How to Choose the Device for PAs and LNAs - RF Cafe Forums
Post subject: How to choose the device for PAs and
LNAs Posted: Thu Nov 17, 2005 4:46 pm
Joined: Thu Nov 17, 2005 4:29 pm
I am working with
a SiGe BiCMOS process that has different size bipolars.
width, we have three choices: 0.4um, 0.6um and 0.9um.
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
considerations or others?
If we somehow determined the total
emitter area of the PA. Which
emitter width to use? Some paper
say that the narrower emitter
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 pm
I am sorry for my comments that are probably
not directly related to SiGe BiCMOS devices, as I havent experienced
using this device before
Just general 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.
Any further advice is appreciated...