I get a big problem in improveing the eff of
I've made my amp output 150W, the
effs versus outputs are as follows:
44.5 13.9% 13.9%
45.5 15.9% 16.3%
46.6 18.5% 18.9%
48.7 23.3% 25%
50.6 29.6% 31.6%
51.6 33.1% 35.7%
The transistor I used was MRF6V4300 of freescale,
the circuit was built in balance configuration.
Actually, I do not think that you have a
problem with the efficiency, because according to
the data sheet it is stated that the efficiency
for 300W is 60%, you are working in half of this
power, therefore, the efficiency which you get is
Take into consideration, that you work
in Balanced configuration and you have some losses
on the output coupler and transmission lines between
the output coupler and the transistors' outputs.
This is also another problem in the two tone
signals measurement for IMD3 test, the IMD3
signals became unstable when the Pout increased
to 100W, it kept jumping from -43dBc to -50dBc.
Last time the output unstable was because
of the high temperature, I sliped off some silica
gel and it got normal, what's the reason for
this IMD3 jumping?
Excessive heat can be a cause for this problem.
Slipping some silica under the transistor is not
an adequate solution. You should be very careful
by implementing a solution for heat evacuation:
a. Under the transistor you have to apply very
thin thin layer of silica, in such way that you
are able to see clearly the transistor metal via
b. The heat sink has to be cooled
by using 2 fans; i.e. one fan takes cool air towards
the heat-sink and the other fan which rotates in
the opposite direction evacuates the hot ait from
the heat-sink towards out.
Read the following
application note for more information:
In addition, try to see if the supply lines
are clear from noise, and if there is no RF signal
coupled back to the supply lines.