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Gate bias - RF Cafe Forums
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Post subject: Gate bias
Posted: Fri Oct 22, 2010 5:59 am
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Joined: Tue Aug 26, 2008
5:18 am
Posts: 22
Location: UK
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Hi,
Can any please explain to me how do we select
the value of gate bias resistor in combination with
inductor in the design of RF power amplifier. Inductor
is frequency dependent but why do we use varios
values of resistor apart from stability.
Thanks.
SDO
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IR |
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Post subject: Re: Gate bias
Posted: Mon Oct 25, 2010 2:00 pm
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Joined: Mon Jun 27, 2005
2:02 pm
Posts: 373
Location: Germany
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Hi,
Don't you mean a voltage divider?
if you mean a single bias resistor, can you
show an example of such circuit?
_________________
Best regards,
-
IR
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SDO |
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Post subject: Re: Gate bias
Posted: Thu Oct 28, 2010 2:48 am
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Joined: Tue Aug 26, 2008
5:18 am
Posts: 22
Location: UK
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Hi,
Thanks for your reply. I am attaching JPeg
of Schematic showing 27R resistor (R39). Please
explain how do we select this select resistor. This
PA has been designed for 60MHz.
I cannot attach/insert
Image, anyhow this resistor is from gate to a series
inductor and after that are decoupling caps on the
gate bias. SO it is like DC--->decoupling caps--->inductor--->resistor--->gate.
It is definitely not a voltage divider but used
to present low impedance at low frequencies.
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IR |
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Post subject: Re: Gate bias
Posted: Thu Oct 28, 2010 4:33 am
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Joined: Mon Jun 27, 2005
2:02 pm
Posts: 373
Location: Germany
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I guess that this is a recommendation by the transistor
manufacturer.
Have you tried to simulate the
circuit with and without the resistor?
This
resistor is most probably used for stability and
it works to stabilize the amplifier by reducing
the gain in low frequencies (Where the gain is extremely
high). The resistor works for DC to very low frequencies
in which the reactance of the inductor has almost
no influence.
_________________
Best regards,
-
IR
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Posted 11/12/2012
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