Nonlinear wideband (power) amplifier - RF Cafe Forums
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Post subject: Nonlinear wideband (power) amplifier Posted: Tue May 16, 2006 5:21 am
Joined: Tue Dec 13, 2005 2:42 am
Location: Czech Rep.
I just want to ask you.
I would like to build a wideband 'power' amplifier working let's say in C Class. (I'm speaking about 150-450MHz band approximately, 0.5-1W out.)
Does the nonlinear wideband amplifier even exists? ...Because I haven't found anything about it.
Do you have some design recommendation?
Thank you for help,
Post subject: Broadband Class C amplifierPosted: Tue May 16, 2006 6:33 pm
Joined: Wed Feb 22, 2006 3:51 pm
Class C amplifiers are unfortunately inherently not wideband. Here's why
Class C amplifiers are defined by having a conduction angle of less than 180 degrees. This results in a pulse of current being applied to the output network, which resonates at the operating frequency. This resonance reduces the harmonics which are necessarily generated with less than 180 degrees conduction angle. The Q may vary, but the resonance is critical to the proper operation of the circuit.
Because the current pulse is not symmetrical, both even and odd harmonics are generated. So in your specifications, a 150 MHz input signal would result in 300 and 450 MHz spurious signals, which would not be filtered out - not so good.