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Why is high load resistance good? - RF Cafe Forums
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Below are the old forum threads, including responses to the original posts.
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Post subject: Why is high load resistance good?
postPosted: Fri Jul 08, 2005 3:21 pm
This question is probably
too basic so I feel a little foolish asking it here. I'm not an RF engineer
but I'm reading a thesis where they're talking about GaN transistors
and everyone is bragging about how it has a large breakdown voltage
and can take large load resistances. They say the large load resistance
helps in matching.
Why does the large load resistance aid in
I see it mentioned all over the place but even introductory
texts I've looked at mention it as if "everyone already knows this".
Sat Jul 09, 2005 12:58 pm
I believe this has to do with the
fact some power amplifiers require isolators at he output to improve
IP3 and to protect the the amplifer from reflections due to an antenna
failure, for example,
GaN is less susceptible to these issue
compared to GaAs and LDMOS.
But don't take my word for it, I
have no idea what I'm talking about.
Unread postPosted: Mon Jul 11, 2005 3:36 am
Joined: Tue Mar 15, 2005 11:43
my best to elaborate this issue. Yes, GaN and SiC are well-known for
their high impedance. Maybe you could look at the point of view, due
to they have wide bandgap, so it's possible to operate under high-voltage
operation with small current, that's why the impedance is higher.
Secondly, regarding the "They say the large load resistance helps
in matching. " it refers to Bode-Fano theorem.
Because when the
impedance is high, means the loss in input and output matching circuit
will not be significantly affect the overall circuit performance, as
it won't turn the impedance phase too much.
That is one significant
property that enable " single-stage wideband power amplifier design"
I hope it helps.
Let me know if you need any help.
my best to elaborate.