How to choose the device for PAs and LNAs - RF Cafe Forums
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Post subject: How to choose the device for PAs and LNAs
Posted: Thu Nov 17, 2005 4:46 pm
Nov 17, 2005 4:29 pm
I am working with a SiGe BiCMOS
process that has different size bipolars.
For emitter width, we have
three choices: 0.4um, 0.6um and 0.9um.
I have read some paper
saying that for a PA, there is a relationship
between the maximum
output power and the emitter area. Does anybody
know what is the
exact relationship? Is that coming from the parasitic
If we somehow determined the total emitter area of
the PA. Which
emitter width to use? Some paper say that the narrower
gives better NFmin and higher Ft. How can that be explained?
Even if that is true, it would apply to LNAs. Can PAs benefit from this?
(given that we don't care about noise of PAs)
Post subject: Posted: Thu Nov 24,
2005 4:23 am
Joined: Tue Mar 15, 2005 11:43
I am sorry for
my comments that are probably not directly related to SiGe BiCMOS devices,
as I havent experienced using this device before
comments on device for PA and LNA design. Usually for LNA design, we
choose device with higher cut-off frequency as the noise figure will
be lower, for example HEMT devices.
As for PA design, we choose
device based on the power requirement, that related to device impedance,
gate width, etc. For example, in most cases, MESFET is preferable for
PA design, while HEMT is preferable for LNA design.
advice is appreciated...