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
Joined: Thu 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
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...