By the way, the amplitude of the first harmonics of a single ended class
E amplifier (without lowpass filter!) is 0.51/QL (2f) and 0.08/QL (3f)
with respect to the carrier (1f) amplitude. QL is the loaded Q of the
series resonant tank, XL/Rload. Example:

If QL = 5.1, a reasonable value, the amplitude of the 2f harmonic will
be 0.51/5.1 = 0.1 compared to the carrier i.e. -20dBc.

In a perfectly balanced push-pull circuit, the 2f harmonic will
disappear so the first harmonic problem will be 3f at -36dBc which is
"16dB easier" to filter and further from the carrier as well :-).


73
Johan SM6LKM

----

Stefan Schäfer wrote:
> Hi Johan, 
>  
> What are you planning? This sounds like QROO? Why using a push-pull class E 
> stage when a single stange can do it?
> I am interested! :-)
>  
> Stefan/DK7FC