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I am not sure if the equations are correct for practical devices (especially short channel ones). But check the source and drain contact resistant. Are they comparable to the channel resistance give by these equations?
hi mona123,
yes, the assumption is the amplifier is still linear and the output collector waveform is a pure sinusoidal plus DC for a pure sinusoidal input. i agree with you.
ac small signal usually has nothing to do with dc but we are talking about large signal here as we are interested in the peak collector swing i.e. maximum collector voltage). so it is really "large" signal.
more specifically, because the minimum instantaneous collector voltage (which is the sum...
How about this?
For example, for a BJT, collector voltage Vc=DC voltage @ collector + AC voltage @ collector
So for class A with RFC (or LC tank) at the collector:Vc=Vcc+Vb*gm*RL, where Vb is the AC voltage seen at the base. If Vb increases such that Vb*gm*RL reaches an amplitude of Vcc then...
i know typically measured gain is always lower than the post-layout simulation by 1~3dBs but i don't know if 5 dB is considered unusual? did you include the parasitic capacitors for post layout simulation? were your metal connections thick/wide enough? or does these result exclude the loss of...
i think it depends on the DC current drawn by the opamp (and any other components you may have). if very little DC current is drawn (<<1mA) may be it could be a good idea, otherwise the GND node will deviate its idea DC potential.
PA stability
ok, if you think of the entire 3-stage as a "single stage" and apply k-factor (or otherwise) and find out that this "single stage" is stable. does this guarantee that the three stage is stable?
all i can think of now is that if you guarantee that each stage is unconditionally...
make sure you have good decoupling, especially to decouple the 160MHz one. the decoupling capacitor (for 160MHz you may need ~1000pF) shall be as close as possible to the transistor. also reduce the pcb trace length connected to the transistor, if they are not necessary. if you are using...
Thanks for your help!
I just checked with UCSD high speed group (they have pretty good device work for RF PAs) as well and could only find these models but not the actual parameters of real devices which means it is still not possible to see and compare the actual charateristics such as I-V...
Does anyone have nonlinear models or design kit for GaAs/InGaP HBTs?
GaAs/InGaP HBTs are ideal candidates for RF power amplifiers and I am trying to compare their characteristics with other devices (MESFET, HEMT, CMOS etc) from differnet process technology. I've found nonlinear models for most...
these sparked spots are due to resonance which is inevitable due to parasitic inductor of the capacitor. therefore beyond the resonant frequency the capacitor acts as a inductor (which not what you want normally). larger capacitor typically have lower resonant frequency (which means the useful...
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