Problem with plotted IP3 curve
when i plot the IP3 curves , i get the ordinary 3dB/dB curve but at higher Prf ,i get a weired slope larger than the 3 dB/dB
does anyone faced this before? or saw it in any papper?
Because you have too much gain expansion on your amplifier
couild u explain more or provide any refrences
regards
When the amplifier is driven in high power,it is possible to have higher gain than the small signal region for the reason of self-biasing or DC biasing shifting.However,if this gain expansion is too much,you will see the IM3 seems increase more than 3dB/dB.That doesnot mean your IP3 becomes worse since the Pout increase more than 1dB/dB as well.
thnx but this is not the case as the fundmental doesn't increase , only the IM3
You could be seeing IP5 products come into play. Take a look at the spectrum at these high levels, you will probably see IP5 and perhaps even IP7 products starting so show up.
Dave
www.keystoneradio.com