Post subject: slope of IIP3 graph Posted: Sun Jan 22,
2006 9:59 am
hi to all,
i am getting a strange resu;t, let
me desicribe that first.
When I am plotting I and III harmonics
of a Common Source Amplifier (for IIP3 ) , I am getting slope of
'3' of III harmonic curve , but when I cascade it with another Common
Source Amplifeir , I get slope of less then '3' !!!
it strange ???
Please help me . . . . .
I have second
doubt that if it is correct that slope will decrease then everyone
must use cascading as it increases IIP3 point !
please . .. . . .. . .. . .
Post subject: Posted: Sun Jan 22, 2006 1:38 pm
the second amplifier.. Back off on the input power.
Post subject: Posted: Sun Jan 22, 2006 1:52 pm
really could not understand first reply
Post subject: Posted: Sun Jan 22, 2006 3:15
Joined: Mon Jun 27, 2005 2:02 pm
IP3 is measured
under 'small signal' conditions.
To be more specific according
to the IEEE: the IMR3 (3rd order Intermodulation Ratio), which is
the difference between the 1st order signal to the 3rd order (in
dB) should be greater than 20dBc.
For each 1dB increment
in the fundamental signal (1st order) the IM3 product is increased
When you cascade 2 amplifiers and you want to measure
the cascaded IP3, you should check that both amplifiers are working
in small signal region and far enough from P1dB. If the slope is
no more 3:1, that means that one of the amplifiers is working in
non-linear region i.e. close to compression. The meaning of backing
off is to reduce the input power to the amplifier and by that to
decrease the output power and backing it off from compression. Try
to reduce the input power to the first amplifier and measure the
Post subject: Posted:
Mon Jan 23, 2006 1:47 am
really very very impressed by IR's
Thanks a lot ,